GI Bacteriology

• The first thing we do is macroscopic examination (by naked eyes): so we can check the color:

        If it is yellow so it is normal.• It could be red: this means that

there is bleeding or mucus

        Some times it has fresh red color: this is maybe due to injury in the opening of anus (out side the bowel).

        If it is black this means there is hemorrhage in the stomach. (Very important).

Microscopic examination

• It is simple way, you take glass slide, and put one drop of saline, with a stick we touch the stool and then we spread it on the slide, then we have to put a cover slip.

• We can use the slide to look for RBCs, WBCs, or parasites (by adding Iodine or something else).

• We check each field and if the number of WBCs more than 10/high power field that means there is an infection. (High power field = 40X).

• We look for more than one field and take the average of them.

The bacteria that cause infections to GIT are:

1.  Salmonella

2.    Shigella3.    Helicobacter pylori4.    Campylobacter jejuni All of them cause diarrhea,

so we do the culture to know which one of them is the causative agent of the infection.

** E.coli is considered in adults as normal flora, but in children it is considered as pathogenic.

Salmonella spp.

Salmonella spp.

Colonies on SS Agar

Show Black

Discoloration,

Indicative of H2S

Formation.

#G –ve , rod shape,

facultative anaerobic.

Salmonella spp.

• IMViC - + - -• KIA: K/A with H2S in

between the slant and the butt.

• Cause food poisoning• Diarrhea and typhoid

fever.

Shigella spp.

G –ve, rod shape, facultative anaerobic.

IMViC : (+) + - -

KIA : K/A

Cause shigellosis and dysentery.

Proteus spp.

Typical Appearance of

Swarming Motion of

Proteus spp. on Agar Surface3

main characteristics of

proteus:

1 -Swarming:

2 -Urease test +ve (the only

one that has this feature)

3 -KIA : K/A/ H2S ,

Proteus spp.

  3 -KIA : K/A/ H2S,

Clostridium spp.

Staining Clostridium

spp. with Shaeffer-

Fulton Method

Positively Stains the

Endospores

Escherichia coli

• E. coli Colonies on MacConkey Agar Show Pink Discoloration, Indicative of Lactose Fermentation.

Escherichia coli

E. coli Gives an A/A

Pattern when Grown in

both

Kligler-Iron Agar (KIA)

and Triple Sugar-Iron

(TSI) Agar

Escherichia coli

E. coli Shows a + + - - IMViC Pattern

Staphylococcus aureus

Typical Appearance of Gram-Positive Cocci in

Clusters

Staphylococcus aureus

S. aureus Shows a Positive Coagulase Reaction

Vibrio cholerae

• Late fermentation occurred on TCBS plate representing V. cholerae

Campylobacter jejuni

• Campylobacter jejuni infection causes cramping, diarrhea, abdominal pain and fever within 2 to 5 days after a person has been exposed to the organism. Campylobacter jejuni is one of the most common bacterial causes of diarrhea.

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