Purpose: This study measured the biofilms formed by different bacterial strains on glass slides and quantified changes in biofilm mass and biofilm-associated cell populations after brief contacts between biofilms and either media agar or food products.
Methods: Two Listeria monocytogenes and Escherichia coli strains and a single Staphylococcus aureus strain were inoculated separately in tryptic soy broth containing a 1 x 2 cm2 glass slide and incubated for 24, 48 or 72 h at 37°C. Biofilms formed by individual bacterial strains and biofilm-associated cell populations were determined. The biofilms were subsequently allowed to have brief contacts (1 - 3 times), through gentle touching, with either agar or food products including meat and soft white cheese (2 cm2). Changes in biofilm mass on glass slides and cell populations embedded in biofilms were quantified. Biofilms that were not in contact with the agar or foods served as controls.
Results: A nonpathogenic E. coli formed more biofilms than an E. coli O157:H7 strain. Biofilms formed by S. aureus and L. monocytogenes were essentially similar. Biofilm mass increased as incubation time increased within 48 h of the incubation. Biofilm mass at 48 and 72 h of the incubation was not significantly different. More frequent contacts with agar or foods did not remove more biofilms or biofilm-associated cells from glass slides. More S. aureus biofilms were removed followed by Listeria and E. coli biofilms. The populations of bacteria embedded in biofilms after brief contacts with agar or food decreased 0.00 to 0.54 log CFU/cm2. Greater reductions in cell populations were observed with S. aureus and Listeria biofilms.
Significance: Results suggest that biofilms could serve as a source of contamination for foods that come in contact with them.