Background. Proteus vulgaris attach to available surfaces in industrial environments, can develop into extensive biofilm. Such bacterial layer is a potential source of contamination of foods that may lead to spoilage or transmission foodborne pathogens. The purpose of these investigations was to evaluate the influence of limited nutrients availability in the medium on the morphological changes and biosynthesis of bacterial surface-associated EPS by P. vulgaris. The relationship between the dimension of cells, EPS production and P. vulgaris biofilm development process on stainless steel surfaces (type 316L) was also examined.
Material and methods. P. vulgaris ATCC 6380 was used in this study. The cultures were incubated at 37°C on the Enterobacteriaceae enrichment broth according to Mossel [1962]. During the investigations the medium with optimal and 10 times diluted optimal of nutrient availability were used. For cells dimension analysis a Carl-Zeiss Axiovert 200 inverted microscope and a scanning electron microscope (LEO 435VP) was applied. Isolation of exopolysaccharides was based on the procedure employed by Forde and Fitzgerald [1999]. To determine the level of P. vulgaris adhesion to the surface of stainless steel, the method described by Le Thi et al. [2001] was used.
Results. In all experimental variants the area of P. vulgaris cells was changed upon long-term starvation. Altering of physical dimension of bacteria was effected by the decreasing value of the cell length. The change of P. vulgaris morphology promoted the beginning stages of biofilm formation process on the surface of stainless steel. Under starvation conditions P. vulgaris produced more EPS. It was observed with an increase of incubation period. These extracellular molecules initiated more advanced stages of P. vulgaris biofilm formation on examined surfaces.
Conclusion. The data support the notion thatcellular factors influencing P. vulgaris adhesion process to abiotic materials should be examined under conditions in which marine bacteria are widely distributed. Analysis of both physical dimension of cells and EPS secretion by marine bacteria under starvation conditions will help to eradicate the attached bacteria.