Yersinia
Microbiology:
Zoonotic infections.
Short rods, aka, coccobacilli
Bipolar Gram-staining: their tips stain darker than their middles.
Type three secretion systems secrete immune-suppressing effectors into host cells, which allows Yersinia to survive and replicate.
Plague
Yersinia Pestis causes plague.
Infected fleas and lice transmit the bacteria to humans.
Virulence factors and their genes:
Antiphagocytic protein capsule (Factor 1 gene).
Outer membrane proteins degrade complement proteins C3b and C5a; this prevents bacterial opsonization and phagocyte migration (Plasminogen activator gene).
Plasminogen activator proteases also degrade fibrin clots, which may facilitate bacterial spread in the host (Plasminogen activator gene).
Bubonic plague is characterized by fever, headache, chills, and weakness; replication in the lymph nodes produces swelling and tenderness – "buboes" refers to the visible lymph node swellings that typically appear in the axilla or groin.
Septicemic plague occurs when infection spreads throughout the body via the bloodstream or lymph; it produces fever, chills, and extreme weakness, as well as abdominal pain, and, possibly, shock or bleeding into the skin or other organs.
Pneumonic plague can quickly lead to respiratory failure and death; and, because is spread in respiratory droplets, transmission is human–to-human.
Treatment includes streptomycin or gentamycin; because disease progression is rapid, and infection can spread to the lungs, early administration of these antibiotics is crucial.
Yersiniosis
Yersinia enterocolitica and Yersinia pseudotuberculosis cause enterocolitis, especially in children.
They are associated with undercooked pork.
Young children tend to experience bloody diarrhea, cramps, and fever.
Older children tend to experience fever, and a pain in the right side of the abdomen that may be confused with appendicitis.
In most cases, supportive care is sufficient.
Image reference:
Center for Disease Control