title: ksgA mutations confer resistance to kasugamycin in Neisseria gonorrhoeae.
abstract: The aminoglycoside antibiotic kasugamycin (KSG) inhibits translation initiation and thus the growth of many bacteria. In this study, we tested the susceptibilities to KSG of 22 low-passage clinical isolates and 2 laboratory strains of Neisseria gonorrhoeae. Although the range of KSG minimum inhibitory concentrations (MICs) was narrow (seven-fold), clinical isolates and laboratory strains fell into three distinct classes of KSG sensitivity, susceptible, somewhat sensitive and resistant, with MICs of 30, 60-100 and 200 microg/mL, respectively. Two genes have previously been shown to be involved in bacterial KSG resistance: rpsI, which encodes the 30S ribosomal subunit S9 protein; and ksgA, which encodes a predicted dimethyltransferase. Although sequencing of rpsI and ksgA from clinical isolates revealed polymorphisms, none correlated with the MICs of KSG. Ten spontaneous KSG-resistant (KSG(R)) mutants were isolated from laboratory strain FA1090 at a frequency of <4.4x10(-6) resistant colony-forming units (CFU)/total CFU. All isolated KSG(R) variants had mutations in ksgA, whilst no mutations were observed in rpsI. ksgA mutations conferring KSG resistance included four point mutations, two in-frame and one out-of-frame deletions, one in-frame duplication and two frame-shift insertions. These data show a narrow range of susceptibilities for the clinical isolates and laboratory strains examined; moreover, the differences in MICs do not correlate with nucleotide polymorphisms in rpsI or ksgA. Additionally, spontaneous KSG(R) mutants arise by a variety of ksgA mutations.
authors.affiliation: Department of Microbiology-Immunology, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA.
authors.forename: Paul M
authors.initials: PM
authors.lastname: Duffin
authors.forename: H Steven
authors.initials: HS
authors.lastname: Seifert
mesh_terms: D000617:Aminoglycosides / Q000494:pharmacology*; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics*; D004252:DNA Mutational Analysis; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D024881:Drug Resistance, Bacterial; D005260:Female; D006069:Gonorrhea / Q000382:microbiology; D006801:Humans; D008297:Male; D008780:Methyltransferases / Q000235:genetics*; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D009154:Mutation; D009344:Neisseria gonorrhoeae / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D012269:Ribosomal Proteins / Q000235:genetics; D017422:Sequence Analysis, DNA
chemical_list: D000617:Aminoglycosides; D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004269:DNA, Bacterial; D012269:Ribosomal Proteins; D008780:Methyltransferases; C047346:16S rRNA (adenine(1518)-N(6)-adenine(1519)-N(6))-dimethyltransferase; C100305:kasugamycin