Resumo

In Enterobacteriaceae, the carbapenem resistance has been linked to the presence of efflux pumps, decreased membrane permeability associated with loss of porins and to KPC type carbapenemases. The former has become a common mechanism; however, its presence in Serratia marcescens is still rare. We have detected earlier an outbreak of clonal-related Serratia marcescens isolates, which showed the presence of blaKPC gene and had the plasmid profile determined. In this work, we carried out the molecular characterization of these clinical isolates of Serratia marcescens. The minimum inhibitory concentration was determined by broth microdilution according to recommendations of CLSI (2012). Identifications of beta-lactamase genes, plasmid incompatibility group and the transposon Tn4401 isoform were performed with primers and conditions previously described. Plasmid DNA was isolated according to the protocol of Kieser and used to transform E.coli DH5α cells. Transformants were selected on Mueller Hinton agar containing ampicillin at 100ug/mL. The isolates showed multidrug resistance phenotype, which is usually characteristic of KPC-producing bacteria. They were sensitive only to tigecycline and gentamicin. Apart from the ,blaKPC-2 gene, all the isolates also showed to carry a class 1 integron and the aadA1 gene in its variable region. All the isolates showed a common plasmid of about 60 Kb belonging to the IncK group, which was also present in the transformants and carried the blaKPC-2 gene. The acquisition of this plasmid yielded transformants with increased MICs for beta-lactams, despite they remained in the range of susceptibility, suggesting the presence of other resistance mechanisms in the individual donors. The region between the gene blaKPC-2 and ISKpn7 was analyzed and revealed no deletion, indicating the presence of isoform Tn4401b. It was recently reported the same isoform Tn4401b in a KPC-producing S.marcescens in Brazil, however in an IncL/M plasmid, showing the plasticity of the genetic elements that conventionally carry the blaKPC gene. Our results highlights the importance of infections caused by S. marcescens resistant to carbapenems, due to the limited treatment options, since this species has intrinsic resistance to antibiotics such as colistin.