For the accessory genome, we determined the presence of the Typhimurium virulence plasmid (pSTV). This plasmid has been extensively studied in regard to its role in invasiveness in the murine model [19–23]; its importance in human systemic infections is still controversial [24–27]. Three genetic markers were used to determine the presence of pSTV: spvC, rck and traT, that are genes involved in resistance
to serum and survival in macrophages (Omipalisib Figure 1B) [19, 28]. The antibiotic resistance determinants studied were those contained in integrons, and the presence of the plasmid-borne cmy-2 gene (Figure 1C), conferring resistance to extended spectrum cephalosporins. The cmy-2 gene is of major public health relevance since it confers resistance to ceftriaxone, the drug of choice for treatment Compound C solubility dmso of children with invasive Salmonella infections. In a previous study, we reported the rapid dissemination of this resistance in Typhimurium from Yucatán, Mexico, and its association with systemic infections in children [29]. Most cmy-2 genes have been located in large plasmids (> 100 kb), and were not found as an integron-born cassette [30, 31]. The integron is a recombination https://www.selleckchem.com/products/arn-509.html and expression system that captures genes as part of a genetic element called a gene cassette (Figure 2A). Class
1 integrons are found extensively in clinical isolates, and most of the known antibiotic resistance gene cassettes belong to this class [32–35]. They are frequently located on plasmids and transposons, which further enhances the spread of the gene cassettes [32]. Class 1 integrons have been detected in different Salmonella serovars in many countries [36–41]. Among the most studied cases are the chromosomally located integrons present in the so-called Salmonella genomic island 1 (SGI1) (Figure 2B). SGI1 is a 43 kb integrative-mobilizable chromosomal element on which antibiotic resistance genes are clustered, flanked by two class 1 integrons [42, 43]. The first cassette carries the aadA2 gene, which confers resistance to streptomycin and spectinomycin, and the second cassette contains pse-1, which confers resistance to ampicillin. In between them are floR, tetR and tetG genes, conferring Chlormezanone resistance
to chloramphenicol-florfenicol and tetracycline. A cryptic retronphage element is found as the last element of SGI1 in Typhimurium strains [43, 44]. In the present work, analysis of the whole set of genetic markers targeting both housekeeping and accessory genes allowed us to determine genetic subgroups within the Mexican Typhimurium population. Results Distribution, genetic relatedness and antimicrobial resistance of MLST genotypes The multilocus genotype for 114 Typhimurium isolates sampled from food-animal and human sources in four regions of Mexico, was determined. The seven-locus scheme recommended in the Salmonella MLST database [45] was applied to 66 isolates, in order to compare the diversity of our isolates with those reported in the database.
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