Study on Biofilm Formation and Multiplex PCR of icaABCD Operon in Staphylococcus capitis

Aims: The ability to form biofilm is a major virulence factor in the virulence of the Coagulase negative Staphylococcus (CoNS) group of bacteria. Being the most predominant member of CoNS, the ability of S. epidermidis in causing biofilm-associated infections has been well established. On the other hand, S. capitis and has always been regard as a non-pathogenic species although recently it was found to be responsible in a variety of infections. In clinical settings, the majority of infections by CoNS is associated with the use of foreign bodies or medical devices such as catheters, where the bacteria were able to persist on these surfaces as a layer of biofilm. Hence, the objective of this study was to investigate the biofilm formation capabilities in clinical isolates of S. capitis. Subsequently the presence of icaABCD genes were also determined using a set of four primers via multiplex PCR.

Methodology: S. capitis was isolated and identified from 17 out of 200 clinical samples. Biofilm formation assay was performed quantitatively using a microtitre plate method. Mulitplex PCR primers for icaABCD genes were designed from DNA sequences coding for the icaA, B, C, and D structural genes of S capitis JF930147.1 which was compared together with five other species of Staphylococcus. Amplification of the icaABCD genes was performed using the designated primers.

Results: From the 17 strains of S. capitis clinical isolates, 14 were identified as S. capitis subspcapitis while the remaining three were identified as S. capitis subsp ureolyticus. Except for two of the S. capitis subsp capitis isolates, the remaining strains were able to form biofilm, with majority of them were strong biofilm formers. Multiplex PCR was successful in amplifying the four icaABCD genes which was demonstrated in all the S. capitis isolates, including the two non-biofilm forming isolates.

Conclusion: Majority of the S. capitis isolates were able to form biofilm phenotypically suggesting the possibility in causing opportunistic infections through indwelling medical devices. Multiplex PCR however was able to detect the presence of the icaABCD genes in all the S. capitis isolates. This suggests that the biofilm assessment on microtitre plate is not a definitive tool in determining the production of polysaccharide intercellular adhesion (PIA) but the production of the icaABCD genes could be a better assessment in determining biofilm production in Staphylococcus.