Biofilm formation on intraocular lenses by a clinical strain encoding the ica locus: A scanning electron microscopy study

Abstract

PURPOSE. To determine whether the Staphylococcus epidermidis strain carries the intercellular adhesion (ica) locus, which encodes production of adhesins mediating adherence to biomaterials and to study, with scanning electron microscopy, the morphologic features of this coagulase-negative Staphylococcus strain that adheres to intraocular lenses (IOLs). METHODS. Polymerase chain reaction amplification was used to investigate whether the isolate under study (S. epidermidis clinical strain N890074) carries the ica locus. Sterile intraocular lenses (IOLs) were incubated in bacterial suspension either for 5 minutes or 1 hour. IOLs were then examined by scanning electron microscopy. RESULTS. Polymerase chain reaction amplification revealed that S. epidermidis N890074 contained the ica locus. The bacteria appeared to be anchored to the surface of the lenses by several different means-particularly by leglike appendages and a slime layer-which probably came into play step by step. CONCLUSIONS. For the first time in ophthalmology, to the authors' knowledge, photographs showing leglike appendages involved in the first phase of adhesion have been obtained. They also clearly visualize the slime layer containing the embedded bacteria. This study provides information about the nature and the genesis of these attachment processes. Adherence is known to be greater when the bacterial DNA contain the ica locus. Full knowledge of the pathogenesis of bacterial adhesion is necessary to gain a better understanding of IOL infection and endophthalmitis.