Clinical usefulness of biofilm formation and associated genes with staphylococcus epidermidis blood isolates

Park, Kyung Hwa; Choi, Su Mi; Jung, Sook In; Shin, Jong Hee

Abstract

BACKGROUND/AIMS: To evaluate the clinical usefulness of biofilm production and related genes for discriminating between pathogens, colonizers, and contaminants with Staphylococcus epidermidis blood isolates.
METHODS
Forty S. epidermidis blood isolates, including 19 pathogens, 11 colonizers, and 10 contaminants, were tested. Biofilm production was determined in 96-well polystyrene microtiter plates using crystal violet staining. Relative units (rU), given by the optical density (OD) of the clinical isolates divided by the OD of a standard biofilm-negative strain, were used for quantification. Polymerase chain reactions for the icaABCD, atlE, and aap genes were performed to evaluate biofilm-related genes. The diagnostic accuracy of biofilm-related genes was assessed using the sensitivity, specificity, and positive predictive value.
RESULTS
Biofilm production of the catheter-related isolates, including pathogens and colonizers, was significantly greater than that of contaminants (50% vs. 20%, p=0.012). For catheter-related isolates, rU was significantly greater for ica-positive isolates than for ica-negative isolates (1.72+/-0.84 vs.0.94+/-0.22; p=0.003). The prevalence of atlE and aap did not differ between the three groups. Seven S. epidermidis were isolated together with other microorganisms from intravascular catheters, and their biofilm production was relatively low. The positive predictive value of icaABCD was 83% for discriminating between catheter-related isolates and contaminants.
CONCLUSIONS
Pathogens and colonizers had similar biofilm production capacities and prevalences of related genes, whereas catheter-related isolates and contaminants differed. The biofilm production ability and presence of these genes cannot be used for clinical decision-making regarding true pathogens. The ica operon might be useful for differentiating between contaminants and catheter-related isolates in catheter-related infection (CRI). Further studies of other related genes and protein expression are needed to assess the clinical usefulness of biofilm production for clinical isolates.