Analysis of antimicrobial resistance genes detected in multiple drug resistant (MDR) Salmonella enterica serovar Typhimurium and Escherichia coli animal isolates
Glenn, Lashanda Mari
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The presence of multiple drug resistant foodborne pathogens is a concern in both animal and human health. To understand the development of resistance to antimicrobials used in veterinary and human medicine, one must determine what genes are responsible for these resistances. DNA microarray was used to determine the presence of antimicrobial resistance genes in Salmonella Typhimurium and Escherichia coli animal isolates from the NARMS database. Salmonella Typhimurium and E. coli were selected and subjected to antimicrobial susceptibility testing. DNA was isolated from subset isolates, fluorescently labeled, and hybridized to a microarray chip containing 775 antimicrobial resistance gene probes and 487 multiple drug resistance plasmid gene probes. The presence of class I integrons was determined using PCR of integrase I (intI1); size of integrons was determined by PCR of the conserved region. Plasmid replicon typing using multiplex PCR was used to determine the presence of 18 plasmids often associated with multiple drug resistance and Enterobacteriaceae. Isolates positively hybridized to aminoglycoside, beta-lactam, chloramphenicol, tetracycline and sulfamethoxazole resistance gene probes on the array. Integrase intI1 gene was detected via both PCR and microarray analysis. The sequencing of amplified conserved regions within class I integrons revealed several antimicrobial resistance gene cassettes. Plasmid replicon typing indicated the presence of numerous plasmid incompatibility groups that are associated with multiple drug resistance. Overall, there was a positive association between the antimicrobial susceptibility and resistance genes detected via microarray. The presence of variable sized class I integrons, IncA/C plasmid genes, and MDR associated plasmids may indicate the importance of these genetic elements in the accumulation and spread of antimicrobial resistance genes in the animal microbial community.