Microbial Identification Methods

Microbial Identification Methods

• Phenotypic Methods: Observe organism appearance and behavior. Examples include enzymatic activities, environmental conditions for growth, and susceptibility to antibiotics.

• Immunologic Methods: Detect specific antibodies to a suspected pathogen in a patient sample. This often involves faster laboratory kits for identification.

• Genotypic Methods: Examine genetic material for identification. These methods are often more precise and automated, and don't always require growth of the microorganism. They can identify viable, non-culturable microbes.

Specimen Collection

• Specimen collection success depends on proper techniques. Aseptic techniques (free of microbes) are crucial, such as keeping containers and tools sterile. Sample only the infected site, avoiding surrounding areas.

Phenotypic Methods (Detailed)

• Immediate Direct Examination: Microscopic observation is a rapid method for determining characteristics. Common stains include Gram stain and acid-fast stain.

• Selective and Differential Growth: Specialized media can encourage growth of specific pathogens present in small numbers. Selective media allows only target bacteria to grow, while differential media visually distinguishes microbes.

Biochemical Testing

• Physiological reactions to nutrients & substrates of bacteria provide evidence of the enzyme systems present in a species. The Mycobacterial Growth Indicator Tube (MGIT) detects slow-growing mycobacteria (like Mycobacterium tuberculosis).

Immunologic Methods (Serology)

• In vitro testing of serum, urine, cerebrospinal fluid, or tissue samples for specific antibodies.

• Immunochromatography (Lateral Flow Test): Used for rapid tests, like pregnancy tests and COVID-19 tests, as they detect antigens or antibodies in a sample.

• Antibody Titers: Determine the concentration of antibodies in a sample. Used to diagnose autoimmune disorders, determine past exposures, and identify specific bacterial strains. Methods including titration to dilutions.

Genotypic Methods (PCR)

• Polymerase Chain Reaction (PCR): Creates many copies of DNA or RNA to identify microbes quickly.

• Hybridization: Analyzes genetic material segments for identification. Probes (segments of DNA or RNA) can be used in a process called Fluorescence in situ hybridization (FISH) to identify a microbe.

Additional Methods

• Electrophoresis: Separating antibodies and antigens using electrophoresis to detect their presence.

• Enzyme-Linked Immunosorbent Assay (ELISA): Visualizes antigen-antibody reactions, commonly used in clinical laboratory diagnosis. Relies on solid supports (like microtiter plates).