A total of 47 extended-spectrum-cephalosporin-resistant Escherichia coli strains isolated from stray dogs in 2006 and 2007 in the Republic of Korea were investigated using molecular methods. Extended-spectrum ␤-lactamase (ESBL) and AmpC ␤-lactamase phenotypes were identified in 12 and 23 E. coli isolates, respectively. All 12 ESBL-producing isolates carried bla CTX-M genes. The most common CTX-M types were CTX-M-14 (n ‫؍‬ 5) and CTX-M-24 (n ‫؍‬ 3). Isolates producing CTX-M-3, CTX-M-55, CTX-M-27, and CTX-M-65 were also identified. Twenty-one of 23 AmpC ␤-lactamase-producing isolates were found to carry bla CMY-2 genes. TEM-1 was associated with CTX-M and CMY-2 ␤-lactamases in 4 and 15 isolates, respectively. In addition to bla TEM-1 , two isolates carried bla DHA-1 , and one of them cocarried bla CMY-2 . Both CTX-M and CMY-2 genes were located on large (40 to 170 kb) conjugative plasmids that contained the insertion sequence ISEcp1 upstream of the bla genes. Only in the case of CTX-M genes was there an IS903 sequence downstream of the gene. The spread of ESBLs and AmpC ␤-lactamases occurred via both horizontal gene transfer, accounting for much of the CTX-M gene dissemination, and clonal spread, accounting for CMY-2 gene dissemination. The horizontal dissemination of bla CTX-M and bla CMY-2 genes was mediated by IncF and IncI1-I␥ plasmids, respectively. The clonal spread of bla CMY-2 was driven mainly by E. coli strains of virulent phylogroup D lineage ST648. To our knowledge, this is the first report of bla DHA-1 in E. coli strains isolated from companion animals. This study also represents the first report of CMY-2 ␤-lactamase-producing E. coli isolates from dogs in the Republic of Korea.

This study was undertaken to screen methicillin-resistant Staphylococcus aureus (MRSA) in animal carcasses and slaughterhouse workers and characterize MRSA isolates identified during 2010-2012 in Korea. A total of 830 (16.4%) S. aureus and 65 (1.3%) MRSA were isolated from 9669 carcass samples. MRSA was more frequently detected in chicken carcasses (1.2%) than in cattle (0.3%) and pig carcasses (0.6%). The prevalence of MRSA in workers was 6.9% (4/58) in chicken slaughterhouse workers, but no MRSA was detected in pig and cattle slaughterhouse workers (0/41). Two different lineages of MRSA were identified (i.e., human-associated type [ST5, ST59, and ST72] and livestock-associated [LA] type [ST398, ST541, and ST692]); only LA MRSA was observed in chicken carcasses, whereas both types were found in cattle and pig carcasses and workers. All human-associated MRSA isolates carried enterotoxin and/or leukotoxin genes, whereas LA MRSA types did not carry these genes, except ST692 type. However, all LA MRSA isolates were multiresistant, whereas human-associated types were susceptible or resistant to fewer than two antimicrobials except ST5. Furthermore, one or more resistance genes were attributed for resistance to aminoglycosides (aac(6')-Ie-aph(2″), ant(4')-Ia, and aph(3')-IIIa), tetracycline [tet(K), tet(L), tet(M), and tet(S)], macrolide-lincosamide-streptogramin B (ermA, ermB, ermC, and ermT), lincosamide [lnu(B)], phenicol-lincosamide-oxazolidinone-pleuromutilin-streptogramin A (cfr), chloramphenicol (fexA), and fusidic acid [fus(C)]. To our knowledge, this is the first report of tet(S) gene in MRSA isolates and first detection of a unique (ST692) type of MRSA in occupational workers. Detection of new types of human-associated and LA MRSA with multiple resistance and virulence genes in food animal products constitutes a potential threat to public health.

The objective of this study was to determine the prevalence of Acinetobacter spp. in bulk tank milk (BTM) samples from different provinces of Korea and to analyze their antimicrobial susceptibility. Altogether, 2,287 BTM samples were investigated. Among them, Acinetobacter spp. were isolated from 176 BTM samples. Out of 176 Acinetobacter spp., 57 isolates were identified as Acinetobacter baumannii. None of the isolates were resistant to cefepime, imipenem, meropenem, ciprofloxacin, levofloxacin, or colistin. Resistance to amikacin, gentamicin, piperacillin, and cefotaxime was 2.3, 7.4, 2.3, and 4.0%, respectively. Acinetobacter spp. were least susceptible to tetracycline (17.6%), followed by trimethoprim-sulfamethoxazole (15.9%), ceftazidime (10.8%), and ampicillin-sulbactam (10.2%). Overall, A. baumannii strains were susceptible to most of the antimicrobial agents tested compared with other Acinetobacter spp. The Acinetobacter isolates showed 17 different patterns of antimicrobial resistance. The most frequent resistance profile observed was ampicillin-sulbactam (n=13), followed by tetracycline (n=9), ceftazidime-tetracycline (n=8), and trimethoprim-sulfamethoxazole-tetracycline (n=8). The results of this study confirmed that Acinetobacter, including A. baumannii strains, are present in BTM, which clearly showed the importance of examining BTM not only for foodborne pathogens but also for Acinetobacter spp., which could be of public health concern. To the best of our knowledge, this is the first report of Acinetobacter spp. in BTM samples from Korea.

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The purpose of this study was to determine the prevalence and characteristics of CTX-M β-lactamases in Escherichia coli among healthy swine and cattle in Korea. A total of 1212 fecal samples obtained from healthy pigs (n=558) and cattle (n=654) were screened for CTX-M-type extended spectrum β-lactamase (ESBL)-producing E. coli isolates. One hundred and twenty-one E. coli that produced ESBL were subjected to phenotypic and genotypic characterization. A high number (120/558, 21.5%) of swine fecal samples showed the presence of CTX-M β-lactamase-producing E. coli compared to cattle samples (1/654, 0.2%). The most predominant CTX-M-type identified was CTX-M-14 (n=82), followed by CTX-M-15 (n=16). Isolates producing CTX-M-3, CTX-M-27, CTX-M-55, and CTX-M-65 were also identified. Overall, the bla(TEM-1) gene was associated with CTX-M β-lactamase in 55 E. coli isolates. Transfer of bla(CTX-M) gene was demonstrated from 76 out of 121 bla(CTX-M)-positive E. coli isolates to the recipient E. coli J53 by conjugation. Plasmid DNA isolation from the transconjugants revealed a large (90-120 Kb) conjugative plasmid. ISEcp1 and IS903 were detected upstream and downstream of bla(CTX-M) genes in 117 and 91 E. coli isolates, respectively. Our results demonstrated that a combination of clonal expansion and horizontal transmission is spreading bla(CTX-M) genes among swine E. coli. The horizontal dissemination of bla(CTX-M) genes among E. coli was mostly mediated by IncF or IncI1-Iγ plasmids. To the best of our knowledge, this study represents the first report of CTX-M-3, CTX-M-27, CTX-M-55, and CTX-M-65 β-lactamases in bacterial isolates from food animals in Korea. This study revealed that the CTX-M β-lactamase-producing E. coli are widely disseminated among healthy pigs but very rare in cattle in Korea. Increasing prevalence of bla(CTX-M) genes in intestinal E. coli of food animals is a matter of concern and should be carefully monitored.