Multiple Outbreaks of Nosocomial Salmonellosis in Russia and Belarus Caused by a Single Clone of Salmonella enterica Serovar Typhimurium Producing an Extended-Spectrum β-Lactamase

Thirty-four cefotaxime-resistant Salmonella enterica serovar Typhimurium isolates representative of the isolates that caused outbreaks of gastroenteritis in 10 hospitals in seven regions of Russia and Belarus from 1994 to 2003 were analyzed. All isolates produced the CTX-M-5-like extended-spectrum beta-lactamase, which confers high-level resistance to cefotaxime and ceftriaxone and decreased susceptibility to ceftazidime. The bla(CTX-M) genes were located on small (7.4- to 12-kb) non-self-transferable plasmids approximately 20 bp downstream of the ISEcp1 insertion sequences. Some isolates carried additional conjugative plasmids mediating resistance to penicillin-inhibitor combinations and various non-beta-lactam agents, including tetracycline, chloramphenicol, gentamicin, tobramycin, and co-trimoxazole. Despite the minor differences in susceptibility patterns, all isolates were considered clonally related on the basis of arbitrarily primed PCR and pulsed-field gel electrophoresis analysis. The similarities of the restriction profiles of the CTX-M-coding plasmids further supported the clonal origin of these isolates.