Effect of phage on survival of Salmonella enteritidis during manufacture and storage of cheddar cheese made from raw and pasteurized milk

The ability of Salmonella Enteritidis to survive in the presence of phage, SJ2, during manufacture, ripening, and storage of Cheddar cheese produced f rom raw and pasteurized milk was investigated. Raw milk and pasteurized mil k were inoculated to contain 10(4) CFU/ml of a luminescent strain of Salmon ella Enteritidis (lux) and 10(8) PFU/ml SJ2 phage. The milks were processed into Cheddar cheese following standard procedures. Cheese samples were exa mined for Salmonella Enteritidis (lux). lactic acid bacteria, molds and yea sts, coliforms, and total counts, while moisture, fat, salt, and pH values were also measured. Salmonella Enteritidis (lux) was enumerated in duplicat e samples by surface plating on MacConkey novobiocin agar. Bioluminescent c olonies of Salmonella Enteritidis were identified in the NightOwl molecular imager. Samples were taken over a period of 99 days. Counts of Salmonella Enteritidis (lux) decreased by 1 to 2 log cycles in raw and pasteurized mil k cheeses made from milk containing phage. In cheeses made from milks to wh ich phage was not added, there was an increase in Salmonella counts of abou t 1 log cycle. Lower counts of Salmonella Enteritidis (lux) were observed a fter 24 h in pasteurized milk cheese containing phage compared to Salmonell a counts in raw milk cheese with phage. Salmonella Enteritidis (lux) surviv ed in raw milk and pasteurized milk cheese without phage, reaching a final concentration of 10(3) CFU/g after 99 days of storage at 8 degreesC. Salmon ella did not survive in pasteurized milk cheese after 89 days in the presen ce of phage. However, Salmonella counts of approximately 50 CFU/g were obse rved in raw milk cheese containing phage even after 99 days of storage. In conclusion, this study demonstrates that the addition of phage may be a use ful adjunct to reduce the ability of Salmonella to survive in Cheddar chees e made from both raw and pasteurized milk.