Effect of Pseudomonas aeruginosa on the sanitizer sensitivity of Salmonella Enteritidis biofilm cells in chicken juice

Salmonella Enteritidis may be encountered in poultry processing plants in the form of biofilms on food contact surfaces. Little is known about the fate of Salmonella in mixed-species biofilms with other bacteria commonly found in food processing environment. Thus, the objectives of this study were to determine biofilm formation and sanitizer resistance of two S. Enteritidis strains (rdar and bdar, cellulose expression positive and negative, respectively), in the absence and presence of Pseudomonas aeruginosa, under conditions encountered in poultry processing plants. S. Enteritidis in single-species and dual-species biofilms with P. aeruginosa at two mixed ratios (Salmonella: Pseudomonas cells at 1:1 and 0.01:1, respectively) were formed on stainless steel coupons in chicken juice for 6 days at 25 °C. On days 1 and 6 of the incubation period, biofilm cell populations were determined before and after chlorine treatment (50 ppm, 1 min). Results showed that population of S. Enteritidis in dual-species biofilms was significantly lower (P < 0.05) than that in single-species biofilms on day 6. On the other hand, S. Enteritidis in dual-species biofilms demonstrated greater chlorine resistance, with an average of 1 log CFU/cm2 lower reduction than that in single-species biofilms, except for the rdar strain which became more sensitive to chlorine treatment in dual-species biofilms after 6 days. Fluorescence microscopy images showed that more glycoconjugates were present in the dual-species biofilms, which might have contributed to the enhanced chlorine resistance of S. Enteritidis. Thus, this study indicates that although the presence of P. aeruginosa could negatively influence S. Enteritidis biofilm formation, it might protect Salmonella cells from sanitizer treatment in poultry processing environment.