Chapter 7: Overview of Conventional Cultivation and Systems for Identification

Flashcards covering bacterial cultivation, media types, environmental growth requirements, identification methods (genotypic and phenotypic), colonial morphology, enzymatic tests, and MALDI-TOF MS.

Bacterial Cultivation

The process of growing and isolating microorganisms present in a clinical specimen to determine the cause of infection and obtain sufficient growth for identification and characterization.

Liquid Media (Broth)

A type of growth media where growth is indicated by turbidity, nephelometry, or pH indicators.

Solid Media

Growth media with an added solidifying agent like agar, which provides for isolation of pure colonies and identification of colony morphological characteristics.

Semi-Solid Media

Broth containing a small amount of agar, creating a diffusion gradient and restricting oxygen diffusion to identify optimal oxygen concentrations for growth.

Enrichment Media

Contains specific nutrients or chemicals that enhance the growth of particular pathogens, such as buffered charcoal-yeast extract agar for Legionella pneumophila.

Nutritive Media

Supports the growth of most non-fastidious organisms, an example being tryptic soy agar.

Selective Media

Inhibits all organisms except those 'selected' by containing compounds like bile salts, dyes, and antibiotics (e.g., phenylethyl alcohol agar).

Differential Media

Allows colonies of one species to be differentiated from other bacteria growing on the plate based on metabolic visible characteristics using an indicator dye or chemical reaction (e.g., MacConkey agar).

Environmental Requirements for Bacterial Growth

Crucial factors include oxygen and carbon dioxide availability (most pathogens are facultative anaerobes), temperature (35-37°C for most pathogens), pH (near neutral 6-7.5), and moisture content.

Isolation Streak Technique

A common bacterial streaking technique used to obtain isolated colonies for enumeration and characterization.

Genotypic Criteria (Bacterial Identification)

Characterization of the bacterial genome using molecular techniques to detect the presence of specific genes, which does not necessarily indicate a viable organism.

Phenotypic Criteria (Bacterial Identification)

Observable physical characteristics for bacterial identification, including microscopic morphology, staining characteristics, colonial macroscopic morphology, metabolic characteristics, and antimicrobial susceptibility.

Colonial Morphology

Characterization of bacterial colonies based on size, pigmentation, shape, density/opacity, surface texture, consistency, and changes in the agar (e.g., hemolysis, pH indicators).

Catalase Test

An enzymatic test that differentiates staphylococci from streptococci by detecting the production of catalase, which catalyzes hydrogen peroxide into water and oxygen, causing effervescence.

Oxidase Test

An enzymatic test that differentiates groups of gram-negative bacteria by detecting oxidase, indicated when it reacts with 1% tetra-methyl-p-phenylenediamine dihydrochloride.

Urease Test

An enzymatic test that helps identify some members of the Enterobacteriaceae family by detecting urease, which hydrolyzes urea into ammonia, water, and carbon dioxide.

Indole Test

An enzymatic test that presumptively identifies Escherichia coli by detecting tryptophanase, an enzyme that degrades tryptophan into pyruvic acid, ammonia, and indole.

Pyrrolidonyl Arylamidase (PYR) Test

An enzymatic test that identifies Enterococcus and Streptococcus sp. by detecting 1-pyrroglutamyl-aminopeptidase, which hydrolyzes PYR to produce β-naphthylamine.

Hippurate Hydrolysis Test

An enzymatic test that identifies Streptococcus agalactiae, Campylobacter jejuni, and Listeria monocytogenes by detecting hippuricase, which hydrolyzes hippurate to produce glycine (deep purple color).

MALDI-TOF MS (Matrix-Assisted Laser Desorption Ionization Time of Flight Mass Spectrometry)

A state-of-the-art technology for rapid, accurate identification of common bacteria and yeast by analyzing their protein spectrum based on the time it takes for ionized proteins to travel through a vacuum.

Rapid Identification Schemes

Schemes that utilize a series of tests, often starting with Gram stain morphology, to quickly identify microorganisms, typically differing from conventional schemes in speed and workflow.

Bacterial Susceptibility

The characteristic of bacteria being affected or inhibited by antimicrobial agents.

Bacterial Resistance

The characteristic of bacteria not being affected or inhibited by antimicrobial agents.