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Cheese Technology

Recent encounters with E. coli and listeria in U.S. food industry

Dr. Mali Reddy

Dr. Mali Reddy serves as president of the American Dairy and Food Consulting Laboratories and International Media and Cultures (IMAC Inc.), Denver, Colorado. He holds several degrees including Doctor of Veterinary Medicine, M.S. and Ph.D. degrees in food technology and microbiology. He is a guest columnist for this week’s issue of Cheese Market News®.

Recently in the United States we have encountered a major pathogenic bacterial contamination issue due to E. coli 0157:H7 cases in McDonald’s restaurants involving 14 states in the U.S. As of Dec. 3 it has resulted in one death and 104 cases of hospitalization with foodborne illnesses. Another pathogenic bacteria, Listeria monocytogenes, has contaminated meat, which has resulted in the closure of a Boar’s Head plant — with 60 people hospitalized and 10 deaths — due to Listeria infection in 19 states. As of the month of October 2024, there is another instance wherein carrots are being identified as culprits for harboring pathogenic E. coli bacteria, resulting in massive recalls and a confirmed 39 illnesses, 15 hospitalizations and one death in 18 states.

We have also had several recalls of cheese due to contamination with Listeria bacteria as well as E. coli. With the advent of recent recalls, the FDA is getting more active in checking every step of food manufacturing in accordance with the Food Safety Modernization Act of 2011 and 2022.

Let us delve into the genesis, nature and prevalence of these pathogenic bacteria and viruses associated with the cheese industry.

In 1993, E. coli 0157: H7 was recognized as a serious, life-threatening foodborne pathogen that causes sickness in humans by producing Shiga-like toxins, resulting in severe bleeding in the intestines, etc. Cattle harbor these bacteria, without any ill effects, shedding them in their feces, from which they gain entrance into raw milk. Thus, several cases were registered where human beings have been infected through consumption of cheese(s) contaminated with E. coli.

Listeria monocytogenes was recognized as a human pathogen in 1929. The largest outbreak of listeriosis occurred in 1985 in Los Angeles due to consumption of Spanish cheeses made with contaminated non-cultured raw milk. Since then, in the past four decades, several other cheeses including soft cheeses, mold-ripened cheeses and long hold Cheddar, etc., have been recalled due to contamination with Listeria. This became a serious threat to the cheese industry.

According to the Centers for Disease Control and Prevention, food poisoning sickens at least 48 million people in the U.S. each year, including 128,000 who are hospitalized, with registered deaths of 3,000. The most common food poisoning is due to Norovirus, which causes stomach flu and infects 19 to 21 million people each year. Salmonella sickens about 1.3 million people. Listeria infects 1,600 people each year with a confirmed death toll of 260. E. Coli causes about 74,000 infections in the U.S., leading to 2,000 hospitalizations and 16 deaths.

Although norovirus-inflicted food poisoning is the major cause of infecting people in the U.S., unlike bacterial pathogens, less attention has been given to eliminate this viral contaminant. Norovirus is an inhabitant of raw milk. Although pasteurization can inactivate this virus, it is quite heat resistant and can survive even at low pH — thus it poses a severe risk factor in the form of a post-pasteurization contaminant. The symptoms of norovirus infection are vomiting, diarrhea, abdominal cramps, fever, nausea and fatigue.

Knowing that all these viral and bacterial infections stemming from food sources are causes of food poisoning, what must we in the dairy and food industry do to curb or eliminate these devastating pathogenic bacteria and viruses in order to manufacture the safest cheese with zero defect? The following are some of the ways and means to control or eliminate these economically devastating infections.

• Raw milk

The major entry of pathogenic bacteria (Listeria, E. coli, etc.) and viruses (norovirus etc.) into a cheese manufacturing facility is through raw milk. It has been well established that activation of the Lactoperoxidase (LP) system in raw milk (in the milk silos at the plant) through the use of milk silo cultures is the best preventative measure to not only inactivate psychrotrophic bacteria (which destroy milk protein-casein and fat) but also curb the multiplication of the pathogenic bacteria and viruses. The protection of raw milk through the use of milk silo cultures must be instituted as a part of total quality management. It is a scientifically proven fact that LP activation, followed by pasteurization, will inactivate pathogenic bacteria, viruses, etc.

• Cheese manufacturing

Cheese vats and all other equipment used to manufacture cheese must be cleaned and sanitized using a scheduled strict protocol.

Starter culture is the best legal therapeutic ingredient to curb pathogenic bacteria and viruses — preferably, usage of bulk starter, since it has the pathogenic bacteria-inhibiting growth end products which also can activate the LP system (even in pasteurized milk) to curb any post-pasteurization contamination. Also, bulk starters with phosphate base phage-resistant media are preferred, since phosphate ions are inhibitory to the growth of Listeria, even in the cheese vat.

• Brining

Brine tanks must be inoculated with brine guard cultures (natural biological control) to reduce the growth and survival of pathogenic and spoilage microorganisms due to residual sugars, proteins, peptides and other nutrients, which leak out of cheese blocks into brine.

• Packing and shredding

The utmost precautions must be taken not to contaminate cheese at this stage. The sanitation of tables, cutters and employee garments must be strictly monitored and adhered to. Employees who are exhibiting signs of sickness due to stomach flu (norovirus, etc.) should not be allowed to handle the product.

Use of anti-caking agents produced only using high heat and spray drying must be employed, and all dry blended product should be eliminated to avoid contamination with pathogenic bacteria and norovirus due to open human intervention.

• Employee training

All production employees must be taught regarding the nature and prevalence of pathogenic bacteria and their devastating effect on the health of the consumer and themselves. Training classes must also be attended by supervisors, managers and laboratory personnel. These training classes will also benefit employees to safeguard their own health and their family members. Training will eliminate the fear of the unknown, since knowledge is power, strength and insurance. Classes must be designed and taught by professionals in such a way that even staff with minimal knowledge should be able to understand and implement.

• Plant environment

The utmost precautions must be taken in the plant to eliminate growth of yeast, molds and pathogenic bacteria on floors, floor drains, walls and ceilings. Floor drains must be sanitized periodically. Also, since the discharged whey on floors contains most of the sugars, it is a good idea to destroy these sugars using industrial-grade enzymes so that pathogenic bacteria will not grow in the floor drains. Use of minute quantities of lactase enzyme and oxidase enzymes will reduce these sugars in the floor drains. Since Listeria monocytogenes is sensitive to copper ions, perhaps the use of mild copper or chelated copper solution, approved by the EPA, can be applied to floor drains to control pathogens.

CMN

The views expressed by CMN’s guest columnists are their own opinions and do not necessarily reflect those of Cheese Market News®.

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