Surveillance of nalidixic acid-resistant and extended-spectrum beta-lactamase-producing Salmonella spp. isolated from human feces

Nalidixic acid (NA)-resistant and extended-spectrum beta-lactamase (ESBL)-producing Salmonella sp. isolates from human specimens are associated with clinical failure or delayed response in subjects treated with fluoroquinolone or third-generation cephalosporins. We studied drug susceptibility in 604 Salmonella enterica isolates from human feces in 2007. Of these, 39 (6.5%) were resistat to NA. Of these, 46% were resistant to two or more drugs and 2% susceptible to NA were resistant to multiple drugs (p < 0.001). Three ESBL-producing Salmonella sp. isolated were of the CTX-M family gene type. One strain of plasmid-mediated AmpC beta-lactamase belonged to the CMY-2 family gene type. Our results thus showed that NA-resistant isolates were resistant to antimicrobial agents and confirmed the presence of a small number of isolates producing ESBL and AmpC beta-lactamase.