Investigation of sasX, ACME and various virulence factors in coagulase negative staphylococci isolated from blood cultures

The role of CoNS in blood stream infections has increased due to prolonged hospitalization, urinary and intravascular catheterization, increased health care services such as widespread use of implantable medical devices, and changes in the patient population (such as increased premature neonates; geriatric patients with multiple morbidity and chronic diseases, immunosuppressive patients). In this study, it was aimed to investigate virulence-related sasX, arginine catabolic mobile element (ACME) genes, biofilm production and some biofilm-related virulence factor genes in CoNS strains isolated from blood cultures and determine their frequency in strains identified as infectious agent and contaminant. In total, 150 strains of CoNS isolated from blood cultures were included in the study. Based on clinical and microbiological data, 50 of the isolated strains were grouped as infectious agent and 100 as contamination isolates. The strains were identified at the species level with an automated bacterial identification system. The presence of sasX, ACME, mecA and biofilm-related virulence factor genes was investigated by the in-house PCR method. Phenotypically, biofilm formation was investigated by the micro-plaque method. Of the CoNS strains included in the study, 95 (63.3%) were identified as S. epidermidis, 25 (16.7%) as S. hominis, 22 (14.7) as S. haemolticus, 6 (4%) as S.capitis, 1 (0.7%) as S. intermedius and 1 (0.7%) as S. warneri. Of all strains, 125 (83.3%) had the MecA gene positive, while no differences were found in the MecA positivity ratio between the infectious agent and contamination groups (p=0.877). The presence of sasX was positive in the contamination group with 14 (14%) strains and in the infectious agent group with 5 (10%) strains, i.e. in 19 strains in total. No differences were found between the strains in the infectious agent and contamination groups in terms of the sasX positivity ratio (p=0.327). The presence of any of the ACME-related ArcA, kdpA, and opp3B operons was found to be positive in 32 (32%) of the strains in the contamination group and 6 (12%) of the strains in the infectious agent group. When the gene regions were evaluated separately, 30 (30%) strains in the contamination group were ArcA positive, 7 (7%) strains were kdpA positive, 8 (8%) were opp3B positive, 6 (12%) were ArcA positive, 1 (2%) was kdpA positive and 3 (6%) were opp3B positive. The ACME and ArcA positivity ratios were significantly higher in the strains in the contamination group (p=0.008 and p=0.015, respectively). An examination of phenotypical biofilm-forming properties showed that 67 (44.7%) of all strains did not form a biofilm, 39 (26%) formed a weak biofilm, 15 (10%) a medium biofilm and 29 (19.3%) formed a strong biofilm. While 52% of the strains in the infectious agent group had any level of biofilm formation, this ratio was 57% in the strains in the contamination group. While there was no significant difference in the ratio of biofilm-forming strains between the groups (p=0.561), 14% of the strains in the contamination group and 30% of the strains in the infectious agent group were found to be strongly biofilm-forming, and the difference between the groups was significant in terms of their biofilm-forming level (p=027). Biofilm-related IcaA, icaD, IS256, aap and bhp virulence genes were found to be positive in strains in the contamination group at 33%, 45%, 43%, 74% and 6% respectively, and 64%, 62%, 64%, 74% and 8% in strains in the infectious agent group, respectively. IcaA, icaD ve IS256 positivity ratios were significantly higher in the infectious agent group than in the contamination group (p<0.001, p=0.050, p=0.015, respectively), while no differences were found between the two groups in terms of aap and bhp positivity ratios. IcaA and icaD co-positivity was found to be 29% in the contamination group and 56% in the infectious agent group, and the difference between the groups was significant (p=0.001). IcaA, icaD ve IS256 co-positivity was 17% in strains in the contamination group, 38% in strains in the infectious agent group, and the difference was significant in terms of the ratio of having all three genes together (p=0.005). Of all the strains in the study, 46 (80.7%) of the total 57 strains in which icaA and icaD were co-positive presented any level of biofilm formation. Any level of biofilm positivity was significantly higher in the IcaA and icaD co-positive strains than in the strains where IcaA or icaD was positive or both were negative (p<0.001). In conclusion, strong biofilm generation and single or multiple presence of biofilm-related icaA, icaD and IS256 genes were found to be higher in strains classified as infectious agent, while especially ACME-related ArcA positivity was found to be higher in strains in the contamination group. These findings suggest that the presence of certain gene regions in CoNS strains may guide the distinction of infectious agent and contamination.