MICROBIAL TYPING

• Microbial typing refers to the characterization of microorganisms beyond their species level.

CHARACTERISTICS OF TYPING METHODS:

1. TYPEABILITY: It refers to the ability of the method to type and generate a result for each isolate to be tested.

2. REPRODUCIBILITY: It refers to the ability of the method to produce similar results when tested repeatedly in different laboratory centres.

3. DISCRIMINATIVE POWER: It refers to the ability of the method to generate distinct units of information making a clear differentiation between the types at the subspecies level.

4. PRACTICALITY: It refers to ease of use and interpretation, cost and affordability.

CLASSIFICATION OF MICROBIAL TYPING:

• Typing methods are broadly categorized into 2 types which are as follows:

1. Phenotypic method: detects characteristics expressed by microorganism.

2. Genotypic method: direct DNA- based analysis of chromosomal or extrachromosomal genetic elements.

PHENOTYPIC METHODS:

1. BACTERIOPHAGE TYPING:

Strains of an organism can be further differentiated into subspecies level based on their sensitivity to bacteriophages. It is obsolete now.

2. BACTERIOCIN TYPING:

Bacteriocin is an antimicrobial- like proteinaceous substance produced by one bacterium that inhibits other strains of the same or other closely related bacteria.

Example: Colicin secreted by Gram -negative bacterium and megacine secreted by Gram positive bacterium.

3. BIOTYPING:

It refers to intra-species classification based on different biochemical properties of organisms.

4. ANTIBIOGRAM TYPING:

It refers to differentiating organisms into individual groups based on their resistance pattern to different antimicrobials.

5. SEROTYPING:

It refers to a typing method based on the antigenic properties of an organism.

GENOTYPIC METHODS:

• It includes the following methods:

1. Restricted Fragment Length Polymorphism(RFLP)
2. Ribotyping
3. Pulse Field Gel Electrophoresis(PFGE)
4. Amplified Fragment Length Polymorphism(AFLP)
5. Sequencing based methods which include Nucleotide sequencing and Whole genome sequencing.

• In general, genotypic methods are more reliable and have better reproducibility and discriminative power than phenotypic methods. They are expensive in nature.
• It is used to determine multidrug resistant pathogens.

APPLICATIONS OF MICROBIAL TYPING:

• It is an important tool for hospital microbiologists and epidemiologists.
• It is used to determine relatedness between different microbial strains of same species and thereby it helps to:

1. Investigate an outbreak.
2. Determine the source and route of infection.
3. Differentiate virulent strains from avirulent strains of the same species.
4. Differentiate between recurrence and infection with new strain.
5. Trace cross infection.