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GIT-block
Microbiology Lab.
Dr./ Tamer Ata
Contents
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Bacterial enteritis
Fungal intoxication
Parasitological slides
Blood culture
Bacterial enteritis
Bacterial enteritis
Mostly Gram negative bacilli including
1. Vibrio spp.
2. Shigella spp.
3. Salmonella spp. (food poisoning & enteritis)
4. E. coli (EHEC O157/H7 & EPEC & ETEC& EIEC)
5. Campylobacter SPP.
Lab. Diagnosis
• Specimen: stool
• CULTURE of specimen for isolation of the
pathogen:
On selective and differential media as
XLD= Xylose Lysine Deoxycolate Agar
• Identification of the isolated organism
• Serological
• Typing in outbreaks to trace source of infection
Culture media
XLD media
• Selective media for enteric Gram
negative bacilli
• Also differential media as can
differentiate lactose fermenters
(LF) from non lactose fermenters
(NLF)
• LF → yellow colonies
• NLF → pink colonies + black color
(H2S production)
LF colonies on XLD media
Possibility of the organism?
E. coli
Other test to confirm
diagnosis?
• Biochemical reactions as
API 20 E
• Serological
characterization? To
differentiate it from flora
NLF colonies on XLD media
Possibility of the organism?
Shigella spp.
Further identification
between the spp. by?
1. Biochemical reactions as
API 20 E
2. Serological characterization
Disease caused: Bacillary
dysentery
NLF colonies with H2S production
on XLD media
Possibility of the organism?
• Salmonella spp.
Further identification
between the spp. by?
1. Biochemical reactions as
API 20 E
2. Serological
characterization.
Disease caused: infective
enteritis or enteric fever
API 20 E
PRINCIPLE?
• Bacteria suspension placed in
the small tubules of the strip
• Each one is a lyophilized
biochemical reaction
• After incubation it gives colors
which converted into numbers
• From index we can identify the
spp. Bacteria by its number
Uses: identification of
bacterial spp. Also used in
typing
Vibrio colonies on TCBS media
• Possible bacteria:
V. cholera
• Confirmatory tests:
1. Serological typing
2. PCR
3. Biochemical reaction as
+ve cholera red reaction
• Disease caused by the
organism: cholera
• Type of the media:
selective media
Vibrio colonies on TCBS media
Fungal intoxication
Aspergillus spp. on Sabouraud’s
dextrose agar (SDA)
• Suspected toxin:
Ochratoxin
• Pathological effect of the
toxin: nephrotoxic,
immunosuppressive,
carcinogenic and neurotoxic
Aspergillus by lactophenol cotton
blue
Parasitology
Head of Taenia worm
• Classification: Cestodes
T. saginata (beef tape worm)
• mode of infection:
ingestion of larva in
undercooked meat beef)
• Disease : asymptomatic or
diarrhea
• diagnosis: detect egg in
stool
• treatment: praziquantel
Enterobius vermicularis (pin worm)
Enterobius vermicularis (pin worm)
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Classification: Nematodes
Infective stage: D shaped egg
Diagnostic stage: egg
Sensitive method for diagnosis:
adhesive anal tape technique.
• Habitat: caecum or large intestine
• Clinically: nocturnal anal itching
• Treatment: Mebendazole
Ascaris larva
Ascaris larva
• Classification: NEMATODES
• Habitat: small intestine and bile ducts
• Clinically: intestinal obstruction, biliary
obstruction
• Infective stage: egg
• Diagnostic stage: egg
• Treatment: Mebendazole
Blood culture
Blood culture
• Uses: Diagnose of
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enteric fever in the first week
Brucellosis or Malta fever
Bacteremia and septicemia
Infective endocarditis
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specimen: 5-10 cc venous
blood under aseptic
technique (at least 2 or 3
specimen taken from
different limb)
Blood culture
Principle:
1. Blood added to 50 cc nutrient broth (ratio 1/10 or 1/5) then
incubated at 37°C for 7 days
2. Each day the culture is examined for signs of bacterial growth
3. If signs of bacterial growth are detected sub-culture, (or daily
subculture), on blood, chocolate and Mac-Conkey agar were
done to isolate and identify the organism
4. If 7 days pass without isolation of any growth, reported as
negative sample
Blood culture
Signs of bacterial growth as
• Hemolysis
• Turbidity
• Surface pellicle
Advantage of big volume
• More nutrition for the
organism
• Dilute antibiotic if the
patient receiving antibiotic
THANKS