PRACTICAL

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PRACTICAL

• Identification of unknown bacterium

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Why species level identification required?

• To know which species is involved in the
  particular condition
• To know the subspecies
• To further know the types
• Immunotypes, serotypes, chemotypes etc
• Epidemiological studies

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Basic steps to follow
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Pure culture follow up-Day 1
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Pure culture follow up-Day 1
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First day preliminary findings

• Growth characteristics
• Gram stain
• Catalase
• Oxidase
• Motility

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Presumptive follow up
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Members of enterobacteriaceaeoxidase Negative
Non enterobacteriaceae Oxidase positive

• Escherichia
• Klebsiella
• Citrobacter
• Salmonella
• Shigella
• Proteus
• etc

Vibrios Pseudomonas etc
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Members of enterobacteriaceaeoxidase
Negative(example)

• LF (ONPG) NLF
• Escherichia Salmonella
• Klebsiella Shigella
• Citrobacter Proteus

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A gram negative rod on BA/Macconkey agars
Non hemolytic, moist, irregular, flat, centrally
raised, 3-5 mm colonies,
Lactose fermenting, Flat,irregular centrally
raised, moist 2-4 mm colonies
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Tests to read on second day

• Check whether the culture is pure
• Repeat catalase, oxidase,gram and motility to
  confirm previous days findings

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Biochemical tests
TSI A/A, Gas , H2S Negative SIM H2S,Neg,
Indole Positive., Motile Motility (PW) Motile
It could be ESCHERICHIA, CITROBACTER,OR
ENTEROBACTER
Glucose Positive (Acid and
Gas) Lactose Positive Sucrose Negative /
Positive Mannitol Positive Indole
Positive MR Positive VP Positive Citrate
Negative Urease Negative
Macconkey LF Gram Gram Negative rods Catalase
Positive Oxidase Negative
LAO - Melonate - KCN _
So it is Escherichia coli
One of the members of Enterobacteriaceae
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For further details Contact

• Jasmn98