Biofilm formation of Salmonella Enteritidis under food-related environmental stress conditions and its subsequent resistance to chlorine treatment

• Low nutrient condition increased Salmonella Enteritidis biofilm density at 4 and 25 °C.
• The chlorine resistance of biofilm formed under diluted TSB at 25 °C was enhanced.
• Biofilms formed at 4 °C or acidic pH were very sensitive to chlorine treatment.
• Temperature and nutrient availability were dominant factors for biofilm formation.
• A positive correlation existed between cellulose production and biofilm resistance.

This study determined the effects of temperature (4 and 25 °C), pH (5.3, 7.3, and 8.3), and nutrient availability (TSB and 20 times diluted TSB (1/20 TSB)) on Salmonella Enteritidis biofilm formation and its resistance to chlorine treatment (pH 6.8, 50 ppm for 1 min). The results showed that biofilm density was significantly higher (P < 0.05) at 25 °C or in 1/20 TSB, regardless of pH and bacterial strains. Moreover, 1/20 TSB significantly enhanced the chlorine resistance of biofilms formed at 25 °C, especially for S. Enteritidis with rdar morphotype, with an average reduction of 1.52 log CFU/cm2 compared to that of biofilm in TSB with 4.07 log reduction. All biofilms formed at 4 °C were very sensitive to chlorine treatment. In most cases, acidic pH sensitized biofilms to chlorine treatment compared with neutral and alkaline pHs. The further analysis of cellulose production of biofilms indicated that it had a positive impact on biofilm resistance to chlorine treatment. This study suggests that environmental stress conditions encountered in food processing plant might alter S. Enteritidis biofilm resistance to sanitizer treatment possibly by acting on the cellulose production.