Speciation, Detection of Virulence Factors and Antibiotic Susceptibility of Coagulase Negative Staphylococci

Background and aim: Coagulase-Negative Staphylococci (CoNS), although predominant in the normal skin flora, can cause severe human diseases, as evident from their increasing incidence in recent years. Detailed characterization of CoNS isolates through speciation, and antibiotic susceptibility may be needed to differentiate pathogenic from contaminating isolates and plan effective therapy. Aim: To isolate and speciate CoNS from various clinical specimens, detect different virulence factors, and determine the antibiotic susceptibility profile.
Materials and methods: A hospital-based cross-sectional study was done using 110 clinical isolates of CoNS throughout one year in the Department of Microbiology, Government Medical College, Thrissur, Kerala, India. The isolates were identified, speciated using standard methods, virulence factors like biofilm formation and DNase were determined, as well as antibiotic susceptibility using the Kirby Bauer disc diffusion method. Statistical analysis was done by counts and percentages using MS Excel version 2010.
Results: Staphylococcus epidermidis was the most frequent isolate, 49.1%, Staphylococcus haemolyticus 27.3%, and Staphylococcus schleiferi 11.8%. Blood samples yielded maximum isolates. Biofilm production by the Congo Red Agar method was seen in 18.2% isolates, and 14.5% showed DNase production. Antibiotic susceptibility testing showed maximum resistance to Penicillin (95.5%) and Erythromycin (80.9%) with Methicillin resistance in 17.3% and 100 % sensitivity to Vancomycin. Biofilm-producing strains were more antibiotic-resistant.
Conclusion: The multiple antibiotic resistance and pathogenic potential of biofilm producers emphasize the importance of developing simple, reliable, and inexpensive methods to identify virulence factors and determine the antibiotic sensitivity of CoNS.