Lactoferrin increases the susceptibility of S. epidermidis biofilms to lysozyme and vancomycin

Abstract

Purpose. The tear cationic protein lactoferrin increases the activity of various antimicrobial agents against suspended bacterial cultures including Staphylococcus epidermidis, the predominant causative agent of intraocular lens biofilm infections. We investigated the ability of lactoferrin to enhance the activity of vancomycin and lysozyme against biofilms of a clinical S. epidermidis isolate. Methods. Biofilms were prepared on soft contact lenses and cells released from the biofilm surface were collected from the surrounding broth. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against the intact biofilm, released cells and suspended bacteria were evaluated using vancomycin with and without lactoferrin. Results. Lactoferrin induced a two-fold reduction in the MBC of vancomycin for biofilm (p < 0.01) and biofilm-released cells from 64 µg/ml to 32 µg/ml and similarly decreased the MIC for biofilm-released cells (p < 0.01) from 32 µg/ml to 16 µg/ml. With or without lactoferrin, the MIC of vancomycin for suspended cells (2 and 4 µg/ml respectively) was less (p < 0.01) than that of both the biofilm (32 and 32 µg/ml) and biofilm-released cells (16 and 32 µg/ml). Lactoferrin did not reduce the MIC of lysozyme, but, at a lysozyme concentration of 16 mg/ml, did significantly (p < 0.05) reduce the number of viable biofilm and biofilm-released cells. Conclusions. Lactoferrin displays potential as an adjunctive agent to vancomycin in the treatment of S. epidermidis biofilm infections, such as endophthalmitis, associated with intraocular lenses.