Fact sheet on coagulase-positive staphylococci and Staphylococcus aureus

General
Staphylococcus aureus (S. aureus) is a bacterium commonly found on the skin and mucous membranes of humans and animals. It belongs to the group of coagulase-positive staphylococci.
In foods, S. aureus is feared because of its potential to produce enterotoxins. These bacteria cause, in addition to gastrointestinal illnesses, skin and wound infections, abscesses and urinary tract infections.

Because S. aureus food intoxications are not notifiable, the exact number of such cases is not known. Due to their wide distribution among humans and animals, however, it can be assumed that they are among the most frequent causes of foodborne gastrointestinal illnesses. Humans are often the origin of contamination of foods. However, raw animal foods (e.g. raw milk) can also be contaminated with this pathogen.

Characteristics

• Coccus-shaped bacteria
• Gram-positive
• Oxidase-negative
• Catalase-positive
• Toxin producer

Origin / Occurrence

• Natural component of the skin flora in humans (especially scalp and hair) and on the mucous membranes of the nasopharynx (e.g. nasal secretions and saliva)
• Also occurs in farm and companion animals
• Due to their wide distribution in humans and animals, these microbes are also regularly found in our environment

Significance

• S. aureus is a potential foodborne pathogen because it can produce toxins that cause severe intoxications (poisonings) in humans
• S. aureus enterotoxins are often heat-stable and can survive heating steps
• S. aureus strains from humans more frequently have the ability to produce enterotoxins than strains from animals
• Relatively resistant to desiccation (relevant for dried foods)

Important

There are also antibiotic-resistant strains (methicillin-resistant Staphylococcus aureus – MRSA) that can, for example, cause severe wound infections. These infections are mostly transmitted to patients in hospitals. Farm animals can also carry this pathogen. Therefore meat can be contaminated with MRSA. However, MRSA in foods do not pose an acute health risk to consumers.

Clinical picture

• Minimal intoxication dose: usually at least 10⁵ CFU/g
• Incubation time: 1 to 6 hours
• Duration of illness: 1 to 2 days
• Symptoms: nausea, vomiting, diarrhea. Due to severe fluid loss, dizziness and circulatory collapse may occur. Fatal cases are very rare

Examples of affected foods

• Raw meat and sausage products, especially raw cured products
• Dairy products, cheese, especially raw milk cheese
• Raw eggs, egg-containing dishes
• Cream-containing desserts, cakes and prepared dishes
• Dough-based products and deli salads

Growth conditions and toxin production

• Temperature:
  • Optimum: +35 °C to +40 °C
  • Minimum: +6 °C
  • Generally no growth above +50 °C
  • Toxin production: +10 °C to +45 °C
• pH value:
  • Growth at pH 4.5 to 9.3 (exceptions even down to pH 4.0)
  • Toxin production from pH 4.8
• a_w value: growth at a water activity of at least 0.86 (relatively resistant to drying)
• Salt tolerance: up to max. 20%; growth still possible at 6.5 to 10%
• Oxygen requirement: facultatively anaerobic; toxin production is markedly stronger under aerobic conditions than under anaerobic conditions

Killing by heating

• At +72 °C for at least 2 minutes exposure time the bacteria are killed (Note: check core temperature) → note: the toxins are often heat-stable!
• The toxins of S. aureus are often heat-stable: inactivation only from +100 °C for 30 to 60 minutes

1. Train staff regarding potential errors and improvement measures
2. Regular hand cleaning and disinfection and/or regular glove changes
3. Regular change of work clothing. Ensure cleanliness of work clothing
4. Train staff regarding infection control requirements
5. Verification by visual on-site inspections and follow-up testing

Deficiencies in infection control:
This creates a risk of transmission of pathogenic microorganisms from humans to food-contact surfaces or directly to foods

Examples:

Salmonella from excreters or ill employees
Staphylococcus aureus from employees with inflamed or purulent wounds or colonization of the nasopharynx

1. Employees who are ill with or suspected of infections with Salmonella, EHEC/STEC, Shigella, Vibrio cholerae, hepatitis A or E viruses or other infectious gastrointestinal diseases, or who excrete the above bacterial pathogens, must not work in food establishments handling highly perishable foods and kitchens according to the Infection Protection Act (IfSG) (see IfSG § 42)
2. The same applies to employees with inflamed or purulent wounds. Uninfected wounds must be treated hygienically correctly
3. Regular training/instruction of employees on required infection control measures
4. Verification by visual on-site inspections, checks of training records and follow-up testing

1. Check cleaning and disinfection procedures:
   1. Hygiene plan
   2. Execution of cleaning and disinfection, e.g. disinfectant dosing, contact time, use of suitable and clean materials and cleaning cloths
2. Avoid moisture residues and biofilms. Ensure good drying of equipment, utensils and surfaces
3. Train staff regarding potential errors and improvement measures
4. Repeat cleaning and disinfection
5. Verification by visual on-site inspections, environmental testing and follow-up testing

1. Request cold chain traceability during transport or from the supplier
2. Check incoming and storage temperatures
3. Monitor cooling temperatures and cold chains during processing, transport and sale
4. If overripening (or exceeded shelf life) is suspected, carry out appropriate storage tests
5. Verification by follow-up testing

1. Review workplace organization
   1. Separate work areas, equipment and utensils for raw and processed foods
   2. Separation of "clean" and "dirty" areas and activities
2. Train staff regarding potential errors and improvement measures
3. Verification by visual on-site inspections and follow-up testing

1. Check products at goods receipt for e.g. incoming/transport temperature, shelf life, packaging, deviations or abnormalities
2. The same applies to goods before use in production. In case of doubt, do not use the food and consult supervisors
3. Check microbiological specifications. If necessary, arrange laboratory testing of suspicious products or request results from the supplier
4. Verification by follow-up testing

1. Check processes, production protocols and documentation
2. Killing of vegetative bacteria at a core temperature of +72 °C for at least 2 minutes. Inactivation of heat-stable toxins from +100 °C for 30 to 60 minutes
3. Check correctness of processes and temperatures
   1. In general, holding temperatures above +60 °C are required
   2. Rapid cooling: within 3 hours a core temperature of at least +7 °C must be reached (special caution is required for large quantities)
4. Verification by follow-up testing

1. Check processes, environmental conditions, production protocols and documentation
2. Verification by follow-up testing

1. Maintain distance from fields with livestock; keep wild animals away from fields using, e.g., fences or nets
2. Water hygiene: contaminated water must not be used for irrigation. Irrigation and drainage systems must be appropriate. Regular monitoring of microbiological water quality
3. No microbiologically contaminated fertilizers may be used in crop production
4. Personnel and work hygiene during harvest and downstream steps
5. Remove soil or contamination by washing
6. Verification by follow-up testing