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Purpose: The preclinical pharmacokinetic and pharmacodynamic properties of a potent fluoroketolide RBx14255 against Streptococcus pneumoniae and Haemophilus influenzae was compared with telithromycin and human clinical dose was predicted for preclinical development. Methods: The in vitro pharmacokinetic characterization was performed for solubility, Caco-2 permeability, microsomal stability, CYP inhibition and plasma protein binding. In vivo pharmacokinetic studies were performed in Swiss albino mice, Sprague Dawley rats and Beagle dogs. The pharmacodynamic studies were carried out in mouse against S. pneumoniae in systemic infection and against S. pneumoniae and H. influenzae in rat lung infection models. Results: RBx14255 showed superior potency and efficacy in mouse and rat infection models. RBx14255 showed pH dependent solubility (0.41 mg/mL at pH 6.8 and >1 mg/mL at pH 1.2), moderate Caco-2 permeability (A to B: 12 nm/s) with high efflux ratio. It showed high plasma protein binding (>97%) in mouse and low binding (45-70%) in rat, dog and human. The compound is mainly metabolized through CYP3A4. Pharmacokinetic parameters and absolute bioavailability of both, RBx14255 and telithromycin are similar in mouse. Both the ketolides showed low plasma clearance (18% of the normal hepatic blood flow rate) in mouse, moderate to high clearance in rat and dog. Mean oral bioavailability was high in mouse (≥85%), moderate in rat (RBx14255: 15% and telithromycin: 51%) and high to moderate in dog (RBx14255: 98% and telithromycin: 56%). The predicted efficacious dose for a 70 kg man ranges from 124 mg BID to 226 mg BID. Conclusion: RBx14255 displayed significantly better pharmacodynamics which correlates with the pharmacokinetic properties against S. pneumoniae and H. influenzae as compared to telithromycin. The predicted human efficacious doses are in the range of 124-226 mg, making it amenable to oral dosage form drug in human. This could be a promising clinical candidate for future studies.

Antibiotic macrolides are experiencing renewed interest in anti-infective therapy since the advent of ketolides. This therapeutic class was introduced in order to broaden the narrow antibacterial spectrum of macrolides and to cope with the emergence of germs resistant to Erythromycin A and its hemisynthetic derivatives or neomacrolides (Clarithromycin, Roxithromycin, Azithromycin, Dirithromycin). From a pharmacochemical point of view, ketolides were first of all obtained by operating chemical modulations on Erythromycin A to obtain the neomacrolides, then, by replacing the neutral sugar (L-cladinose) in C3 by a ketone function coupled with the creation of an oxazolidinone like heterocycle in C11 and C12 in place of the hydroxyls present in these positions (Telithromycin, Cethromycin, Solithromycin). These modulations have enabled the improvement of the chemical stability of ketolides in gastric acid medium and increase their affinity for the ribosomal target, hence the broadening of their spectrum of action towards Gram positive germs including strains resistant to other macrolides and to neomacrolides. Therefore, the objective of this systematic review is to report the various pharmacochemical aspects undertaken since 1952 in the macrolide series based on the structure of Erythromycin A. These aspects will focus on the pharmacomodulations that have led, year after year, to the optimization of stability, the improvement of the pharmacodynamic and pharmacokinetic profile and that have allowed the development of neomacrolides, ketolides and neoketolides, which are today essential in the management of severe bronchopulmonary infections.

There is an urgent need for new antibiotics to mitigate the existential threat posed by antibiotic resistance. Within the ketolide class, solithromycin has emerged as one of the most promising candidates for further development. Crystallographic studies of bacterial ribosomes and ribosomal subunits complexed with solithromycin have shed light on the nature of molecular interactions (π-stacking and H-bonding) between from the biaryl side-chain of the drug and key residues in the 50S ribosomal subunit. We have designed and synthesized a library of solithromycin analogs to study their structure-activity relationships (SAR) in tandem with new computational studies. The biological activity of each analog was evaluated in terms of ribosomal affinity (K(d) determined by fluorescence polarization), as well as minimum inhibitory concentration assays (MICs). Density functional theory (DFT) studies of a simple binding site model identify key H-bonding interactions that modulate the potency of solithromycin analogs.

Background Solithromycin, the fourth generation of ketolides, has been demonstrated potent antibacterial effect against commonly-isolated gram-positive strains. However, Staphylococcus aureus (S. aureus) strains with a higher solithromycin MIC have already been emerged, the mechanism of which is unknown. Methods Antimicrobial susceptibility test was performed on 266 strains of S. aureus. The antibiotic resistance phenotype of erm-positive strain was determined by D-zone test. Spontaneous mutation frequency analysis was performed to compare the risk levels for solithromycin resistance among different strains. Efflux pumps and mutational analysis of ribosomal fragments as well as erm(B) gene domains were detected. Quantitative reverse transcription polymerase chain reaction was conducted to compare the transcriptional expression of the erm gene between the constitutive macrolide-lincosamide-streptogramin B (cMLSB)- and inducible MLSB (iMLSB)-phenotypes. Results In the erm-positive S. aureus strains, the minimum inhibitory concentration (MIC)50/90 of solithromycin (2/> 16 mg/L) was significantly higher than that in the erm-negative strains (0.125/0.25 mg/L). Of note, the MIC50 value of the strains with iMLSB (0.25 mg/L) was significantly lower than that of the strains with cMLSB (4 mg/L). A comparison among strains demonstrated that the median mutational frequency in isolates with cMLSB (> 1.2 × 10− 4) was approximately > 57-fold and > 3333-fold higher than that in iMLSB strains (2.1 × 10− 6) and in erythromycin-sensitive strains (3.6 × 10− 8), respectively. The differential antibiotic in vitro activity against strains between cMLSB and iMLSB could not be explained by efflux pump carriers or genetic mutations in the test genes. The expression of the erm genes in strains with cMLSB did not differ from that in strains with iMLSB. Conclusions The reduced susceptibility to solithromycin by S. aureus was associated with the cMLSB resistance phenotype mediated by erm. Electronic supplementary material The online version of this article (10.1186/s12879-019-3779-8) contains supplementary material, which is available to authorized users.

Background India is among the nations reporting substantial healthcare burden linked to pneumococcal infections. Nafithromycin is a novel lactone ketolide antibiotic, which recently entered Phase 3 development in India for the indication of community-acquired bacterial pneumonia (CABP). Objectives To assess the in vitro activity of nafithromycin against serotyped invasive and non-invasive Streptococcus pneumoniae isolates, collected from nine medical centres across India. Methods A total of 534 isolates of S. pneumoniae were collected during 2015–20 and serotyped as per CDC protocol. A subset of erythromycin-non-susceptible S. pneumoniae (n = 200) was screened for the presence of erm(B) and mef(A/E) genes. A subset of MDR isolates (n = 54) were also subjected to MLST. The MICs of antibiotics were determined by the reference agar-dilution method (CLSI). Susceptibilities of the comparators were interpreted as per CLSI criteria. Results Fifty-nine distinct serotypes were identified among the 534 isolates. Among erythromycin-non-susceptible isolates, erm(B) and mef(A/E) genes were found in 49% and 59% strains respectively, while MLST showed clonal diversity. Azithromycin (67.6% non-susceptible) and clindamycin (31.8% non-susceptible) showed limited activity. Penicillin (for non-meningitis) or quinolone non-susceptibility was low ( Conclusions Indian pneumococcal isolates show poor susceptibilities to macrolides, in concordance with the global trend. Nafithromycin overcomes erm as well as mef-mediated macrolide resistance mechanisms expressed individually or concurrently in S. pneumoniae. This study supports continued clinical development of nafithromycin for pneumococcal infections including CABP.

Macrolides and ketolides comprise a family of clinically important antibiotics that inhibit protein synthesis by binding within the exit tunnel of the bacterial ribosome. While these antibiotics are known to interrupt translation at specific sequence motifs, with ketolides predominantly stalling at Arg/Lys-X-Arg/Lys motifs and macrolides displaying a broader specificity, a structural basis for their context-specific action has been lacking. Here, we present structures of ribosomes arrested during the synthesis of an Arg-Leu-Arg sequence by the macrolide erythromycin (ERY) and the ketolide telithromycin (TEL). Together with deep mutagenesis and molecular dynamics simulations, the structures reveal how ERY and TEL interplay with the Arg-Leu-Arg motif to induce translational arrest and illuminate the basis for the less stringent sequence-specific action of ERY over TEL. Because programmed stalling at the Arg/Lys-X-Arg/Lys motifs is used to activate expression of antibiotic resistance genes, our study also provides important insights for future development of improved macrolide antibiotics., Macrolides and ketolides antibiotics selectively interfere with the translation of a specific subset of proteins. Here the authors show how the macrolide erythromycin and the ketolide telithromycin interplay with the nascent polypeptide chain to arrest translation.

ObjectivesTo determine the mechanism of induction of erm(47) and its atypical expression in the Gram-positive opportunistic pathogen Helcococcus kunzii, where it confers resistance to a subset of clinically important macrolide, lincosamide and streptogramin B (MLSB) antibiotics.MethodsThe resistant H. kunzii clinical isolate UCN99 was challenged with subinhibitory concentrations of a wide range of ribosome-targeting drugs. The methylation status of the H. kunzii ribosomal RNA at the MLSB binding site was then determined using an MS approach and was correlated with any increase in resistance to the drugs.ResultsThe H. kunzii erm(47) gene encodes a monomethyltransferase. Expression is induced by subinhibitory concentrations of the macrolide erythromycin, as is common for many erm genes, and surprisingly also by 16-membered macrolide, lincosamide, streptogramin, ketolide, chloramphenicol and linezolid antibiotics, all of which target the 50S ribosomal subunit. No induction was detected with spectinomycin, which targets the 30S subunit.ConclusionsThe structure of the erm(47) leader sequence functions as a hair trigger for the induction mechanism that expresses resistance. Consequently, translation of the erm(47) mRNA is tripped by MLSB compounds and also by drugs that target the 50S ribosomal subunit outside the MLSB site. Expression of erm(47) thus extends previous assumptions about how erm genes can be induced.

Community-acquired bacterial pneumonia (CABP) is a leading cause of death worldwide. However, antibacterial agents used to treat common pathogens in CABP are marked by adverse drug events and increasing antimicrobial resistance. Solithromycin is a new ketolide antibiotic, based on the macrolide antibiotic structure, being studied for use in CABP. It has efficacy in vitro against the common causative pathogens in CABP including Streptococcus pneumoniae, Haemophilus influenzae, and atypical pathogens. In Phase II and Phase III clinical trials, it has been demonstrated efficacious as a single agent for treatment of CABP with an apparently milder adverse event profile than alternative agents.

Mycoplasmagenitalium is an important sexually transmitted pathogen responsible for both male and female genital tract disease. Appreciation of its significance in human disease has been hampered by its slow growth in culture, difficulty in isolating it, and lack of commercial molecular-based tests for rapid detection. Comparatively few in vitro data on antimicrobial susceptibility are available due to the scarcity of clinical isolates and difficulty in performing susceptibility tests to determine minimum inhibitory concentrations for M. genitalium. Antimicrobial agents that inhibit protein synthesis such as macrolides, along with fluoroquinolones that inhibit DNA replication, have been the treatments of choice for M. genitalium infections. Even though international guidelines recommend azithromycin as first-line treatment, rapid spread of macrolide resistance as well as emergence of quinolone resistance has occurred. Increasing rates of treatment failure have resulted in an urgent need for new therapies and renewed interest in other classes such as aminocyclitols, phenicols, and streptogramins as treatment alternatives. Limited data for new investigational antimicrobials such as the ketolide solithromycin suggest that this drug may eventually prove useful in management of some resistant M. genitalium infections, although it is not likely to achieve cure rates >80% in macrolide-resistant strains, in a similar range as recently reported for pristinamycin. However, agents with completely new targets and/or mechanisms that would be less likely to show cross-resistance with currently available drugs may hold the greatest promise. Lefamulin, a pleuromutilin, and new nonquinolone topoisomerase inhibitors are attractive possibilities that require further investigation.

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Aim: A sensitive method to quantify nafithromycin and its N-desmethyl metabolite in human plasma was necessary for Phase I pharmacokinetic studies. Methodology: A precise and accurate LC–MS/MS bioanalytical method has been developed and validated for the simultaneous quantification of nafithromycin (NFT, WCK 4873) and N-desmethyl metabolite (M1, WCK 4978) in human plasma. Clarithromycin was used as an internal standard. Protein precipitation technique was used as sample preparation approach. The calibration curve was linear (r ≥ 0.99) over the concentration range of 10–5000 ng/ml for NFT and M1. Method was validated as per US FDA guideline. Conclusion: The proposed method was successfully applied for determination of plasma levels of the NFT and M1 during Phase I clinical studies.

Erythromycin and its analogs are used to treat respiratory tract and other infections. The broad use of these antibiotics during the last 5 decades has led to resistance that can range from 20% to over 70% in certain parts of the world. Efforts to find macrolides that were active against macrolide-resistant strains led to the development of erythromycin analogs with alkyl-aryl side chains that mimicked the sugar side chain of 16-membered macrolides, such as tylosin. Further modifications were made to improve the potency of these molecules by removal of the cladinose sugar to obtain a smaller molecule, a modification that was learned from an older macrolide, pikromycin. A keto group was introduced after removal of the cladinose sugar to make the new ketolide subclass. Only one ketolide, telithromycin, received marketing authorization but because of severe adverse events, it is no longer widely used. Failure to identify the structure-relationship responsible for this clinical toxicity led to discontinuation of many ketolides that were in development. One that did complete clinical development, cethromycin, did not meet clinical efficacy criteria and therefore did not receive marketing approval. Work on developing new macrolides was re-initiated after showing that inhibition of nicotinic acetylcholine receptors by the imidazolyl-pyridine moiety on the side chain of telithromycin was likely responsible for the severe adverse events. Solithromycin is a fourth-generation macrolide that has a fluorine at the 2-position, and an alkyl-aryl side chain that is different from telithromycin. Solithromycin interacts at three sites on the bacterial ribosome, has activity against strains resistant to older macrolides (including telithromycin), and is mostly bactericidal. Pharmaceutical scientists involved in the development of macrolide antibiotics have learned from the teachings of Professor Satoshi Omura and progress in this field was not possible without his endeavors.

As we face an alarming increase in bacterial resistance to current antibacterial chemotherapeutics, expanding the available therapeutic arsenal in the fight against resistant bacterial pathogens causing respiratory tract infections is of high importance. The antibacterial potency of macrolones, a novel class of macrolide antibiotics, against key respiratory pathogens was evaluated in vitro and in vivo . MIC values against Streptococcus pneumoniae , Streptococcus pyogenes , Staphylococcus aureus , and Haemophilus influenzae strains sensitive to macrolide antibiotics and with defined macrolide resistance mechanisms were determined. The propensity of macrolones to induce the expression of inducible erm genes was tested by the triple-disk method and incubation in the presence of subinhibitory concentrations of compounds. In vivo efficacy was assessed in a murine model of S. pneumoniae -induced pneumonia, and pharmacokinetic (PK) profiles in mice were determined. The in vitro antibacterial profiles of macrolones were superior to those of marketed macrolide antibiotics, including the ketolide telithromycin, and the compounds did not induce the expression of inducible erm genes. They acted as typical protein synthesis inhibitors in an Escherichia coli transcription/translation assay. Macrolones were characterized by low to moderate systemic clearance, a large volume of distribution, a long half-life, and low oral bioavailability. They were highly efficacious in a murine model of pneumonia after intraperitoneal application even against an S. pneumoniae strain with constitutive resistance to macrolide-lincosamide-streptogramin B antibiotics. Macrolones are the class of macrolide antibiotics with an outstanding antibacterial profile and reasonable PK parameters resulting in good in vivo efficacy.

A subset of Gram negative bacterial pathogens use a type 3 secretion system (T3SS) to open up a conduit into eukaryotic cells in order to inject effector proteins. These modulate pathways to enhance bacterial colonization. In this study we screened established bioactive compounds for any that could repress T3SS expression in enterohemorrhagic Escherichia coli (EHEC) O157. The ketolides, telithromycin and subsequently solithromycin both demonstrated repressive effects on expression of the bacterial T3SS at sub-minimum inhibitory (sub-MIC) concentrations, leading to significant reductions in bacterial binding and actin-rich pedestal formation on epithelial cells. Pre-incubation of epithelial cells with solithromycin resulted in significantly less attachment of E. coli O157. Moreover, bacteria expressing the T3SS were more susceptible to solithromycin and there was significant preferential killing of E. coli O157 when added to epithelial cells pre-exposed to the ketolide. This killing was dependent on expression of the T3SS. Taken together, this research indicates that the ketolide may traffic back into the bacteria via the T3SS from accumulated levels in epithelial cells. Considering that neither ketolide induces the SOS response, non-toxic members of this class of antibiotic, such as solithromycin, should be considered for future testing and trials in relation to EHEC infections. These antibiotics may also have broader significance for treating other pathogenic bacteria, including intracellular bacteria, that express a T3SS. Fil: Fernández Brando, Romina Jimena. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; Argentina. University of Edinburgh; Reino Unido Fil: Yamaguchi, Nao. University of Edinburgh; Reino Unido Fil: Tahoun, Amin. University of Edinburgh; Reino Unido. Kafrelsheikh University; Egipto Fil: McAteer, Sean P.. University of Edinburgh; Reino Unido Fil: Gillespie, Trudi. University of Edinburgh; Reino Unido Fil: Wang, Dai. University of Edinburgh; Reino Unido. Xiamen University; China Fil: Argyle, Sally A.. University of Edinburgh; Reino Unido Fil: Palermo, Marina Sandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; Argentina Fil: Gally, David L.. University of Edinburgh; Reino Unido

Macrolide antibiotics inhibit protein synthesis by targeting the bacterial ribosome. They bind at the nascent peptide exit tunnel and partially occlude it. Thus, macrolides have been viewed as 'tunnel plugs' that stop the synthesis of every protein. More recent evidence, however, demonstrates that macrolides selectively inhibit the translation of a subset of cellular proteins, and that their action crucially depends on the nascent protein sequence and on the antibiotic structure. Therefore, macrolides emerge as modulators of translation rather than as global inhibitors of protein synthesis. The context-specific action of macrolides is the basis for regulating the expression of resistance genes. Understanding the details of the mechanism of macrolide action may inform rational design of new drugs and unveil important principles of translation regulation.

Solithromycin, a novel macrolide and the first fluoroketolide, is being developed as a therapy for community-acquired bacterial pneumonia, with a distinct mechanism that provides activity against macrolide-resistant bacteria. The pharmacokinetics, metabolism, and excretion of solithromycin were studied in healthy male subjects after oral administration of a single 800-mg (∼100-μCi) dose of [ 14 C]solithromycin. Solithromycin was well tolerated, and absorption from the solution occurred with a median time to peak concentration of 4.0 h. Solithromycin and the total radioactivity had similar profiles with no long-lived metabolites. The whole-blood total radioactivity was approximately 75% of the plasma total radioactivity. Recovery was essentially complete (mean, 90.6%), with 76.5% and 14.1% of the dose recovered in feces and urine, respectively. Unchanged solithromycin (CEM-101) was the predominant circulating radioactive component in plasma (77% of the total radioactivity area under the concentration-time curve [AUC]), with two minor plasma metabolites, CEM-214 and CEM-122 ( N -acetyl-CEM-101), each accounting for approximately 5% of the total radioactivity. Urinary excretion was predominantly like that of the parent. Solithromycin was primarily eliminated in the feces after extensive metabolism via a complex metabolic pathway with CEM-262 as the major constituent (27.36% of the administered dose). Overall oxidative pathways, presumably carried out mostly by CYP3A4, represented the majority of the metabolism, with N -acetylation present to a lesser extent. No disproportionate human metabolites were observed.

Ketolides are promising new antimicrobials effective against a broad range of Gram-positive pathogens, in part because of the low propensity of these drugs to trigger the expression of resistance genes. A natural ketolide pikromycin and a related compound methymycin are produced by Streptomyces venezuelae strain ATCC 15439. The producer avoids the inhibitory effects of its own antibiotics by expressing two paralogous rRNA methylase genes pikR1 and pikR2 with seemingly redundant functions. We show here that the PikR1 and PikR2 enzymes mono- and dimethylate, respectively, the N6 amino group in 23S rRNA nucleotide A2058. PikR1 monomethylase is constitutively expressed; it confers low resistance at low fitness cost and is required for ketolide-induced activation of pikR2 to attain high-level resistance. The regulatory mechanism controlling pikR2 expression has been evolutionary optimized for preferential activation by ketolide antibiotics. The resistance genes and the induction mechanism remain fully functional when transferred to heterologous bacterial hosts. The anticipated wide use of ketolide antibiotics could promote horizontal transfer of these highly efficient resistance genes to pathogens. Taken together, these findings emphasized the need for surveillance of pikR1/pikR2-based bacterial resistance and the preemptive development of drugs that can remain effective against the ketolide-specific resistance mechanism.

Nafithromycin (WCK 4873), a novel antimicrobial agent of the lactone ketolide class, is currently in phase 2 development for treatment of community-acquired bacterial pneumonia (CABP). A total of 4,739 nonduplicate isolates were selected from a 2014 global surveillance program at medical institutions located in 43 countries within the United States, Europe, Latin America, and the Asia-Pacific region. Nafithromycin and comparator agents were used for susceptibility testing by reference broth microdilution methods. Nafithromycin was active against Staphylococcus aureus (MIC 50/90 , 0.06/>2 μg/ml), including erythromycin-resistant strains exhibiting an inducible clindamycin resistance phenotype (MIC 50/90 , 0.06/0.06 μg/ml) and telithromycin-susceptible strains (MIC 50/90 , 0.06/0.06 μg/ml), but it exhibited limited activity against most telithromycin-resistant and clindamycin-resistant isolates that were constitutively resistant to macrolides (MIC 50/90 , >2/>2 μg/ml). Nafithromycin was very active (MIC 50/90 , 0.015/0.06 μg/ml) against 1,911 Streptococcus pneumoniae strains, inhibiting all strains, with MIC values of ≤0.25 μg/ml. Telithromycin susceptibility was 99.9% for Streptococcus pneumoniae strains, and nafithromycin was up to 8-fold more potent than telithromycin. Overall, 37.9% of S. pneumoniae strains were resistant to erythromycin, and 19.7% were resistant to clindamycin. Nafithromycin was highly active against 606 Streptococcus pyogenes strains (MIC 50/90 , 0.015/0.015 μg/ml), inhibiting 100.0% of isolates at ≤0.5 μg/ml, and MIC 50/90 values (0.015/0.015 to 0.03 μg/ml) were similar for the 4 geographic regions. Nafithromycin and telithromycin demonstrated comparable in vitro activities against 1,002 Haemophilus influenzae isolates and 504 Moraxella catarrhalis isolates. Overall, nafithromycin showed potent in vitro activity against a broad range of contemporary (2014) global pathogens. These results support the continued clinical development of nafithromycin for treatment of CABP.

Disk diffusion and MIC quality control (QC) ranges were determined for nafithromycin, a new lactone-ketolide, following the completion of a nine-laboratory, Clinical and Laboratory Standards Institute (CLSI) document M23-defined tier 2 study. Five QC strains consistent with the spectrum of activity of nafithromycin were tested: Staphylococcus aureus ATCC 25923 (disk only), S. aureus ATCC 29213 (broth only), Enterococcus faecalis ATCC 29212 (broth only), Streptococcus pneumoniae ATCC 49619 (disk and broth), and Haemophilus influenzae ATCC 49247 (disk and broth). Nafithromycin disk diffusion QC ranges were determined to be 25 to 31 mm for S. aureus ATCC 25923, 25 to 31 mm for S. pneumoniae ATCC 49619, and 16 to 20 mm for H. influenzae ATCC 49247. Nafithromycin MIC QC ranges were determined to be 0.06 to 0.25 μg/ml for S. aureus ATCC 29213, 0.016 to 0.12 μg/ml for E. faecalis ATCC 29212, 0.008 to 0.03 μg/ml for S. pneumoniae ATCC 49619, and 2 to 8 μg/ml for H. influenzae ATCC 49247. All disk diffusion and MIC QC ranges established in this study were approved by the CLSI Subcommittee on Antimicrobial Susceptibility Testing at their June 2015 meeting and were initially reported in the 2017 M100S document. The QC ranges established in this study should be used for determining the in vitro activity of nafithromycin in phase 2 and phase 3 human clinical trials and subsequently for testing patient isolates and isolates in phase 4 surveillance studies.

An efficient synthesis of α-amino-γ-lactone ketolide (3) was developed, which provided a versatile intermediate for the incorporation of a variety of aryl and heteroaryl groups onto the C-21 position of clarithromycin via HBTU-mediated amidation. The biological data for this important new class of macrolides revealed significantly potent activity against erythromycin-susceptible strains as well as efflux-resistant and erythromycin MLSB-resistant strains of S. pneumoniae and S. pyogenes. In addition, ketolide 11o showed excellent in vitro antibacterial activity against H. influenzae strain as compared to telithromycin. These results indicate that C-21 substituted γ-lactone ketolides have potential as a next generation macrolide antibiotics.

We present here the novel ketolide RBx 14255, a semisynthetic macrolide derivative obtained by the derivatization of clarithromycin, for its in vitro and in vivo activities against sensitive and macrolide-resistant Streptococcus pneumoniae . RBx 14255 showed excellent in vitro activity against macrolide-resistant S. pneumoniae , including an in-house-generated telithromycin-resistant strain ( S. pneumoniae 3390 NDDR). RBx 14255 also showed potent protein synthesis inhibition against telithromycin-resistant S. pneumoniae 3390 NDDR. The binding affinity of RBx 14255 toward ribosomes was found to be more than that for other tested drugs. The in vivo efficacy of RBx 14255 was determined in murine pulmonary infection induced by intranasal inoculation of S. pneumoniae ATCC 6303 and systemic infection with S. pneumoniae 3390 NDDR strains. The 50% effective dose (ED 50 ) of RBx 14255 against S. pneumoniae ATCC 6303 in a murine pulmonary infection model was 3.12 mg/kg of body weight. In addition, RBx 14255 resulted in 100% survival of mice with systemic infection caused by macrolide-resistant S. pneumoniae 3390 NDDR at 100 mg/kg four times daily (QID) and at 50 mg/kg QID. RBx 14255 showed favorable pharmacokinetic properties that were comparable to those of telithromycin.

Lipoglycopeptide, ketolide, and quinolone antibiotics are currently in clinical development, with specific advantages over available molecules within their respective classes. The lipoglycopeptide oritavancin is bactericidal against MRSA, vancomycin-resistant enterococci, and multiresistant Streptococcus pneumoniae, and proved effective and safe for the treatment of acute bacterial skin and skin structure infection (ABSSSI) upon administration of a single 1200 mg dose (two completed phase III trials). The ketolide solithromycin (two phase III studies recruiting for community-acquired pneumonia) shows a profile of activity similar to that of telithromycin, but in vitro data suggest a lower risk of hepatotoxicity, visual disturbance, and aggravation of myasthenia gravis due to reduced affinity for nicotinic receptors. Among quinolones, finafloxacin and delafloxacin share the unique property of an improved activity in acidic environments (found in many infection sites). Finafloxacin (phase II completed; activity profile similar to that of ciprofloxacin) is evaluated for complicated urinary tract and Helicobacter pylori infections. The other quinolones (directed towards Gram-positive pathogens) show improved activity on MRSA and multiresistant S. pneumoniae compared to current molecules. They are in clinical evaluation for ABSSSI (avarofloxacin (phase II completed), nemonoxacin and delafloxacin (ongoing phase III)), respiratory tract infections (zabofloxacin and nemonoxacin (ongoing phase III)), or gonorrhea (delafloxacin).

Ketolides, the third generation of expanded-spectrum macrolides, have in the last years become a successful weapon in the endless war against macrolide-resistant pathogens. Ketolides are semisynthetic derivatives of the naturally produced macrolide erythromycin, displaying not only improved activity against some erythromycin-resistant strains but also increased bactericidal activity as well as inhibitory effects at lower drug concentrations. In this study, we present a series of novel ketolides carrying alkyl-aryl side chains at the C-6 position of the lactone ring and, additionally, one or two fluorine atoms attached either directly to the lactone ring at the C-2 position or indirectly via the C-13 position. According to our genetic and biochemical studies, these novel ketolides occupy the known macrolide binding site at the entrance of the ribosomal tunnel and exhibit lower MIC values against wild-type or mutant strains than erythromycin. In most cases, the ketolides display activities comparable to or better than the clinically used ketolide telithromycin. Chemical protection experiments using Escherichia coli ribosomes bearing U2609C or U754A mutations in 23S rRNA suggest that the alkyl-aryl side chain establishes an interaction with the U2609-A752 base pair, analogous to that observed with telithromycin but unlike the interactions formed by cethromycin. These findings reemphasize the versatility of the alkyl-aryl side chains with respect to species specificity, which will be important for future design of improved antimicrobial agents.

The MIC 90 of RBx 14255, a novel ketolide, against Clostridium difficile was 4 μg/ml (MIC range, 0.125 to 8 μg/ml), and this drug was found to be more potent than comparator drugs. An in vitro time-kill kinetics study of RBx 14255 showed time-dependent bacterial killing for C. difficile . Furthermore, in the hamster model of C. difficile infection, RBx 14255 demonstrated greater efficacy than metronidazole and vancomycin, making it a promising candidate for C. difficile treatment.

Endometriosis is a common gynecological disorder associated with infertility. However, treatment options remain limited at present. Since the pathogenesis involves immune responses, the immunomodulatory effect of macrolide on endometriosis has been the focus of much research. A previous study showed that clarithromycin decreased stromal proliferation and promoted apoptosis of fibroblasts in an endometriosis model in rats; however, the mechanism of the effect remains unknown. The aim of this study is to investigate the effect of clarithromycin, one of the major macrolides, and telithromycin, one of the antibiotics belonging to a macrolide group (ketolide), on IL6 , IL10 and Ccl2 expression in a rat endometriosis model induced by the surgical transplantation of endometrium onto the peritoneum in 8-week-old female Sprague–Dawley rats. After autotransplantation, the rats were given daily administration of clarithromycin (16 mg/kg/day or telithromycin (12 mg/kg/day) for 3 days. The induced lesions were examined 4 days after autotransplantation. After treatment, IL10 expression in the lesions was increased in rats treated with clarithromycin (1.70-fold) and telithromycin (2.88-fold). The drugs attenuated proliferative stromal lesion of the endometriosis model. The results showed that in the endometriosis model, the drugs enhanced expression of IL10 , which may play a role in inhibiting excess inflammatory reaction with its therapeutic effect on the lesion. Macrolide and ketolide therapy may have significant value for the treatment of human endometriosis.

The in vitro activities of modithromycin against Gram-positive and -negative respiratory pathogens, including macrolide-resistant cocci with different resistance mechanisms, were compared with those of other macrolide and ketolide agents. MICs were determined by the broth microdilution method. All 595 test strains used in this study were isolated from Japanese medical facilities. The erm (ribosome methylase) and/or mef (efflux pump) gene, which correlated with resistance to erythromycin as well as clarithromycin and azithromycin, was found in 81.8%, 21.3%, and 23.2% of Streptococcus pneumoniae , Streptococcus pyogenes , and methicillin-susceptible Staphylococcus aureus (MSSA) strains, respectively. Modithromycin showed MIC 90 s of 0.125 μg/ml against these three cocci, including macrolide-resistant strains. In particular, the MIC of modithromycin against ermB -carrying S. pyogenes was ≥32-fold lower than that of telithromycin. The activities of modithromycin as well as telithromycin were little affected by the presence of mefA or mefE in both streptococci. Against Gram-negative pathogens, modithromycin showed MIC 90 s of 0.5, 8, and 0.031 μg/ml against Moraxella catarrhalis , Haemophilus influenzae , and Legionella spp., respectively. The MICs of modithromycin against M. catarrhalis and H. influenzae were higher than those of telithromycin and azithromycin. However, modithromycin showed the most potent anti- Legionella activity among the macrolide and ketolide agents tested. These results suggested that the bicyclolide agent modithromycin is a novel class of macrolides with improved antibacterial activity against Gram-positive cocci, including telithromycin-resistant streptococci and intracellular Gram-negative bacteria of the Legionella species.

We characterized the mechanism of action and the drug-binding site of a novel ketolide, CEM-101, which belongs to the latest class of macrolide antibiotics. CEM-101 shows high affinity for the ribosomes of Gram-negative ( Escherichia coli ) and Gram-positive ( Staphylococcus aureus ) bacteria. The ketolide shows high selectivity in its inhibitory action and readily interferes with synthesis of a reporter protein in the bacterial but not eukaryotic cell-free translation system. Binding of CEM-101 to its ribosomal target site was characterized biochemically and by X-ray crystallography. The X-ray structure of CEM-101 in complex with the E. coli ribosome shows that the drug binds in the major macrolide site in the upper part of the ribosomal exit tunnel. The lactone ring of the drug forms hydrophobic interactions with the walls of the tunnel, the desosamine sugar projects toward the peptidyl transferase center and interacts with the A2058/A2509 cleft, and the extended alkyl-aryl arm of the drug is oriented down the tunnel and makes contact with a base pair formed by A752 and U2609 of the 23S rRNA. The position of the CEM-101 alkyl-aryl extended arm differs from that reported for the side chain of the ketolide telithromycin complexed with either bacterial ( Deinococcus radiodurans ) or archaeal ( Haloarcula marismortui ) large ribosomal subunits but closely matches the position of the side chain of telithromycin complexed to the E. coli ribosome. A difference in the chemical structure of the side chain of CEM-101 in comparison with the side chain of telithromycin and the presence of the fluorine atom at position 2 of the lactone ring likely account for the superior activity of CEM-101. The results of chemical probing suggest that the orientation of the CEM-101 extended side chain observed in the E. coli ribosome closely resembles its placement in Staphylococcus aureus ribosomes and thus likely accurately reflects interaction of CEM-101 with the ribosomes of the pathogenic bacterial targets of the drug. Chemical probing further demonstrated weak binding of CEM-101, but not of erythromycin, to the ribosome dimethylated at A2058 by the action of Erm methyltransferase.

The in vitro activity of CEM-101, a new fluoroketolide, was determined against Gram-positive organisms with various macrolide susceptibility profiles. Experiments for determination of the MICs and minimum bactericidal concentrations (MBCs), timed killing, single-step and multistep mutation rates, the erythromycin induction of resistance, postantibiotic effect (PAE), and drug interactions were performed for CEM-101; and the results were compared to those obtained with telithromycin, macrolides, and lincosamides. The MBCs of CEM-101 remained lower overall than those of telithromycin, and CEM-101 displayed a 2-fold greater potency than the ketolide. Timed-killing curve testing showed that CEM-101 had greater bactericidal activity than telithromycin (a ≥3-log 10 -CFU/ml decrease in the initial inoculum at 24 h) against the staphylococcal isolates tested. The propensity of CEM-101 to cause resistance was low, as determined from the rates of resistance determined in single-step mutational studies (−8 or 10 −9 ). In multipassaging studies, mutants of two strains (both of which were USA300 isolates) resistant to CEM-101 emerged. That number was comparable to the number resistant to clindamycin but less than the number resistant to telithromycin. Erythromycin induced CEM-101 resistance in Staphylococcus aureus and Streptococcus pneumoniae , similar to telithromycin; however, in seven of eight beta-hemolytic streptococci, CEM-101 resistance induction was not observed. CEM-101 showed a significant concentration- and exposure-dependent PAE against the strains tested, with the values ranging from 2.3 to 6.1 h for Gram-positive organisms (these times were longer than those for telithromycin). No antagonism was found in synergy analyses, with enhanced inhibition being most noted for combinations with CEM-101 and ceftriaxone, gentamicin, and trimethoprim-sulfamethoxazole. Overall, this new antimicrobial agent (CEM-101) showed good antimicrobial characteristics compared with those of the agents in its class and exhibited measured parameter values similar or superior to those of utilized comparators, indicating that CEM-101 warrants further clinical evaluation.

Objectives Telithromycin, a ketolide antibiotic, has an antibacterial range that covers intracellular parasitic pathogens that survive or multiply intracellularly in alveolar macrophages. The intracellular pharmacokinetics of TEL in alveolar macrophages was evaluated in vitro. Methods Telithromycin (50 µm) was applied to NR8383 as cultured alveolar macrophages, followed by incubation at 37°C or 4°C. After incubation, the amount of telithromycin in cells was determined. Key findings Telithromycin exhibited high accumulation in NR8383 and its intracellular accumulation was temperature dependent. Also, telithromycin distributed to the organelles and cytosol in NR8383 and, in particular, it accumulated in the acidic organelle compartments. Conclusions This study suggests that the high accumulation of telithromycin in NR8383 is due to its high influx via active transport systems and trapping in acidic organelles, such as lysosomes. Moreover, this study provides important information for optimizing the treatment of respiratory intracellular parasitic infections based on the intracellular pharmacokinetics of antibiotics and parasitic sites.

BACKGROUND: Airway mucus hypersecretion is an important problem in chronic respiratory diseases including bronchial asthma. Chlamydophila pneumoniae is recently confirmed to be a pathogen in bronchial asthma, but the relationship between C. pneumoniae and mucus hypersecretion is uncertain. In this study, we examined whether C. pneumoniae induces MUC5AC mucin in airway epithelial cells. We also examined the effects of macrolide and ketolide antibiotics on the C. pneumoniae-induced mucus production. METHODS: MUC5AC production in bronchial epithelial cells after stimulation with C. pneumoniae was analyzed by ELISA and quantitative RT-PCR. NF-kappaB and phosphorylated ERK were also analyzed. For inhibition study, cells were pretreated with azithromycin, clarithromycin and telithromycin before stimulation. RESULTS: C. pneumoniae dose-dependently induced MUC5AC production and gene expression. The ERK-NF-kappaB pathway was involved in C. pneumoniae-induced MUC5AC production. Macrolides and ketolides dose-dependently reduced C. pneumoniae-induced MUC5AC production. However, azithromycin was apparently less effective than the other antibiotics. Clarithromycin and telithromycin, but not azithromycin, reduced NF-kappaB activation. CONCLUSIONS: Clarithromycin and telithromycin were thought to interfere with the signal pathways between ERK and NF-kappaB. These results suggest that airway mucus hypersecretion is one of the mechanisms of C. pneumoniae-induced bronchial asthma, and that macrolide and ketolide antibiotics represent a novel therapeutic intervention in these patients., Pulmonary pharmacology & therapeutics, 22(6), pp.580-586; 2009

Mycobacterium abscessus infections tend to respond poorly to macrolide-based chemotherapy, even though the organisms appear to be susceptible to clarithromycin. Circumstantial evidence suggested that at least some M. abscessus isolates might be inducibly resistant to macrolides. Thus, the purpose of this study was to investigate the macrolide phenotype of M. abscessus clinical isolates. Inducible resistance to clarithromycin (MIC > 32 μg/ml) was found for 7 of 10 clinical isolates of M. abscessus previously considered susceptible; the remaining 3 isolates were deemed to be susceptible (MIC ≤ 0.5 μg/ml). Inducible resistance was conferred by a novel erm gene, erm (41), which was present in all 10 isolates and in an isolate of Mycobacterium bolletii ( M. abscessus type II). However, the erm (41) alleles were nonfunctional in the three susceptible M. abscessus isolates. No evidence of erm (41) was found in Mycobacterium chelonae , and an isolate of Mycobacterium massiliense appeared to be an erm (41) deletion mutant. Expression of erm (41) in M. abscessus conferred resistance to clarithromycin and erythromycin and the ketolide HMR3004. However, this species was found to be intrinsically resistant, independent of erm (41), to clindamycin, quinupristin (streptogramin B), and telithromycin. The ability to confer resistance to clindamycin and telithromycin, but not quinupristin, was demonstrated by expressing erm (41) in Maycobacterium smegmatis . Exposure of M. abscessus to the macrolide-lincosamide-streptogramin B-ketolide agents increased the levels of erm (41) mRNA 23- to 250-fold within 24 h. The inducible macrolide resistance phenotype of some M. abscessus isolates may explain the lack of efficacy of macrolide-based chemotherapy against this organism.

Ketolides represent the latest generation of macrolide antibiotics, displaying improved activities against some erythromycin-resistant strains, while maintaining their activity against erythromycin-susceptible ones. In this study, we present a new ketolide, K-1325, that carries an alkyl-aryl side chain at C-13 of the lactone ring. According to our genetic and biochemical studies, K-1325 binds within the nascent polypeptide exit tunnel, at a site previously described as the primary attachment site of all macrolide antibiotics. Compared with telithromycin, K-1325 displays enhanced antimicrobial activity against wild-type Escherichia coli strains, as well as against strains bearing the U2609C mutation in 23S rRNA. Chemical protection experiments showed that the alkyl-aryl side chain of K-1325 interacts specifically with helix 35 of 23S rRNA, a fact leading to an increased affinity of U2609C mutant ribosomes for the drug and rationalizing the enhanced effectiveness of this new ketolide.

In addition to their conventional antimicrobial activity, the macrolide group of antibiotics are known to have a number of anti-infammatory/ immunomodulatory activities, which may be of beneft to patients with chronic obstructive pulmonary disease (COPD), both in the stable state and during acute exacerbations. These activities involve interactions of the macrolides with the various components of infammation in patients with COPD, namely the ciliated airway epithelium, the immune and phagocytic cells of the host and their proinfammatory mediators, as well as with the microbes themselves. There are a number of factors that have been shown to cause injury to the bronchial epithelium and its mucociliary mechanism, including bacterial, chemical, mechanical and host-derived factors. The macrolide, azalide, ketolide group of antibiotics has been shown in many studies to be cytoprotective of human ciliated epithelium in vitro, protecting against both chemical mediator- and bacterial-mediated injury. Mucus hypers...

Objectives: Mucus hypersecretion is a prominent feature in patients with chronic respiratory tract infections such as cystic fibrosis and diffuse panbronchiolitis, and the clinical effectiveness of macrolide antibiotics has been reported in these patients. Because human neutrophil peptide-1 (HNP-1), an antimicrobial peptide in neutrophils, exists in high concentrations in the airway fluid of these patients, we examined the direct effect of HNP-1 on MUC5AC mucin production using NCI-H292 cells. The effects of macrolide antibiotics on the response were also examined. Methods: MUC5AC synthesis was assayed using RT-PCR and ELISA. Phosphorylation of ERK1/2 was determined by western blotting. Results: Stimulation with HNP-1 or lipopolysaccharide (LPS) derived from Pseudomonas aeruginosa increases the production of MUC5AC mRNA and protein, and an additive effect was found upon co-stimulation with both HNP-1 and LPS. Azithromycin and clarithromycin had inhibitory effects on overproduction of MUC5AC induced by HNP-1 or LPS stimulation. Telithromycin also had an inhibitory effect on MUC5AC production induced by LPS, but not on production by HNP-1. Phosphorylation of ERK1/2 was induced by HNP-1 or LPS stimulation, and azithromycin, clarithromycin and telithromycin had inhibitory effects on ERK1/2 phosphorylation induced by LPS, but not by HNP-1. Conclusions: These findings suggest that neutrophil-derived defensins as bacterial components contribute to excessive mucus production in patients with respiratory tract infections, and that macrolide and ketolide antibiotics directly inhibit these actions by interfering with intracellular signal transduction. However, the mechanism of telithromycin inhibition of MUC5AC synthesis may differ from the response induced by azithromycin and clarithromycin.

Ketolides, characterized by possessing a 3-keto group in place of the l-cladinose moiety of erythromycin A, are the recent generation of antimicrobials derived semi-synthetically from the 14-membered ring macrolide erythromycin A. The multi-step synthetic route to ketolides can be shortened by using 5-O-desosaminyl erythronolide A as a precursor, which reduces the steps for the removal of l-cladinose attached at the C-3 position in erythromycin A. Deletion of an eryBV gene encoding mycarosyl glycosyltransferase in the erythromycin-producer Saccharopolyspora erythraea resulted in the accumulation of 5-O-desosaminyl erythronolide B. In vivo expression of the cytochrome P450 gene pikC, which encodes the substrate-flexible hydroxylase from the pikromycin biosynthetic pathway of Streptomyces venezuelae, in the eryBV deletion mutant strain of Sac. erythraea led to 5-O-desosaminyl erythronolide A production.

This Minireview summarizes the changes in the field of bacterial resistance to macrolide, lincosamide, streptogramin, ketolide, and oxazolidinone (MLSKO) antibiotics since the nomenclature review in 1999. A total of 66 genes conferring resistance to this group of antibiotics has now been identified and includes 13 new rRNA methylase genes, four ATP-binding transporter genes coding for efflux proteins, and five new inactivating enzymes. During this same time period, 73 new genera carrying known rRNA methylase genes and 87 new genera carrying known efflux and/or inactivating genes have been recognized. The number of bacteria with mutations in the genes for 23S rRNA, L4 and L22 ribosomal proteins, resulting in reduced susceptibility to some members of the group of MLSKO antibiotics has also increased and now includes nine different Gram-positive and 10 different Gram-negative genera. New conjugative transposons carrying different MLSKO genes along with an increased number of antibiotics and/or heavy metal resistance genes have been identified. These mobile elements may play a role in the continued spread of the MLSKO resistance genes into new species, genera, and ecosystems.

A telithromycin-resistant clinical isolate of Streptococcus pneumoniae (strain P1501016) has been found to contain a version of erm (B) that is altered by a 136-bp deletion in the leader sequence. By allele replacement mutagenesis, a second strain of S. pneumoniae (PC13) with a wild-type erm (B) gene was transformed to the telithromycin-resistant phenotype by introduction of the mutant erm (B) gene. Whereas the wild-type PC13 strain showed slight telithromycin resistance only after induction by erythromycin (telithromycin MIC increased from 0.06 to 0.5 μg/ml), the transformed PC13 strain is constitutively resistant (MIC of 16 μg/ml). Expression of erm (B) was quantified by real-time reverse transcription-PCR in the presence of erythromycin or telithromycin; erm (B) expression was significantly higher in the transformed PC13 strain than the wild-type strain. Furthermore, the transformed strain had significantly higher levels of ribosomal methylation in the absence as well as in the presence of the antibiotics. Growth studies showed that the transformed PC13 strain had a shorter lag phase than the wild-type strain in the presence of erythromycin. Telithromycin resistance is conclusively shown to be conferred by the mutant erm (B) gene that is expressed at a constitutively higher level than the inducible wild-type gene. Elevated erm (B) expression results in a higher level of rRNA methylation that presumably hinders telithromycin binding to the ribosome.

The Japanese Society of Chemotherapy (JSC) conducted the first nationwide surveillance of bacterial respiratory pathogens during the period from January to August 2006. With the cooperation of 32 medical institutions throughout Japan, a total of 924 strains belonging to seven clinically relevant bacterial species were collected from adult patients with well-diagnosed respiratory tract infections (RTIs). Antimicrobial susceptibility testing of the 887 evaluable strains (205 Staphylococcus aureus, 200 Streptococcus pneumoniae, 9 Streptococcus pyogenes, 165 Haemophilus influenzae, 91 Moraxella catarrhalis, 74 Klebsiella pneumoniae, and 143 Pseudomonas aeruginosa) to 42 antibacterial agents was conducted at the Central Laboratory of the Research Center for Anti-infective Drugs of the Kitasato Institute, according to recommendations issued by the Clinical and Laboratory Standards Institute (CLSI). The antibacterial agents employed were 25 beta-lactams, three aminoglycosides, four macrolides (including one azalide and one ketolide), one lincosamide, one tetracycline, two glycopeptides, five fluoroquinolones, and one oxazolidinone. The incidence of methicillin-resistant S. aureus (MRSA) was 63.4%, and the incidences of penicillin-intermediately resistant S. pneumoniae (PISP) and penicillin-resistant S. pneumoniae (PRSP) were 35.0% and 4.0%, respectively. Among H. influenzae, 21.2% of the strains were found to be beta-lactamase-nonproducing ampicillin (ABPC)-intermediately resistant (BLNAI), 29.1% to be beta-lactamase-nonproducing ABPC-resistant (BLNAR), and 4.8% to be beta-lactamaseproducing ABPC-resistant (BLPAR) strains. The incidence of extended-spectrum beta-lactamase-producing K. pneumoniae was 2.7% (2 of 74 strains). Three (2.1%) of the 143 P. aeruginosa strains were found to be metallo-beta-lactamaseproducing, including 1 (0.7%) multidrug-resistant strain. Through the nationwide surveillance, we obtained fundamental antimicrobial susceptibility data of clinically relevant bacterial pathogens in adult RTI to various antibacterial agents. These data will be a useful reference for future periodic surveillance studies, as well as for investigations to control antimicrobial-resistant pathogens.

There is increasing evidence that atypical respiratory pathogens such as Chlamydophila pneumoniae and Mycoplasma pneumoniae may contribute to the pathogenesis of both stable asthma and asthma exacerbations. It is postulated that these organisms may contribute to inflammation in the airways possibly by activating inflammatory mechanisms in the respiratory tract. The macrolide class of antibiotics may have a part to play in the management of asthma by exerting anti-inflammatory effects on the chronically inflamed airways in addition to their anti-infective action. The ketolide antibiotics may also have similar properties. This paper discusses the role of these antibiotics in the management of asthma.

This study aims to compare the resistance phenotypes conferred by various genes encoding enzymes that phosphorylate erythromycin. The mph genes were cloned into Escherichia coli AG100A susceptible to macrolides and ketolides following disruption of the AcrAB pump. An 882 bp sequence containing a premature stop codon, homologous to the three other previously described mph genes and present widely among Enterobacteriaceae, was found to confer resistance to erythromycin by phosphorylation. The mph(C) gene, as reported for mph(B), also conferred resistance to spiramycin. The mph(A) gene was unique in conferring resistance to azithromycin. The four investigated genes conferred resistance to telithromycin.