Virulence and antimicrobial-resistance gene profiles determined by PCR-based procedures for Salmonella isolated from samples of animal origin

Abstract

The virulence (V) and antimicrobial resistance (R) gene profiles of Salmonella isolates collected from samples of animal origin in a Spanish Region were determined by PCR-based procedures, and compared with V and R gene profiles of clinical strains from the same region. Some V-profiles were serotype-specific, i.e. S. Panama carried all the V-genes tested (invE/A, phoP/Q, stn, iroB, slyA, hin/H2, and agfA), whereas S. Enteritidis lacked hin/H2, and S. Hadar and all but one of the S. Typhimurium isolates, lacked agfA. Salmonella V-plasmids (spv ) were found in serotypes Enteritidis, non-motile [9,12:-:-], Typhimurium and its monophasic variant [4,5,12:i:-]. Twenty-six out of the 56 animal-origin isolates showed some drug resistance. In the nalidixic acid-R isolates, mutations in the Ser-83 and/or Gly 133 codons in the gyrA gene were identified. Seventeen R-genes grouped into different R-profiles were detected, [pse1–aadA2–sul1–tet(G)–floR]-profile being the most frequent. Most of the serogroup B isolates, collected from pork or beef products, displayed multidrug-R and carried class 1-sul1 integrons. The integrons contained the following gene cassettes: pse1, aadA2, dfr17–aadA5, dfr1–aadAla, oxa1–aadA1a and dfr12–aadA2. All of them, except the dfr17–aadA5 gene cassette configuration , were also present in integrons of clinical isolates. Integrons could be plasmid- and/or chromosome-located, and those with oxa1–aadA1a and dfr12–aadA2 gene cassettes were located in spv -plasmids, which also carried the transposon associated genes tpnA, tpnR and merA . Conversely, all S. Enteritidis, S. Tennessee, and non-motile isolates collected from poultry samples showed drug susceptibility to all antibiotics tested. Moreover, among S. Enteritidis clinical isolates both ampicillin-R (encoded by tem1 genes, plasmid- or chromosome-located) and quinolone-R (due to mutations involving gyrA gene) were frequent. The efficiency, rapidity, and flexibility of the PCR-protocols applied was high. All of them can be performed directly on aliquots of a bacterial culture, using sequence-specific primers, the same basic equipment, and the same basic PCR-program.