Search

In a post hoc analysis of samples from an intrapartum azithromycin randomized clinical trial, we found that children whose mothers had been treated with the drug had higher prevalence of macrolide-resistance genes msr(A) and ermC at 28 days but not at 12 months. The 2 genes were positively associated in the nasopharynx. Clinical Trials Registration NCT1800942. [ABSTRACT FROM AUTHOR]

Herein, 15 phenylpiperazine 3-benzyl-5,5-dimethylhydantoin derivatives (1–15) were screened for modulatory activity towards Msr(A) efflux pump present in S. epidermidis bacteria. Synthesis, crystallographic analysis, biological studies in vitro and structure–activity relationship (SAR) analysis were performed. The efflux pump inhibitory (EPI) potency was determined by employing ethidium bromide accumulation assay in both Msr(A) efflux pump overexpressed (K/14/1345) and deficient (ATCC 12228) S. epidermidis strains. The series of compounds was also evaluated for the capacity to reduce the resistance of K/14/1345 strain to erythromycin, a known substrate of Msr(A). The study identified five strong modulators for Msr(A) in S. epidermidis. The 2,4-dichlorobenzyl-hydantoin derivative 9 was found as the most potent EPI, inhibiting the efflux activity in K/14/1345 at a concentration as low as 15.63 µM. Crystallography-supported SAR analysis indicated structural properties that may be responsible for the activity found. This study identified the first synthetic compounds able to inhibit Msr(A) efflux pump transporter in S. epidermidis. Thus, the hydantoin-derived molecules found can be an attractive group in search for antibiotic adjuvants acting via Msr(A) transporter.

The aim of this study was to determine both the occurrence and the genetic basis of resistance to erythromycin among 1 235 Staphylococcus spp. isolates obtained between 2000 and 2006 from (a) raw milk and meat (1 704 samples), (b) foodstuffs produced from these (451 samples), and (c) contact surfaces at processing plants and dairy farms (363 samples) in the Czech Republic. Isolates were screened by broth microdilution method for resistance to erythromycin and further 11 antimicrobial agents. In addition, isolates were screened by agar dilution (erythromycin range 1-128 mg/l) and D-zone test for inducible resistance to macrolides, lincosamides and streptogramin B (iMLSB). Forty isolates were found to be either resistant, or intermediate, to erythromycin (3.2% of isolates); of these, more than 50% were identified as S. epidermidis. A total of 15 (1.2%) resistant isolates of staphylococci originated from foodstuffs. Resistance mediated by methylation - i.e. iMLSB-resistance (10 isolates with the erm(A) or erm (C) gene) and constitutive MLSB-resistance (one isolate with the erm (B) and erm (C) genes) - exhibited a significantly high level of resistance to erythromycin with minimum inhibitory concentrations (MIC) of 64 - >128 mg/l (MICmode = >128 mg/l). In contrast, the efflux mechanism encoded by the msr(A) gene (13 isolates; MICrange = 4-128, MICmode = 128 mg/l), the inactivation mechanisms of resistance encoded by the mph(C) gene (three isolates; MICrange = 8-32 mg/l), and/or their combination (13 isolates; MICrange = 4-128, MICmode = 64 mg/l) led to lower MIC values. The efflux gene

Background/aim: Macrolide and lincosamide antibiotics are used for the treatment of staphylococcal infections, especially for penicillin-allergic patients. In the present study, we evaluate the prevalence of resistance to macrolide and lincosamide antibiotics among staphylococci isolates. Materials and methods: A total of 200 staphylococcal clinical isolates were collected from January 2012 to April 2013. Minimal inhibitory concentrations of erythromycin and clindamycin were determined by agar dilution method. An erythromycin-clindamycin induction test was performed for isolates that were only resistant to erythromycin. Representative erythromycin-resistant isolates were examined for erythromycin resistance genes using PCR. Results: Among staphylococci isolates, resistance frequencies of erythromycin and clindamycin were 65.5% and 20.5%, respectively. Erythromycin resistance was found to be mediated by putative efflux (50.4%) and target site modification (49.6%). Inducible target site modification resistance was detected in 19.1% of erythromycin-resistant isolates. Among the examined 36 staphylococci isolates, msr(A), erm(C), erm(A), and mef(A/E) genes were detected in 55.6%, 30.6%, 25%, and 0%, respectively. Conclusion: Results of the current study indicate the presence of high rates of macrolide resistance and inducible phenotypes among staphylococcal isolates. It is also essential to keep in mind variations of resistance rates among various age groups and specimen types. [ABSTRACT FROM AUTHOR]

The consequence of excessive use of macrolides is a high occurrence of mechanisms responsible for resistance to these drugs. Of 97 erythromycin-resistant bacterial strains gathered in the Wrocław area in Poland, 60% exhibited very high resistance, and those with the inducible MLS (macrolide-lincosamide-streptogramin B) resistance phenotype predominated. Direct genetic investigation revealed that the erm genes coding for ribosomal methylases are the most frequently occurring erythromycin resistance-determining genes. No genetic resistance determinant was detected in 13% of the erythromycin-resistant strains. The efflux mechanism occurs in strains isolated from the nasopharyngeal cavity twice as often as in those isolated from other material, where the mechanism connected with target site modification predominates. Measurements of radiolabelled antibiotic accumulation inside bacterial cells revealed that in highly resistant strains (MIC > 1024 μg/ml), an important factor responsible for the resistance is the permeability barrier at the cell wall level. This would be a hitherto unknown mechanism of resistance to erythromycin in Staphylococcus aureus. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this study was to evaluate the prevalence of resistance to macrolide–lincosamide–streptogramin (MLS) antibiotics as well as to assess the molecular basis of this resistance amongst 72 Staphylococcus saprophyticus urinary isolates collected from 2005 to 2009 in University Hospital of Caen (France). Of the 72 strains studied, 33 (45.8%) were resistant to at least one MLS antibiotic, including 24 (72.7%) with an M phenotype, 5 (15.2%) with an inducible MLSB phenotype, 3 (9.1%) with a combined M+L phenotype and 1 (3.0%) with an L phenotype. All isolates were susceptible to the combination of streptogramins A and B. The resistance genes erm(A), erm(B), erm(C), msr(A) and lnu(A) were detected alone in 0, 0, 5 (15.2%), 24 (72.7%) and 1 (3.0%) of the 33 MLS-resistant isolates, respectively, whereas 2 strains (6.1%) were positive for both msr(A) and lnu(A). All msr(A)-positive isolates exhibited an M phenotype, whereas all five erm(C)-positive and all three lnu(A)-positive strains displayed, respectively, an inducible MLSB phenotype and an L phenotype with a positive Hodge test. Plasmid analysis indicated that erm(C) and lnu(A) genes were borne by small-size plasmids (ca. 2.5kb), whereas larger plasmids (30–90kb) harboured msr(A). In conclusion, these findings show a high prevalence of MLS resistance in S. saprophyticus, which was mainly associated with the presence of the msr(A) gene. Since S. saprophyticus colonises the gastrointestinal tract, it may constitute an unexpected reservoir for MLS resistance genes, in particular msr(A), amongst coagulase-negative staphylococci. [ABSTRACT FROM AUTHOR]

The gene msr(A) confers inducible resistance to 14-membered-ring macrolides and type B streptogramins (MSB resistance) in staphylococci. The encoded hydrophilic protein (Msr(A)) is 488 amino acids and contains two ATP-binding motifs characteristic of the ABC transporters. The classical organisation of ABC transporters requires interaction between the two cytoplasmically located ATP-binding domains with two hydrophobic domains positioned in the membrane. Msr(A) appears to mediate drug efflux and yet contains no hydrophobic membrane spanning domains. In addition, Msr(A) functions in previously sensitive heterologous hosts such as Staphylococcus aureus in the absence of other plasmid encoded products. Current research on Msr(A) and related determinants in Gram-positive cocci and in antibiotic producing organisms is reviewed. Alternative hypotheses for the mechanism of action of Msr(A) (i.e. active transport vs. ribosomal protection) are discussed. Evidence indicating Msr(A) may have a role in virulence in addition to conferring antibiotic resistance is also considered. [Copyright &y& Elsevier]

Herein, 15 phenylpiperazine 3-benzyl-5,5-dimethylhydantoin derivatives (1–15) were screened for modulatory activity towards Msr(A) efflux pump present in S. epidermidis bacteria. Synthesis, crystallographic analysis, biological studies in vitro and structure–activity relationship (SAR) analysis were performed. The efflux pump inhibitory (EPI) potency was determined by employing ethidium bromide accumulation assay in both Msr(A) efflux pump overexpressed (K/14/1345) and deficient (ATCC 12228) S. epidermidis strains. The series of compounds was also evaluated for the capacity to reduce the resistance of K/14/1345 strain to erythromycin, a known substrate of Msr(A). The study identified five strong modulators for Msr(A) in S. epidermidis. The 2,4-dichlorobenzyl-hydantoin derivative 9 was found as the most potent EPI, inhibiting the efflux activity in K/14/1345 at a concentration as low as 15.63 µM. Crystallography-supported SAR analysis indicated structural properties that may be responsible for the activity found. This study identified the first synthetic compounds able to inhibit Msr(A) efflux pump transporter in S. epidermidis. Thus, the hydantoin-derived molecules found can be an attractive group in search for antibiotic adjuvants acting via Msr(A) transporter. [ABSTRACT FROM AUTHOR]

Members of the ATP-binding cassette (ABC)-F protein subfamily collectively mediate resistance to a broader range of clinically important antibiotic classes than any other group of resistance proteins and are widespread in pathogenic bacteria. Following over 25 years' of controversy regarding the mechanism by which these proteins work, it has recently been established that they provide antibiotic resistance through the previously recognized but underappreciated phenomenon of target protection; they bind to the ribosome to effect the release of ribosome-targeted antibiotics, thereby rescuing the translation apparatus from antibiotic-mediated inhibition. Here we review the ABC-F resistance proteins with an emphasis on their mechanism of action, first exploring the history of the debate about how these proteins work and outlining our current state of knowledge and then considering key questions to be addressed in understanding the molecular detail of their function.