rifampin and kasugamycin

Most bacteria use an indirect pathway to generate aminoacylated glutamine and/or asparagine tRNAs. Clinical isolates of

Topics: Aminoacylation; Aminoglycosides; Animals; Drug Resistance, Bacterial; Drug Synergism; Edeine; Injections, Intraperitoneal; Mice; Microbial Sensitivity Tests; Mycobacterium tuberculosis; Organ Specificity; Protein Biosynthesis; Rifampin; RNA, Transfer; Streptomycin; Tuberculosis

The methyltransferases RsmG and KsgA methylate the nucleotides G535 (RsmG) and A1518 and A1519 (KsgA) in 16S rRNA, and inactivation of the proteins by introducing mutations results in acquisition of low-level resistance to streptomycin and kasugamycin, respectively. In a Bacillus subtilis strain harboring a single rrn operon (rrnO), we found that spontaneous ksgA mutations conferring a modest level of resistance to kasugamycin occur at a high frequency of 10(-6). More importantly, we also found that once cells acquire the ksgA mutations, they produce high-level kasugamycin resistance at an extraordinarily high frequency (100-fold greater frequency than that observed in the ksgA(+) strain), a phenomenon previously reported for rsmG mutants. This was not the case for other antibiotic resistance mutations (Tsp(r) and Rif(r)), indicating that the high frequency of emergence of a mutation for high-level kasugamycin resistance in the genetic background of ksgA is not due simply to increased persistence of the ksgA strain. Comparative genome sequencing showed that a mutation in the speD gene encoding S-adenosylmethionine decarboxylase is responsible for the observed high-level kasugamycin resistance. ksgA speD double mutants showed a markedly reduced level of intracellular spermidine, underlying the mechanism of high-level resistance. A growth competition assay indicated that, unlike rsmG mutation, the ksgA mutation is disadvantageous for overall growth fitness. This study clarified the similarities and differences between ksgA mutation and rsmG mutation, both of which share a common characteristic--failure to methylate the bases of 16S rRNA. Coexistence of the ksgA mutation and the rsmG mutation allowed cell viability. We propose that the ksgA mutation, together with the rsmG mutation, may provide a novel clue to uncover a still-unknown mechanism of mutation and ribosomal function.

Topics: Aminoglycosides; Bacillus subtilis; Bacterial Proteins; Drug Resistance, Microbial; Methyltransferases; Mutation; RNA, Ribosomal, 16S

Strains of Escherichia coli can be isolated that require erythromycin for growth. With one strain, AM, a range of antibiotics, including chloramphenicol, tetracycline, spectinomycin, kasugamycin and rifampicin, will substitute for erythromycin on solid and in liquid media; nalidixic acid supports growth in liquid but not on solid media. With a second strain, 103, chloramphenicol, tetracycline and spectinomycin support growth in liquid media but on solid medium only chloramphenicol substitutes for erythromycin. In media of higher than normal ionic strength, strain AM, but not strain 103, can grow in the absence of antibiotics. Possible reasons for these complex phenotypes are discussed.

Topics: Aminoglycosides; Anti-Bacterial Agents; Bacterial Proteins; Chloramphenicol; Culture Media; DNA, Bacterial; Erythromycin; Escherichia coli; Phenotype; Rifampin; RNA, Bacterial; Spectinomycin; Tetracycline