This slide show describes about different steps involved in the identification of unknown bacterial samples

1. STEPS TO IDENTIFY UNKNOWN
BACTERIAL SAMPLES (PART-1)
Dr C R Meera
Assistant Professor & HOD
Department of Microbiology
St. Mary’s College Thrissur

2. Steps to identify unknown bacterial samples; Dr C R Meera, St.Mary’s College, TCR
Classification Vs Identification ?
• Classification is the separation of organisms into
distinct groups
• Identification is the determination of correct
place of an organism in a previously established
plan of classification

3. • Bergey’s Manual has been the internationally
accepted reference for the identification of
bacteria since 1923.
• Bergey’s Manual of Systemic Bacteriology
arranges related bacteria into 33 groups called
sections
• Sections - Morphology, staining reactions,
nutrition, cultural characteristics, physiology,
cellular chemistry and biochemical test
results for specific metabolic end products.
Steps to identify unknown bacterial samples; Dr C R Meera, St.Mary’s College, TCR

4. Steps to identify unknown bacterial samples; Dr C R Meera, St.Mary’s College, TCR
Steps involved in the Identification of bacteria
• Morphological
• Cultural characteristics
• Biochemical tests

5. Steps to identify unknown bacterial samples; Dr C R Meera, St.Mary’s College, TCR
1. Morphological
Shape : Spheres, short rods, long rods,
commas, spirals, filaments,
Arrangement : Single, pairs, chains, clusters
Capsules : Present or absent
Gram stain : Positive or negative
Spore stain : Non spore or spore former
(Central, Sub terminal or Terminal spore)
Motility : Motile or non motile
Courtesy:microbeonline.com

6. Steps to identify unknown bacterial samples; Dr C R Meera, St.Mary’s College, TCR
2. Cultural characteristics
On Nutrient agar plate
Colonies : Golden, yellow, white,
glistening
Growth : Absent (0), slight (+),
moderate (2+), abundant (3+)
Form : Circular, irregular, rhizoid
Margins : Entire, lobate, undulate, serrate,
filamentous
Elevation : Flat, raised, convex, umbonate
Density : Opaque, translucent

7. Steps to identify unknown bacterial samples; Dr C R Meera, St.Mary’s College, TCR
2. Cultural characteristics
In Nutrient broth media
Surface growth: Ring, pellicle, none
Turbidity : Heavy, slight, none
Sediment : Abundant, scanty, none, granular, flocculent

8. Steps to identify unknown bacterial samples; Dr C R Meera, St.Mary’s College, TCR
2. Cultural characteristics
On Special media
a) Differential / Selective media
Egs:
Mc Conkey agar :Inhibit G +ve bacteria; differentiate lactose
fermenters and non lactose fermenters
Mannitol salt agar: Promote halopiles like Staphylococcus,
inhibit the non halophiles
Eosin Methylene Blue (EMB) agar :Inhibit G +ve bacteria;
differentiate enteric lactose fermenters and non
fermenters as well as identify colon bacillus, E. coli
b) Enriched media
Eg:
Blood agar :Differentiate hemolytic microorganisms like
Streptococcus spp. from non hemolytic species
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9. Steps to identify unknown bacterial samples; Dr C R Meera, St.Mary’s College, TCR
3. Biochemical Tests
a) Carbohydrate fermentation test: Red to yellow; with or without gas
b) IMViC tests
Indole production test : Formation of red layer
Methyl-red (MR) test : Presence of red color
Voges - Proskauer (VP) test : Deep rose (pink) color
Citrate utilization test : Color change of media from green to blue
c) Urease test : Red to deep pink
d) Nitrate reduction test : Red color
e) Catalase activity : Bubbles on the release of free oxygen gas (O2)
f) Oxidase test : Development of pink, then maroon and finally
black coloration on the bacterial colonies
g) Triple Sugar Iron (TSI) test : Alkaline (red) or/ acidic (yellow) color change
in slant and butt region; with or without gas
production

10. Steps to identify unknown bacterial samples; Dr C R Meera, St.Mary’s College, TCR