Abstract:
Biofilms are microbial community adhered to biotic or abiotic surfaces and embedded within an
extracellular Polymeric matrix. They have potential to resist antibiotics and disinfectants,
causing health concerns in medical and food industries. Biofilm formation is affected by nutrient
availability, temperature and other environmental factors. The present study was conducted to
study the mono- and dual-species biofilm formation of bacteria, using Escherichia coli,
Salmonella and Proteus, and their combinations, in two different nutritional levels of the growth
medium (undiluted Luria-Bertani Broth - LBB and 1:100 diluted LBB). Biofilm forming ability
was assessed by crystal violet microtiter plate assays, incubated at 28 ºC. The optical density
was measured at 600nm wavelength. Undiluted LBB was more inductive in biofilm formation
compared to 1:100 diluted LBB. E. coli formed a stronger biofilm (1.31 ± 0.32) in undiluted LBB
than in diluted LBB (0.41 ± 0.15). Similar patterns were observed for Salmonella, Proteus and
their combinations tested. Proteus also exhibited greater biofilm formation (2.0894±0.32) at
undiluted media and lower in diluted media (1.1174±0.37). Salmonella showed optical density
of 1.8602±0.24 at undiluted media and 1.0312±0.33 at diluted media. Combinations of
Salmonella-Proteus, Salmonella-E. coli and Proteus-E. coli also demonstrated greater biofilm
formation in undiluted LBB (2.08 ± 0.35, 0.92 ± 0.32 and 1.67 ± 0.41) compared to that in diluted
LBB (1.25 ± 0.41, 0.72 ± 0.15 and 1.12 ± 0.34). Results also revealed that the biofilm formation
by dual species was greater than that of mono-species. The combination of Salmonella with
Proteus showed significantly higher biofilm formation than the combination of Salmonella with
E. coli, and E. coli with Proteus, in both the diluted and undiluted LBB. The study indicated the
effect of nutritional levels on biofilm formation of E. coli, Salmonella Proteus and their
combinations, with greater biofilm formation at higher nutritional levels.
