SPINAL IMPLANT MATERIALS: ATTACHMENT AND BIOFILM PRODUCTION BY PROPIONIBACTERIUM ACNES AND SUBSEQUENT EFFECT OF EXPOSURE TO ANTIBIOTICS

Abstract

Introduction: Propionibacterium acnes (P. acnes), a common anaerobic skin commensal, has been implicated in biomaterial-related infections (BRI). Bacteria can adhere to biomaterial surfaces and grow as a bio-film held together by exopolymer, exhibiting increased antimicrobial resistance. To our knowledge, images of P. acnes biofilms have not previously been published. We have demonstrated the ability of P. acnes to adhere to surgical steel and to develop a biofilm on this material. However its ability to adhere to and develop a biofilm on titanium, a commonly used surgical implant material, has not been fully investigated.

Aims:

1. To determine the quantitative adherence and biofilm development of P. acnes on titanium compared to surgical steel.

2. To assess the subsequent effect of penicillin, the therapeutic drug of choice, on mature P. acnes biofilms.

Method: Six clinical isolates of P. acnes were assayed for adherence to materials with and without plasma glycoprotein conditioning film by chemiluminescence and culture. Biofilm development was assessed by chemiluminescence, fluorescence microscopy, environmental (ESEM) and scanning electron microscopy (SEM). Mature biofilms were exposed to plasma concentrations of penicillin and quantified by chemiluminescence and culture. Unpaired student’s t tests and univariate linear regression models were calculated using SPSS software (version 12).

Results: Univariate linear regression showed that P. acnes adherence to titanium was 18% (p=0.001) greater than to steel. Adherence was reduced by the presence of the conditioning film on titanium by 28% (p=0.001), but this made no significant difference to P. acnes adherence to steel. P. acnes biofilms were clearly demonstrated, along with bacterial expolymer, showing an interesting similarity to biofilms of S. epidermidis. P. acnes grows as a thick biofilm on both materials held together by exopolymer and our preliminary results suggest that biofilms on titanium might be less susceptible to antimicrobials after 24 hours of penicillin treatment; a reduction of 94% on steel and 81% on titanium (p=0.057, p=0.39 resp).

Conclusions: P. acnes adheres to steel and titanium, a crucial first step in BRI. Greater numbers of P. acnes adhere to titanium than to steel. The naked surface of titanium is microporous, assisting adhesion. A conditioning film reduces P. acnes adherence to titanium but not to steel. P. acnes develops as a biofilm on steel and titanium. Results indicate that pathogenesis of P. acnes infection on titanium is more successful than on steel. P. acnes biofilms on titanium may be harder to eradicate with antimicrobial agents.