Detection of sasX Gene and Distribution of SCCmec types in Invasive and Non-invasive Coagulase Negative Staphylococci

Background: Coagulase negative staphylococci (CoNS) which belong to normal microbiata of the skin and mucous membranes are opportunistic pathogens. SasX, a newly described protein is thought to play an important role in nasal colonization and virulence of meticillin-resistant Staphylococcus aureus (MRSA) and it may be acquired from CoNS by horizontal gene transfer. It has been considered that understanding the function of sasX gene may help in clarifying the relevance of the different adhesion mechanisms in the pathogenesis of infections associated with biofilm.

Aims: In this study our aim was to investigate the sasX gene presence, SCC mec types and antimicrobial resistance patterns of invasive (n:89) and non-invasive (n:91) coagulase negative staphylococci isolates.

Study Design: Cross sectional study.

Methods: A total of 180 CoNS strains were included in the study.  Non-invasive isolates (n: 91) were obtained from the hands of healthy volunteers who do not work at the hospital (n: 30), nasal vestibule isolates of healthy volunteer hospital workers (n: 26) and isolates from central venous catheter colonization (n:35). Invasive isolates (n:89) were isolated from peripheral blood cultures of inpatients who do not have catheters. All isolates were identified by conventional microbiological methods and automated systems and if needed with MALDI-TOF. SCC mec typing, sasX and mec gene detection, antibiotic susceptibility and sequence analysis of sasX gene were performed.

Results: sasX gene was found to be positive in peripheral blood, central venous catheter colonization, nasal vestibule isolates and negative for hand isolates. sasX gene was present in 17 isolates, no statistical significance was found between invasive and non invasive isolates (p=0.173), sequence analysis of the sasX genes, showed high homology to related proteins of Staphylococcus phage SPbeta-like and S. epidermidis RP62A. SCC mec type V was the most prevalent regardless of species. SCC mec type II was more frequent in invasive isolates and also type II ratio was found to be statistically important for invasive and non-invasive S. epidermidis isolates (p=0.029). S. haemolyticus isolates had the overall highest resistance rates. Resistance to ciprofloxacin, trimethoprim-sulfamethoxazole and erythromycin were found to be higher in isolates from catheter colonization and blood culture isolates. S. hominis isolates had the highest rate for inducible clindamycin resistance. None of the isolates were resistant to vancomycin, teicoplanin and linezolid.

Conclusion: Here we documented the characteristics of our CoNS isolates for sasX and SCC mec types. Further studies about the role of sasX at virulence in coagulase negative staphylococci, especially from clinical samples such as tracheal aspirate and abscess isolates and distribution of SCC mec types is needed.