Salmonella

Question 1

Disease

Answer 1

• enterocolitis, enteric fevers (typhoid fever), & septicemia with metastatic infections (osteomyelitis).

Question 2

Important Properties

Answer 2

• don’t ferment lactose;produce H2S
• O antigens subdivide into groups A–I.
• 2 H antigen forms; phases 1 and 2. Only one of 2 synthesized at a time,
  depending on which gene sequence is in correct alignment for mRNA transcription.
• Vi antigens (capsular
  polysaccharides)-> antiphagocytic & S. typhi virulence factor-> typhoid
  fever agent.

-3 species: S. typhi, Salmonella
choleraesuis, & Salmonella enteritidis.

• typhoidal species-> S. typhi and S. paratyphi.
• nontyphoidal species-> serotypes of S. enterica-> choleraesuis often
  involved in metastatic infections.

Question 3

Pathogenesis: Enterocolitis

Answer 3

• invasion of epithelial & subepithelial tissue of small & large
  intestines.
• Penetrate mucosal cells into lamina propria-> diarrhea &
  inflammation.
• Neutrophils limit infection
  to gut & adjacent mesenteric lymph nodes; bacteremia infrequent.

Gastric acid-> host
defense; gastrectomy or use of antacids lowers infectious dose.

Question 4

Pathogenesis: Typhoid

Answer 4

• begins in small intestine
• organisms enter, multiply in
  mononuclear phagocytes of Peyer’s patches->spread to phagocytes of liver, gallbladder, & spleen-> bacteremia & fever caused
  by endotoxin.
• Survival & growth of the organism
  within phagosomes in phagocytic cells-> predilection for invasion of
  the gallbladder->carrier state & excretion of bacteria in feces for
  long periods.

Question 5

Pathogenesis: Septicemia

Answer 5

• 2 settings: patient with underlying chronic disease (sickle cell anemia or cancer), or child enterocolitis.
• Septic course more indolent
• Bacteremia-> seeding of many organs, with osteomyelitis, pneumonia, & meningitis

Osteomyelitis in SCA child-> Salmonella Septicemia
- previously damaged
tissues (infarcts & aortic aneurysms) most frequent sites of metastatic abscesses.

• vascular graft infections.

Question 6

Epidemiology

Answer 6

• ingestion of food & water contaminated by human & animal wastes.
• Salmonella typhi-> human temporarily excrete organism during or shortly after attack of
  enterocolitis or chronic carriers who excrete organism for years.
• Animal source-> raw or undercooked poultry & eggs
• Dogs, turtles, snakes, lizards, & iguanas.

Question 7

Clinical findings

Answer 7

• incubation period of 12 to 48 hours
• enterocolitis->nausea & vomiting->
  abdominal pain & diarrhea (vary from mild to severe, with or without blood).
• lasts a few days, self-limited, nonbloody diarrhea, doesn’t require medical care except in very young
  & old.
• HIV-> greater number of
  Salmonella infections->more severe diarrhea & metastatic infections.

-Typhoid fever & enteric fever (S. paratyphi A, B, & C->fever & constipation than vomiting & diarrhea predominating.
- bacteremia sustains, high fever, delirium, tender abdomen, & enlarged spleen occur.
- Rose spots (rose-colored
macules on abdomen) -> typhoid

• Leukopenia & anemia.
• Liver function tests abnormal
• resolves by 3rd week/ intestinal hemorrhage or perforation
  can occur.

-carrier rate higher women with previous gallbladder disease
& gallstones.

• Septicemia-> S. choleraesuis.
• fever, little or no enterocolitis, focal symptoms associated with affected
  organ, bone, lung, or meninges.

Question 8

Lab Diagnosis

Answer 8

• Enterocolitis-> organism isolated from stool sample.
• Enteric fevers-> blood culture
  during 1st 2 weeks of illness.
• Bone marrow & stool cultures positive.
• form non–lactose-fermenting (colorless) colonies on MacConkey’s or EMB agar.
• TSI agar, alkaline slant & acid butt, with both gas & H2S (black color in the butt), produced.
• S. typhi exception-> doesn’t form gas & produces only small amount of H2S.
• Organism-> urease-negative
• isolate identified & grouped by slide agglutination test into serogroup A, B, C, D, or E based on its O antigen.
• organism difficult to recover, diagnosis serologically detected by rise in antibody titer in patient’s serum (Widal test).

Question 9

Treatment

Answer 9

• Enterocolitis->self-limited-> resolves without treatment.
• Fluid & electrolyte replacement.
• Antibiotic treatment doesn’t shorten illness or reduce symptoms; prolong organisms excretion-> increase frequency of carrier state, & select mutants resistant to antibiotic.
• Antimicrobial agents indicated
  for immunocompromised or neonates at risk for septicemia & disseminated abscesses.
• Drugs retard intestinal motility (reduce diarrhea) appear to prolong
  duration of symptoms & fecal excretion of organisms.
• typhoid fever & septicemia with metastatic infection-> ceftriaxone or ciprofloxacin.
• Ampicillin or ciprofloxacin->S. typhi chronic carriers.

Question 10

Prevention

Answer 10

• public health & personal hygiene measures.
• Proper sewage treatment-> chlorinated water supply monitored for contamination by coliform bacteria, cultures of stool samples from food handlers to detect carriers, handwashing before food
  handling, pasteurization of milk, & proper cooking of poultry, eggs, & meat.
• 2 vaccines-> confer limited protection against S. typhi.

1) Vi capsular polysaccharide of S. typhi (intramuscularly),
2) live, attenuated strain (Ty21a) of S.typhi (orally).

• recommended for travel or
  reside in high-risk areas & close contact with organism.
• new conjugate vaccine against typhoid fever with Vi capsular polysaccharide coupled to carrier protein is safe & immunogenic in young children.