Introduction of Epidemiological Markers
Epidemiological markers are Important to analyze multiple isolates within a given species to determine whether they represent a single strain or multiple strains. The descendants of single isolation in pure culture comprise a strain. A single isolate with distinctive characteristic[s] may also represent a strain. Members of the same species that have small differences between them can be distinguished by additional methods. These species are then subdivided into subspecies, subgroups, biotypes, serotypes, variants, etc. The process of differentiating strains based on their phenotypic and genotypic differences is known as ‘typing’.
These typing methods are applied in the following sectors-
a. hospital infection control,
b. epidemiological studies,
c. and understanding the pathogenesis of infection.
Strain typing method:
It is mainly divided into 2 types
1. Phenotypic methods of detection epidemiological markers
a. Biotyping: The identification of different bacteria types based on reaction to biochemical tests.
b. Serotyping: A serotype is a term used to refer to a group of organisms within a species that have the same type and number of surface antigens.
c. Phage typing: Phage typing is a method used for detecting single strains of bacteria.
d. Multi Locus Enzyme Electrophoresis (MLEE): It is a technique in molecular biology for the typing of multiple loci.
e. Antibiotic Sensitivity test (AST): It uses widely for evaluating antibiotic resistance and determining patient treatment plans in clinical settings.
f. Pyocin typing: It is a bacteriocin of Pseudomonsa aeruginosa that kills other strains of the same species.
g. Bacteriocin typing: Bacteriocins are proteinaceous or peptidic toxins produced by bacteria to inhibit the growth of similar or closely related bacterial strains or strains.
h. Dienes typing for Proteus species: After inoculation of two different strains of Proteus species at different places of the same non-inhibitory medium (blood), swarming of the two strains remains separated by a narrow visible furrow. However, in the case of two identical strains of proteus, the swarming of two coalesce without signs of demarcation and this condition is the Dienes phenomeno. It uses to determine whether the same or different strains of Proteus and therefore use as strain typing in epidemiology.
i. Slime test for Staphylococci: The production of slime material in staphylococci produces in vivo colonization. It can detect in vitro by determining the type of colony morphology produced in Congo red agar. Bacteria in the biofilm exhibit increased resistance to components of the host’s immune system and antimicrobial drugs. Biofilm forming ability has increasingly been recognized as an important virulence factor in this organism.
k. Syngersitic hemolysis: Synergistic hemolysis phenomenon is common in alpha-toxin-producing Clostridium perfingens, streptococcal CAMP factor in presumptive streptococcal grouping i.e. group B streptococci( Streptococcus agalactiae), Listeria monocytogens in association with Staphylococcus aureus.
2. Genotypic methods of detection epidemiological markers
b. Pulse Field Gel Electrophoresis (PFGE)
b. Restriction Fragment Length Polymorphism (RFLP)
c. Chromosal REA
d. Plasmid profiling
e. Arbitrarily primed PCR
Further Readings on Epidemiological markers