Survival of a Five-Strain Cocktail of Escherichia coli O157:H7 during the 60-Day Aging Period of Cheddar Cheese Made from Unpasteurized Milk

Abstract

The U.S. Food and Drug Administration Standard of Identity for Cheddar cheeses requires pasteurization of the milk, or as an alternative treatment, a minimum 60-day aging at > or =2 degrees C for cheeses made from unpasteurized milk, to reduce the number of viable pathogens that may be present to an acceptable risk. The objective of this study was to investigate the adequacy of the 60-day minimum aging to reduce the numbers of viable pathogens and evaluate milk subpasteurization heat treatment as a process to improve the safety of Cheddar cheeses made from unpasteurized milk. Cheddar cheese was made from unpasteurized milk inoculated with 10(1) to 10(5) CFU/ml of a five-strain cocktail of acid-tolerant Escherichia coli O157:H7. Samples were collected during the cheese manufacturing process. After pressing, the cheese blocks were packaged into plastic bags, vacuum sealed, and aged at 7 degrees C. After 1 week, the cheese blocks were cut into smaller-size uniform pieces and then vacuum sealed in clear plastic pouches. Samples were plated and enumerated for E. coli O157:H7. Populations of E. coli O157:H7 increased during the cheese-making operations. Population of E. coli O157:H7 in cheese aged for 60 and 120 days at 7 degrees C decreased less than 1 and 2 log, respectively. These studies confirm previous reports that show 60-day aging is inadequate to eliminate E. coli O157:H7 during cheese ripening. Subpasteurization heat-treatment runs were conducted at 148 degrees F (64.4 degrees C) for 17.5 s on milk inoculated with E. coli O157:H7 at 10(5) CFU/ml. These heat-treatment runs resulted in a 5-log E. coli O157: H7 reduction.

Behavior of Different Shiga Toxin-Producing Escherichia coli Serotypes in Various Experimentally Contaminated Raw-Milk Cheeses

“…However, the rate of increase in STEC for the BTC and the two UPCs (approximately 0.5 to 2.5 log 10 CFU · g Ϫ1 , depending on the cheese-making scheme and serotype) clearly indicates bacterial growth. Schlesser et al (24) have also observed a 1-to 2-log 10 -CFU · g Ϫ1 increase in an artificially inoculated cocktail of E. coli O157:H7 during cheddar cheese-making operations. At the initial stages of preparation of the BTC and the two UPCs, the temperature (Ͼ30°C) is ideal for STEC growth and the moderate acidification can only slow down this growth.…”

“…The presence of pathogenic bacteria, including STEC, in cheeses is a major concern for food safety authorities. To address the problem, the U.S. Food and Drug Administration requires a minimum of 60 days' aging for cheeses made from unpasteurized milk (23,24).…”

“…To date, most authors have focused their work on the behavior of E. coli O157:H7 during cheese manufacturing (23)(24)(25)(26)(27)(28)(29), but little is known about the behavior of other STEC serotypes.…”

UV Light Inactivation of Human and Plant Pathogens in Unfiltered Surface Irrigation Water

“…A five-strain cocktail of a pathogen species was added to 1-liter water samples. Multiple-strain cocktails are commonly used in human and plant pathogen studies for more comprehensive assessments because it is common for more than one strain to be present in a food-borne illness or plant disease outbreak (22,23). Bacterial cocktails were produced by adding 10 ml of stationary-phase culture of each strain together and thor- …”

Consumption of Raw or Unpasteurized Milk and Milk Products by Pregnant Women and Children

“…In addition, the 1987 FDA ban on interstate raw dairy transport allows for an exception of cheese made from raw milk, provided the cheese has been aged a minimum of 60 days and is clearly labeled as unpasteurized. However, there is evidence that E coli can survive in cheese products even after a 60-day aging period, 29 and recent outbreaks of E coli O157 illness associated with such unpasteurized, aged cheese have been documented in Arizona, California, Colorado, and New Mexico. 30 …”