Estafilococos coagulase negativos isolados de pacientes com infecção de corrente sanguínea: aspectos microbiológicos e imunológicos

Abstract

Coagulase-negative staphylococci (CNS) are the most frequent agents of bloodstream infection (BSI) and resistance to antimicrobial agents and bacterial adhesion to biomaterials contribute to its virulence. The objective of this work was to study the microbiological and immunological aspects of ECN causing ICS in patients hospitalized in HC-UFTM. The species were identified by biochemical tests and confirmed by PCR for sep, mva and fbl genes. Evaluation of antimicrobial resistance was done by microdilution tests and presence of mecA gene by PCR. Biofilm production was verified by spectrophotometry and research of icaAB and atlE genes. Induction of TNFα, IL-1β, IL-6, IL-8, IL-10 and IL-12 was assessed by stimulating human PBMC with heat-inactivated bacteria and subsequent determination by flow cytometry. A total of 90 isolates from blood cultures (n = 68) and swabs (n = 22) were analyzed, with 78.90% (n = 71) S. epidermidis, 8.89% (n = 8) S. haemolyticus, 3.33% (n = 3) S. saprophyticus, 2.22% (n = 2) S. cohnii, 2.22% (n = 2) S. capitis, 2.22% (n = 2) S. lugdunensis, 1, 11% (n = 1) S. hominis and 1.11% (n = 1) S. xylosus. All samples were resistant to oxacillin, with MICs ≥ 256μg/mL in 31.11% of them, only one sample was negative for the mecA gene and all were sensitive to vancomycin, with MIC 4μg/mL at 65.56%. Biofilm production was observed in 61.76% of the samples causing ICS and 43.64% of colonizing, and 30.83% of the samples in the first group and 40.91% in the second showed intense production (OD > 3.000 BU) (p <0.01). Strong and statistically significant (p <0.01) production occurred in 36.36% of S. epidermidis. The icaAB gene was positive in 54.44% of ECN and atlE in 76.67%, with a statistically significant difference between species (p < 0.0001). Levels of IL-12 were smaller for infective CNS and significantly greater (p < 0.05) for S. haemolyticus. Significantly higher levels (p < 0.05) of IL-6 were induced by S. epidermidis. It can be concluded that ECN agents of ICS feature S. epidermidis as the most frequent species; High levels of oxacillin resistance, but sensitivity to vancomycin; biofilm production, but not essentially related to icaAB and atlE genes and the most virulent strains were able to generate greater induction of immune response mediators.