Clinical Microbiology. (MLCM- 201) Prof. Dr. Ebtisam. F. El Ghazzawi. Medical Research Institute (MRI) Alexandria University. Intended Learning Outcomes.
Prof. Dr. Ebtisam. F. El Ghazzawi.
Medical Research Institute (MRI)
Pathogens Primarily within the Enteric Tract
Shigella species cause enterocolitis. Enterocolitis caused by Shigella is often called bacillary dysentery. The term dysentery refers to bloody diarrhea. Shigelleosis is only a human disease, its natural habitat is limited to the intestinal tract. The organism is transmitted by the oral-fecal route.
The four Fs-fingers, flies, food and feces – are the principal factors in transmission. After a short incubation period (1-2 days), there is a sudden onset of abdominal pain, fever, and watery diarrhea. The diarrhea has been attributed to an exotoxin acting in the small intestine.
A day or so later, as the infection involves the ileum and colon, the number of stools increases, they are less liquid but often contain mucus and blood.
Each bowel movement is accompaning by straining and tenesmus (rectal spasms) which resulting lower abdominal pain.
In adult cases fever and diarrhea subside spontaneously in 2-5 days.
However in children and the elderly, loss of water and electrolytes may lead to dehydration, acidosis and even death.
Specimens: Include fresh stool, mucus flecks, and rectal swabs for culture. Large numbers of fecal leukocytes and some red blood cells often are seen microscopically.
Culture: Culturing on differential media e.g. Mac-Conkey’s or EMB agar and on selective media e.g. Salmonella Shigella agar (SS agar) gives colourless colonies (NLF) should be subjected to biochemical examination.
Serology: Normal persons often have agglutinins against several Shigella species. However, serial determinations of antibody titers may show a rise in specific anitbody.
The major pathogen in the genus Vibrio is the Vibriocholerae which is the cause of cholera. While Vibrioparahaemolyticus causes diarrhea associated with eating raw or improperly cooked seafood.
I. Vibrio cholera:
V. cholera is transmitted by fecal contamination of water and food primarily from human sources.
A major epidemic of cholera spanned the 1960s,1970s, 1991 and 1992 had spread to many countries all over the world.
The factors that predispose to epidemics are poor sanitation, malnutrition, overcrowding and inadequate medical services.
Vibrio cholera produces an enterotoxin that causes cholera, a profuse watery diarrhea that can rapidly lead to dehydration and death.
There are no red blood cells or white blood cells in the stool.
Rice water stool is the term often applied to the nonbloody effluent.
There is no abdominal pain and subsequent symptoms are referable to the marked dehydration.
The loss of fluid and electrolytes leads to cardiac and renal failure.
Acidosis and hypokalemia also occur as a result of loss of bicarbonate and potassium in the stool.
Culture of the diarrhea stool show colourless colonies on Mac Conkey’s agar.
The organism is oxidase positive, ferment sucrose and mannose. It grows on media containing 6% NaCl.
Is a marine organism transmitted by ingestion of raw or undercooked seafood, especially shellfish such as oysters. Vibrioparahaemolyticus secrets enterotoxin similar to that of cholera and its clinical picture varies from mild to quite severe watery diarrhea, nausea, vomiting, abdominal cramps and fever.
The enteritis tends to subsides spontaneously in 1-4 days with no treatment other than restoration of water and electrolyte balance.
It grows in 8% NaCl solution.
It grows on TCBS agar where it yields green colonies. It is oxidase positive and grows on blood agar.