Bacterial Culture Media Flashcards
Media is classified based on?
- Chemical constituents
- Physical nature - liquid, semi solid, solid
- Function - supportive, enriched, selective, differential
Chemical constituents categories
Defined - All conc’ns + components known
Complex - Ingredients + conc’ns unknown
Media types - diff functions
Supportive - supports any organisms e.g. soy agar
Enriched - general purpose media enriched with blood; increase num of microbes to detectable levels
—heat to release nutrients from blood
Selective - allows growth of particular organisms and inhibits growth of others
Differential - diff groups based on biological characteristics
Examples of selective media
- MacConkey agae has Bile salts - allow certain microorganisms to grow e.g. E coli
- eosin Y and methylene blue - inhibits gram +ve bacteria
- Bile salts and crystal violet - inhibits gram +ve bacteria
- 7.5% NaCl - selects Staph spp.
Examples of differential media
Blood agar - haemolytic vs non-haemolytic
—> (alpha haemolysis - strep haemolysis,
beta haemolysis - strep viridians,
gamma haemolysis - enterococcus faecalis)
MacConkey agar (selective+differentiating) - lactose fermenter - E coli (red) vs non-fermenter (pale) - salmonella
Anaerobe cultures requirements
Culturing anaerobes requires:
- -appropriate media = low oxidation-reduction potential
- -substrates obtained by microorganisms in their natural habitat
Anaerobic culture - specimen
Throat, rectal swabs, urine, bronch washes, cervico-vaginal mucosal swabs, sputum
Liquid media - purpose
Liquid media provide greater sensitivity for the isolation of small numbers of microorganisms
Growth in liquid media also can be ordinarily quantitated (T/F)
False
Bacteria grown in liquid cultures often form colloidal suspensions (T/F)
True
Examples of liquid media
Peptone water, nutrient broth, glucose broth, brain-heart infusion broth, alkaline peptone water, selenite F broth, Tetrathionate broth, Robertson’s cooked meat broth
Peptone water use
Sugar fermentation test, indole test
Nutrient broth use
Routine culture
Glucose broth use
Blood culture, Fastidious organisms e.g. Streptococci
BHI broth use
Whole blood, bone marrow, body fluid culture
Alkaline peptone water use
Enrichment media - Vibrio
Selenite F Broth use
Enrichment media - Salmonella + shigella
Specimen: feces
Tetrathionate Broth use
Salmonella culture
Specimen: feces
Robertson’s cooked meat broth use
Anaerobic bacterial culture
Solidifying agent in culture media
Agar is used as a solidifying agent in most culture media.
Solid media can be altered via agar in what way?
By varying the concentration of agar, it is possible to make the medium solid or semisolid.
Solid media vs liquid media
Solid media function
Solid media
- less sensitive than liquid media,
- isolated colonies that can be quantified and identified
Examples of solid media
Nutrient agar, MacConkey agar, blood agar, Chocolate agar, Deoxycholate citrate agar, Thiosulfate citrate bile salt sucrose agar, Loeffler’s serum slope, Lowenstein-Jensen medium
Nutrient agar use
Routine culture
What solid media cultures gram negative bacteria e.g. E coli?
MacConkey agar
Blood agar use
Routine culture, culture of fastidious organisms e.g. Streptococci
What solid media cultures H influenzae and Neisseria?
Chocolate agar
What solid media cultures Vibrio cholerae?
Thiosulfate citrate bile salt sucrose agar
Solid media responsible for culture of Salmonella spp and Shigella spp
Deoxycholate citrate agar
Solid media responsible for culture of Corynebacterium diptheriae
Loeffler’s serum slope
Solid media responsible for culture of Mycobacterium tuberculosis
Lowenstein-Jensen medium
Selective media examples
Mannitol salt agar, Thayer-Martin medium, MacConkey agar medium, Thiosulfate citrate bile salt sucrose agar, Charcoal yeast extract Lowenstein Jensen media Sabouraud's dextrose agar
Selective media that
- inhibits streptococcus spp and
- facilitates growth of staphylococcus spp
Mannitol salt agar
Selective media that
- inhibits gram +ve cocci and
- facilitates growth of Neisseria spp
Thayer-Martin medium
Selective media that
- inhibits gram positive cocci and
- tests lactose fermentation
MacConkey agar medium
Selective media that
- inhibits enteric bacilli and
- tests sucrose fermentation
Thiosulfate citrate bile salt sucrose agar
Selective media that
- inhibits gram +ve cocci and
- facilitates growth of Legionella spp
Charcoal yeast extract
Selective media that
- inhibits cocci and
- facilitates growth of Mycobacterium spp
Lowenstein Jensen media
Selective media that
- inhibits most bacteria and
- facilitates growth of most fungi
Sabouraud’s dextrose agar
Which of the three tests conducted in this identification process did not require the use of an incubator?
- Coagulase test
- Catalase test
- Novobiocin sensitivity test
- Mannitol salt agar plate
Catalase test
