Identification of Bacteria

• Phenotypic methods

- Bacterial shapes/size

- colony characters

- microscopically examination

- biochemical tests

​

• Molecular methods

​

• Serology

Phenotypic characteristics

1. Morphology

A. Shape and size

B. Cultural characteristics

a) Colony morphology

- color

- shape (circular, irregular or radiate)

- surfaces (smooth, wavy, rough, granular)

- size

- elevation (flat, elevated, low convex, convex, umbonate)

- edges (entire, undulate, crenated, lobate, ciliate)

- opacity (translucent, transparent, opaque)

- consistency (mucoid, firm, friable, membranous, butyrous)

Contd.. Morphology

b) Growth in liquid media

in peptone water, nutrient broth, and BHI, bacterial growth appears in following forms

​

i) Turbid

​

ii) Deposit formation

​

iii) Surface pellicle formation- aerobes grow on surface of media.

Contd.. Morphology

C. Microscopically

- Stained film (Gram, Acid fast)

​

- Unstained film (hanging drop)

2. Resistance

- to antibiotic, chemotherapeutic agents and bacteriocin

​

- temp.

​

- disinfectant

-

3. Metabolism

- aerobic or anaerobic growth

​

- oxygen and carbondioxide requirements

​

- production of pigment, toxins and hemolysins

-

Biochemical test

1. Sugar fermentation

2. Voges Proskauer (VP) test

3. MR test

4. Citrate utilization

5. Indole production

6. H2S production

7. Phenylalanine deaminase test

​

Biochemical test

8. Urease

9. Oxidase reaction

10. Catalase production

11. Nitrate reduction test

12. Egg yolk reaction

13. Growth in presence of KCN

14. Litmus milk

15. Composite media

16. Amino acid decarboxylase test

4. Antigenic structure

- somatic

- flagellar

​

5. Pathogenicity test

- ID50

- LD50

​

6. Serological tests

- agglutination

- precipitation

- serum neutralization

​

7. Molecular diagnostics

- PCR

​