Analysis of Virulence Factors and Antimicrobial Resistance in Salmonella Using Molecular Techniques and Identification of Clonal Relationships Among the Strains

Abstract

A total of 50 Salmonella enterica strains were isolated from clinical samples from 2009 to 2012 and analyzed for the presence of virulence genes found in SPI-1, SPI-2, and plasmids. The distribution and frequency of the antimicrobial resistance genes and plasmids were revealed, and pulsed-field gel electrophoresis (PFGE) patterns were investigated. Five genes were identified from the seven strains with resistance or intermediate resistance to ampicillin: blaSHV-1 (present in six strains), qnrS1 (present in five strains), blaTEM-1 (present in three strains), blaCTX-M-1 (present in one strain), and qnrB1 (present in one strain). One trimethoprim-sulfamethoxazole-resistant strain was positive for sulI but negative for sulII. In addition, we detected TEM-1 and qnrS1 in one strain; SHV-1 and qnrS1 in two strains; TEM-1, SHV-1, CTX-M-1, and qnrS1 in one strain; TEM-1, SHV-1, and qnrB1 in one strain; and SHV-1 and sulI genes in one strain together. Plasmid-based replicon typing assay revealed that all 50 strains carried FIIS, 13 carried I1, 1 carried I2, 4 carried P, 1 carried A/C, and 4 carried X1 replicon. PFGE was used to type 46 of the 50 strains and classify them into 22 major groups, 33 pulsotypes, and 8 major clusters. All strains carried all the virulence genes of interest on both Salmonella Pathogenicity Islands 1 and 2 and plasmids suggested high potential for pathogenicity. All antimicrobial-resistant strains contained at least one of the resistance genes of interest, confirming a phenotype-genotype association in antimicrobial resistance.