Independent emergence of quinolone resistance in CTX-M-5 b-lactamase-producing isolates of Salmonella typhimurium from Russia, Belarus and Kazakhstan

Abstract number: O86

Kozyreva V., Tapalski D., Azizov I., Edelstein M.

Objectives: Extended-spectrum cephalosporins and quinolones are used as primary treatment for severe salmonellosis. Therefore, the emergence of simultaneous resistance to these drugs in clinical isolates of Salmonella is of great therapeutic concern. This study was performed to investigate the molecular epidemiology of resistance to cefotaxime (CTX) and nalidixic acid (NA) among S. Typhimurium (Sty) isolates from Russia, Belarus and Kazakhstan.

Methods: A total of 44 clinical Sty isolates collected in 2002–07 were studied including 11 from Gomel region (Belarus), 24 from Irkutsk, Smolensk and Voronezh regions (Russia) and 9 from Karaganda (Kazakhstan). Four additional CTX-M-5-producing strains isolated in 1996–99 in various regions of Russia and Belarus and reported earlier to belong to a single clonal group [Edelstein et al. 2004] were included in this study for comparison. Susceptibility testing was performed by agar dilution method according to CLSI guidelines. Molecular typing was done using fluorescent multiple-locus variable-number tandem-repeats analysis (MLVA). PCR and sequencing were used to identify the CTX-M b-lactamase genes and to characterise their genetic context as well as to determine the gyrA QRDR sequences. The CTX-M-coding plasmids were compared using RFLP analysis with PstI and PvuII endonucleases.

Results: All the isolates studied shared a common phenotype of CTX resistance reversible by clavulanic acid. The resistance was due to production of CTX-M-5 ESBL whose gene was associated with ISEcp1 element and located on small (~7.4 kb) plasmid exhibiting identical RFLP pattern in all the isolates. Eighteen isolates were resistant to NA, none of them were resistant to ciprofloxacin. MLVA grouped the isolates into 8 types linked to each other with only 1 or 2 VNTR loci distinguishing each type. The quinolone-resistant isolates were distributed among 6 MLVA types, 3 of which also included NA-susceptible isolates. Resistance to NA strongly correlated with the presence of known mutations: Ser83-Phe, Asp87-Asn, -Tyr, or -Gly in the GyrA QRDR sequences which were otherwise identical in all isolates. Notably, the isolates of different MLVA types had different GyrA mutations.

Conclusions: This study supports the clonal origin of CTX-M-5-producing Sty isolates which continue to spread in Russia, Belarus and Kazakhstan and provides the evidence of frequent and independent acquisition of quinolone resistance among these isolates.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Location: Barcelona, Spain
Presentation type:
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