SHIGELLA

4 Species including:

SPECIES

MICROSCOPIC APPEARANCE

Gram Stain: Gram-negative.
Morphology: Straight rods.
Size: Not available.
Motility: Non-motile.
Capsules: None.
Spores: None.
Other: Identification of Shigella spp. is sometimes difficult due to the fact that some E. coli strains share the ability to cause bacillary dysentery.

MACROSCOPIC APPEARANCE

Subgroup A: Appears with a pinkish tinge.
Subgroups B and C: Unavailable.
Subgroup D: Appears colorless at first, then pink.

KEY BIOCHEMICAL REACTIONS

METABOLIC PROPERTIES

Facultatively anaerobic. Chemoorganotrophic, having both a fermentative and respiratory type metabolism. Ferments glucose and other carbohydrates with acid production, but no gas.

HABITAT

Intestinal pathogen of man and primates often located in contaminated food and water.

PATHOGENICITY

Shigellae are pathogens of man and other primates and although there have been occasional reports of infections in dogs, other animals are resistant to infection.

Causative agent of bacillary dysentery (shigellosis), a descending intestinal illness characterized by abdominal pain, fever, large volumes of watery stools, and, 1 to 2 days later, smaller volumes of watery stools that often contain much blood and mucus and many leukocytes. The pathogenicity of shigellosis involves invasion and inflammation of the colonic epithelium, destruction of the superficial mucosa, sloughing of the mucosa, and production of the mucosal ulcers. Shigella spp. rarely invade beyond the mucosa; recovery of the bacterium in blood is rare. Shigella dysenteriae can cause a severe form of dysentery that has been reported to have fatality rates of up to 20%.

Infection with Shigella spp. other than S. dysenteriae usually is self-limited and rarely fatal except in the elderly and in undernourished children. Although infections are frequently mild and self-limiting, antibiotic treatment may be required. (2)

RECOMMENDED MEDIA

For culture: Tryptic Soy Agar (TSA).
For selective isolation: MacConkey Agar, Eosin Methylene Blue (EMB) Agar, Salmonella Shigella (SS) Agar, Deoxycholate Agar, and GN (Hajna) Broth.
For maintenance: Egg Medium for short-term maintenance and lyophilization or liquid nitrogen for long-term storage.

INCUBATION

Temperature: 35 degrees C.
Time: 18-24 hours.
Atmosphere: Aerobic.

REFERENCES

1. Holt, J.G., et al. 1994. Bergey's Manual of Determinative Bacteriology , 9th ed. Williams & Wilkins, Baltimore, MD.

2. Holt, J.G., et al. 1986. Bergey's Manual of Systemic Bacteriology , Vol. I & II. Williams & Wilkins, Baltimore, MD.

3. The Oxoid Vade-Mecum of Microbiology . 1993. Unipath Ltd., Basingstoke, UK.

4. Murray, P.R., et al. 1995. Manual of Clinical Microbiology , 6th ed. American Society for Microbiology, Washington, D.C.

5. Internet: www.hardlink.com /Bacterial Database Search, February, 1998.

6. Hensyl, B.R., et al. 1990. Stedman's Medical Dictionary , 25th ed. Williams & Wilkins, Baltimore, MD.

7. Koneman, et al. 1997. Color Atlas and Textbook of Diagnostic Microbiology , 5th ed. Lippincott, Philadelphia, PA.


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