Thermal Resistance of Egg-Associated Epidemic Strains of Salmonella enteritidis

Seventeen strains of Salmonella enteritidis isolated from patients and various implicated products from 5 egg-associated outbreaks of salmonellosis were investigated for plasmid content, phage type and thermal resistance. D values obtained at 57.2 and 60°C in liquid whole egg for all strains were within ranges reported by previous investigators. Sublethal heat shock at 40°C for 2 hr or 48°C for 30 min increased thermotolerance 2- to 3-fold. The induced thermotolerance decayed to control levels after 2–3 cycles of cell duplication at a lower temperature. Most strains contained a 39-Mda plasmid and were phage type 8. No correlation was observed between thermotolerance and presence or absence of plasmid or phage type.