Eugene Muller

Mechanism of Salicylate-Mediated Inhibition of Biofilm in Staphylococcus epidermidis

The inclusion of 5 mM salicylic acid (SAL) in medium inhibited both growth and biofilm production by Staphylococcus epidermidis by up to 55%. The inhibition was not due primarily to chelation of cations. Excess divalent cations restored growth and biofilm production in chelated medium and in medium containing EDTA but not in medium containing SAL. ELISA analyses demonstrated that SAL inhibited production of teichoic acid, slime-associated proteins, and type 1 antigen by as much as 95%. However, it inhibited polysaccharide/adhesin production by only 50%--a figure paralleling the reduction in growth. The equivalent inhibitory effects of SAL on a pair of isogenic strains, one of which was a polysaccharide/adhesin-deficient mutant, confirmed that the primary effect of SAL was a reduction in the production of biofilm components rather than a reduction in the retention of these components in the slime layer prior to assembly into a biofilm.

The Pathogenic Role of Staphylococcus epidermidis Capsular Polysaccharide/Adhesin in a Low-Inoculum Rabbit Model of Prosthetic Valve Endocarditis

BACKGROUND The capsular polysaccharide/adhesin (PS/A) antigen of Staphylococcus epidermidis was required to produce endocarditis in a rabbit model in which infection resulted from hematogenous spread of bacteria from a contaminated catheter in the jugular vein. However, many prosthetic valve endocarditis (PVE) infections probably result from direct contamination of the valve with small numbers of bacteria during surgery. The role of PS/A in this situation was evaluated by modifying a rabbit model of endocarditis to partially mimic PVE. METHODS AND RESULTS A Teflon catheter was contaminated with graded inocula of either PS/A-positive S epidermidis strain M187sp11 or the PS/A-negative, isogenic strain M187sn3 and inserted into the left ventricle through the aortic valve. The PS/A-positive strain had a 50% infectious dose of 1.1 x 10(2) cfu (95% CI, 3.3 to 3.7 x 10(3)) compared with 8.5 x 10(4) cfu of the PS/A-negative strain (95% CI, 8.6 x 10(3) to 8.5 x 10(5)). The odds for developing endocarditis were estimated to be 42 times higher for any given inoculum level of the PS/A-positive strain (P = .1). When the PS/A-positive strain was adherent to a catheter surface it survived in rabbit blood, whereas under the same conditions the PS/A-negative strain was killed approximately 90% in 1 hour. CONCLUSIONS Direct contamination of an intraventricular foreign body by low levels of PS/A-positive S epidermidis results in endocarditis in rabbits, but at suitably high doses PS/A-negative strains have sufficient virulence to infect cardiac vegetations. PS/A enhances but is not absolutely required for bacterial virulence in a rabbit model of PVE.

Factors affecting staphylococcus epidermidis adhesion to contact lenses

Background. Staphylococcus epidermidis is a major causative agent of infectious keratitis associated with contact lens wear. Adhesion of this bacterium to contact lenses may contribute to the pathogenesis of infection and could be influenced by lens surface properties, packaging/storage solutions, and vary among different strains according to the level or type of adhesins expressed. Methods. Adhesion of six clinical isolates of S. epidermidis to three different contact lens materials was tested. Adhesion assays were performed on lenses immediately after removal from their packages, and also after lenses were soaked in sterile phosphate buffered saline (PBS) for 7 days to dilute the packaging solution. Results. For lenses tested immediately upon removal from their packaging, adhesion to polymacon (in PBS with 0.1% polyvinyl alcohol) was significantly greater than to etafilcon A (in borate buffered saline) and vifilcon A (in PBS). After soaking, adhesion to polymacon lenses was significantly less than to the other lens materials. This pattern was consistent for all strains, although major differences in baseline adhesion levels existed between strains, with exopolysaccharide (slime)-positive bacteria being more adherent to lenses. Conclusions. Properties of contact lens materials were not the sole determinant of viable S. epidermidis adhesion to lenses. Strain variability, including levels of exopolysaccharide expression, and the solution used for lens immersion also influenced adhesion