Caracterização dos SCCmec e produção de biofilme em Staphylococcus aureus no Hospital Universitário de Santa Maria

Abstract

Staphylococcus aureus, in particular those resistant to methicillin (MRSA), are reported worldwide as pathogens of high prevalence in the etiology of infections. Its versatility as an important etiological agent results from the combination of its virulence factors, highlighting the ability to evade the host's immune system, often through the production of biofilm, as well as developing resistance to multiple antimicrobials. In MRSA, resistance is due mainly to the presence of the mecA gene, carried in a mobile genetic element (SCCmec). Since the emergence of the first MRSA strain associated with the hospital environment (HA-MRSA), significant changes in its epidemiology could be detected with the emergence of community-associated resistant strains (CA-MRSA), differentiated by risk factors, SCCmec typing and distribution of resistance genes. This work aimed to characterize the strains of S. aureus isolated in the Hospital Universitário de Santa Maria (HUSM), through the SCCmec typing, as well as to evaluate different methods to determine biofilm formation. For the SCCmec typing, 113 MRSA, mecA-positive genes, were evaluated in three periods: 38 (2008), 37 (2011) and 38 (2015) isolates were obtained from different clinical specimens of patients attended at the HUSM. The typing was performed through PCR and the antimicrobial susceptibility profile through automated methodology (MicroScan® and Vitek® 2). We verified that SCCmec type I was the most isolated (39.8%), followed by type IV (23.0%), type II (15.1%) and type III (6.2%). Non-typed isolates represented 15.9%. As to the origin of the strains analyzed we observed the prevalence of HA-MRSA (72.6%) about CA-MRSA (27.4%). All MRSA were multiresistant, presenting high rates of resistance to clindamycin and erythromycin, in addition to a significant decrease in resistance to gentamicin, rifampicin and sulfamethoxazole-trimethoprim. There was 100% sensitivity to vancomycin and linezolid. For the determination of the biofilm production we evaluated 132 S. aureus of the year 2011 at the HUSM. The Microtiter Method (MtP), considered gold standard, in addition to the Tube Method (TM), Congo Red Agar Method (CRA) and the search for the icaA, icaC and icaD genes were tested. The antimicrobial susceptibility profile of the biofilm producing strains was carried out using the Disk Diffusion and Broth Microdilution techniques. In 42/132 (31.8%) the biofilm production was detected by one or more of the 4 methodologies tested. MtP was considered superior to TM and CRA, since it detected 31/132 (23.5%) isolates biofilm producers. In TM there was positivity in 9/132 (6.8%) and CRA in only 1 isolate (0.8%). Genotypically we detect that our isolates possibly produce biofilm by an ica-independent mechanism. In general these biofilm producing isolates were very sensitive to the antimicrobials tested. Through these results we can conclude that in HUSM there was a predominance of multiresistant HA-MRSA strains, type I being the most circulating. In addition, when compared to the standard method, TM, CRA and icaA, icaC and icaD genes search were not reliable to identify biofilm producing strains in our isolates.