Phenotypic and genotypic characterisation of biofilm formation in staphylococcus capitis

Biofilm formation is a major concern in infection caused by S. capitis in newborn babies. Phenotypic and genotypic characteristics of biofilm formation in clinical S. capitis isolates from newborns in Royal Woman’s Hospital in Melbourne were investigated. Of 60 S. capitis isolates, 52 belonged to the subspecies urealyticus and the remaining eight to the subsp. capitis. The most prevalent types, that persisted for 6 years in the unit belonged to subsp. urealyticus. Biofilm formation and antibiotic resistance were also mainly displayed by subsp. urealyticus. Sequence analysis showed that the ica operon in S. capitis was 4160 bp in length. PCR demonstrated its presence in all the isolates. The ica operon harboured in S. capitis is closely related to that of other species of staphylococci. It contains four structural genes icaA, icaD, icaB and icaC, which are co-transcribed from the icaA promoter. A negative regulator icaR gene is located upstream of icaA and transcribed in an opposite orientation. In sillico analysis of ica operon demonstrated the putative function and mechanisms of ICA proteins in polysaccharide biosynthesis and the origin on ica genes present in S. capitis genomes. In vitro biofilm formation and the expression of biofilm-related genes induced by sub-inhibitory concentrations of erythromycin revealed different responses. The expression of icaA and sarA genes was up-regulated, and icaR was down-regulated in the subsp. urealyticus biofilm producer. In contrast, a reverse expression was displayed by the biofilm-negative subsp. capitis isolate. This suggests biofilm formation in S. capitis is regulated by icaR and sarA, and the two subspecies may adopt different regulatory pathways in the two subspecies. The erythromycin induced biofilm formation may have clinical implications according to the doses of erythromycin used clinically. Gene transformation protocols for S. capitis were developed and optimised and will be used as a platform for future work. In summary, this study revealed distinctive phenotypic and genotypic characteristics of the two subspecies of S. capitis which relate to their epidemiology under the clinical setting of newborn intensive care. Isolates of the predominant subsp. urealyticus clones were characterised by their higher antibiotic resistance and biofilm formation ability, and distinct gene expression profiles. Differentiating the subspecies S. capitis revealed will be valuable in understanding their role in bloodstream infections of newborns in hospitals.