title: Isolation of spectinomycin resistance mutations in the 16S rRNA of Salmonella enterica serovar Typhimurium and expression in Escherichia coli and Salmonella.
abstract: Two single-base mutations in 16S rRNA conferring high-level resistance to spectinomycin were isolated on a plasmid-borne copy of the rrnD operon from Salmonella enterica serovar Typhimurium. Neither of the mutations (C1066U and C1192U) had appreciable effects on cell growth, but each had differential effects on resistance to spectinomycin and fusidic acid. Both mutations also conferred resistance to spectinomycin in Escherichia coli strains containing deletions of all seven chromosomal rrn operons and expressing plasmid-encoded Salmonella rRNA exclusively. In contrast, when expressed in E. coli strains containing intact chromosomal rrn operons, the strains were sensitive to spectinomycin. However, chromosomal mutations arose that allowed expression of the rRNA-dependent spectinomycin resistance phenotype. It is proposed that in heterogeneous rRNA populations, the native E. coli rRNA out-competes the heterologous Salmonella rRNA for binding to ribosomal proteins, translation factors, or ribosome assembly, thus limiting entry of the antibiotic-resistant 30S subunits into the functioning ribosome pool.
authors.affiliation: J.W. Wilson Laboratory, Department of Molecular and Cellular Biology and Biochemistry, Brown University, 69 Brown Street, Providence RI 02912, USA. Michael_O'Connor@Brown.edu
authors.forename: Michael
authors.initials: M
authors.lastname: O'Connor
authors.forename: Albert E
authors.initials: AE
authors.lastname: Dahlberg
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D005672:Fusidic Acid / Q000494:pharmacology; D008826:Microbial Sensitivity Tests; D009154:Mutation; D010957:Plasmids / Q000235:genetics; D012336:RNA, Ribosomal, 16S / Q000235:genetics / Q000378:metabolism*; D012475:Salmonella / Q000235:genetics / Q000378:metabolism; D012486:Salmonella typhimurium / Q000187:drug effects* / Q000235:genetics; D000198:Spectinomycin / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D012336:RNA, Ribosomal, 16S; D005672:Fusidic Acid; D000198:Spectinomycin