Isolation and Evaluation of Biofilm-Forming Bacteria from Frequently Used Food-Contact Surfaces in a Food Microbiology Laboratory

Abstract

Bacteria that form biofilms on frequently touched surfaces pose a persistent problem for food-handling and laboratory environments, since cells embedded within a self-produced polymeric matrix resist routine cleaning far more effectively than their free-floating counterparts. This study set out to isolate culturable bacteria from three heavily used surfaces in a food microbiology teaching laboratory a sink, a laboratory bench/platform, and a laminar air-flow (LAF) cabinet work surface and to screen the resulting isolates for biofilm-forming ability using simple, low-cost microbiological methods. Swabs collected from all three surfaces were enriched in nutrient broth and plated onto Nutrient Agar, MacConkey Agar, Eosin Methylene Blue Agar and Potato Dextrose Agar. For each surface, one representative isolate was purified from each of Nutrient Agar (NA), MacConkey Agar (MAC) and Eosin Methylene Blue Agar (EMB) through two successive rounds of sub-culturing, giving nine surface-medium isolates in total, before being screened for biofilm formation using the crystal violet tube assay in triplicate (n = 3 independent tubes per isolate), with absorbance measured at 570 nm. All nine isolates produced a visible, stained film adherent to the glass wall after 48 hours, confirming that each was capable of forming a biofilm. Biomass was consistently highest for MAC isolates and EMB isolates and lowest for NA isolates at every surface, and sink-derived isolates produced more biofilm than bench/platform-derived isolates, which in turn exceeded laminar-cabinet-derived isolates, at every medium (mean OD570 range 0.12–0.54 across the nine isolates). A one-way ANOVA confirmed that differences among the nine surface-medium groups were statistically significant (F(8,18) = 2435.3, p < 0.001). Taken together, these results show that biofilm-competent bacteria can be readily recovered from surfaces that undergo routine cleaning, that biofilm-forming capacity varies systematically by both isolation medium and originating surface, and that isolates from the same environment can differ substantially in how much biofilm they produce. Because isolates were not identified beyond their isolation medium and surface of origin, and no uninoculated negative-control tube was included to establish a validated optical-density cut-off, the findings should be read as a preliminary, though now replicated, screen rather than a definitive characterization; they nonetheless support the case for including biofilm-specific checks alongside conventional hygiene monitoring in food-handling and teaching laboratories.