Epidemiologic surveillance study was conducted in southern Japan to determine the antimicrobial resistance phenotypes and characterize the β-lactamase genes and the plasmids harboring these genes in Salmonella enterica serovar Infantis (S. Infantis) isolates from broilers. Between January, 2007 and December, 2008, a total of 1,472 fecal samples were collected and examined at the Laboratory of Veterinary Public Health, Kagoshima University, Japan. In 93 (6.3%) isolates recovered, 33 (35.5%) isolates showed resistance to cefotaxime, an extended-spectrum cephalosporin (ESC), conferred by TEM-20, TEM-52 and CTX-M-25 extended-spectrum β-lactamases (ESBLs). In addition to ESC-resistance, eight (8.6%) isolates exhibited resistance to cefoxitin mediated by CMY-2 AmpC β-lactamase. Plasmid analysis and polymerase chain reaction replicon typing revealed the blaTEM-20 and blaCMY-2 genes were associated with IncP plasmids, blaTEM-52 was linked with a non-typable plasmid and blaCTX-M-25 was carried by an IncA/C plasmid. Non-β-lactam resistance to streptomycin, sulfamethoxazole, and oxytetracycline encoded by the aadA1, sul1, and tet(A) genes, respectively, was found in 86 (92.5%) isolates. Resistance to kanamycin and ofloxacin was exhibited in 12 (12.9%) and 11 (11.8%) isolates, respectively, the former was mediated by aphA1-Iab. These data indicate that S. Infantis isolates producing ESBLs and AmpC β-lactamase have spread among broiler farms in Japan. These data demonstrated that the incidence of ESC-resistant S. Infantis carrying blaTEM-52 remarkably increased and S. Infantis strains harboring blaCMY-2, blaTEM-20, or blaCTX-M-25 genes emerged from broilers in Japan for the first time in 2007 and 2008.

ABSTRACT. Cefotaxime (CTX)-resistant and -susceptible Salmonella enterica serovar Infantis isolates obtained from broilers raised on a farm in January 2010 in Japan were characterized to establish their resistance determinants. The CTX-resistant isolates produced CTX-M-14 extended-spectrum β-lactamase and harbored 2 distinct plasmid of approximately 140-and 95-kb, whereas the CTX-susceptible isolates harbored one 140-kb plasmid. The 95-kb plasmids were replicon typed as IncI1 carrying the bla CTX-M-14 gene, while the 140-kb plasmids were IncP and harbored the aphA1, aadA1, tetA, and sul1 genes. Genetic fingerprinting by pulsed-field gel electrophoresis revealed similar macrorestriction profiles amongst CTX-resistant and susceptible isolates, suggesting a clonal relationship. The presence of CTX-resistant S. Infantis on a broiler farm has occurred through the acquisition of IncI1 resistance plasmid. KEY WORDS: β-lactamase, broiler, CTX-M-14, extended-spectrum plasmid replicon typing, Salmonella Infantis.doi: 10.1292/jvms.11-0488; J. Vet. Med. Sci. 74(9): 1213-1216, 2012 Amongst members of the Enterobacteriaceae family, Escherichia coli (E. coli) and Klebsiella pneumoniae have been implicated as potential producers of extendedspectrum β-lactamases (ESBLs) which possess hydrolyzing activity against third-generation cephalosporins. In recent years, several reports have described other bacterial species within the Enterobacteriaceae family capable of producing ESBLs. Of these, Salmonella spp. producing ESBLs have been detected in salmonellosis cases both in humans [9,10,17] and domestic animals [18].Salmonella enterica serovar Infantis (S. Infantis) is one of the predominant serotypes isolated from broilers in Japan [19]. In the late 1990s, S. Infantis isolates harboring ESBLs were recovered from hospitalized patients in South America [14]. More recently, S. Infantis producing ESBLs were found not only in human patients but also in domestic animals and commercial meats [3,5]. Most of these produced the CTX-M-type ESBLs, indicating the probability that dissemination of 3rd-generation cephalosporin-resistant S. Infantis associated with various types of β-lactamases is gradually expanding world-wide. In this article, we characterized S. Infantis isolates carrying CTX-M-14 ESBL derived from broiler chickens.Ten S. Infantis isolates obtained from 30 broiler cecal samples collected at a poultry processing plant in western Japan in January 2010 were used in this study. The broiler chickens involved in this survey were sampled from 3 different flocks raised on the same commercial farm. The isolation of the bacteria was done as follows; approximately 1 g of cecal contents was aseptically mixed with 5 ml of sterilized distilled water. Then, 1 ml of suspension was enriched in 10 ml of tetrathionate broth (Merck KGaA, Darmstadt, Germany) and incubated at 42°C. After 24 hr of incubation, a loopful from each of enriched broth was streaked onto plates of selective deoxycholate hydrogen sulfide lactose (DHL) agar (Oxoid Ltd., Basing...