Staphylococcal food poisoning (SFP)- Staphylococcus aureus enterotoxins

Staphylococcal food poisoning (SFP) is a type of foodborne illness that occurs when people consume food contaminated with toxins produced by the bacterium Staphylococcus aureus (Staph). Staph is a common bacterium that can be found on the skin, in the nose, and in the environment of about 25% of people and animals. Staph usually does not cause any harm to healthy people, but it can produce toxins that are resistant to heat and digestion and can cause gastrointestinal symptoms such as nausea, vomiting, diarrhea, and abdominal cramps.

The main source of contamination of SFP is the improper handling of food by people who carry Staph on their hands or in their nose. Staph can transfer to food if people do not wash their hands before touching it, or if they cough or sneeze on it. Staph can also contaminate food through contact with contaminated equipment, such as knives or meat grinders. Staph can grow and produce toxins in foods that are not cooked after handling, or that are left at room temperature for more than two hours. Foods that are frequently involved in SFP outbreaks include meat and meat products, poultry and egg products, milk and dairy products, salads, pastries, sandwiches, ice creams, and salted foods.

Staphylococcal enterotoxins (SEs) are the main causative agents of staphylococcal food poisoning (SFP), a common and acute form of food-borne illness characterized by nausea, vomiting, diarrhea, and cramps. SEs are produced by some strains of Staphylococcus aureus, a gram-positive bacterium that can contaminate food through improper handling, storage, or processing. SEs are small secreted proteins that have both superantigenic and emetic activities, meaning that they can stimulate a massive immune response and induce vomiting.

SEs are highly resistant to environmental conditions that can easily destroy the bacteria, such as heat, drying, freezing, and proteases. They can remain active in food even after cooking or pasteurization, unless exposed to very high temperatures for long periods, such as autoclaving at 121°C for 60 minutes. They are also soluble in water and can accumulate in broth, minced food, and raw milk.

To date, 24 different types of SEs have been described, based on sequence homology, but only a few of them have been fully characterized. The most common types involved in SFP outbreaks are SEA to SEE, which are encoded by prophages, mobile genetic elements that can integrate into the bacterial chromosome. Other types of SEs are carried by plasmids, pathogenicity islands, enterotoxin gene clusters, or staphylococcal cassette chromosomes. Each type of SE has a different potency and specificity for binding to class II MHC molecules on antigen-presenting cells and T cell receptors on T cells.

Staphylococcal food poisoning (SFP) is a gastrointestinal illness caused by eating foods contaminated with toxins produced by the bacterium Staphylococcus aureus (Staph). The toxins are resistant to heat and cooking and can cause illness even if the bacteria are killed.

The symptoms of SFP usually begin abruptly with severe nausea and vomiting starting about 30 minutes to 8 hours after the contaminated food is eaten. Other symptoms include abdominal cramping, diarrhea, weakness, sweating, chills, headache, and fever. The symptoms usually last no longer than 1 day and resolve without treatment. However, some people may experience dehydration due to fluid loss, especially infants, children, elderly, and immunocompromised people.

In rare cases, SFP can cause severe illness or complications. Some strains of Staph produce toxins that can affect the nervous system and cause symptoms such as blurred or double vision, muscle weakness, tingling or numbness of the skin, difficulty swallowing, changes in voice, and loss of movement in limbs. These symptoms may indicate a serious condition called staphylococcal enterotoxin-mediated toxic shock syndrome (TSS), which can be life-threatening if not treated promptly. Another rare complication of SFP is staphylococcal enterocolitis, which is an inflammation of the colon that can cause bloody diarrhea and abdominal pain.

Staphylococcal food poisoning (SFP) is one of the most common causes of foodborne illness worldwide. It is estimated that SFP affects more than 240,000 people annually in the United States and accounts for about 25% of all foodborne outbreaks in Europe. SFP can occur in any region and season, but it is more frequent in warm and humid climates and during summer months when food is more likely to be left at unsafe temperatures.

SFP is usually associated with foods that are not cooked after handling, such as sliced meats, dairy products, salads, pastries, and sandwiches. These foods can be contaminated by S. aureus bacteria that are carried by food handlers or animals or present in the environment. The bacteria can produce enterotoxins in the food if it is stored at temperatures between 7°C and 48°C for more than two hours. The enterotoxins are heat-stable and can survive cooking or reheating. Therefore, food contaminated with S. aureus enterotoxins may not smell bad or look spoiled but can still cause illness if consumed.

The incidence of SFP varies depending on the surveillance system, the diagnostic methods, and the reporting practices of each country. However, some general trends can be observed. For example, SFP outbreaks are more common in institutional settings, such as schools, hospitals, nursing homes, and prisons, where large quantities of food are prepared and served to many people. SFP outbreaks are also more likely to occur during festive occasions, such as weddings, picnics, and parties, where food hygiene may be compromised. Furthermore, SFP outbreaks tend to involve multiple types of foods that are contaminated by a common source, such as a food handler or a utensil.

The most frequently reported enterotoxins involved in SFP outbreaks are SEA, SEB, SEC, SED, and SEE. However, other enterotoxins, such as SEG to SER, have also been detected in food samples and human cases. The emergence of new enterotoxins poses a challenge for the diagnosis and prevention of SFP, as they may not be detected by conventional methods or neutralized by available vaccines. Moreover, the occurrence of MRSA strains that produce enterotoxins has raised concerns about the potential transmission of antibiotic resistance through food.

The prevention and control of SFP rely on good hygiene practices throughout the food chain, from production to consumption. This includes washing hands before handling food, avoiding cross-contamination between raw and cooked foods, cooking foods to their safe minimum internal temperature, refrigerating foods within two hours of preparation or serving, and discarding foods that have been left at room temperature for too long. Additionally, education and awareness campaigns for food handlers and consumers can help reduce the risk of SFP.

Staphylococcal food poisoning is caused by the ingestion of toxins produced by Staphylococcus aureus bacteria, not by the bacteria themselves. The toxins are heat-stable and can survive cooking or reheating of food. The toxins act as superantigens, which are molecules that can activate a large number of T cells and trigger a massive inflammatory response in the body.

The toxins bind to major histocompatibility complex (MHC) class II molecules on antigen-presenting cells and T cell receptors on T cells, forming a bridge that stimulates T cell proliferation and cytokine production. Cytokines are chemical messengers that regulate immune and inflammatory responses. Some of the cytokines involved in staphylococcal food poisoning are interleukin-2 (IL-2), interferon-gamma (IFN-gamma), tumor necrosis factor-alpha (TNF-alpha), and interleukin-1 beta (IL-1 beta).

The high levels of cytokines cause various effects on different organs and tissues, such as:

• The gastrointestinal tract: The cytokines damage the intestinal mucosa, causing increased permeability, fluid loss, and diarrhea. They also stimulate the vagus nerve, which connects the brain and the gut, and activate the vomiting center in the brainstem, causing nausea and vomiting.
• The cardiovascular system: The cytokines cause vasodilation, which is the widening of blood vessels, and hypotension, which is low blood pressure. They also increase the heart rate and reduce the contractility of the heart muscle, leading to reduced cardiac output and shock.
• The nervous system: The cytokines cause fever, headache, fatigue, and malaise. They also affect the central nervous system, causing confusion, seizures, or coma in severe cases.

The symptoms of staphylococcal food poisoning usually appear within 30 minutes to 8 hours after eating contaminated food and last for no more than 24 hours. The severity of the illness depends on the amount and type of toxin ingested, as well as the age and health status of the person. Most people recover without complications, but some may develop dehydration, electrolyte imbalance, or kidney failure. Rarely, staphylococcal food poisoning can be fatal, especially in infants, elderly people, or immunocompromised people.

Staphylococcal food poisoning is usually diagnosed based on the clinical symptoms and the history of food ingestion. However, laboratory tests can be done to confirm the presence of toxin-producing Staphylococcus aureus bacteria or their toxins in stool, vomit, or food samples. These tests are usually not ordered except during an outbreak or when the diagnosis is uncertain.

Some of the laboratory methods for detecting Staphylococcal food poisoning are:

• Conventional culture method: This method involves isolating and identifying S. aureus from the samples by using selective and differential media, such as Baird-Parker agar. S. aureus colonies appear as black, shiny, circular, smooth colonies with an entire margin and a wide opaque zone around the colonies.
• Bioassays: These are tests that examine the toxin in animals or cell cultures based on the capacity of the sample to induce SFP symptoms. For example, a sample containing SEA toxin can cause vomiting and diarrhea in monkeys or kittens within a few hours of ingestion. However, these tests are not very sensitive, specific, or ethical.
• Molecular biology: These are techniques that use gene-specific nucleotide sequences as probes to detect and differentiate different enterotoxin genes in the samples. For example, colony blot hybridization, polymerase chain reaction (PCR), and multiplex PCR can amplify and identify SE genes from S. aureus isolates or food samples. These methods are fast, reliable, and sensitive, but they require expensive equipment and trained personnel.
• Serologic test: These are tests that use antibodies to detect antigens or toxins in the samples. For example, gel diffusion test and agglutination test use latex particles coated with specific anti-SE antibodies to show visible precipitation or clumping of the sample if it contains SEs. These tests are simple and rapid, but they lack specificity and sensitivity.
• Chromatography method: This is a technique that uses liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) to separate and identify SEs in the samples. This method can detect low concentrations of soluble protein food samples and isolate the toxins from food matrices. This method is accurate and sensitive, but it requires sophisticated equipment and expertise.
• Immunoassays: These are tests that use immunosensing elements to detect SEs in the samples and produce a measurable output signal. For example, colorimetric, fluorescence, chemiluminescence, electrochemiluminescent, refractive index, and Raman scattering immunoassays can measure the intensity of light or color change when SEs bind to specific antibodies on a sensor surface. These methods are rapid, sensitive, and specific, but they may require calibration and validation.

Staphylococcal food poisoning (SFP) is usually a self-limiting illness that does not require specific treatment. The main goal of therapy is to rehydrate and restore the electrolyte balance of the patients who have lost fluids due to vomiting and diarrhea. This can be achieved by drinking plenty of water, oral rehydration solutions, or intravenous fluids in severe cases. Antiemetic drugs may also be given to reduce nausea and vomiting.

Antibiotics are not recommended for the treatment of SFP, as they have no effect on the preformed enterotoxins that cause the symptoms. Moreover, antibiotics may increase the risk of antibiotic resistance, adverse reactions, and superinfection by other pathogens. However, antibiotics may be considered in some situations, such as when the patients have a high fever, blood in the stool, signs of systemic infection, or underlying conditions that compromise their immune system.

The best way to prevent SFP is to avoid the consumption of contaminated food or beverages. This can be achieved by following some basic food safety practices, such as:

• Washing hands thoroughly before and after handling food, especially raw meat and dairy products.
• Cooking food thoroughly and at the right temperature to kill any bacteria present.
• Refrigerating or freezing food promptly after cooking or purchasing to prevent bacterial growth and toxin production.
• Discarding any food that looks, smells, or tastes spoiled, or that has been left at room temperature for more than two hours.
• Avoiding cross-contamination between raw and cooked food, or between different types of food, by using separate utensils, cutting boards, and containers.
• Cleaning and sanitizing all surfaces and equipment that come in contact with food.
• Educating food handlers and consumers about the symptoms and causes of SFP and the importance of reporting any suspected cases to the health authorities.

By following these simple steps, you can reduce your risk of getting sick from SFP and enjoy your food without worries.

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