The comparative study on the effects of chloramphenicol, erythromycin and lincomycin on polylysine synthesis in an Escherichia coli cell-free system

Pleiotropic antibiotic resistance mutations associated with ribosomes and ribosomal subunits in Mycobacterium smegmatis

Viomycin-resistant strains isolated from Mycobacterium smegmatis demonstrated pleiotropic resistance to tuberactinomycin-N, capreomycin, streptomycin, and kanamycin as a result of mutational alteration of ribosomes, even though they were selected for resistance to a single antibiotic. The pleiotropic drug resistance of three mutants isolated by stepwise selection for resistance to viomycin was due to alteration of the 30S ribosomal subunit. One mutant, strain A, isolated independently by multiple-step selection to viomycin resistance, was resistant to viomycin, tuberactinomycin-N, and capreomycin through an alteration of the 50S ribosomal subunit, whereas it was sensitive to kanamycin but resistant to streptomycin through an alteration of the 30S ribosomal subunit. Three streptomycin-resistant strains, which were isolated by one-step selection at a high concentration of streptomycin, did not show significant co-resistance to any other antibiotics tested in culture and cell-free systems; streptomycin resistance in these mutants was localized on the 30S ribosomal subunit.

Analysis of lincomycin resistance mutations in Escherichia coli

High level lincomycin resistant strains of Escherichia coli were isolated and screened for altered ribosomal proteins and functions. Amongst 58 strains investigated by electrophoresis one had an altered ribosomal protein S7, another one a mutated L14 and two showed altered L15 proteins. A correlation between these alterations and lincomycin resistant growth could not be demonstrated by genetic analysis for any of the mutants. In vitro, however, extracts from the two L15 mutants were less sensitive to inhibition by the drug. A gene locus (linR) responsible for the lincomycin resistance phenotype was mapped at min 30 of the Escherichia coli chromosome near tyrR; it seems to be identical to the previously described linB locus (Apirion, 1967); however, in contrast to these reports it does not seem to alter any ribosomal function.

Susceptibilities of gram-negative bacteria to combinations of antimicrobial agents in vitro

Combinations of either clindamycin or erythromycin with gentamicin, colimycin, or carbenicillin were studied for their antimicrobial effects on clinical isolates of Escherichia coli, Klebsiella sp., Proteus mirabilis, Serratia marcescens, Enterobacter aerogenes, and Pseudomonas aeruginosa. No antagonistic effects of the antibiotic combinations were observed. Synergistic effects of the antibiotic combinations were noted against most strains of E. coli tested, especially when either clindamycin or erythromycin was combined with gentamicin or colimycin. Of 16 other combinations of antibiotics examined with strains of E. coli as the test organisms, only the combination of penicillin G with either gentamicin or colimycin showed consistent synergy. The marked synergy of clindamycin combined with either gentamicin or colimycin was further demonstrated by following the kinetics of the bactericidal action of the antibiotic combinations and the effects on bacterial protein synthesis.

Peptidyl puromycin synthesis; effect of several antibiotics which act on 50 S ribosomal subunits

The effects of several antibiotics which are know to bind with 50 S ribosomal subunits, on the formation of several di- and tri-peptidyl puromycins have been examined. Tylosin and spiramycin inhibited the formation of phenylalanyl-(14)C-phenylalanyl-puromycin, glycyl-(14)C-phenyllalanyl-puromycin, leucyl-(14)C-phenylalanyl-puromycin, N(epsilon)-carbobenzoxylysyl-(14)C-phenylalanyl-puromycin, and valyl-glycyl-(14)C-phenylalanyl-puromycin as well as N-acetyl-(14)C-phenylalanyl-puromycin. Of these compounds, erythromycin and oleandomycin selectively inhibited the formation of phenylalanyl-(14)C-phenylalanyl-puromycin. Although chloramphenicol and lincomycin inhibited the formation of most of these peptidyl puromycins, the formation of phenylalanyl-(14)C-phenylalanyl-puromycin and leucyl-(14)C-phenylalanyl-puromycin was found to be resistant to these antibiotics. So far, no significant effect of siomycin has been observed on pepetidyl puromycin formation in the absence of G factor.