Staphylococcus aureus is a spherical gram-positive bacterium, a member of the Bacillota, and is a common member of the body's microbiota, often found in the upper respiratory tract and on the skin. It is often positive for catalase and nitrate reduction and is a facultative anaerobe that can grow without the need for oxygen. Although Staphylococcus aureus usually acts as a component of the human microbiota, it can also become an opportunistic pathogen, which is a common cause of skin infections including abscesses, respiratory infections such as sinusitis and food poisoning. Pathogenic species often drive infections by producing virulence factors such as potent protein toxins and expression of a cell surface protein that binds and inactivates antibodies. Staphylococcus aureus is one of the leading pathogens for antimicrobial resistance-related deaths, and the emergence of antibiotic-resistant strains such as methicillin-resistant Staphylococcus aureus (MRSA) is a global problem in clinical medicine. Despite much research and development, no vaccine for Staphylococcus aureus has been approved.

About 20% to 30% of the human population are long-term carriers of Staphylococcus aureus which can be found as part of the normal flora of the skin, in the nostrils and as a normal inhabitant of the lower reproductive tract of women. S. aureus can cause a variety of diseases, from minor skin infections such as acne, impetigo, ulcers, cellulitis, folliculitis, carbuncles, burning skin syndrome and abscesses, to life-threatening diseases such as pneumonia, meningitis, osteomyelitis, endocarditis. , toxic shock syndrome, bacteremia and sepsis. It is still one of the five most common causes of hospital-acquired infections and is often the cause of post-operative wound infections. Each year, about 500,000 patients in US hospitals get a staph infection, mostly from Staphylococcus aureus. Up to 50,000 deaths each year in the United States are related to Staphylococcus aureus infections.

Discovery of Staphylococcus aureus

In 1880, Alexander Ogston, a Scottish surgeon, discovered that staphylococci could cause wound infections after noticing clusters of bacteria in pus from a surgical abscess during a procedure he was performing. He named it Staphylococcus after its clustered appearance visible under a microscope. Then, in 1884, German scientist Friedrich Julius Rosenbach identified Staphylococcus aureus and distinguished and separated it from Staphylococcus albus, a related bacterium. In the early 1930s, doctors began using a more effective test to detect the presence of an Staphylococcus aureus infection through the coagulase test, which detects an enzyme produced by the bacterium. Before the 1940s, Staphylococcus aureus infections were fatal in most patients. However, doctors have found that the use of penicillin can cure Staphylococcus aureus infections. Unfortunately, by the late 1940s, resistance to penicillin had become widespread among this bacterial population, and outbreaks of resistant strains began to occur.

Evolution of Staphylococcus aureus

Staphylococcus aureus can be divided into ten dominant human lineages. There are also many small lines, but these are not seen as often in the population. The genomes of bacteria within the same genus are largely conserved, with the exception of mobile genetic elements. Mobile genetic elements commonly found in Staphylococcus aureus include bacteriophages, pathogenicity islands, plasmids, transposons, and staphylococcal cassette chromosomes. These elements enabled Staphylococcus aureus to continuously evolve and acquire new characteristics. There is great genetic variation within Staphylococcus aureus species. A study by Fitzgerald et al. (2001) found that approximately 22% of the S. aureus genome is non-coding and therefore can vary from bacterium to bacterium. An example of this variation is seen in the virulence of species. Only a few strains of S. aureus are associated with infections in humans. This suggests that there is a large range of infectivity within species.


It has been suggested that a possible reason for the large heterogeneity within the species may be due to its dependence on heterogeneous infections. This occurs when many different types of Staphylococcus aureus cause an infection within a host. Different strains may secrete different enzymes or confer different resistance to antibiotics in the group, increasing their pathogenicity. There is therefore a need for a large number of mutations and acquisitions of mobile genetic elements.


Another notable evolutionary process within the S. aureus species is its coevolution with its human hosts. Over time, this parasitic relationship led to the bacteria's ability to be carried in the nasopharynx of humans without causing symptoms or infection. This allows it to be transmitted through the human population, increasing its fitness as a species. However, only about 50% of the human population are carriers of Staphylococcus aureus, with 20% being persistent carriers and 30% intermittent carriers. This leads scientists to believe that there are many factors that determine whether Staphylococcus aureus is carried asymptomatically in humans, including factors that are specific to an individual person. According to a 1995 study by Hofman et al., these factors may include age, sex, diabetes, and smoking. They also identified several genetic variations in humans that lead to an increased ability of Staphylococcus aureus to colonize, specifically a polymorphism in the glucocorticoid receptor gene that results in greater corticosteroid production. Finally, there is evidence that any type of this bacterium can become invasive, as it depends a lot on human factors.


Although Staphylococcus aureus has rapid reproductive and microevolutionary rates, there are numerous barriers that prevent evolution with the species. One such barrier is AGR, which is a global accessory gene regulator within bacteria. This such a regulator is linked to the level of virulence of the bacteria. Loss of function mutations within this gene were found to increase the fitness of the bacterium containing it. Staphylococcus aureus must therefore make a trade-off to increase their success as a species, trading reduced virulence for increased drug resistance. Another obstacle to evolution is the Sau1 Type I restriction modification (RM) system. This system exists to protect the bacterium from foreign DNA by digesting it. The exchange of DNA between the same sex is not blocked, since they have the same enzymes and the RM system does not recognize the new DNA as foreign, but the transmission between different sexes is blocked.

What is Staphylococcus aureus food poisoning?

Staphylococcus aureus is a common bacterium found in the nose and skin of about 25 percent of healthy people and animals. Staphylococcus aureus is capable of producing seven different toxins and is often the cause of food poisoning.


It is mostly transferred to food products such as milk and cheese through contact with food workers who carry Staphylococcus aureus.

Staphylococcus aureus food poisoning (SFP) is usually not life-threatening. Most cases of SFP do not require treatment, as the condition will go away on its own. Most people get over food poisoning in about two days.

Symptoms of Staphylococcus aureus food poisoning

SFP causes symptoms similar to a severe case of gastroenteritis, or inflammation of the digestive tract. Symptoms can appear quickly, sometimes in as little as 30 minutes after eating contaminated food. But it usually takes up to six hours for symptoms to develop.

Symptoms of SFP include:

  • Diarrhea
  • Vomiting
  • Nausea
  • Abdominal cramping
Illness is generally mild, and most people recover within one to three days.

Causes for Staphylococcus aureus food poisoning

SFP is caused by contaminated food products. S. aureus has a high salt tolerance and can grow in ham and other meats, and in dairy products. The toxins produced by the bacteria are also resistant to heat and cannot be destroyed by cooking.


Once food is contaminated, bacteria begin to multiply. The food products most associated with SFP are milk and cheeses. And the most common cause of contamination is contact with food workers who carry the bacteria.

Foods that require a lot of handling and are stored at room temperature are often included in SPF. This includes:
  • Sandwiches
  • Puddings
  • Cold salads, such as tuna, chicken, macaroni, or ham salad
  • Sliced deli meats
  • Cream-filled pastries

Diagnosis of Staphylococcus aureus food poisoning

In most cases, SFP does not require medical attention. It often clears up with rest and fluids. But contact your doctor if your illness lasts longer than three days, or if you cannot drink enough fluids to prevent dehydration.


Your doctor can diagnose SFP with a physical exam and a review of your symptoms. They may also ask questions about your recent activities and what you have eaten. If symptoms are severe, your doctor may order blood tests or a stool culture.

These tests can help determine if the Staphylococcus aureus bacteria are present and can also help your doctor rule out other possible causes.

Treatment of Staphylococcus aureus poisoning

SFP usually takes one or two days. Medical intervention is often unnecessary as this disease usually resolves on its own. Treatment usually involves rest and increased fluid intake. But some people may need medical help.


SFP can be dangerous in young children, infants, adults and people who have HIV.

Because the most common complication of SFP is dehydration, treatment with intravenous fluids may be necessary. In severe cases, you may be admitted to hospital for observation to prevent complications.

Outlook of Staphylococcus aureus food poisoning

People who contract SFP but are otherwise healthy usually have no lasting effects as the bacteria clears the body.

However, children, older adults and those with weakened immune systems can experience severe dehydration that requires hospital treatment. SFP can be fatal among these people. Immediate medical treatment increases their chances of a full recovery.

Prevention of Staphylococcus aureus food poisoning

To prevent food poisoning and the spread of bacteria, take the following precautions:

  • Avoid unpasteurized milk
  • Wash hands and fingernails thoroughly before cooking, eating, or serving food
  • Maintain clean and sanitary surfaces for food preparation
  • Store hot foods at temperatures over 140˚F (60˚C) and cold foods under 40˚F (4˚C)
  • Do not prepare food for others if you have wounds or sores on your hands or wrists