CTX-M-producing Salmonella spp. in Hong Kong:: an emerging problem

Two Salmonella enterica serovar Typhimurium isolates and one S. enterica serovar Enteritidis isolate that were resistant to 4 mu g cefotaxime ml(-1) and produced CTX-M-type extended-spectrum beta-lactamases (ESBLs) were characterized from patients in Hong Kong during 2003-2004. The S. Typhimurium strain isolated in 2003 produced a CTX-M-9 ESBL and harboured a b/a(CTX-M-9) gene that was associated with a class I integron-containing gene cassette and orf513 similar to those of In60. The second S. Typhimurium strain and the S. Enteritidis strain, both isolated in 2004, produced CTX-M-14; the former also produced TEM-1. The b/a(CTX-M-14) gene in these two isolates was associated with the insertion sequence ISEcp1. The CTX-M genes were present on a transferable plasmid of 62, 70 or 92 kb. PFGE of Xbal-restricted total DNA from the two S. Typhimurium isolates indicated that they were not clonally related. These three isolates were also resistant to one of the other non-p-lactam antimicrobial agents tested. This is the first report of a CTX-M-9 ESBL in Salmonella in Hong Kong and the presence of b/a(CTX-M-9) and b/a(CTX-M-14) in S. Typhimurium.