Investigação fenotípica e molecular de carbapenemases em Serratia spp.

Abstract

Serratia spp., commonly associated with healthcare-associated infections, it is capable of carrying a variety of genes that confer resistance to antimicrobials, representing an important challenge in terms of choosing the appropriate therapy. The objective of this study was to identify the species of Serratia spp., the presence of genes associated with resistance to carbapenems and to evaluate the relationship of similarity between the samples. A total of 103 samples isolated from patients treated at a university hospital between 2002 and 2020 were analyzed. Phenotypic identification was performed by biochemical tests, mass spectrometry and the VITEK®2 automated system. In addition, species-specific biomarkers were investigated by the analysis of the mass spectra. The antimicrobial susceptibility profile was determined by disk diffusion. The detection of genes encoding enzymes with carbapenemase activity (blaKPC, blaGES, blaNDM and blaOXA-48) was performed by PCR. The similarity between the samples was studied from the observation of the groupings graphically represented in dendrogram and phylloproteomic tree. All samples were identified as Serratia marcescens by biochemical tests. The results obtained by MALDI TOF showed that all samples were characterized by genus, 62 (60.1%) were identified as S. marcescens and 12 (11.6%) as Serratia ureilytica. Analysis of S. ureilytica by VITEK® 2 identified the samples as S. marcescens with high confidence. For the evaluation of biomarkers of the species S. marcescens, samples (n=62) that exhibited a score ≥ 2.00 were used, indicating 24 specific peaks. Samples identified as S. ureilytica with a score ≥ 2.00 were also selected, and it was possible to verify the presence of 48 species-specific peaks. The peaks found showed low intensity. High resistance rates were observed for aminoglycosides (n=41;39.7%), aztreonam (n=36;34.9%) and sulfamethoxazole-trimethoprim (n=27;26.2%). About 1/3 of the samples were multidrug resistant. Regarding carbapenems, a low resistance rate was observed, ranging from 1.9% to 15.5%. Only three (2.8%) samples showed amplification products compatible with the blaKPC gene, in addition to another sample that showed blaNDM. GES-16 carbapenemase was not detected, an enzyme that was first described in 2005 in the same hospital as the study and whose gene was located in a non-conjugative plasmid, which may justify its non-dissemination in the study hospital. The data suggest the importance of investigating other mechanisms associated with carbapenem resistance. The clusters based on mass spectra showed high similarity between the samples and the phyloproteomic tree, showing no discrimination between S. marcescens and S. ureilytica, indicating a great proximity between them. The identification of S. ureilytica exclusively by MALDI TOF, in opposition to the other methodologies used, draws attention to the difficulty of identification between species with very close protein spectra, suggesting in this case the use of whole genome sequencing