Assessment of biofilm formation of E. meningoseptica, D. acidovorans, and S. maltophilia in lens cases and their growth on recovery media

PURPOSE: Bacterial biofilm formation in contact lens cases is a risk factor in the development of both microbial and infiltrative keratitis. This investigation evaluated three emerging pathogens: Stenotrophomonas maltophilia, Elizabethkingia meningoseptica, and Delftia acidovorans for biofilm formation and metabolic activity in lens cases. Also, growth of these bacteria on different media was assessed to optimize recovery conditions. METHODS: The three bacteria were incubated in lens cases with different concentrations of tryptic soy broth. Biofilm formation was evaluated by measuring metabolic activity using MTT and enumerating the number of viable bacteria. To determine the optimal recovery media, dilutions of these microorganisms were plated on six different media. The number of colony forming units (CFU) was recorded after 48, 72, and 96 h of incubation at 32°C and 37°C for S. maltophilia, and at 37°C for E. meningoseptica and D. acidovorans. RESULTS: All three microorganisms established biofilms in the lens cases, with significant numbers of CFU recovered. Biofilms of S. maltophilia and E. meningoseptica were metabolically active. Significant reduction in metabolic activity and number of viable S. maltophilia occurred when the incubation temperature was raised from 32°C to 37°C (p<0.05). The metabolic activity of the biofilms increased with greater organic load present. The highest percent recovery for all three organisms was given by Columbia blood agar, followed by chocolate. CONCLUSION: Based on the results, the presence of the three emerging pathogens present in lens cases and from corneal isolates can be accurately determined if proper growth media and incubation temperatures are utilized.