Salmonella
Salmonella
Microbiology:
Salmonella causes foodborne infections.
Does not ferment lactose, unlike the other members of Enterobacteriacea;
Produces hydrogen sulfide.
Infects both humans and non-human animals
Exception: Typhoid-causing strains are strict human pathogens.
Intracellular pathogens that can invade all tissue types, including the brain.
Virulence genes are encoded on Pathogenicity islands I and II:
Type three secretion systems inject effector proteins into host cells.
Salmonella-secreted invasion proteins, which facilitate entry into host cells.
Immune evasion proteins.
Infection is acquired after consumption of contaminated foods, especially eggs, poultry, and dairy.
Salmonellosis
Gastroenteritis, characterized by inflammation of the intestinal lining, is the most common form of Salmonellosis in the U.S.
Symptoms include nausea, vomiting, diarrhea, fever, and cramps.
Gastroenteritis is usually self-limiting, and requires only supportive care (i.e., water and ion replenishment).
Salmonella Typhimurium, the isolate often associated with gastroenteritis, resides in Salmonella-containing vacuoles (SCVs) within phagocytes; this protective endosome allows the bacteria to survive and replicated safely inside host cells.
Septicemia causes typical bacteremia symptoms, including fever, chills, and low blood pressure.
In a small subset of patients, localized infections can develop, particularly in the joints and cardiovascular endothelium.
Salmonella septicemia is most common in young children and older adults, and in individuals with HIV or other immune deficiencies.
Be aware that recurrent septicemia is an AIDS-defining condition.
Treatment includes Fluoroquinolone or Cephalosporin antibiotics.
Enteric fevers
Typhoid fever is associated with Salmonella Typhi
Paratyphoid fever, a milder form is associated with Salmonella serotypes Paratyphi A, Paratyphi B, and Paratyphi C.
Be aware that S. Paratyphi B is also referred to as Salmonella Schottmeulleri, and S. Paratyphi C is also referred to as Salmonella Hirshfeldi.
Symptoms & Pathogenesis:
Approximately 10 days after ingestion of the bacteria, individuals experience fever, fatigue, and other non-specific symptoms; indicate that some patients develop "rose spots," which are small red macules on the trunk.
Approximately 20 days after ingestion, patients experience gastrointestinal symptoms, which can include constipation or diarrhea, nausea, and vomiting.
We show that Typhoid-associated strains, such as Salmonella Typhi, move through the lining of the intestine and are engulfed by macrophages.
Macrophages carry the microbes to the bone marrow, liver, and spleen, where bacterial replication occurs.
This sets the stage for bacteremia and the non-specific symptoms patients experience.
Infection increases splenic cellularity and leads splenomegaly in some patients; liver enlargement has also been reported.
Ultimately, the bacteria colonize the gallbladder and re-infect the intestines, producing gastrointestinal symptoms.
Treatment includes administration of fluoroquinolones or ciprofloxacin.
Asymptomatic carriers maintain typhoid-associated strains within populations; for example, enteric fever is endemic in Southeast Asia and parts of Africa.