GIT-block Microbiology Lab. Dr./ Tamer Ata

Contents Bacterial enteritis Fungal intoxication Parasitological slides Blood culture

Bacterial enteritis

Bacterial enteritis Mostly Gram negative bacilli including Vibrio spp. Shigella spp. Salmonella spp. (food poisoning & enteritis) E. coli (EHEC O157/H7 & EPEC & ETEC& EIEC) 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? Biochemical reactions as API 20 E 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? Biochemical reactions as API 20 E 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: Serological typing PCR 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) 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 enteric fever in the first week Brucellosis or Malta fever Bacteremia and septicemia Infective endocarditis specimen: 5-10 cc venous blood under aseptic technique (at least 2 or 3 specimen taken from different limb)

Blood culture Principle: Blood added to 50 cc nutrient broth (ratio 1/10 or 1/5) then incubated at 37°C for 7 days Each day the culture is examined for signs of bacterial growth 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 If 7 days pass without isolation of any growth, reported as negative sample

Blood culture Signs of bacterial growth as Advantage of big volume Hemolysis Turbidity Surface pellicle More nutrition for the organism Dilute antibiotic if the patient receiving antibiotic

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