Abstract: This study aims to explore the prevalence and drug resistance of Salmonella London from pork at the market in Guangzhou from May to October 2016. One hundred and ninety-eight samples were collected from the market in Guangzhou. Twenty-eight strains of S. London from pork were isolated. The KB method was used to test the drug resistance, and the drug-resistant genes were identified by PCR. The results showed that the positive rate of Salmonella from pork was 74. 2% (147/198), the isolation rate of S. London was 19% (28/147). The drug sensitivity test of S. London showed that they were resistant to sulfisoxazole (78.6%) and tetracycline (75.0%), followed by streptomycin (71.4%), compound sulfamethoxazole (67.9%), ampicillin (67.9%), gentamicin (67.9%), chloramphenicol (46.4%) and florfenicol (42.8%), respectively. Also, the antibiotic resistance to nalidixic acid (3.6%) and polymyxin B (3.6%) is rare. And 71.4% (20/28) of the strains were resistant to three or more antimicrobial agents. The detection rate of β-lactam resistance gene bla_TEM is 10.7%; the detection rates of quinolone resistance genes qnrA, oqxAB and aac(6')-lb-cr are 3.6%, 10.7% and 7.1%, respectively. Only 3.6% of the isolates carried colistin resistance gene mcr-1. It was found that S. London was one of the major epidemics in pork from markets in Guangzhou. It is highly resistant to traditional antimicrobials such as sulfisoxazole, tetracycline, streptomycin, compound sulfamethoxazole, ampicillin, carrying multiple drug-resistant genes, and has multi-drug resistant phenotypes. These results suggest that we need to conduct normalized detection and monitoring of Salmonella in the market, strengthen the supervision of the use of antibiotics, and ensure public health and food safety.

Key words: Guangzhou, Salmonella London, pork, drug resistance