Laboratory Diagnosis of Infectious Diseases

Flashcards covering key vocabulary related to laboratory diagnosis of infectious diseases, including microscopy, culture techniques, and specific media.

Diagnostic Microbiology

A process used to determine the cause (pathogen) of an illness, potentially involving isolation and identification of the pathogen.

Microscopy

A category of diagnostic tests involving direct microscopic examination to determine the presence and potentially identify organisms.

Direct Examination (Wet Mount)

A method of examining specimens directly, potentially with the addition of substances like KOH or India ink.

Calcofluor White

Stains cellulose and chitin and is used for identifying fungi.

Dark Field Microscopy

A microscopy type where the specimen is brightly illuminated against a dark background, increasing contrast.

Phase Contrast Microscopy

Microscopy that uses parallel beams of light to amplify differences in light diffracted by the specimen and background.

Fluorochromes

Dyes that absorb short-wave light and emit energy at a higher wavelength (visible light).

Direct Immunofluorescence

Detects antigens by conjugating a fluorophore to a primary antibody.

Indirect Immunofluorescence

Uses two antibodies, where the fluorophore is conjugated to a secondary antibody for increased sensitivity.

Electron Microscopy

Microscopy that uses magnetic coils to focus electrons, providing very high resolution and allowing visualization of viral particles.

Transmission electron microscope

Electron microscopy where light passes through the specimen, 2D.

Scanning electron microscope

Electron microscopy where electrons bounce off the surface: 3D effect

Purpose of Culturing Specimens

Growing enough of an organism to use in identification tests or antibiotic susceptibility testing.

Routine Culture Conditions

Culture conditions that include aerobic conditions at 37°C for 24 hours, typically using blood agar.

Non-Selective and Enriched Media

Culture media that support the growth of most organisms, including many fastidious organisms.

Selective Media

Culture media that inhibits the growth of unwanted organisms.

Differential Media

Culture media that show characteristic reactions.

Specialised Media

Culture media with a composition designed specifically for particular microbes, which may not grow without specific supplements.

CHROMID

Commercial media containing specific chromogenic substrates that cause microbes to produce specific colors after incubation.

Anaerobic

Conditions where organisms cannot tolerate oxygen; will die.

Capnophilic

A condition with 5% CO2, suitable for capnophilic organisms such as Streptococcus pneumoniae.

Microaerophilic

Prefer ~5% O2 some also like ~10% CO2, use candle jar.

Blood Culture Systems

A system used to detect organisms in the blood, often involving automated machines that signal positive growth.

Viral Culture – Cell Monolayers

Viruses are cultured in monolayers of (usually mammalian) cells grown on the walls of flasks.

Continuous Cell Lines

Cell lines that can be maintained indefinitely in the lab; immortalised.

Primary Cell Lines

Cell lines that will die out after 20-80 passages.

Cytopathic Effect

The damage or structural changes caused to host cells by viral invasion.

Sabouraud’s Dextrose Agar

Common media for fungi that can be made selective and inhibits bacteria.

Corn Meal Agar

Agar that is useful for suppressing vegetative growth and inducing chlamydospore formation by Candida albicans.

Dimorphic Growth

The ability of some fungi to switch between yeast and mold forms depending on temperature.