Clinical Microbiology

(MLCM- 201)Prof. Dr. Ebtisam. F. El Ghazzawi.

Medical Research Institute (MRI)

Alexandria University

Intended Learning Intended Learning OutcomesOutcomesBy the end of this lecture the student should be able

to understand all about Pathogens Primary within the Enteric Tract, Types, pathogens, and there Laboratory Diagnostic tests.

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.

a. 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.

b. 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.

c. Serology: Normal persons often have agglutinins

against several Shigella species. However, serial

determinations of antibody titers may show a rise

in specific anitbody.

The Vibrios are curved, comma-shaped

gram-negative motile rods. They are found

in marine and surface waters.

Vibrio choleraeGram stain

The major pathogen in the genus Vibrio is

the Vibrio cholerae which is the cause of

cholera. While Vibrio parahaemolyticus

causes diarrhea associated with eating raw

or improperly cooked seafood.

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. Vibrio

parahaemolyticus 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.

AssignmentCampylobacter,Helicobacter

Questions……………species cause enterocolitis.The term dysentery refers to…………….The …………….are curved, comma-shaped

gram-negative motile rods.The major pathogen in the genus Vibrio is the

……………..which is the cause of …………..

Recommended TextbooksManual of Clinical Microbiology, Vols. 1 and 2: Eighth

Edition Patrick R. Murray