Abstract
CTX-M enzymes are the most prevalent extended-spectrum beta-lactamases (ESBLs) in Brazil and around the world. The spread of CTX-M lies in their ability to be mobilized by insertion sequences and integrons. This study aimed to identify the mobile genetic structures associated with bla(CTX-M) genes from clinical Enterobacteriaceae strains. Twenty-eight clinical non-clonal Enterobacteriaceae were screened by PCR for the presence of bla(CTX-M) genes and class 1 integrase (int1), and for the association of bla(CTX-M) with class 1 integrons. Plasmid incompatibility groups were assessed by PBRT. Wild-type plasmids were transformed into electrocompetent E. coli, and the S1-PFGE technique was used to verify the presence of high-molecular-weight plasmids in both wild-type strains and E. coli transformants. Sequencing showed that strains carried bla(CTX-M-2) (n = 25) and bla(CTX-M-59) (n = 3) genes inserted into the 3'-end of complex class 1 integrons. Thirteen strains also carried bla(TEM) and bla(SHV) genes. CTX-M-2/59-containing complex class 1 integrons were also present in E. coli transformants. The most frequent Inc groups were IncA/C (n = 10) and IncF (n = 8). Heavy plasmids were observed in both wild-type strains and E. coli transformants. The presence of the same bla(CTX-M-2-group)-containing genetic structure in seven Enterobacteriaceae species isolated at seven hospital wards shows the great mobility potential of complex class 1 integrons. Also, this is the first report of TEM-15, SHV-45, and SHV-55 in Latin America. The genetic environment of bla(CTX-M-2) accounts for their maintenance and spread among Gram-negative bacteria.
Highlights
CTX-M enzymes are the most prevalent extended-spectrum beta-lactamases (ESBLs) in Brazil and around the world
PCR results showed that all strains carried CTX-M-2-group encoding genes, which were identified by sequencing as blaCTX-M-2 (n = 25) and blaCTX-M-59 (n = 3)
S1-PFGE results (Figures 2 and 3, Table 1) showed that all but two wild-type strains possessed high-molecular-weight plasmids, ranging from 48.5 kb to 436.5 kb. This technique showed that, except for strain 205/05, which transferred four plasmids to its respective transformant EC205, only one plasmid was transferred to each E. coli transformant, which harbored plasmids sizing from 48.5 kb to 179 kb that carried the blaCTX-M-2-group-containing complex class 1 integrons
Summary
CTX-M enzymes are the most prevalent extended-spectrum beta-lactamases (ESBLs) in Brazil and around the world. CTX-M2 group of enzymes, are encoded by genes frequently located in complex class 1 integrons, which are the result of the fusion of the insertion sequence ISCR1 to the 3’CS of class 1 integrons, a combinatorial event that allows the structure to become mobile at high frequency rates, and capable of moving great portions of DNA [15]. These structures are frequently mobilized to conjugative plasmids that facilitate their spread. Some resistance-associated plasmid incompatibility (Inc) groups have been considered epidemic due to their presence in bacteria from different sources and
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