Growth of Listeria monocytogenes, Salmonella spp., Escherichia coli O157:H7, and Staphylococcus aureus on Cheese during Extended Storage at 25°C

• Published in: Journal of food protection 2014-08, Vol.77 (8), p.1275-1288
• Main Authors: WAN MEI LEONG, GEIER, Renae, ENGSTROM, Sarah, INGHAM, Steve, INGHAM, Barbara, SMUKOWSKI, Marianne
• Format: Article
• Language: English
• Subjects: Acidity; Bacteria; Biological and medical sciences; Boundary conditions; Campylobacter; Cheese; Cheese - analysis; Cheese - microbiology; Chloride; Colony Count, Microbial; Dairy products; E coli; Escherichia coli O157 - growth & development; Escherichia coli O157 - isolation & purification; Food contamination & poisoning; Food industries; Food preservation; Food safety; Food Storage; Fundamental and applied biological sciences. Psychology; Illnesses; Listeria; Listeria monocytogenes - growth & development; Listeria monocytogenes - isolation & purification; Microorganisms; Milk; Pasteurization; Pathogens; Salmonella; Salt; Staphylococcus aureus - growth & development; Staphylococcus aureus - isolation & purification; Temperature; Temperature control; United States
• ISSN: 0362-028X; 1944-9097
• DOI: 10.4315/0362-028X.JFP-14-047

Potentially hazardous foods require time/temperature control for safety. According to the U.S. Food and Drug Administration Food Code, most cheeses are potentially hazardous foods based on pH and water activity, and a product assessment is required to evaluate safety of storage >6 h at 21°C. We tested the ability of 67 market cheeses to support growth of Listeria monocytogenes (LM), Salmonella spp. (SALM), Escherichia coli O157:H7 (EC), and Staphylococcus aureus (SA) over 15 days at 25°C. Hard (Asiago and Cheddar), semi-hard (Colby and Havarti), and soft cheeses (mozzarella and Mexican-style), and reduced-sodium or reduced-fat types were tested. Single-pathogen cocktails were prepared and individually inoculated onto cheese slices (∼10(5) CFU/g). Cocktails were 10 strains of L. monocytogenes, 6 of Salmonella spp., or 5 of E. coli O157:H7 or S. aureus. Inoculated slices were vacuum packaged and stored at 25°C for ≤ 15 days, with surviving inocula enumerated every 3 days. Percent salt-in-the-moisture phase, percent titratable acidity, pH, water activity, and levels of indigenous/starter bacteria were measured. Pathogens did not grow on 53 cheeses, while 14 cheeses supported growth of SA, 6 of SALM, 4 of LM, and 3 of EC. Of the cheeses supporting pathogen growth, all supported growth of SA, ranging from 0.57 to 3.08 log CFU/g (average 1.70 log CFU/g). Growth of SALM, LM, and EC ranged from 1.01 to 3.02 log CFU/g (average 2.05 log CFU/g), 0.60 to 2.68 log CFU/g (average 1.60 log CFU/g), and 0.41 to 2.90 log CFU/g (average 1.69 log CFU/g), respectively. Pathogen growth varied within cheese types or lots. Pathogen growth was influenced by pH and percent salt-in-the-moisture phase, and these two factors were used to establish growth/no-growth boundary conditions for safe, extended storage (≤25°C) of pasteurized milk cheeses. Pathogen growth/no-growth could not be predicted for Swiss-style cheeses, mold-ripened or bacterial surface-ripened cheeses, and cheeses made with nonbovine milk, as insufficient data were gathered. This challenge study data can support science-based decision making in a regulatory framework.