Shiga toxin-producing Escherichia coli (STEC)
are food-borne pathogens that cause diarrhea, hemorrhagic colitis, and
hemolytic-uremic syndrome, which may result in death. A major priority for the
food industry is to avoid the presence of STEC in the food production chain. In
this sector, biofilm represents a real problem by contaminating the facility
and being resistant to traditional cleaning and disinfection protocols.
Bacterial factors, such as proteins, cellulose or poly-N-acetylglucosamine
(PGA) have been associated with biofilm formation in E. coli. The aims of the
study were to evaluate the ability of human STEC isolates representing the most
pathogenic seropathotypes to form biofilms and to characterize the matrix
composition of some of these STEC biofilms. To evaluate biofilm formation,
overnight cultures were diluted in M9 broth supplemented with 0.4% glucose and
were inoculated in polystyrene microplate which was incubated under static
condition for 24h at 30° C. Bacterial biomass fixed to the bottom of wells was
then quantified by crystal violet staining. Matrices of some STEC biofilm were
also observed by using confocal microscopy. Importance of matrices components
in the integrity of mature (24h) biofilm was then investigated by enzymatic
digestion of DNA, proteins, cellulose or PGA. We have shown that biofilm
formation was variable among STEC isolates (DO595nm: 0.04 to 2.0).
Interestingly, strains belonging to seropathotype A (O157:H7) have significantly
higher potential to form biofilm than other STEC seropathotype. By using
confocal microscopy, PGA was only detected in seropathotype A biofilms. In two
of these seropathotype A biofilms, cellulose was also detected. Furthermore,
enzymatic treatments indicated that proteins appear to play an important role
in STEC biofilm integrity while DNA, PGA and cellulose do not. This is the
first study that described a more important potential of biofilm formation for
seropathotype A (O157:H7) isolates than other STEC seropathotypes.