Human salmonella and concurrent decreased susceptibility to Quinolones and extended-spectrum Cephalosporins

The National Antimicrobial Resistance Monitoring System monitors susceptibility among Enterobacteriaceae in humans in the United States. We studied isolates exhibiting decreased susceptibility to quinolones (nalidixic acid MIC >= 32 mu g/mL or ciprofloxacin MIC >= 0.12 mu g/mL) and extended-spectrum cephalosporins (ceftiofur or ceftriaxone MIC >= 2 mu g/mL) during 1996-2004. Of non-Typhi Salmonella, 0.19% (27/14,043) met these criteria: 11 Senftenberg; 6 Typhimurium; 3 Newport; 2 Enteridis; and 1 each Agona, Haifa Mbandaka, Saintpaul, and Uganda. Twenty-six isolates ha gyrA mutations (11 at codon 83 only, 3 at codon 87 only, 12 at both). All Senftenberg isolates had parC mutations (S80I and T57S); 6 others had the T57S mutation. The Mbandaka isolate contained qnrB2. Eight isolates contained bla(CMY-2); 1 Senftenberg contained bla(CMY-23). One Senftenberg and 1Typhimurium isolate contained bla(SHV-12); the Mbandaka isolate contained bla(SHV-30). Nine Senftenberg isolates contained bla(OXA-1); 1 contained bla(OxA-9). Further studies should address patient outcomes, risk factors, and resistance dissemination prevention strategies.