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Fourteen different aminoglycoside antibiotics (AGs) were challenged with aminoglycoside acetyltransferases (AACs) of actinomycete origin in order to examine their 'double stage activity' that is arbitrarily defined as antibiotic activity retainable after enzymatic modification. In kanamycin (KM)-group AGs tested [KM, dibekacin (DKB), amikacin and arbekacin (ABK)], ABK retained activity after acetylations by AAC(3), AAC(2') and AAC(6'). DKB also retained a weak activity after acetylation by AAC(2'). In gentamicin (GM)-group AGs tested [GM, micronomicin, sisomicin (SISO), netilmicin (NTL) and isepamicin], GM, SISO and NTL retained activites after acetylation by AAC(2'). In neomycin (NM)-group AGs tested [ribostamycin, NM, paromomycin], NM retained activity after acetylation by AAC(6') and AAC(2'). None of astromicin (ASTM)-group AGs tested (ASTM and istamycin B) retained activity after acetylation by AAC(2') and AAC(6'). The activities of acetylated ABK derivatives by AAC(3) and AAC(2') were distinctively high, compared to the others. Streptomyces lividans TK21 containing the cloned aac genes were markedly sensitive to AGs that retained activities after acetylation, indicating the substantial effect of 'double stage activity'.

Aminoglycoside antibiotics (AGs) with a free 2'-amino group were subjected to enzymatic N-acetylation using a cell free extract that contained an aminoglycoside 2'-N-acetyltransferase, AAC (2'), derived from a kasugamycin-producing strain of Streptomyces kasugaensis. TLC and antibiotic assay of the incubated reaction mixtures revealed that a modified compound retaining substantial antibiotic activity was formed from arbekacin (ABK), while modification of the other AGs resulted in the marked decrease in antibiotic activity. Structure determination following isolation from a large scale reaction mixture showed the modified ABK to be 2'-N-acetyl ABK. In addition, 2',6'-di-N-acetyl ABK was formed as a minor product. The same conversion also occurred with dibekacin (DKB) resulting in the formation of 2'-N-acetyl DKB and 2',6'-di-N-acetyl DKB. MIC determination showed antibacterial activity (1.56 approximately 3.13 micrograms/ml) of 2'-N-acetyl ABK against a variety of organisms. By contrast, 2'-N-acetyl DKB showed no substantial antibiotic activity. We believe 2'-N-acetyl ABK has the highest and broadest antibacterial activity, compared with known N-acetylated AGs.

Only a limited number of strains of methicillin-resistant Staphylococcus aureus (MRSA) moderately resistant to arbekacin (ABK) have been isolated clinically. Three inactivated products of ABK have been obtained by reaction with excess amounts of a crude enzyme preparation extracted from an ABK-resistant MRSA strain (MIC, 25 micrograms/ml). The 2"-O-phosphate was the major product together with small amounts of the 6'-N-acetate and the double modification product. The structures of these modification products were determined by MS and NMR spectral analyses.

The degrees of binding of [3H]dibekacin to LiCl-treated cores of E. coli ribosomes were reduced by increasing LiCl concentrations. The 1.15 M LiCl core lost 70 approximately 80% of the original binding capacity. The antibiotic attachment to the 1.15 M LiCl core was restored by reconstitution with the split proteins (SP), which were obtained by the treatment of 70S ribosomes with LiCl at concentrations of 0.8 approximately 1.15 M. The basic proteins, split off during the transition from 0.4 M LiCl core to 0.8 approximately 1.15 M LiCl core, seemed to be involved in the drug binding. SP0.4 approximately 1.15, which was obtained by the treatment of the 0.4 M LiCl core with 1.15 M LiCl, was fractionated by CM-Sephadex C-25 column chromatography, and each fraction was assayed for protein composition and the capability of restoring the ability of the 1.15 M LiCl core to bind the drug. Of ribosomal proteins eliminated with 1.15 M LiCl, the addition of either S9 or L6 alone to the 1.15 M LiCl core was observed to restore approximately 50% of the binding as compared to the 70S ribosome alone, and both proteins restored about 70% of the binding. The results suggested that ribosomal proteins S9 and L6 were involved in the attachment of [3H]dibekacin to the ribosome. The antibiotic binding to the 70S ribosome and 1.15 M LiCl core reconstituted with S9 and L6 was considerably inhibited by unlabelled dibekacin or kanamycin, and partially inhibited by gentamicin or neomycin, but was not significantly affected by streptomycin or viomycin.

Actinomycetes were characterized in terms of resistance to 11 different aminoglycoside antibiotics (AGs). Strains freshly isolated in AG containing media showed wide varieties of multiple AG resistance, while the majority of ISP (International Streptomyces Project) cultures and the actinomycete strains isolated in an AG free medium were susceptible to all or most of the AGs tested. Marked characteristics were noted in multiple AG resistance of gray and yellow colored actinomycetes and AG-producing strains. In gray colored isolates, multiple resistance to kanamycin A, dibekacin, ribostamycin, butirosin A, istamycin A and neamine was often observed. Yellow colored isolates having multiple AG resistance were mostly resistant to neamine, ribostamycin and streptomycin and, to a lesser extent, istamycin A, dibekacin and butirosin A. Most of the AG producers tested showed unique multiple AG resistance patterns.

Streptomyces tenebrarius ISP 5477, which produces nebramycins, was highly resistant to the following aminoglycoside antibiotics: neamine, ribostamycin, butirosin A, neomycin B, paromomycin, kanamycin A, dibekacin, gentamicin C complex, lividomycin A, istamycin B and streptomycin. Polyphenylalanine synthesis on the ribosomes of this strain was highly resistant to neamine, ribostamycin, butirosin A, kanamycins A, B and C, dibekacin, gentamicin C complex and istamycin B, moderately resistant to lividomycin A and streptomycin, but sensitive to neomycin B and paromomycin. Moreover, cell free extract of the strain contained phosphotransferase and N-acetyltransferase. The former enzyme was confirmed to be an aminoglycoside 6-phosphotransferase which inactivated streptomycin; the latter inactivated kanamycins B and C, dibekacin, neamine, neomycin B, paromomycin, lividomycin A, butirosin A and ribostamycin, but did not inactivate kanamycin A, gentamicin C complex and sagamicin, suggesting an aminoglycoside 2'-acetyltransferase. These results indicated that the high resistance of S. tenebrarius ISP 5477 to a wide range of aminoglycoside antibiotics is due to ribosomal resistance and to the inactivating enzymes, aminoglycoside N-acetyltransferase(s) and aminoglycoside 6-phosphotransferase.

The effects of habekacin on corneal ulceration, caused by Pseudomonas aeruginosa IFO 3455, were studied in mice, in comparison with gentamicin and tobramycin. The minimal inhibitory concentrations of the antibiotics for the organism were: habekacin 2 microgram/ml, gentamicin 2 microgram/ml, and tobramycin 1 microgram/ml. Habekacin showed protective and therapeutic effects on Pseudomonas keratitis. The 50% effective dose was approximately 1 microgram per mouse, when the drug was topically applied three hours after the infection, and about 0.2 mg per mouse, when the antibiotic was intramuscularly injected one hour after the bacterial challenge to the cornea. Significant therapeutic and protective activities of habekacin were observed even by starting the topical and/or intramuscular treatment after the corneal ulcers were formed: i.e. 15 hours after the bacterial infection. Complete cure of Pseudomonas keratitis was found within a week in a number of the infected mice by both topical and systemic administrations of the drug. The protective and therapeutic effects of habekacin were comparable to those of gentamicin and tobramycin.

The nephrotoxicity of rats caused by dibekacin (3',4'-dideoxykanamycin B) or kanamycin with or without dextran was effectively reduced by D-glucaro-delta-lactam potassium salt, as evidenced by lower levels of blood urea nitrogen and kidney edema rate, better excretion of antibiotics,and less morphological damage. Protection was dosage related, and potentiated with increasing doses, but only when the two drugs were given simultaneously. Among three alkali-metal salts examined, the potassium salt was almost equal to the lithium salt, but surpassed the sodium salt in effectiveness. Inorganic salts, in particular potassium chloride were found to be effective for the protection of normal rats, but their effect decreased for the dehydrated rats, especially in the presence of dextran.

The occurrence in beta-lactam treated patients of unstable L-forms of Pseudomonas aeruginosa insensitive to various antibiotics and synergistic effect of combined action of cell wall-affecting antibiotics and macrolide on Pseudomonas infection led us to examine the effects of macrolide on P. aeruginosa pretreated with cell wall-affecting antibiotics. The effects of macrolide antibiotics such as midecamycin acetate (MOM) on P. aeruginosa was investigated, a rapid killing effect by MOM was noted after treatment with suboptimal doses of cell wall-affecting antibiotics such as polymyxin B, carbenicillin, dibekacin or fosfomycin. Incorporation of [14C]MOM into intact P. aeruginosa cells was not significant, but was apparent into L-form cells or cells pretreated with cell wall-affecting antibiotics. The incorporated radioactivity was found in the 70 S ribosome fraction, binding with the 50 S subunits of ribosome in both cases. These results indicate that under certain conditions a macrolide antibiotic can enter the P. aeruginosa cell.

Synergistic effects of the cell wall-affecting antibiotics, dibekacin (DKB) and fosfomycin (FOM) and a macrolide antibiotic, midecamycin (MDM) or its derivative 9,3"-di-O-acetylmidecamycin (MOM) against Pseudomonas aeruginosa were investigated in vitro and in vivo. Synergistic effects were evaluated by estimating the number of viable bacteria at varying intervals after the two kinds of antibiotics were added to the logarithmic phase of the bacterial solution. Six hours after addition of antibiotic, the viable bacterial count of the culture treated with FOM and MOM underwent 2 log reduction compared to that which treated with FOM alone. Thus synergistic effect was significant. The number of viable bacteria treated with DKB and MDM showed slight reduction at 3 hours after addition of the two antibiotics and a marked reduction was noted after 20 hours compared with the control. Synergistic action was also demonstrated in in vivo experiments using mice. Three experimental mouse infection models, intraperitoneal infection, subcutaneous infection with carrageenan solution and burn infection were used. FOM was administered subcutaneously. DKB was administered intramuscularly. MDM or MOM was administered by the oral route. In all three experiments the survival rate of infected mice treated with FOM and MOM increased significantly compared to control mice. Similar synergistic effect was also obtained with DKB and MDM.

Two pairs of butirosin analogs were isolated from the fermentation broths obtained by cultivating a neamine-negative mutant of the butirosin-producing organism Bacillus circulars in the medium supplemented with 6'-N-methylneamine and gentamine C2, respectively. These antibiotics were characterized as 6'-N-methylbutirosins A and B (NMB-A & NMB-B), and 3', 4'-dideoxy-6'-C-methylbutirosins A and B (DCB-A & DCB-B), respectively, by chemical and spectroscopic studies. NMB-A and NMB-B exhibited broad-spectrum antibacterial activities with in vitro potency similar to or slightly less than that for butirosin A, but with greater activities against butirosin-resistant strain which contains acetylating enzyme AAC- (6')-I. The activities of NMB-A and NMB-B against Pseudomonas aeruginosa strains were relatively weak. DCB-B had broad-spectrum activity, and exhibited greatly improved activity against butirosin-resistant organisms which contain acetylating enzymes AAC(6')-I and AAC(6')-IV, and phosphorylating enzyme APH(3')-II. These new butirosin analogs were also active against some of the clinical isolates resistant to butirosins, dibekacin and/or gentamicin.