What is the purpose of bacterial culture?
To obtain a pure bacterial isolate for examination and identification.
Which features can be examined in bacterial cultures?
Colony morphology, microscopic appearance, biochemical properties, antibiotic resistance, serotype, MALDI-TOF results, and PCR-detected genes.
Which bacteria are unculturable on nutrient media?
Mycobacterium leprae, Treponema pallidum, and obligate intracellular Chlamydia spp.
What pH range is optimal for bacterial growth?
An optimal pH of 7.2–7.4.
How are bacteria classified by their atmospheric requirements?
As aerobic, microaerophilic, capnophilic, obligately anaerobic, or facultatively anaerobic.
What is the optimal growth temperature range for mesophilic bacteria?
30–40°C.
What temperature can psychrotrophic bacteria grow at?
Sometimes close to 0°C.
What is the maximum sodium chloride tolerance for Vibrio spp.?
Up to 3% sodium chloride.
What is the maximum sodium chloride tolerance for Staphylococcus spp.?
Up to 10% sodium chloride.
At what temperature can Listeria grow?
Listeria can grow at 4°C.
What pH can Enterococcus spp. tolerate?
Enterococcus spp. tolerate pH 9.6.
How does an anaerobic culture system create an anaerobic atmosphere?
It uses an envelope that generates hydrogen and carbon dioxide.
What verifies the anaerobic condition in the culture system?
An indicator that changes colour.
What catalyst is used in an anaerobic culture system?
A palladium catalyst.
What are liquid media used for in microbiology?
Enrichment, selective growth, and biochemical tests.
What agar concentration do semisolid media contain?
0.1–0.5% agar.
What are solid media with 1.5–2% agar used to examine?
Single colonies and colony morphology.
Name three examples of liquid culture media.
Peptone water, brain-heart infusion, and meat-peptone broth.
Where can solid media be placed for microbial culture?
In Petri dishes or tubes as slant agar.
What does a selective medium do in microbiology?
It favours a particular organism by suppressing other bacteria.
How does an enrichment medium typically multiply pathogens?
It uses liquid broth to multiply pathogens present in low numbers before agar inoculation.
What feature allows a differential medium to distinguish organisms?
It contains a diagnostic compound or coloured indicator.
Name a basic component of culture media besides peptone and water.
Additional nutrients such as minerals, amino acids, sugars, vitamins, or extracts.
What solidifying agents are commonly used in culture media?
Agar or gelatin.
What is chocolate agar made from?
Heated blood agar with lysed blood cells.
Which substances are released from lysed blood cells in chocolate agar?
NAD and hemin.
Which bacteria require NAD and hemin from chocolate agar?
Haemophilus and Actinobacillus species.
What does streak inoculation progressively dilute on agar?
Cells across a solid agar surface.
What results from streak inoculation on solid agar?
Isolated colonies of individual cells.
What is the purpose of subculturing isolated colonies?
To obtain a pure culture of a single bacterial strain.
Which media type is stab inoculation used for?
Liquid or semisolid media.
Which inoculation method isolates single colonies on solid media?
Streak inoculation.
What are pour or spread plates used to count?
Bacteria as colony-forming units.
Which features are examined in colony morphology?
Size, shape, margin, elevation, consistence, colour or pigmentation, smell, texture, and haemolysis.
On which agar is haemolysis always examined?
Blood agar.
What type of haemolysis is complete on blood agar?
Beta haemolysis.
What type of haemolysis is incomplete on blood agar?
Alpha haemolysis.
What does a mucous colony indicate?
Capsule or slime production typical of highly virulent fresh cultures.
What is MacConkey agar selective-diagnostic for?
Enterobacteriaceae.
Why does MacConkey agar inhibit Gram-positive bacteria?
Because it contains bile salts.
What does neutral red indicate on MacConkey agar?
Lactose fermentation.
Test your knowledge with 17 questions on Bacterial Culture and Media.
1. What is the primary purpose of bacterial culture in a clinical laboratory?
2. Which finding represents a microscopic examination of a bacterial culture?
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