Properties

Pathogenesis

Clinical findings

Laboratory diagnosis

Treatment & Prevention

Gram-negative, non-lactose fermenting rods.

Produce no gas from fermentation of glucose.

Do not produce H₂S.

Nonmotile.

Have O antigens (polysaccharide) in their cell walls; used to divide the genus into 4 groups: A, B, C & D.

Only a human disease; transmitted from person to person, usually by asymptomatic carriers.

Factors in transmission: fingers, flies, food & feces.

Cause disease in gastrointestinal tract, produce bloody diarrhea (dysentery) by invading the mucosa of the distal ileum & colon.

Local inflammation accompanied by ulceration occurs.

Most severe form of disease is dysentery: frequent passage of blood-stained mucopurulent stools.

After an incubation period of 1-4 days, symptoms begin with fever & abdominal cramps, followed by diarrhea, which may be watery at first but later contains blood & mucus.

Diarrhea frequently resolves in 2 or 3 days.

Young children & elderly people are most severely affected.

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

On TSI agar, they cause an alkaline slant & an acid butt, with no gas & no H₂S.

Methylene blue stain of fecal sample to determine whether PMNs are present.

Presence of PMNs indicates invasive organisms such as Shigella, Salmonella, or Campylobacter rather than a toxin-producing organism such as V cholerae, E coli or Clostridium perfringens.

Main treatment for shigellosis is fluid & electrolyte replacement.

In mild cases, no antibiotics are indicated.

In severe cases, a fluoroquinolone, e.g., ciprofloxacin, is the drug of choice.

Trimethoprim-sulfamethoxazole is an alternative choice.

Antiperistaltic drugs are contraindicated in shigellosis, because they prolong the fever, diarrhea, & excretion of the organism.

Prevention:

- proper sewage disposal.

- chlorination of water.

- personal hygiene.

- hand washing by food handlers.

No vaccine, & prophylactic antibiotics are not recommended.