Microbial adherence on poly(methyl methacrylate) (PMMA) surfaces.

Infection remains a major complication following the use of implanted biomaterials. Often these infections are caused by low-virulence organisms or by a mixture of organisms (polymicrobial). In this study two methods were used to quantitate the bacteria which had adhered to poly(methyl methacrylate) (PMMA) samples. The bacteria were eluted from the sample using an ultrasonic cleaner. The number eluted was then counted by colony counts, which determines viable organisms and by particle counting which counts both viable and nonviable organisms. A known adherent strain of Staphylococcus epidermidis and a strain of Proteus mirabilis were used. In general the adherence of S. epidermidis was greater than that of Proteus. When the two organisms were used together, there was an alteration in the adherence pattern which generally increased the adherence of Proteus and had no effect or decreased the adherence of S. epidermidis. The use of both quantitation techniques provided important information on the adherence of organisms to PMMA to which gentamicin had been added. It was evident that organisms did adhere to the PMMA plus gentamicin samples but were not viable when eluted. The amount of adherence to PMMA plus gentamicin was similar to that of PMMA alone at 30 min but was markedly decreased at 24 h. There was a considerable dead biofilm mass on the PMMA plus gentamicin samples which might be a significant promoter of late infections by providing a surface attractive to other strains of bacteria.