Project leader: Dr. S. Bertrand, Dr. W. Mattheus and Dr. R. Vanhoof
The Shigella genus belongs to the Enterobacteriaceae. The suspicion of Shigella by cultivation technique is based on their inability to ferment lactose and because they tend to be biochemically inert. They cannot be differentiated with DNA/DNA hybridization from Escherichia coli.
Shigellosis is the most communicable of the bacterial diarrheas. Human serves as the natural host and the disease is transmitted by fecal-oral route with as few as 200 viable organisms being able to cause the disease.
There are four species: Shigella dysenteriae, Shigella flexneri, Shigella boydii and Shigella sonnei. Each species except Shigella sonnei is further subdivised in serovars (= serotypes) based on the characterization of the O-antigen. They were given an Arabic number.
Fever, watery diarrhea with cramping abdominal pain and generalized myalgia are the most common early symptoms. Fluid and electrolyte losses may be present early in the illness owing to the action of enterotoxin on the intestinal epithelial cells. After two or three days the bowel movements become less frequent and there is a decrease in the quantity of stool. The presence of bright red blood and mucus in the feces and the onset of tenesmus indicate the dysenteric phase of the disease and suggest the bacterial penetration of the bowel.
Most of the Belgium cases are imported by abroad travels. Epidemics do occur in closed communities such as nurseries and prisons. Outbreaks can occur at any time of the year but are most common in the summer.
All Shigella isolates sent to the Reference Center are cultured on Kligler and tested for mannitol and xylose fermentation and indol reaction to orient the serogrouping (species determination) and serotyping and to verify the identification done by the original laboratory.
Serogrouping and serotyping are performed by slide agglutination (commercial antisera). When necessary additional biochemical tests are realized to confirm the identification.
All Shigella strains are conserved by freezing at -80°C.