Complex class 1 integrons harboring CTX-M-2-encoding genes in clinical Enterobacteriaceae from a hospital in Brazil

Abstract

Introduction: 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.

Methodology: 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.

Results: 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.

Conclusions: 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.