Phenotypic Expression of Salmonella enterica Due to Environmental Stress

Salmonella enterica remains a major food safety concern in poultry, and processing-related stress can influence its survival and persistence. This study evaluated the phenotypic expression of S. enterica serotypes Kentucky (SK), Infantis (SI), Schwarzengrund (SS), and Typhimurium (ST) following antimicrobial and temperature stressors. A pre-harvest isolate of each serotype was gradually exposed to increasing concentrations of peracetic acid (PAA) and quaternary ammonium compounds (QACs), starting at 40 ppm and 1 ppm, respectively, until minimum inhibitory and bactericidal concentrations (MICs/MBCs) were established. Stressed cells were then subjected to cold (4 °C, 60 min) and heat (55 °C, 6 min) shock and assessed for sanitizer tolerance, biofilm formation and recovery, and antibiotic resistance. Sanitizer tolerance after daily conditioning varied among S. enterica serotypes, with ST and SK showing the highest tolerance to PAA and QACs, respectively. The tolerance of PAA variants increased by 10–20 ppm and QAC variants by 2–8 ppm following stress exposure. The double-stressed variants of ST significantly (p < 0.05) formed more biofilm than the control after PAA, whereas no significant differences were observed among the variants for other serotypes. Biofilm recovery was higher for the stressed variants of SI and SS (p < 0.05) following PAA stress but remained the same across all serotypes after QAC stress. QAC-stressed variants showed more phenotypic changes across the antibiotics tested. Notably, the stressed variants of SK, SS, and ST displayed increased MICs, including a 2- to 4-fold rise in azithromycin for the SK and ST variants. There was an increase in the MICs of ceftriaxone and nalidixic acid for some SK and SS variants. These findings suggest that environmental stress can significantly enhance the tolerance, survival, and persistence of S. enterica.