INTEGRATIVE ASSESSMENT OF PHENOTYPIC AND MOLECULAR APPROACHES FOR EVALUATING BIOFILM FORMATION IN CLINICAL ISOLATES OF COAGULASE-NEGATIVE STAPHYLOCOCCI

Abstract

Several bacterial species once dismissed as harmless commensals are increasingly implicated in human infection. Coagulase-negative staphylococci (CoNS) are a prominent example, causing a broad spectrum of disease in hospitalised patients and, in particular, those in intensive care. Biofilm formation is a key virulence attribute that promotes the survival and dissemination of CoNS. This study undertook an integrated phenotypic and molecular assessment of biofilm formation in clinical CoNS isolates. Clinical CoNS isolates were evaluated for biofilm-forming ability by two approaches: a quantitative phenotypic assay using the microtitre-plate method, and molecular detection of the ica genes responsible for biofilm formation by polymerase chain reaction (PCR). Taking the genotypic method as the reference standard, the sensitivity and specificity of the phenotypic method were determined. Most CoNS were recovered from urine and blood cultures. S. epidermidis, S. haemolyticus and S. saprophyticus were the predominant species. Of 522 isolates, 489 (93.7%) carried at least two biofilm-associated genes and were classified as biofilm producers by the genotypic method. Against this reference standard, the microtitre-plate method was 95.7% sensitive and 100% specific for the detection of biofilm formation. Advances in molecular biology have identified specific genes governing virulence traits such as biofilm formation, clarifying the mechanisms of pathogenicity; however, molecular methods remain costly for routine use. These findings indicate that the simple, inexpensive microtitre-plate technique offers good sensitivity and specificity and can be readily adopted in diagnostic laboratories for the detection of biofilm formation in CoNS.