Detection of biofilm formation in Staphylococcus epidermidis from implant infections. Comparison of a PCR-method that recognizes the presence of ica genes with two classic phenotypic methods.
Biofilm-forming ability is increasingly being recognized as an important virulence factor in Staphylococcus epidermidis. This study compares three different techniques for the detection of biofilm-positive strains. The presence of icaA and icaD genes responsible for biofilm synthesis was investigated by a PCR method in a collection of 80 S. epidermidis strains isolated from orthopedic implant infections. The results from molecular analysis were compared with those obtained by two classic phenotypic methods, the Congo red agar (CRA) plate test and the microtiter plate test (MtP). Fifty-seven percent of all the examined strains were found icaA/icaD-positive, of which only three were not positive for CRA test. Differently, by the MtP method, 66% of the strains were found to be biofilm-producers but only a limited agreement with the PCR-method was noticeable because of the observation of (icaA/icaD+)/MtP- strains (8%) and of a surprising ambiguous result of (icaA/icaD-)/MtP+ strains (16%). The category of the weak biofilm-producers provided the highest contribution to these mismatching results (10%). The better agreement between the CRA plate test with the molecular detection of ica genes indicates the former as a reliable test for the phenotypic characterization of virulence of clinical isolates. However, MtP method remains a precious tool for the in vitro screening of different biomaterials for the adhesive properties using a reference strain.
Arciola
Carla Renata
CR
Research Unit on Implant Infections, Rizzoli Orthopedic Institute, Bologna, Italy. carlarenata.arciola@ior.it
Campoccia
Davide
D
Baldassarri
Lucilla
L
Donati
Maria Elena
ME
Pirini
Valter
V
Gamberini
Simonetta
S
Montanaro
Lucio
L
D001422:Bacterial Adhesion; D001431:Bacteriological Techniques; D001672:Biocompatible Materials; D018441:Biofilms / Q000254:growth & development*; D015815:Cell Adhesion Molecules / Q000032:analysis / Q000235:genetics; D007595:Joint Prosthesis / Q000382:microbiology; D016133:Polymerase Chain Reaction / Q000379:methods*; D016459:Prosthesis-Related Infections / Q000382:microbiology*; D013212:Staphylococcus epidermidis / Q000201:enzymology* / Q000254:growth & development / Q000302:isolation & purification*
D001672:Biocompatible Materials; D015815:Cell Adhesion Molecules