THE PRESENCE OF ICAAD GENES IN COMMENSALS OF COAGULASE-NEGATIVE STAPHYLOCOCCUS AND EVALUATION OF PHENOTYPIC BIOFILM FORMATION BY CRA AND CRAVC METHODS

A total of 28 commensals of coagulase negative Staphylococcus or CoNS strains were successfully isolated from healthy volunteers. Amplification of the icaAD genes showed that 21% of these isolates harbour these genes which involve in biofilm formation. The ability of these strains to form biofilm was further evaluated phenotypically using both Congo Red Agar (CRA) and a modified Congo Red Agar with vancomycin or CRAvc. Only 32% of the isolates were biofilm positive on CRA as compared to inoculation on CRAvc which displayed a higher number of biofilm producer at 92.8%. However, analysis on the correlation between icaAD genes and the biofilm formation revealed that on CRA, 14.3% of the strains were biofilm tve-ica tve and 17.9% were biofilm tve-ica–ve while on CRAvc, 21.4% were biofilm tve-ica tve and a higher number of strains at 71.4% were biofilm tve-ica–ve. This indicates that growth on CRA gives a more accurate insight on the ability of the strains to produce biofilm although the possibility of the strains forming biofilm by a different mechanism than the icaAD genes cannot be ruled out. Two strong biofilm forming isolates namely C6 and C15 were further subjected for identification via the sodA gene and were found to be S. haemolyticus and S. epidermidis respectively.