Yersinia enterocolitica
Gram-negative, coccobacillary rods
Identification & Growth
Identification
- Urease-positive, oxidase-negative, motile at 25 °C and non-motile at 37 °C
- CIN agar: bull's-eye colonies (red centre)
Growth Conditions
- Grows well at 25–28 °C; CIN agar for 48 h on targeted stool culture
Clinical Significance
- Enteritis, mesenteric adenitis mimicking appendicitis, post-transfusion bacteremia
Intrinsic Resistance
- Chromosomal beta-lactamases A and B: ampicillin, amoxicillin-clavulanate and first-generation cephalosporins should not be reported
Bench Alerts
- Only isolated if CIN medium and 25 °C incubation are specifically requested
- Ask about recent pork consumption and blood transfusion
Clinical Notes
Clinical presentations
- Acute enterocolitis with diarrhea, abdominal pain and fever, which can mimic acute appendicitis (pseudoappendicitis) due to mesenteric lymphadenitis.
- Post-infectious manifestations include reactive arthritis and erythema nodosum, especially in HLA-B27-positive individuals.
- Bacteremia and sepsis can occur in patients with iron overload (hemochromatosis, thalassemia) due to the organism's iron dependence.
- Transfusion-transmitted infection from contaminated blood products is a rare but serious complication.
Specimens and collection
- Stool culture requires selective media such as CIN (cefsulodin-irgasan-novobiocin) agar and prolonged incubation, often with cold enrichment.
- Multiplex PCR enteric pathogen panels increase sensitivity and reduce detection time compared to culture.
- Blood cultures should be requested in patients with iron overload risk factors and signs of sepsis.
Epidemiology and at-risk populations
- Transmitted mainly by ingestion of raw or undercooked pork and unpasteurized milk.
- Young children are most affected by symptomatic enterocolitis, while adults more often develop reactive sequelae.
- Prolonged food refrigeration does not eliminate risk, as the bacterium can grow at refrigerator temperatures (psychrotolerant).
Resistance and therapeutic implications
- Produces chromosomal beta-lactamases that confer intrinsic resistance to ampicillin and first-generation cephalosporins.
- Uncomplicated enterocolitis is generally self-limited and does not require antibiotic therapy in most cases.
- Bacteremic or severe infections are treated with fluoroquinolones, trimethoprim-sulfamethoxazole or third-generation cephalosporins based on susceptibility.
Bench and reporting notes
- Gram-negative coccobacillus, oxidase-negative, with typical motility at 22-25°C and absent motility at 37°C.
- Slow growth on routine media can be facilitated by cold enrichment (4°C) for several weeks when clinical suspicion is strong.
- Serotyping and biotyping can be performed at reference laboratories for outbreak epidemiological investigation.
Sources
Educational decision-support content. It does not replace laboratory validation, current guidelines or review by the responsible professional.
FAQ: Frequently Asked Questions
How to identify Yersinia enterocolitica in the lab?
Yersinia enterocolitica is identified through urease-positive, oxidase-negative, motile at 25 °c and non-motile at 37 °c, cin agar: bull's-eye colonies (red centre).
What are the intrinsic resistances of Yersinia enterocolitica?
This organism is naturally resistant to chromosomal beta-lactamases a and b: ampicillin, amoxicillin-clavulanate and first-generation cephalosporins should not be reported. These drugs should not be reported as susceptible.
Where is Yersinia enterocolitica commonly found?
It is typically associated with enteritis, mesenteric adenitis mimicking appendicitis, post-transfusion bacteremia.
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