This document discusses techniques for differentiating between strains of microorganisms based on their phenotypic and genotypic differences, known as typing. Phenotypic techniques detect expressed characteristics, while genotypic techniques analyze genetic elements directly. Some common typing techniques mentioned are biotyping, phage typing, serotyping, antibiogram typing, plasmid analysis, restriction endonuclease analysis, pulsed-field gel electrophoresis, and nucleotide sequence analysis.

1. Dr Vinodh Kumar,O.R
Division of Epidemiology
ICAR-Indian Veterinary Research Institute
Izatnagar, Uttar Pradesh, India

2. Analyse multiple isolates
within a given species
Study the small differences
between the same species.
 In epidemiological
studies, and to study the
pathogenesis of infection.
The process of
differentiating strains
based on their
phenotypic and
genotypic differences is
known as 'typing'.

3. Phenotypic techniques
detect characteristics expressed by the microorganism
Genotypic techniques
direct DNA-based analysis of chromosomal or
extrachromosomal genetic elements

4. Based on size, staining properties, biochemical
properties and antigenic properties
Biotyping
Phage typing
Bacteriocine typing
Serotyping
Antimicrobial Susceptibility Typing (Antibiogram):
Protein typing
Multilocus Enzyme Electrophoresis (MLEE)

5.  Based on study of the microbial DNA, the
chromosome and plasmid, their composition,
homology and presence or absence of specific genes
Plasmid analysis
Restriction Endonuclease Analysis
PFGE of Chromosomal DNA
Southern blot analysis
Nucleotide Sequence Analysis

6. Metabolic activities expressed by an isolate, colonial
morphology and environmental tolerances
Manual or automated
referred as ‘biotypes’

7. Based on the pattern of resistance or susceptibility to
a standard set of bacteriophages
 referred as ‘phage types’

8.  Based on the susceptibility to a set of bacterial
peptides (bacteriocine) produced by certain bacteria.
Bacterocines produced by a particular strain are
usually only active against other strains of the same
species.

9.  Based on antigenic determinants expressed on the
cell surface
referred as ‘Serotypes’

10.  Based on comparison of different isolates to a set of
antibiotics

11. Based on major or minor differences in the range of
proteins made by different strains
comparisons among multiple strains are difficult

12. The isolates are analysed for differences in the
eletrophoretic mobilities of a set of metablolic
enzymes
referred to as ‘electromorph’

13.  Based on the number and sizes of plasmids carried by
an isolate
Can be determined by preparing a plasmid extract
and subjecting to gel electrophoresis

14. A restriction endonuclease enzymatically cuts DNA at
a specific nucleotide recognition sequence
Bacterial DNA is digested with endonucleases that
have relatively frequent restriction sites

15. A variation of agarose gel electrophoresis
The orientation of the electric field across the gel is
changed periodically
Large fragments can be effectively separated by size

16. Detect only the particular restriction fragment
fragments transferred to nitrocellulose membranes
and detected by labelled DNA probes
Variations in the number and sizes of the fragments
Ribotyping:
 Blotting of restriction enzyme digestion of rRNA,
and one or more tRNAs

17. Genotype information
Automated techniques to sequence
Possible to compare multiple isolates.