Yersinia enterocolitica Study Notes

Yersinia enterocolitica

Overview

• The presented information is based on Dr. Ahmed Abdelhamid's lecture on Yersinia enterocolitica and referenced literature.
• Main reference: Matthews KR, Kniel KE, Montville TJ (2017): Food Microbiology an Introduction, pp. 297-305.

Outbreak Events

• March-August 2011 Outbreak

  • Caused by Yersinia enterocolitica linked to consumption of glass-bottled pasteurized milk from Brunton Dairy, Pennsylvania.
  • Statistics:
  • Number of Y. enterocolitica culture-positive cases: at least 16
  • Hospitalizations: 7 patients (44% of cases); 3 individuals in the intensive care unit.
  • Source of Pathogen: Y. enterocolitica not found in milk samples but isolated from:
  • Unopened ice cream container
  • Homemade yogurt made with milk from the dairy.
  • Contamination Insight:
  • Bottles reused without proper sanitization led to post-pasteurization cross-contamination.

• 2006 Outbreak Example

  • Connected to Brawn, a traditional Norwegian dish composed of layered pork meat, veal, lard, and spices.
  • Statistics:
  • 11 patients developed yersiniosis; 4 hospitalized and 2 fatalities recorded.
  • Reservoir Insight:
  • Pigs can harbor Yersinia in nasal cavities; possibly contaminated during handling, especially through slicing.

Yersinia Classification and Pathogenicity

• Species Overview: There are 11 species of Yersinia, with 4 identified as human pathogens.
  1. Y. pestis
  • Identified by Alexandre Yersin in 1894.
  • Known cause of the bubonic plague, historically termed "Black Death" from 1347 to 1352, resulting in about 25 million deaths in Europe (approximately 25% of the population).
  1. Y. pseudotuberculosis
  • Foodborne illness caused by an intestinal pathogen of rodents and birds infecting humans.
  • First identified in 1883.
  1. Y. enterocolitica
  • Linked to human gastroenteritis since its recognition in New York State in 1939.
  • Renamed Y. enterocolitica in 1964.
  • Gained recognition as a foodborne pathogen in the 1970s.

Y. enterocolitica Characteristics

• Taxonomic Classification:

  • Family: Enterobacteriaceae
  • Characteristics:
  • Gram-negative
  • Non-lactose fermenter
  • Facultative anaerobe
  • Oxidase negative
  • Motile via peritrichous flagella

• Growth Characteristics:

  1. Temperature:
  • Psychrotrophic, capable of growth below 4 °C; optimal growth at 28-30 °C
  • Doubling time: ~34 minutes at 30 °C; slower at lower temperatures (5 hours at 7 °C, 40 hours at 1 °C).
  • Survives repeated freezing/thawing.
  1. Survival:
  • Higher survival in nutrient-rich, cooked foods than raw foods.
  • Grows in refrigerated meats, vacuum-packed foods, pasteurized products (e.g., milk, eggs, tofu, cottage cheese).
  • Rapid proliferation on cooked beef or pork within 24 hours at 25 °C and also in refrigerated seafood and vegetables albeit more slowly.
  1. pH and Salt Tolerance:
  • pH Range: 4 to 10 (optimal at 7.6).
  • Salt tolerance: Up to 5% NaCl.
  • Produces urease to hydrolyze urea, releasing ammonia which increases cytoplasmic pH and enhances acid tolerance.
  1. Thermal Sensitivity:
  • Inactivated through pasteurization: 71.8 °C for 18 seconds or 62.8 °C for 30 minutes; 80 °C for 10-20 seconds achieves >99.9% reduction in viability.
  1. Chemical Susceptibility:
  • Sensitive to organic acids (like lactic and acetic) and chloride, though some strains show resistance.
  • Control strategies include maintaining refrigeration below 4 °C, ensuring proper heat processing (e.g., pasteurization), preventing post-pasteurization contamination, and monitoring psychrotrophic growth in cold foods.

• Serotyping and Biotyping:

  • 34 identified serotypes based on O antigens; 14 of these are considered pathogenic.
  • Biotyping classification includes 6 biovars, with biovar 1B commonly isolated from patients in the United States (American strains).

Environmental Reservoirs

• General Distribution:

  • Widespread in the environment, including soil, vegetation, lakes, streams, and wells; most strains not pathogenic.
  • Survival is favored in cold water and temperate climates as opposed to tropical regions.

• Animal Reservoirs:

  • Found in the gastrointestinal tracts of various animals:
  • Mammals: sheep, cattle, deer, dogs, cats, rabbits, rodents
  • Birds, frogs, fish, shellfish, and insects
  • Notable Reservoir: Pigs are primary sources of virulent serovars.

Food Sources of Y. enterocolitica

• Growth in Various Foods:
  • Poor competitor against normal food flora; nevertheless can grow in:
  • Vacuum-packaged meats (e.g., pork)
  • Eggs
  • Fish
  • Dairy products (milk, cottage cheese)
  • Seafood (e.g., oysters, crabmeat)

Characteristics of Infection

• Infective Dose:

  • Likely greater than 10^4 CFU.
  • Gastric acidity serves as a primary barrier against infection.

• Susceptible Populations:

  • Particularly affects children under 12 years, the elderly, and individuals with underlying conditions like immunosuppression, malnutrition, alcoholism, and diabetes.

• Symptoms in Children (under 5 years):

  • Symptoms are typically non-specific and self-limiting: diarrhea, low fever, headache, sore throat, abdominal pain.
  • Older children may present with "pseudoappendicitis."
  • Duration of symptoms can last from a few days up to three weeks or longer.

• Symptoms in Adults:

  • Pharyngitis, bacteremia (especially in immunocompromised individuals or following blood transfusions).
  • Bacteremia fatality rate can range between 30-60%.

Foodborne Outbreaks of Y. enterocolitica

• Table of Selected Outbreaks:

  Location	Year	Month	No. of Cases	Serogroup	Source(s)
  Canada	1976	April	138	O:5,27	Raw milk?
  New York	1976	September	38	0:8	Chocolate-flavored milk
  Japan	1980	April	1,051	0:3	Milk
  New York	1981	July	159	0:8	Powdered milk, chow mein
  Washington	1981	December	50	0:8	Tofu and spring water
  Pennsylvania	1982	February	16	0:8	Bean sprouts and well water
  Southern United States	1982	June	172	O:13a,13b	Milk?
  Hungary	1983	December	8	0:3	Pork cheese (sausage)
  Georgia (United States)	1989	November	15	0:3	Pork chitterlings
  Northeastern United States	1995	October	10	0:8	Pasteurized milk?
  Norway	2006	February	11	0:9	RTE pork
  Norway	2011	March	21	0:9	RTE salad mix
  Pennsylvania	2011	June	5	NDC	Raw milk
  Pennsylvania	2012	Unknown	6	ND	Pork chops

  • Notably, in many cases, the bacteria were not isolated from the suspected sources.
  • RTE indicates "ready to eat," and ND means "not determined."

Prevention Strategies

• Recommendations to avoid infection:
  • Raw Milk: Should be avoided by the general public.
  • Chitterlings: Particularly dangerous for children (made from the intestines of pigs).
  • Cross-contamination: Emphasize minimizing cross-contamination in kitchen settings.

Case Study Question

• Scenario: A multistate outbreak of Y. enterocolitica infections reported in the United States, with most patients having consumed chitterlings cleaned and prepared at home during the holiday season.
• Contamination Insights:
  • Most likely source: Raw chitterlings, possibly contaminated during handling or preparation.
• Suggested Mitigation Strategies:
  1. Implement stricter hygiene protocols while preparing chitterlings at home.
  2. Educate the public about the risks of consuming undercooked or improperly handled pork products.