DNA Sequence Analysis of Regions Surroundingbla_CMY-2from MultipleSalmonellaPlasmid Backbones

Abstract

The emergence in the United States of resistance to expanded-spectrum cephalosporin (e.g., ceftriaxone) within the salmonellae has been associated primarily with three large (>100-kb) plasmids (designated types A, B, and C) and one 10.1-kb plasmid (type D) that carry the bla CMY-2 gene. In the present study, the distribution of these four known bla CMY-2 -carrying plasmids among 35 ceftriaxone-resistant Salmonella isolates obtained from 1998 to 2001 was examined. Twenty-three of these isolates were Salmonella enterica serotype Newport, 10 were Salmonella enterica serotype Typhimurium, 1 was Salmonella enterica serotype Agona, and 1 was Salmonella enterica serotype Reading. All 23 serotype Newport isolates carried a type C plasmid, and 5, 4, and 1 serovar Typhimurium isolate carried type B, A, and C plasmids, respectively. Both the serotype Agona and serotype Reading isolates carried type A plasmids. None of the isolates carried a type D plasmid. Hybridization data suggested that plasmid types A and C were highly related replicons. DNA sequencing revealed that the region surrounding bla CMY-2 was highly conserved in all three plasmid types analyzed (types B, C, and D) and was related to a region surrounding bla CMY-5 from the Klebsiella oxytoca plasmid pTKH11. These findings are consistent with a model in which bla CMY-2 has been disseminated primarily through plasmid transfer, and not by mobilization of the gene itself, to multiple Salmonella chromosomal backbones.

Characterization of AmpC-Mediated Resistance in Clinical Salmonella Isolates Recovered from Humans during the Period 1992 to 2003 in England and Wales

“…Conjugal transfer of type A plasmids has been reported to be at a very low frequency (10). In agreement with this observation, in our study none of the type A-related plasmids were transferable by conjugation.…”

“…However, RFLP patterns from plasmids A7 and A11 showed hybridizing-fragment sizes compatible with those reported for the type A plasmids described by Giles et al (10), although a direct comparison would be necessary to fully support this observation. A7 and A11 correspond to isolates from serotypes Heidelberg and Worthington, acquired following visits to Greece and Iraq, respectively.…”

“…Plasmids of type A confer a multidrug-resistant phenotype not only to ␤-lactams but also to multiple classes of antimicrobials (10). In our study all isolates with type A-related plasmids were also resistant to a variety of antimicrobials (among them, chloramphenicol, streptomycin, sulfonamide, and tetracycline).…”

“…All these infections were linked to foreign travel and showed RFLP plasmid patterns consistent with those of plasmids previously seen in the United States. This adds strength to the suggestion that bla CMY-2 has been disseminated primarily through plasmid transfer (10). The fact that two of the isolates that appear to have been acquired domestically in the United Kingdom (A5, A6) presented previously unseen RFLP plasmid patterns suggests that mobilization of the gene to multiple plasmid backbones may also be a possible mechanism.…”

Detection of a bla SHV Extended-Spectrum β-Lactamase in Salmonella enterica Serovar Newport MDR-AmpC

“…Both transconjugant strains were bla TEM and bla SHV positive and negative for the bla CMY gene by PCR. IEF of the transconjugants showed that only two ␤-lactamase genes, encoding enzymes with pIs of 5.4 and 8.0, had transferred, and this was consistent with the fact that the plasmid-mediated ampC gene in serovar Newport strains has previously been shown to be difficult to transfer by conjugation (6). DNA sequencing of S. enterica serovar Newport strain SRC0307-213 showed that it contained a bla CMY-2 gene.…”