Yersinia Enterocolitica

Yersinia Enterocolitica

• Yersinia enterocolitica is a gram-negative bacillus belonging to the Enterobacteriaceae family
• The Yersinia genus is named after Alexander Yersin, who discovered it
• "Enterocolitica" refers to the intestine and colon
• Yersinia enterocolitica causes a diarrheal illness called yersiniosis

Microanatomy and Physiology

• Yersinia enterocolitica has a thin peptidoglycan layer, and stains pink with Safranin dye during Gram stain
• It appears as a small pink rod under a microscope
• It can be motile or non-motile depending on temperature: motile at 25°C and non-motile at 37°C
• It is a facultative anaerobe, capable of surviving in both aerobic and anaerobic environments
• Also facultative intracellular, and it is non-spore forming
• It is oxidase negative, meaning it does not produce the oxidase enzyme

Growth on Media

• Yersinia enterocolitica grows well on MacConkey agar, but it is a non-lactose fermenter, so it forms colorless colonies
• On Cefsulodin-Irgasan-Novobiocin (CIN) agar, after 24 hours, it forms white colonies with sharp borders and a deep red center, resembling bull's-eye colonies

Triple Sugar Iron (TSI) Test

• TSI test assesses hydrogen sulfide production
• Yersinia enterocolitica does not produce hydrogen sulfide, so no black precipitate forms in the test tube

Virulence Factors

• Adhesins like YadA and Ail help it attach to gut epithelial cells
• Type three secretion system (T3SS) delivers Yersinia outer proteins (Yops) into host cells
• Yops block secretion of pro-inflammatory cytokines (TNF-alpha and IL-8) and inhibit macrophage activation, suppressing the host's inflammatory response and helping evade phagocytosis
• Replicates inside Peyer's patches and spreads to mesenteric lymph nodes
• Siderophores are used to get iron from host cells
• Produces an enterotoxin called Yst, which may be involved in diarrheal disease

Transmission and Diseases

• Animals like cattle, deer, pigs, and birds are natural hosts
• Transmitted through the fecal-oral route, often from contaminated milk or pork
• Causes a gastrointestinal infection called yersiniosis
• Can affect the ileum (terminal ileitis), right colon (enterocolitis), or abdominal mesenteric lymph nodes (mesenteric lymphadenitis)
• Mesenteric lymphadenitis can mimic appendicitis, referred to as pseudoappendicitis
• In immunocompromised individuals or those with iron overload conditions (e.g., sickle cell disease or beta-thalassemia), it can spread systemically and cause septicemia

Post-Infectious Sequelae

• Can be associated with post-infectious sequelae, especially in individuals with the HLA-B27 antigen
• Reactive arthritis develops 1-3 weeks after infection, with bacterial antigens possibly depositing in the joints
• Erythema nodosum, inflammation of fat cells under the skin from a delayed hypersensitivity reaction to bacterial antigens

Symptoms

• Enterocolitis: fever, diarrhea with blood and mucus, and abdominal pain
• Pseudoappendicitis: fever, abdominal pain, and tenderness in the right lower quadrant
• Septicemia: fever, chills, hypotension, and tachycardia
• Reactive arthritis: joint pain and swelling
• Erythema nodosum: red or purple painful lesions, mainly on the legs

Diagnosis

• Identifying bacteria in cultures from a stool sample
• Reactive arthritis: identifying inflammatory cells or bacteria in a synovial fluid sample
• Serological tests like tube agglutination or ELISA for increased antibody titers in serum (though less common due to ease of culturing)
• Ultrasound or CT scan to exclude appendicitis in pseudoappendicitis cases

Treatment

• Yersinia enterocolitica infections can be treated with third-generation cephalosporins
• Susceptible to trimethoprim-sulfamethoxazole, aminoglycosides, fluoroquinolones, and tetracyclines