- Microbial typing refers to the characterization of microorganisms beyond their species level.
CHARACTERISTICS OF TYPING METHODS:
- TYPEABILITY: It refers to the ability of the method to type and generate a result for each isolate to be tested.
- REPRODUCIBILITY: It refers to the ability of the method to produce similar results when tested repeatedly in different laboratory centres.
- 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.
- 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:
- Phenotypic method: detects characteristics expressed by microorganism.
- Genotypic method: direct DNA- based analysis of chromosomal or extrachromosomal genetic elements.
- BACTERIOPHAGE TYPING:
Strains of an organism can be further differentiated into subspecies level based on their sensitivity to bacteriophages. It is obsolete now.
- 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.
It refers to intra-species classification based on different biochemical properties of organisms.
- ANTIBIOGRAM TYPING:
It refers to differentiating organisms into individual groups based on their resistance pattern to different antimicrobials.
It refers to a typing method based on the antigenic properties of an organism.
- It includes the following methods:
- Restricted Fragment Length Polymorphism(RFLP)
- Pulse Field Gel Electrophoresis(PFGE)
- Amplified Fragment Length Polymorphism(AFLP)
- 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:
- Investigate an outbreak.
- Determine the source and route of infection.
- Differentiate virulent strains from avirulent strains of the same species.
- Differentiate between recurrence and infection with new strain.
- Trace cross infection.