Resilient by Design: Environmental Stress Promotes Biofilm Formation and Multi-Resistance in Poultry-Associated Salmonella

<i>Salmonella</i> is one of the main causes of food-borne illness worldwide. In most cases, <i>Salmonella</i> contamination can be traced back to food processing plants and/or to cross-contamination during food preparation. To avoid food-borne diseases, food processing plants use sanitizers and biocidal to reduce bacterial contaminants below acceptable levels. Despite these preventive actions, <i>Salmonella</i> can survive and consequently affect human health. This study investigates the adaptive capacity of the main <i>Salmonella enterica</i> serotypes isolated from the poultry production line, focusing on their replication, antimicrobial resistance, and biofilm formation under stressors such as acidic conditions, oxidative environment, and high osmolarity. Using growth curve analysis, crystal violet staining, and microscopy, we assessed replication, biofilm formation, and antimicrobial resistance under acidic, oxidative, and osmotic stress conditions. Disinfectant tolerance was evaluated by determining the Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) of sodium hypochlorite. The antibiotic resistance was assessed using the Kirby-Bauer method. The results indicate that, in general, acidic and osmotic stress reduce the growth of <i>Salmonella</i>. However, no significant differences were observed specifically for serotypes Infantis, Heidelberg, and Corvallis. The <i>S.</i> Infantis isolates were the strongest biofilm producers and showed the highest prevalence of multidrug resistance (71%). Interestingly, <i>S.</i> Infantis forming biofilms required up to 8-fold higher concentrations of sodium hypochlorite for eradication. Furthermore, osmotic and oxidative stress significantly induced biofilm production in industrial <i>S.</i> Infantis isolates compared to a reference strain. Understanding how <i>Salmonella</i> responds to industrial stressors is vital for designing strategies to control the proliferation of these highly adapted, multi-resistant pathogens.