Properties

Pathogenesis

Clinical findings

Laboratory diagnosis

Treatment & Prevention

Never part of normal flora.

Gram-negative rods that do not ferment lactose but do produce H₂S.

Thousands of species separated according to their surface antigens (O, H, Vi & K).

Enterocolitis:

- invasion of epithelial & subepithelial tissue of small & large intestines.

- strains that do not invade do not cause disease.

- organism penetrates into lamina propria with resulting inflammation & diarrhea.

Typhoid:

- organism enter, multiply in phagocytes of Peyer’s patches, & then spread to phagocytes of liver, gallbladder, & spleen.

- this leads to bacteremia, which is associated with onset of fever & other symptoms.

- invasion of gallbladder results in establishment of carrier state & excretion of bacteria in the feces for long periods.

Septicemia:

- accounts for 5-10% of infections.

- occurs especially in patients with sickle cell anemia or cancer or a child with enterolitis.

- bacteremia results in seeding of many organs: osteomyelitis, pneumonia, & meningitis.

- previously damaged tissues such as infarcts & aneurysms, especially aortic aneurysms, are the most frequent sites of metastatic abscesses.

Epidemiology:

- related to ingestion of food & water contaminated by human & animal wastes.

- tyhoid fever is transmitted only by humans.

- animal source is poultry & eggs, dogs & other pets.

Diseases:

- enterocolitis (salmonella food poisoning)

- typhoid fever

- septicemia

Incubation period of 6-48 hours.

Enterocolitis:

- begins with nausea & vomiting.

- progresses to abdominal pain & diarrhea.

- disease lasts a few days, is self-limited.

- causes nonbloody diarrhea.

- transient bacteremia; local infections may occur – infection of atheromatous plaques inside arteries, implanted prostheses, osteomyelitis (particularly in sickle cell disease), meningitis (particularly in neonates).

Typhoid fever:

- caused by salmonella typhi, S paratyphi A, B & C.

- fecal-oral transmission.

- onset of illness is slow, with fever & constipation.

- after first week, bacteremia becomes sustained, high fever, delirium, tender abdomen & enlarged spleen occur.

- other symptoms: anorexia, epistaxis, cough, headache, abdominal pain & tenderness.

- temperature remains elevated for another 10-14 days.

- gallbladder excretes infected bile into the gut & a second invasion of intestine wall occurs.

- resulting inflammation results in typhoid ulcers which may cause severe hemorrhage & intestinal perforation.

- about 3% of typhoid fever patients become chronic carriers.

Organism most easily isolated from a stool sample.

Salmonella form non-lactose-fermenting (colorless) colonies on MacConkey’s or EMB agar.

On TSI agar, an alkaline slant & an acid butt, frequently with both gas & H₂S.

Salmonella isolate can be identified & grouped by the slide agglutination test.

Blood cultures are usually positive early in the illness, later stool or urine becomes positive.

Enterocolitis:

- fluid & electrolyte replacement may be required.

- antibiotic treatment is not useful & may prolong excretion of organisms & select resistant mutants.

Typhoid fever:

- ceftriaxone.

- ampicillin or ciprofloxacin used in chronic carriers of S typhi.

- cholecystetomy may be needed to abolish chronic carrier state.

- focal abscesses drained surgically.

Prevention:

- public health & personal hygiene measures.

- proper sewerage treatment.

- chlorinated water supply.

- hand washing prior to food handling.

- pasteurization of milk.

- proper cooking of poultry & meat.

Vaccines:

- 2 are available, which confer limited (50-80%) protection against S. typhi.

- acetone-killed – administered intramuscularly.

- live, attenuated vaccine taken orally.