Location: Food and Feed Safety Research
Title: Genetic Characterization and Correlation to Multidrug Resistance of Isolates of Salmonella Newport Derived from Beef and Dairy Cattle Authors
Submitted to: American Society for Microbiology
Publication Type: Abstract Only
Publication Acceptance Date: July 5, 2006
Publication Date: September 9, 2006
Citation: Ramlachan, N., Poole, T.L., Edrington, T.S., Anderson, R.C., Nisbet, D.J. 2006. Genetic characterization and correlation to multidrug resistance in isolates of Salmonella enterica serovar Newport derived from beef and dairy cattle [abstract]. American Society for Microbiology. p. 88-89. Technical Abstract: High-throughput genotyping of Salmonella isolates obtained from food production animals is an essential component of food safety to evaluate pathogenic and antimicrobial resistance profiles. A total of 99 strains of Salmonella enterica serovar Newport were studied by pulsed-field gel electrophoresis (PFGE) to elucidate genetic relationships among strains isolated from beef and dairy cattle slaughterhouse hide and carcass samples. Antibiotic susceptibilities were determined and interpreted according to MIC interpretive standards for antibiotics including: amoxicillin/clavulanate, ampicillin, cefoxitin, ceftiofur, cephalothin, chloramphenicol, kanamycin, streptomycin, sulfamethoxazole, tetracycline and ceftriaxone. Some isolates were found to be resistant to 10 or more antibiotics. PFGE of XbaI-digested chromosomal DNA and plasmid DNA fingerprinting profiles were used to assign Salmonella isolates into clonal groups and to determine plasmid content on the basis of size. Cluster analysis based on the unweighted pair group method using an arithmetic averages algorithm identified three main clusters independent of plasmid content, indicating that the divergence of the PFGE subtypes was probably derived from genomic mutations. The majority of pan-susceptible isolates grouped in the same cluster had similar XbaI profiles. The data confirms that strains isolated from beef or dairy cattle were of a unique clonal origin and that a particular PFGE combination profile was predominant and specific for pan-susceptible isolates from beef and dairy cattle. Correlations between antimicrobial resistance phenotype and genotype, as well as predicted pathogenicity and presence of predisposing conjugative elements and competitive fitness for each isolate tested revealed further differentiation within beef or dairy groups. Combined phenotypic and genotypic profiles are necessary for epidemiological studies and public health investigations on S. Newport. The use of such methodologies for genetically determining multidrug resistance status, pathogenicity and ability to transfer and/or uptake such genes in a Salmonella spp. of public health concern, will allow us to elucidate the mechanisms by which S. Newport increases in pathogenicity causing fatal disease in cattle as well as serious cases of human food poisoning.