Epidemiological marker-(Phenotype and Genotype)




Epidemiological marker-(Phenotype and Genotype)
Epidemiological marker-(Phenotype and Genotype)
  • Typing is the integral part of epidemiological investigation.
  • It is the method of identification of organism upto the strain level (origin).
  • Two broad categories:
  • Phenotypic method (Phenotyping)
  • Genotypic method (Genotyping)

Characteristics of epidemiological marker:

  • Typeability
  • Reproducibility
  • Descriminatory power
  • Ease of performance
  • Ease of interpretation

Phenotypic method:

  • Phenotyping method is based on the expressed characteristics.
  • Characteristics of organism that is used for typing is marker.
  • Organism of same source origin or source- type/strain.
  • Phenotyping includes;
    • Biotyping
    • Serotyping
    • Phage typing
    • Antibiogram typing
    • Bacteriocin typing
  • Biotyping:
    • Classified on the basis of physiological or bio-chemical tests.
    • Commonly used characters are morphology, cultural characteristics, biochemical reactions (nitrate reduction test, indole test, pigment production, H2S production, carbohydrate fermentation)
  • Serotyping:
    • Typing method done by the use of hyper-immune anti-sera or purified immunoglobulin to detect specific antigen.
    • Serotyping is generally done for Salmonella, Klebsiella, etc. for detection of O-antigen, H-antigen, R-antigen, K-antigen, etc.
  • Phage typing:
    • Bacteriophage typing identify strains by the pattern of specific set of phages.
    • Generally used for Staphylococcus aureus and for Salmonella Typhi.
  • Antibiogram typing:
    • Typing method on the basis of antibiotic susceptibility or resistance pattern.
  • Bacteriocin typing:
    • On the basis of bacteriocin production.

Genotyping method:

  • Genotyping includes;
  • Plasmid profiling:
    • On the basis of no. of plasmid, size of plasmid in the organism.
  • G+C ratio:
    • Same strains have similar G+C ratio.
  • Ribotyping:
    • 16sRNA is highly specific for organism.
  • Restriction endonuclease enzyme:
    • Whole genome is fragmented using same set of restriction endonuclease enzyme and analyzed.
  • RFLP (Restriction fragment length polymorphism):
    • Particular enzyme is used to fragment whole genome.
  • PFGE (Pulse field gel electrophoresis):
    • Electric field is applied diagonally in two field.
    • The electric field is applied and then pulsed and re-applied perpendicularly.

Epidemiological marker-(Phenotype and Genotype)