Background: Multi-antibiotic resistant organisms (MROs) cause infections in up to 20% of intensive care patients. We showed by scanning electron microscopy (SEM) and culture, that biofilm develops on dry hospital surfaces and some of incorporate MROs. Biofilm exopolysaccharide (EPS) surrounds bacteria protecting them from dehydration and provides increased resistance to removal by disinfectants. Dry surface biofilms have very thick EPS. We suggest that dry surface biofilms are important reservoirs of MRO in the hospital environment. Current cleaning agents are formulated to remove patient secretions but are ineffective against biofilm. Therefore, we aimed to develop a reproducible biofilm that visually mimicked hospital dry surface biofilms in order to develop and test methods of removing biofilm from hospital surfaces.

Methods :

Staphylococcus epidermidis biofilms were grown on  polytetrafluoroethylene coupons, in the Centres for Diseases Control (CDC) biofilm reactor, under shear in 10% of Tryptic Soy Broth  for 48hrs at 35^oC. The media was drained and filtered air pumped into the reactor to mimic the dehydrating effect of air-conditioning for 48hrs, at 24^oC. Fresh media was added to the reactor for 6 hours followed by 42hrs of dehydration. This cycle was repeated three times. Following each dehydration cycle colony forming units/coupon were determined by plate culture and degree of EPS production by SEM.

Results and Conclusions

We have shown that a reproducible dry surface biofilm can be grown in the CDC biofilm reactor by modifying the growth conditions. With increasing cycles of growth and dehydration, CFU gradually increased from 10¹⁰ in the first cycle to 10¹¹ following the 5^th cycle. With increasing cycle number the biofilm EPS thickened and dehydrated resembling that found in biofilms found naturally in hospital environments. This model will allow investigation of the dry surface biofilms and methods of their removal and is fundamental to infectious disease control