A quantitative and qualitative study of biofilm disinfection on glass, metal and PVC surfaces by chlorine, bromine and bromochloro-5,5 dimethylhydantoin (BCDMH)

The present study was conducted on artificial biofilm formed in a laboratory water system using three support surfaces: glass, galvanised iron and polyvinyl chloride (PVC). Biofilm formation was followed by direct count on R2A medium and by scanning electron microscope (SEM) examination. As described, the development of biofilm was not the same on the various surfaces. Biofilm formed on various surfaces had different disinfection patterns as shown by the experimental data. Chlorine was the most efficient disinfectant against biofilm developed on glass and metal surfaces but less effective on PVC. Disinfection of glass and PVC biofilms with bromine was much less effective. Bromochloro-5,5 dimethylhydantoin (BCDMH) was very effective on galvanised iron, less effective on PVC and almost no effect was observed on glass surfaces. Addition of EDTA (1mM) to the biofilm system, prior to disinfection, was more effective in killing the biofilm bacteria, probably due to chelation of divalent ions (Ca²⁺,Mg²⁺) which open the matrix and allow the disinfectant to penetrate easily. Maintaining the system at certain BCDMH concentrations, following a disinfection shock with bromine and chlorine, allowed the system to remain at a low level of bacteria. SEM inspection made it possible to follow the biofilm organisation on the various surfaces before and after disinfection. Following disinfection, on all surfaces, the biofilm bacteria seemed to be “flat” and, after addition of EDTA, detachment of the extracellular polysaccharide polymer (EPS) from the surface was observed. It seems that the EPS perforation process allowed better penetration of the disinfectant into the biofilm barrier affecting bacterial viability. The various chemical and microbiological aspects of biofilm disinfection and future practices are discussed.