ABSTRACT
The study aimed to examine the prevalence and genetic characteristics of ESBL-production and colistin resistance in Salmonella and Escherichia coli from pigs and pork in the border area among Thailand, Cambodia, Lao PDR, and Myanmar. Salmonella (n = 463) and E. coli (n = 767) isolates were collected from pig rectal swab from slaughterhouses (n = 441) and pork from retail markets (n = 368) during October 2017 and March 2018. All were determined for susceptibility to colistin and cephalosporins, ESBL production and mcr and ESBL genes. Salmonella was predominantly found in Cambodia (65.8%). Serovars Rissen (35.6%) and Anatum (15.3%) were the most common. The E. coli prevalence in pork was above 91% in all countries. Colistin-resistance rate in E. coli (10.4%) was significantly higher than Salmonella (2.6%). ESBL-producing Salmonella (1.9%) and E. coli (6.3%) were detected. The blaCTX-M-55 and blaCTX-M-14 were identified. The mcr-1 gene was detected in Salmonella (n = 12) and E. coli (n = 68). The mcr-1/blaCTX-M-55 and mcr-3/blaCTX-M-55 co-concurrence was observed in one Salmonella and three E. coli isolates, respectively. In conclusion, pigs and pork serve as carriers of colistin and new generation cephalosporins resistance. Testing for resistance to last line antibiotics should be included in national AMR surveillance program using One Health approach.
ABSTRACT
A total of 344 commensal Escherichia coli isolates from clinically healthy pigs were examined for antimicrobial resistance phenotypes, class 1 integrons, resistance genes, virulence gene profile, and phylogenetic groups. The majority of E. coli isolates were resistant to tetracycline (96.2%) and ampicillin (91.6%). Up to 98% were multidrug resistant. Seventy-three percent of the isolates carried class 1 integrons. Inserted-gene cassette arrays in variable regions included incomplete sat, aadA22, aadA1, dfrA12-aadA2, and sat-psp-aadA2, of which the aadA2 gene cassette was most prevalent (42.9%). Horizontal transfer was detected in eight E. coli isolates carrying class 1 integrons with dfrA12-aadA2 gene cassette array. Sixteen resistance genes were identified among the E. coli isolates with corresponding resistance phenotype. Ten virulence genes (including elt, estA, estB, astA, faeG, fasA, fedA, eaeA, paa, and sepA) were detected, of which fasA was most commonly found (98.3%). Most of the E. coli isolates belonged to phylogenetic group B1. Significantly positive associations were observed between some virulence genes and some resistance phenotypes and genotypes (p < 0.05). The results support a finding that commensal E. coli have a role as reservoirs for antimicrobial resistance-encoding genes and virulence determinants.
