Mode of action of an antimicrobial biomaterial for use in hydrocephalus shunts

Objectives: Infection remains a major complication of shunting for hydrocephalus. The causative bacteria, mainly staphylococci, gain access to the shunt at operation and colonize the shunt tubing. This leads to biofilm development requiring shunt removal. As there is no clear evidence to support antibiotic prophylaxis, we have developed an impregnated antimicrobial shunt material. This study aimed to elucidate its mode of action in terms of bacterial adherence and killing kinetics. Methods: Plain and impregnated material, with and without plasma protein conditioning film, were exposed to Staphylococcus epidermidis. Bacterial adherence was determined by scanning electron microscopy, chemiluminescence and culture. Time taken to kill 100% of bacteria (tK(100)) was determined by serial chemiluminescence, culture and the use of differential viability microscopy. Results: The antimicrobial material did not reduce bacterial adherence. However, 100% of attached bacteria were killed in 48-52 h, even in the presence of a conditioning film. Conclusions: Impregnated antimicrobial material is likely to reduce shunt infection rates significantly without the risks and side effects of systemic antibiotics.