Fact sheet on pathogenic Yersinia species (e.g., Yersinia enterocolitica)

General
Yersinia spp. is a genus of bacteria belonging to the family Enterobacteriaceae. They are widespread in the environment. Some members play an important role as pathogens in food.

Yersinia enterocolitica is one of the most common causes of foodborne gastroenteritis in Germany and the EU. These bacteria are frequently found in pigs.

→ General information on the family Enterobacteriaceae: see fact sheet on Enterobacteria

Characteristics

• Rod-shaped bacteria
• Gram-negative
• Oxidase-negative
• Catalase-positive

Source / Occurrence

• Yersinia are widespread in our environment (e.g. soil, surface water and animals)
• Yersinia enterocolitica occurs naturally, for example, in pigs, especially in their tonsils, lymph nodes and intestines.

Significance

• Yersinia enterocolitica causes foodborne gastroenteritis
• In Germany this illness is most often associated with consumption of raw pork products (e.g. raw minced pork)
• The presence of Yersinia enterocolitica in ready-to-eat foods should be regarded as critical
• Some strains of Yersinia enterocolitica can multiply even at refrigerator temperatures. Short storage times and low temperatures below +2 °C are necessary to prevent growth

Clinical presentation

• Minimal infectious dose: typically from 10⁴ CFU/g (in exceptions also lower minimal infectious doses)
• Symptoms: diarrhea (sometimes bloody), colic/abdominal cramps, vomiting
• Duration of illness: one to three weeks
• Incubation period: approx. 3 to 7 days
• Symptoms are often mistaken for appendicitis
• Immunosuppressed people, patients with certain underlying diseases such as cancer or hemolytic disorders may develop life-threatening septicemia
• As a further complication, joint inflammation (reactive arthritis) may occur

Examples of affected foods

• Raw animal foods, especially raw pork, ground meat and meat preparations (e.g. raw minced pork …)

Growth conditions

• Temperature:
  • Optimum: +28 °C
  • Minimum: 0 °C
  • Generally no growth above +50 °C
• pH: growth at pH 4.5 to 9.0
• Salt tolerance: max. 5 %
• a_w value: growth at a minimum water activity of 0.97
• Oxygen requirement: growth with and without oxygen (facultatively anaerobic)

Inactivation by heating

• At +72 °C for at least 2 minutes exposure time the bacteria are killed (Note: monitor core temperature)

1. Observe hygiene regulations during the slaughtering process. Tonsils, lymph nodes and intestines must be properly removed during slaughter
2. Check the execution of cleaning and disinfection:
   1. Hygiene plan
   2. Execution of cleaning and disinfection e.g. disinfectant dosing, contact time, use of suitable and clean materials and cleaning cloths
3. Train employees regarding potential errors and improvement measures
4. Verify effectiveness by:
   1. On-site inspections and environmental testing (e.g. contact plate or swab samples)

1. Check workplace organization
   1. Separate work areas, equipment and utensils for raw and processed foods
   2. Separation of 'clean' and 'unclean' areas and operations
2. Train employees regarding potential errors and improvement measures
3. Verify effectiveness by visual on-site inspections and follow-up testing

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

1. Require traceability of the cold chain during transport from the supplier
2. Check incoming and storage temperatures
3. Monitor refrigeration temperatures/cold chains during processing, transport and sale
4. If over-aging (or too long shelf life) is suspected, carry out appropriate storage tests
5. Verify effectiveness by follow-up testing

1. Check processes, production protocols and documentation
2. Inactivation of most bacteria at a core temperature of +72 °C for at least 2 minutes. Exceptions are e.g. heat-stable spores and toxins. In these cases significantly higher temperatures and exposure times are required. Further information can be found in the respective info sheets (fact sheets)
3. Check correctness of processes and temperatures
   1. In general, holding temperatures above +60 °C are required
   2. Rapid cooling: after 3 hours a core temperature of at least +7 °C must be reached (special caution is required for large quantities)
4. Verify effectiveness by follow-up testing

Deficiencies in infection control:
This increases the risk of transmission of pathogenic microorganisms from people to product-contact surfaces or directly to food

Examples:

Salmonella from carriers or ill employees

Staphylococcus aureus from employees with inflamed or purulent wounds or with 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 gastroenteritis, or who excrete the above bacterial pathogens, must not work in food establishments handling 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. Non-infected wounds must be hygienically and properly dressed
3. Regular training/instruction of employees regarding the required infection control measures
4. Verify effectiveness by visual on-site inspections, checks of training records and follow-up testing

1. Train employees 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 employees about infection control requirements
5. Verify effectiveness by visual on-site inspections and follow-up testing

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

1. Maintain distance to fields with animal husbandry; keep wildlife away from fields by e.g. fences or nets
2. Water hygiene: contaminated water must not be used for irrigation. Irrigation and drainage systems must be suitable. Regular monitoring of microbiological water quality
3. No use of microbially contaminated fertilizers in crop production
4. Personnel & work hygiene during harvest or downstream steps
5. Remove soil or contamination by washing
6. Verify effectiveness by follow-up testing