E. coli O157:H7 survives long past 60 days in manufacture and aging of gouda; more evidence

D’Amico et al., report in the current Journal of Food Protection “that the 60-day aging requirement alone is insufficient to completely eliminate levels of viable E. coli O157:H7 in Gouda or stirred-curd Cheddar cheese manufactured from raw milk contaminated with low levels of this pathogen.”

Bet Costco would have liked to know that before the outbreak linked to Gouda that has sickened at least 37 people in five U.S. states.

The complete abstract is below.

Behavior of Escherichia coli O157:H7 during the manufacture and aging of gouda and stirred-curd cheddar cheeses manufactured from raw milk
Journal of Food Protection
D’Amico, Dennis J.; Druart, Marc J.; Donnelly, Catherine W.
This study was conducted to examine the fate of Escherichia coli O157:H7 during the manufacture and aging of Gouda and stirred-curd Cheddar cheeses made from raw milk. Cheeses were manufactured from unpasteurized milk experimentally contaminated with one of three strains of E. coli O157:H7 at an approximate population level of 20 CFU/ml. Samples of milk, whey, curd, and cheese were collected for enumeration of bacteria throughout the manufacturing and aging process. Overall, bacterial counts in both cheese types increased almost 10-fold from initial inoculation levels in milk to approximately 145 CFU/g found in cheeses on day 1. From this point, counts dropped significantly over 60 days to mean levels of 25 and 5 CFU/g in Cheddar and Gouda, respectively. Levels of E. coli O157:H7 fell and stayed below 5 CFU/g after an average of 94 and 108 days in Gouda and Cheddar, respectively, yet remained detectable after selective enrichment for more than 270 days in both cheese types. Changes in pathogen levels observed throughout manufacture and aging did not significantly differ by cheese type. In agreement with results of previous studies, our results suggest that the 60-day aging requirement alone is insufficient to completely eliminate levels of viable E. coli O157:H7 in Gouda or stirred-curd Cheddar cheese manufactured from raw milk contaminated with low levels of this pathogen.

Health officials confirm E. coli in cheese samples

The New Mexico Department of Health has confirmed an outbreak strain of E. coli O157:H7 in an intact sample of cheese sold at Costco stores.

The Alamogordo Daily News and Associated Press say the outbreak strain had been isolated at other laboratories in already opened packages of cheese, but this is the first confirmation from an intact cheese sample.

The findings confirm what scientists have found in the past: 60-days don’t mean much when the cheese is made from unpasteurized or raw milk (see abstract below; thanks Carl).

The Bravo Farms Dutch Style Raw Milk Gouda Cheese was offered for sale and for in-store tasting between Oct. 5 and Nov. 1 at Costco stores in Arizona, Colorado, New Mexico, Nevada and the San Diego, Calif., area.

Health officials say at least 37 people from five states have become sick with E. coli since mid-October. Cases in New Mexico include a 41-year-old man, a 7-year-old girl from Bernalillo County and a 4-year-old boy from Valencia County who are all recovering. Arizona has 19 cases reported, Colorado has 10, California has 3 and Nevada has two. Nationally there have been 15 reported hospitalizations, one case of hemolytic uremic syndrome and no deaths.

People who have any of the cheese should not eat it. People should return the cheese to the place of purchase or dispose of it in a closed plastic bag placed in a sealed trash can. This will prevent people or animals from eating it.

Survival of a five-strain cocktail of Escherichia coli O157:H7 during the 60-day aging period of cheddar cheese made from unpasteurized milk

May 2006

Journal of Food Protection, Volume 69, Number 5 pp. 990-998(9)

Schlesser, J.E.; Gerdes, R.; Ravishankar, S.; Madsen, K.; Mowbray, J.; Teo, A.Y.L.

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 ‰¥2°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 101 to 105 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°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°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°F (64.4°C) for 17.5 s on milk inoculated with E. coli O157:H7 at 105 CFU/ml. These heat-treatment runs resulted in a 5-log E. coli O157: H7 reduction.