Salmonella

Categorization
Cell Wall: Gram Negative Shape: Rod
Biochemistry: Lactose Non-fermenter, Indole Negative Metabolism: Facultative Anaerobe
Life-cycle: Facultative Intracellular
Subclassification
  • The Salmonella genus possesses a large number of individual species and sub-species which are identified and grouped using a variety of characteristics including their capsular serotype. Nearly 2,500 possible capsular serotypes exist. From a clinical perspective the vast majority of serotypes cause "Non-Tyhphoidal Salmonellosis" (NTS) while only a handful (4 serotypes) can cause Typhoid Fever.
Transmission
  • Non-Typhidal Salmonella (NTS)
    • Non-Tyhphoidal Salmonella (NTS) are zoonotic bacteria that can live and grow in a variety of animals, especially birds such as poultry and exotic reptiles. Transmission of NTS is primarily through ingestion of contaminated food/water and often occurs in major outbreaks due the modern centralization of the food supply.
  • Typhoidal Salmonella
    • Typhoidal Strains of Salmonella generally only infect humans (i.e. are not zoonotic) and are transmitted via a fecal-oral transmission. Due to modern advances in hygeine Typhoid Fever is now rare in developed countries.
Clinical Consequences
  • Non-Typhoidal Salmonellosis (NTS)
    • NTS accounts for the vast majority of cases of Salmonellosis and is characterized by food poisoning. Ingestion of contaminated food is followed by a usually watery, non-bloody infectious diarrhea with an incubation time of more than 8h. The usually self-limited diarrhea is accompanied by nausea, vomiting, and abdominal pain. In a small minority of individuals with reduced immunity NTS can spread systemically. Asplenic patients are especially prone to NTS sepsis. Those with Sickle Cell Disease are prone to NTS osteomyelitis.
  • Typhoid Fever
    • Typhoid Fever is caused by only a small handful of Typhoidal strains of Salmonella as described above. Typhoidal strains of Salmonella invade through enterocytes and are phagocytosed by macrophages in Peyer's Patches. The organisms evade killing within phagosomes and disseminate throughout the body within macrophages and colonize immune organs such as the spleen, lymph nodes, liver, and intestinal lymphoid tissue (i.e. Peyer's Patches). Typhoid Fever manifests with fevers and constitutional symptoms along with abdominal pain and in some cases hepatosplenomegaly. Characteristically, patients display a characteristic skin rash composed of small "Rose Spots" on their belly.
    • If untreated, the intestinal Peyer's Patches may undergo necrosis and life-threatening lower GI bleeding ensues. However, some untreated patients return to health but can become "Chronic Carriers", shedding Salmonella from their feces for months or years and thus contaminating the food/water supply, thus contributing to fecal-oral transmission.
Treatment
  • First Choices: Third Generation Cephalosporin
  • Alternative Choices: Bactrim for Non-typhoidal strains