Salmonella is a type of bacteria that can cause foodborne illnesses in humans. There are various strains of Salmonella. Among these, Salmonella enterica is one of the most common species that can infect people. It is responsible for the many cases of food poisoning each year, with symptoms ranging from mild gastrointestinal discomfort to severe illness. According to the Centers for Disease Control and Prevention (CDC), Salmonella cause about 1 million cases of foodborne illness every year. The bacteria can contaminate a wide range of foods, especially raw or undercooked foods such as meat, egg, and poultry.

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With the wide range of foods that salmonella can contaminate, you might ask if cooking can kill the bacteria. In this blog, we will explore the role of cooking in killing Salmonella and preventing foodborne infections.

WHAT IS SALMONELLA?

Salmonella, a Gram-negative bacterium, presents rod-shaped cells with lengths ranging from 2 to 5 micrometers when viewed under a microscope. These cells are non-sporulating, meaning they do not form spores, and they are motile, equipped with flagella that enable them to move.

Salmonella exhibits adaptability in its growth conditions. It is a facultative anaerobe, capable of thriving in both oxygen-rich and oxygen-poor environments. Its optimal growth temperature falls within the range 98°F (37°C) to 107.6°F (42°C), mirroring human body temperature. This characteristic is significant as it enables Salmonella to colonize the human gastrointestinal tract effectively. The optimal pH for Salmonella is between 6.5 to 7.5. The bacteria can also withstand low pH levels of around 4.5. This enables them to survive the acidic conditions of the stomach.

Moreover, Salmonella exhibits relative heat resistance, which raises concerns for food safety.

From a pathogenic standpoint, certain Salmonella strains are known to be harmful to humans and animals, causing diseases such as salmonellosis, typhoid fever, and gastroenteritis. These pathogenic strains possess virulence factors that facilitate host cell invasion and disease progression, including fimbriae, flagella, and type III secretion systems.

Transmission of Salmonella primarily occurs through the ingestion of contaminated food and water. Many food items, particularly those of animal origin, such as poultry, eggs, and meat, can serve as reservoirs for Salmonella. Fecal-oral transmission may transpire when food is mishandled, or when contaminated hands or surfaces come into contact with food.

Symptoms of Salmonella infection

Salmonellosis, an infection caused by the Salmonella bacterium, can be contracted by individuals when they consume food that has been contaminated, including inadequately cooked eggs, meats, poultry, or unpasteurized milk.

The symptoms of salmonellosis usually develop within 12-14 hours of eating the contaminated food, but can range from a few hours to several days.

Symptoms include nausea, vomiting, abdominal pain, headache, chills, diarrhea, prostration, muscular weakness, faintness, fever, restlessness, and drowsiness. These Symptoms typically last for 2-3 days.

The mortality rate for Salmonella food poisoning is 4.1%, but varies depending on age. The mortality rate is highest in infants (5.8%), followed by people over 50 years old (15%).

Up to 5% of people who recover from Salmonella food poisoning become carriers of the bacteria. This means that they can carry the bacteria in their intestines without showing any symptoms, but they can still spread the bacteria to others.

Now, back to the question.

CAN SALMONELLA BE KILLED BY COOKING?

Yes, Salmonella can be effectively killed by cooking when the correct temperatures are reached and maintained. According to a study, exposure to a temperature of 140°F (60°C) to 149°F (65°) for several minutes is sufficient to destroy salmonella bacteria.

The process of killing Salmonella through cooking relies on the application of heat. When food reaches these recommended temperatures and is held at them for a sufficient duration, the heat effectively breaks down the Salmonella bacteria’s cell walls and denatures the proteins within the cells. This process destroys the bacteria’s ability to cause infections, making the food safe to eat.

When preparing food, especially those susceptible to Salmonella contamination, cook it to the recommended temperature. For example, when cooking poultry, such as chicken and turkey, ensure it reaches a minimum internal temperature of 165°F (73.9°C). For ground meats like beef, pork, or lamb, aim for a temperature of 160°F (71.1°C). When cooking eggs, make sure both the egg white and yolk have solidified. Seafood should be heated to 145°F (62.8°C) or until it easily flakes apart with a fork. When reheating leftovers, be certain they reach a temperature of 165°F (73.9°C) to eliminate any potentially harmful bacteria that may have multiplied during storage.

References:

G. Cooper (2018). Food Microbiology. Library Press.

J. Jay, M. Loessner, D. Golden (2005). Modern Food Microbiology (7th edition). Springer.

Y. Motarjemi (2014). Encyclopedia of Food Safety. Academic Press.

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Millions of bacteria live with us. Most of them are harmless (some live inside our bodies), and beneficial to us like Lactobacillus or LAB bacteria. However, 1% of the bacterial population make us sick. Among this 1% are the 7 most common disease-causing bacteria: Salmonella Spp, Eschericha coli  0157:H7, Listeria monocytogenes, Clostridium perfringens, Clostridium botulinum, Staphylococcus aureus, and Campylobacteria jejeuni.

These have caused millions of food-poisoning around the world yearly. According to the Centers for Disease Control and Prevention, in the United States alone, around 48 million people get sick, 128,000 get hospitalized, and 3000 die from food-borne illnesses.

Typical symptoms of food poisoning include fever, muscle pain, nausea, vomiting, and diarrhea. Although people who fall ill recover from illness, some who are vulnerable (the young and old), would die from such poisoning. Pathogenic bacteria are mainly responsible for these food poisoning occurrences. Pathogenic bacteria, along with viruses, and parasites, fall under the biological hazards, one of the three recognized food safety hazards in the food industry. In any HACCP system, there should be zero tolerance to such hazard.

Salmonella Spp. or Salmonella

Salmonella Spp. is a gram-negative, rod-shaped facultative anaerobic bacterium. As part of the genus Salmonella, it has caused the most number of reported outbreaks in the United States every year. Cases of patients that do no see a doctor doesn’t count too in this figure!

The most usual symptoms that may last up to 7 days include nausea, chest pain, diarrhea, and vomiting. Severe illnesses may happen to very young patients, the orderly, and those with weak immune system.

Most cases of salmonellosis come from consuming contaminated meat, poultry and egg. Salmonella infection come from feces or waste from the animal. The is why an egg with a cracked shell isn’t advisable for consumption. Also, do not consume eggs raw unless they are pasteurized.

Eschericha coli  0157:H7

Most strains of Eschericha coli are harmless to humans. In fact, some live normally in the human intestinal tract without making us sick. However, some do us harm, including Eschericha coli 0157:H7. Eschericha coli 0157:H7 is a gram-negative, and rod-shaped bacterium,. This E. coli strain causes millions of food-poisoning cases yearly.

Most outbreaks by this strain result from eating undercooked or raw meat products, usually ground meat. Infection usually happens during slaughtering where animal wastes are present. Contaminated kitchen utensils, and surfaces that are used during food preparation are also causes of fecal contamination. Cases of E. Coli food poisoning have also been reported from consuming dairy products, fruits, and vegetables.

When one suffers from E. Coli food poisoning, he may experience fever, abdominal pain, vomiting, and diarrhea. Most cases reported the patients to experience bloody diarrhea. These symptoms usually last up to 10 days. As of this writing, there is no treatment for this type of food poisoning (antibiotics do not work either).

Listeria monocytogenes

Listeria Monocytogenes or Listeria is a gram-positive, and rod-shaped bacterium. Listeria Monocytogenes causes listeria, which targets the nervous system . Most patients experience fever, loss of balance, nausea, diarrhea, vomiting, and muscle pain. These symptoms usually are experience for hours or days and last up to several weeks.

Since this bacterium can withstand low temperature, it usually infects food items stored in the refrigerator. Freezing food items only slows down the movement of microorganisms, but not destroy them. Reheat food, especially ready-to-eat ones like hot dogs and deli meat to kill any harmful bacteria.

Read more food safety tips regarding your refrigerator.

Clostridium perfringens

Clostridium perfringens is a gram-positive, rod-shaped, anaerobic, and spore-forming bacterium. Its ability to create spores enable it to withstand many food processes. Most food-poisoning cases caused by this bacterium resulted from consuming poultry, meat, gravy and sauces, and pre-cooked foods. Most food associated with  C. perfringens food poisoning are prepared in batches. And usually, they are kept for a considerable long time before serving. These cases usually happen at the cafe, hotels, restaurants, buffets, and cafeterias. Reheating food is must for these kinds of setting especially before serving. Refrigeration for leftover food is a must to slow down bacterial growth,

C. Perfringens food poisoning cause vomiting, abdominal cramps and diarrhea. These symptoms last up to 24 hours.

Clostridium botulinum

Clostridium botulinum is another gram-positive, rod-shaped, and anaerobic spore-forming bacterium known for producing the neurotoxin botulinum. The botulinum toxin is one of the most poisonous toxin known. Unlike most bacteria, Clostridium Botulinum does not need oxygen in order to grow. It is why this bacterium can live happily in food products deprived of oxygen like home-canned goods. The Botulinum toxins are found in various food items like fruits, vegetables, and meat products.

Botulism-contaminated home-canned goods usually occur due to improper processing. One should invest in a suitable pressure canner to do home canning properly. A pressure canner that cannot reach the required pressure will only turn the food into a breeding ground for bacteria.

Remember that Botulism is a potentially-fatal illness. At first, the patient will feel nausea, vomiting, weakness, dizziness a few hours after ingesting the contaminated food. Then the attack on the body’s nervous system will follow: double/blurred vision, trouble breathing, fatigue, dry mouth and throat, and lack of muscle coordination. Most deaths from botulism result from respiratory failure as part of complication. Patients who feel difficulty in breathing may need mechanical ventilation for months to a year.

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Check out this comprehensive post about this bacterium from FDA.

Staphylococcus aureus

Staphylococcus aureus is a gram-positive, and round-shaped bacterium. This bacterium is usually associated with meat products, dairy products, and baked goods.

Remember that foods contaminated with Staphylococcus Aureus do not manifest signs of spoilage like foul odor or discoloration. Never place food in an environment with temperature inside the Danger Zone. The Danger Zone is anywhere from 40 °F (4 °C) to 140 °F (60 °C), the range where the growth of bacteria doubles in number in 20 minutes time.

The usual symptoms of Staphylococcal Food Poisoning include diarrhea, vomiting, nausea, headache, muscle and chest pain. These symptoms usually develop quickly and last for a day. Patients need to drink as much water as possible to hydrate from diarrhea. Rarely, patients develop severe illness and poisoning clears out on its own with 1 to 2 days.

Campylobacteria jejeuni

Campylobacteria Jejeuni is a gram-negative, and spirally-curve bacterium. This bacterium causes millions of food-borne illnesses in the U.S., New Zealand, and in Europe. Campylobacteria Jejeuni normally lives in the intestines of several animals like cattle, swine, rodents, birds, and shellfish. The typical symptoms of the disease include nausea, diarrhea, fever, abdominal pain, headache, and vomiting. Most people would recover from Campylobacteriosis on their own. However, some, especially the very young ones and the elderly with low immunity would need medical treatment.  

Most Campylobacteriosis (the disease caused by this bacterium) occur from consuming raw or undercooked meat. Transmission of Campylobacteria is more common during slaughtering of the animal where animal feces is present. Slaughter houses train workers and food handlers to prevent any forms of contamination. Nonetheless, as an end user, the consumer must thoroughly cook the meat to kill any harmful bacteria.

How To Prevent These Disease-Causing Bacteria

These pathogenic bacteria are harmful to everyone. But these are easily avoided if everyone follows a routine that prevents bacteria from multiplying.

Always keep everything clean before and after. Clean all cooking utensils, appliances, food contact surfaces, etc. to prevent cross- contamination. Before handling food items, thoroughly clean the hands with soap and water.

Prevent cross-contamination. Separate raw food from cooked. If placed together, the bacteria from the raw can contaminate the cooked. Implement this for food inside your refrigerator as well. Have a dedicated container for each food. The ready-to-eat, and cooked should at the top shelves and the raw food like meat at the bottom shelf. This prevents blood or juices from dripping to another food.

Cook food at a proper temperature. As a guide, cook food at at least 165°F (74°C) or higher. It is better to invest in a food thermometer.

Keep food properly. Cold food should stay cold and hot food should stay hot. Store cold food at 40°F (4.4°C) or below and hot food at 140°F (60°C) or higher. Never store food anywhere in the Temperature Danger Zone 40 °F(4.4°C)  and 140 °F (60°C). It is where bacteria doubles in number very quickly.

Check out this post to Know The Factors That Affect Growth of Harmful Microorganisms.

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