| Molecular characterizations including antibiotic susceptibility, presence of class I integron and resistance genes, producing extended spectrum β-lactmases(ESBLs) of 145 Salmonella Typhimurium isolates were surveyed. Meanwhile, the genotype of the isolates were studied via pulsed field gel electrophoresis(PFGE). The Salmonella Typhimurium were isolated from diarrhea of in- and out- patients,retail foods in foodborne disease outbreak areas or communities where the diarrhea patients live as well as the environmental in Shanghai during the time of outbreaks from 2008-2012. After the epidemiological characterization of the isolates were revealed, the inner link between Salmonella Typhimurium isolates in human infections, foods, and environments were analyzed to explore and trance the original vectors of Salmonella that resulted in foodborne disease. The mainly acquired conclusions are as follows:(1) Antimicrobial susceptibility was tested according to agar dilution method recommended by the Clinical and Laboratory Standards Institute(CLSI).All(100%) isolates were resistant to sulfisoxazole, 98(67.6%) were resistant to nalidixic acid, 49.0%, 47.6%, 46.2%, 45.5%, 35.2%, 32.4%, 31.7%, 27.6% and 27.6% were resistance to ceftiofur(Ti), ampicillin(Am), streptomycin(St), tetracycline(Tc), gentamycin(Ge), trimethoprim/sulfamethoxazole(Sx), kanamycin(Ka), amoxicillin/clavulanic acid(Ac) and chloramphenicol(Ch). Two isolates were detected resisting to ciprofloxacin and two to levofloxacin. No significant difference was found between the rates of isolates that derived from human salmonellosis and resisted to ampicillin(Am), amoxicillin/clavulanic acid(Ac), ceftiofur(Ti), ceftriaxone(Cr), nalidixic acid(Na), chlorampHenicol(Ch), gentamicin(Ge), kanamycin(Ka), streptomycin(St), tetracycline(Tc), sulfisoxazole(Fi), and trimethoprim/sulfamethoxazole(Sx) and those from retail foods. One hundred and fourteen(78.6%) isolates resisted to at least three antibiotics, and 52(35.9%) to at least seven.(2) Fifty nine isolates(40.7%)were detected harboring aac(6′)-Ib. 42(30.0%), 12(8.3%), 11(7.6%)and 8(5.5%)isolates carried oqxAB, qnrS, qnrA and qnrB, respectively. No qepA was detected. No significant(P>0.05) difference was found among the prevalence rates of qnrA, qnrB, qnrS, aac(6′)-Ib, oqxAB between Salmonella isolates recovered from human infections and retail foods. Three isolates recovered from human, pork and duck, respectively, were detected harboring mutations of Asp87Asn(n=2) and Asp87Tyr(n=1) in GyrA, and no mutation in ParC was detected. Three kinds of antimicrobial resistance gene cassettes were detected in 17 isolates, among which, 14 carried a 1.6 kb and three carried a 2.0 kb integron. Antimicrobial resistance gene cassettes aadA2 was detected in 15 isolates. Two isolates in human salmonellosis carried dfrA12-aadA2 and aadA1, respectively. Five isolates were detected producing ESBLs,blaOXA were identified in three foodborne isolates, and blaTEM-blaOXA in two isolates recovered from duck and beef.(3) Isolates were subtyped by Pulsed field gel electrophoresis(PFGE). The genotypic diversities were found in 145 Salmonella Typhimurium recovered from different sources. PFGE genotypic DNA profiles of isolates from pork, chicken and duck and those of strains in human infections showed high consistency. three isolates recovered from pork and four clinical ones showed genetic similarity of 100%, one chicken-borne strain and one strain in human infections showed genomic similarity of 100%, strains in retail duck and those in the chicken, pork, and clinical infections had close genetic relationship. This study revealed that retail pork, chicken and duck were likely to be the food carrier that caused human food-borne Salmonella outbreak. The necessary preventive measure is needed during pork, chicken and duck feeding and processing, to reduce the risk of Salmonella infection. |
