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BIOFILM FORMATION BY WILD-TYPE AND PRESSURE-STRESSED ESCHERICHIA COLI O157:H7 AND SALMONELLA ENTERICA SEROVARS ON STAINLESS STEEL IN MILK AT REFRIGERATION AND PHYSIOLOGICAL TEMPERATURES

Abstract

Bacterial biofilms represent a critical public health challenge in food processing, as they enable pathogenic persistence on equipment surfaces and contribute to recurrent contamination. The formation of biofilms by foodborne pathogens such as Escherichia coli O157:H7 and Salmonella enterica on abiotic surfaces, particularly stainless steel, widely employed in food processing plants, significantly compromises food safety by reducing shelf life and facilitating cross-contamination of food products. Although the resistance of biofilms to industrial sanitization treatments is well documented, limited information exists regarding how stress adaptation, including pressure-induced phenotypic changes, modulates biofilm formation capacity in dairy products. This study investigated the biofilm formation of wild-type and pressure-stressed (15,000 PSI or 103 MPa at 25°C for 15 minutes) pathogens from a four-strain cocktail of E. coli O157:H7 and Salmonella enterica serovars, inoculated in sterile milk and cultured on stainless steel surfaces at 4°C and 37°C. A randomized block design with two biologically independent repetitions served as the blocking factor for both bacteria. Bacterial biofilm cell counts were log-transformed and analyzed using Tukey-adjusted analysis of variance. Results demonstrated that about 2 log reductions of biofilm count for both wild-type and pressure-stressed phenotypes compared to control conditions. There were no significant differences in biofilm formation between wild-type and pressure-stressed phenotypes, yet they remained above the detection limit on steel coupons at both temperatures. In this study, no chemical treatments were used as stressors; however, the persistence of viable biofilm cells under stress conditions highlights the adaptability of these epidemiologically important pathogens and the necessity for preventive strategies beyond traditional chemical interventions. These findings provide critical insights into the stress resilience of foodborne pathogens in milk-based environments and contribute to the development of targeted biofilm control strategies in the food industry.

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