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-degrees-C in liquid whole egg for all strains were within ranges reported by previous investigators. Sublethal heat shock at 40-degrees-C for 2 hr or 48-degrees-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.