Characterization of Plasmids Carrying CMY-2 from Expanded-Spectrum Cephalosporin-Resistant Salmonella Strains Isolated in the United States between 1996 and 1998

University of Nebraska at Omaha, Omaha, Nebraska, United States
Antimicrobial Agents and Chemotherapy (Impact Factor: 4.48). 06/2002; 46(5):1269-72. DOI: 10.1128/AAC.46.5.1269-1272.2002
Source: PubMed


Sequencing of DNA from 15 expanded-spectrum cephalosporin (e.g., ceftriaxone)-resistant Salmonella isolates obtained in the United States revealed that resistance to ceftriaxone in all isolates was mediated by cmy-2. Hybridization patterns revealed three plasmid structures containing cmy-2 in these 15 isolates. These data suggest that the spread of cmy-2 among Salmonella strains is occurring through mobilization of the cmy-2 gene into different plasmid backbones and consequent horizontal transfer by conjugation.

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Available from: Fabio Tosini
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    • "Plasmid-mediated β-lactamases were classified into six genetic clusters and blaCMY was the most prevalent one. The blaCMY has been found on plasmid of sizes variable for 7 to 180 kb [5] [6]. Plasmid-mediated quinolone resistance (PMQR) was first discovered in a clinical isolate of Kelebsiella penemoniae from Birmingham, Albama collected in 1998 by Martinez-Martinez. "

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    • "The objective of the current study was to examine the association between the recently emerged genotype MDR ST213 and blaCMY-2 plasmids. ST213 isolates were analyzed by plasmid profiling, PCR replicon typing [19], plasmid PstI restriction profiles [12,20], Southern hybridization, plasmid PCR screening and sequencing of regions scattered throughout the IncA/C plasmids [8], and by their conjugation abilities. We found two divergent types of IncA/C plasmids: one composed of plasmids possessing or lacking the blaCMY-2 region and the other lacking blaCMY-2. "
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    • "B) The presence of the Typhimurium virulence plasmid (pSTV) [GenBank:AE006471] was determined by PCR amplification of three genes involved in virulence spvC, rck and traT [19,28], and by Southern hybridisation on plasmid profiles using spvC as probe. C) The presence of the plasmid-borne cmy-2 gene, conferring resistance to extended spectrum cephalosporins [GenBank:NC_011079] [30,31], was determined by PCR and by Southern hybridisation on plasmid profiles. The chloramphenicol determinant floR was also assessed, since it has been reported that both resistances are often encoded by the same plasmid [48]. "
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    ABSTRACT: Bacterial genomes are mosaic structures composed of genes present in every strain of the same species (core genome), and genes present in some but not all strains of a species (accessory genome). The aim of this study was to compare the genetic diversity of core and accessory genes of a Salmonella enterica subspecies enterica serovar Typhimurium (Typhimurium) population isolated from food-animal and human sources in four regions of Mexico. Multilocus sequence typing (MLST) and macrorestriction fingerprints by pulsed-field gel electrophoresis (PFGE) were used to address the core genetic variation, and genes involved in pathogenesis and antibiotic resistance were selected to evaluate the accessory genome. We found a low genetic diversity for both housekeeping and accessory genes. Sequence type 19 (ST19) was supported as the founder genotype of STs 213, 302 and 429. We found a temporal pattern in which the derived ST213 is replacing the founder ST19 in the four geographic regions analyzed and a geographic trend in the number of resistance determinants. The distribution of the accessory genes was not random among chromosomal genotypes. We detected strong associations among the different accessory genes and the multilocus chromosomal genotypes (STs). First, the Salmonella virulence plasmid (pSTV) was found mostly in ST19 isolates. Second, the plasmid-borne betalactamase cmy-2 was found only in ST213 isolates. Third, the most abundant integron, IP-1 (dfrA12, orfF and aadA2), was found only in ST213 isolates. Fourth, the Salmonella genomic island (SGI1) was found mainly in a subgroup of ST19 isolates carrying pSTV. The mapping of accessory genes and multilocus genotypes on the dendrogram derived from macrorestiction fingerprints allowed the establishment of genetic subgroups within the population. Despite the low levels of genetic diversity of core and accessory genes, the non-random distribution of the accessory genes across chromosomal backgrounds allowed us to discover genetic subgroups within the population. This study provides information about the importance of the accessory genome in generating genetic variability within a bacterial population.
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