Investigation of sas X, ACME and Various Virulence Factors in Coagulase Negative Staphylococcal Strains Identified as Bloodstream Infection Agents and Contamination

Abstract

The aim of this study was to investigate the frequency of sas X, arginine catabolic mobile element (ACME) genes, biofilm formation and some biofilm related virulence factor genes in causative and contaminant coagulase negative staphylococci (CNS) strains isolated from blood cultures. Of the 150 CNS strains included in the study, 50 were grouped as infectious agents and 100 as contaminants. Biofilm formation of the strains was investigated by microplate method and the presence of sas X, ACME, mecA and biofilm associated virulence factor genes ica A, ica D, aap, bhp and IS256 were investigated by inhouse polymerase chain reaction method. While 52% of the strains in the infectious agents group and 57% of the strains in the contamination group phenotypically formed biofilm; when the levels of biofilm positivity were compared, it was observed that the strains in the infectious agents group (30%) formed biofilm at a stronger level than the strains in the contamination group (14%) (p= 0.027). Biofilm-associated ica A, ica D, IS256, aap and bhp genes were found positive in 33%, 45%, 43%, 74% and 6% of the strains in the contamination group and 64%, 62%, 64%, 74% and 8% of the strains in the infectious agents group, respectively. ACME gene regions arc A, kdpA and opp 3B and sasX related gene region were found positive in 30%, 7%, 8% and 14% of the strains in the contamination group and in 12%, 2%, 6% and 10% of the strains in the infectious agents group, respectively. The positivity of ica A, icaD and IS256 genes alone or together in the infectious agents group (p< 0.001, p= 0.050, p= 0.015, respectively) and the positivity of ACME and arcA in the contamination group (p= 0.008, p= 0.015, respectively) were statistically significantly higher. No significant difference was found between the two groups for sas X, aap and bhp genes. In conclusion, among the CNS strains isolated from blood cultures, strains that form strong biofilm and are positive for biofilm-associated gene regions alone or together can be considered as infectious agents, while strains that are found to be arcA positive in the absence of clinical signs of infection can be considered as contaminants.