Dangerous pathogens in meat

Microorganisms can play very important roles in food, and it is possible to classify them into 3 groups, depending on the type of interaction between microorganism and food.

Microorganisms that alter food

Microorganisms in food cause harmful chemical changes, resulting in “microbial spoilage.” Spoilage results in changes in color, odor, flavor, texture and appearance of the food.

Disease-causing microorganisms

The microorganisms in food that may pose a health risk are “PATHOGENIC MICROORGANISMS”, which can affect the health of both humans and animals. The characteristics of the diseases that these microorganisms cause depend on a series of factors inherent to the food, the microorganism in question and the individual being affected. Pathogenic microorganisms can reach food through various routes, always reflecting precarious hygiene conditions during production, storage, distribution or domestic handling.

Microorganisms that cause beneficial changes to food

There are microorganisms that modify the original characteristics of food in order to transform it into a new food. This process is called FERMENTATION. This group includes all microorganisms used in the manufacture of fermented foods. Ex: cheeses; fermented meats; fermented milk drinks; beers, wines, breads, pickles, sauerkraut, olives, etc. In the case of meat, there are selected strains that are added intentionally, known as starter cultures.

MAIN SOURCES OF CONTAMINATION

• Soil and water
• Plants
• Utensils
• intestinal tract
• food handlers
• Animal food
• Animal skin
• Air and dust

Dangerous pathogens in meat

The main pathogenic bacteria that have been evaluated as possible warning include shiga toxin-producing Escherichia coli (STEC), Salmonella, Clostridium botulinum, Clostridium perfringens, Staphylococcus aureus and Listeria monocytogenes.

For each pathogenic bacteria, an understanding of control methods during each step of the manufacturing process is necessary.

Staphylococcus aureus

Staphylococcus aureus is nitrite tolerant, salt tolerant and, if it grows at concentrations of more or less 5 log, it produces a heat-stable toxin. Control of this organism must occur when temperatures are greater than 15.5ºC, the pH is above of 5.3, aqueous activity less than 0.85 or when there is a combination of pH and aqueous activity to prevent growth. Fermentation is extremely important in the manufacturing stage, where controls to limit growth must be implemented to allow competitive exclusion as a result of the inclusion of starter culture bacterial starter within appropriate time and temperature conditions. The aqueous activity of the final product and the pH conditions (pH<5.1 and water activity <0.96) are crucial to prevent proliferation after processing.

Salmonella

Salmonella is a genus of bacteria considered to be of concern. Salmonella is not destroyed by freezing but dies when heated to 55°C for 90 min or 60°C for 12 min.

Salmonella species can be found in the digestive tract of humans and animals. Food and water can be contaminated with the bacteria. Salmonella serotypes can be divided into two main groups – typhoid and non-typhoid.

Non-typhoid is more common and usually causes self-limiting gastrointestinal disease. They only invade the gastrointestinal tract and cause salmonellosis, whose symptoms can be resolved without antibiotics. They can infect a variety of animals and are zoonotic, meaning they can be transferred between humans and other animals. 

Typhoid serotypes affect humans but do not occur in other animals. They can cause foodborne infections, typhoid fever and paratyphoid fever. Typhoid fever is caused by Salmonella invading the bloodstream and can spread throughout the body. In this case there is a higher risk and requires intensive care, including antibiotics.

Clostridium botulinum

If nitrite is included in the formulation, the bacteria Clostridium botulinum is not normally considered a pathogen of concern. Well-founded research and determined concentrations of nitrite (input into the formulation) of 75 to 100 ppm effectively control its growth. As a hindrance/safety, pathogen growth will not occur once the aqueous activity reaches 0.94 (normally at the beginning of the drying phase).

Clostridium perfringens

There are several obstacles for this pathogen such as the inhibitory effects of nitrite inclusion and no growth below 12.2ºC, a pH less than 5.5, or when the aqueous activity is below 0.93. Clostridium perfringens is not normally considered a pathogen of concern.

Escherichia coli

Escherichia coli (STEC) is present in beef raw materials, if formulations include beef, a 5 log reduction should be achieved during the manufacturing process. Lethality during thermal processing is almost always the approach taken, as microbial testing is ineffective in reliably determining the microbial population present. Furthermore, scientific evidence (e.g., articles in specialized journals) has demonstrated a 2 to 4 log decrease through fermentation and drying, although there is a lack of information in the literature reporting a 5 log reduction and sufficient decrease to establish a correlation with trending products and associated processes.

Listeria monocytogenes

As with any ready-to-eat product, L. monocytogenes is considered a pathogen of concern and is addressed through Listeria controls.

Some toxins related to these pathogens

Botulinum Toxin

Clostridium botulinum is an anaerobic bacterium, which under conditions suitable for its reproduction (approx. 10°C, without oxygen and a certain level of acidity), grows and produces seven different serotypes of toxin (A, B, C1, D, E, F, G and H). Botulinum toxin H is the most lethal poison known, a million times more deadly than dioxin, the most lethal poison produced by man. For H-butynoline toxin, the lethal dose that will kill 50% in a test population is a mere 0.00000003mg of the substance per kilogram of body weight. It is estimated that 28g could kill one hundred million people.

Shiga (STEC)

Shiga toxin-producing Escherichia coli (STEC) is an important pathogen transmitted mainly by beef products and is associated with mild to severe and bloody diarrhea. In some individuals, STEC infection can progress to hemolytic uremic syndrome (HUS), a sequel characterized by renal failure and thrombotic thrombocytopenic purpura (TTP), with possible involvement of the central nervous system. Cattle, generally healthy, are the main reservoir of STEC.

Alfatoxin (alpha-hemolysin)

It can present four different conformations, being capable of lysing red blood cells and causing damage to platelets in cases of severe poisoning.

Betatoxin (beta-hemolysin)

It degrades sphingomyelin, causing damage to the erythrocyte membrane and, consequently, leading to hemolysis.

Deltatoxin (delta-hemolysin)

It has surfactant properties, acting as a detergent and being responsible for the effects on the membranes of erythrocytes, macrophages, lymphocytes, neutrophils and platelets. It is also capable of inhibiting the absorption of water by the ileum, due to the alteration of the mechanism of action of cyclic adenosine monophosphate (c-AMP), triggering acute diarrhea.

Gamma-toxin (gamma-hemolysin)

It presents hemolytic activity, the mechanism of which has not yet been properly established.

PVL

Composed of two protein components (S and F), which act synergistically. This protein alters membrane permeability and attacks polymorphonuclear leukocytes and macrophages. This change allows the entry of cations, such as Ca+2, resulting in cell degranulation and inducing cytolysis.

Exfoliatin

Promotes the cleavage of the granular extract of the epidermis, causing severe skin syndromes (scalded skin syndrome and bullous impetigo).

TSST-1

It causes fever, shock and involvement of multiple organ systems, including a scaly rash.

Enterotoxins (A, B, C, D and E)

Pyrogenic, thermostable protein toxins, responsible for food poisoning and can cause vomiting and diarrhea.