Lesson 4

Artificial environments formulated to support microbial growth

Culture media

What is the purpose of culture media in obtaining a pure culture?

Isolation of pure culture

What is the purpose of culture media in infection diagnosis?

Identification of cause of infection

What is the purpose of culture media in counting microorganisms?

Estimation of viable count

What is the purpose of culture media in antimicrobial testing?

Antibiotic sensitivity testing

What is the purpose of culture media in observing microbial reactions?

Biochemical reactions

What is the purpose of culture media in specimen transport?

Transport without contamination

What are culture media used for in pharmaceutical production?

Antibiotics, vaccines and enzymes

What are other applications of culture media?

Industrial and research applications

What is a major nutrient component of culture media?

Carbon source

What type of source provides inorganic nutrients in culture media?

Inorganic source

What nutrient components are derived from proteins?

Proteins and amino acids

What component gives culture media its solid consistency?

Solidifying agent

What component maintains the pH of culture media?

Buffering agent

What is the main liquid component of culture media?

Water

What component indicates pH changes in culture media?

pH indicator

What component supports the growth of organisms under reduced oxygen conditions?

Reducing agent

What component inhibits unwanted microorganisms?

Selective agent

What temperature and time are used to autoclave prepared culture media?

121°C for 15 minutes

What cabinet is used after autoclaving before pouring culture media?

Laminar airflow cabinet

What should be done to culture media before pouring into Petri plates?

Cool slightly

What happens after culture media are poured into sterile Petri plates?

Solidification

Why is culture media preparation standardized?

To prevent compromised microbial growth and laboratory results

What concentration of agar is used in solid media?

1–3%

What is the most commonly used solidifying agent?

Agar

What is agar prepared from?

Seaweeds

What is the consistency of semi

solid media?

What is semi

solid media used to demonstrate?

What is liquid culture media also called?

Broth

How do bacteria grow in liquid media?

Uniform turbidity

What are culture media classified by?

Physical state, composition and function

What type of media contains no additional or special components?

Simple media

What type of media has ingredients with difficult

to

What type of media is prepared from pure chemical substances?

Synthetic media

What type of media has a specific purpose such as enriched, selective, differential or transport?

Special media

What do enriched media contain?

Blood, serum or egg

What type of organisms do enriched media support?

Fastidious organisms

What blood agar is used for?

Hemolytic patterns

What agar is used for growing fastidious bacteria?

Chocolate agar

What are organisms with complex nutritional requirements called?

Fastidious organisms

What are organisms with relatively simple nutritional requirements called?

Non

What type of media inhibits commensal or contaminating bacteria?

Selective media

What substances can be added to selective media to inhibit unwanted bacteria?

Antibiotics, dyes, chemicals or pH alterations

What medium is selective for Neisseria gonorrhoeae?

Thayer

What is EMB?

Selective medium

What medium is used for Campylobacter?

Campylobacter media

What medium is used for Mycobacterium?

Lowenstein

What is the main purpose of selective media?

Restrict unwanted microbial growth

What type of media differentiates colonies based on color?

Differential media

What components produce different

colored colonies in differential media?

What is MacConkey agar?

Differential medium

What is CLED agar primarily used for?

Urine cultures

What is TCBS agar used for?

Isolation and differentiation of Vibrio spp.

What is XLD agar used for?

Isolation and differentiation of Salmonella and Shigella

What type of media is intended for delayed specimen transport?

Transport media

What is the purpose of transport media?

Preserve microbial viability during transport

What transport medium is semi

solid and non

What transport medium is a modified version of Stuart's?

Amies

What transport medium contains modified Thayer

Martin agar?

What transport medium is designed for enteric pathogens from stool?

Cary

What organisms is Stuart's transport medium especially useful for?

Neisseria gonorrhoeae

What organisms is Cary

Blair transport medium used for?

What type of medium is blood agar?

Enriched and differential

What is blood agar routinely used for?

Moderately fastidious bacterial organisms

What is the base medium of blood agar?

Infusion agar or tryptic soy agar

What percentage of blood is added to blood agar?

5–10%

What type of blood is used in blood agar?

Defibrinated sheep, rabbit or human blood

What does blood agar allow observation of?

Hemolytic reactions

What type of medium is chocolate agar?

Enriched medium

How is chocolate agar prepared?

Sheep blood agar with lysed red blood cells

What are the major nutrients in chocolate agar?

Hemin and NAD

What factor is hemin also called?

Factor X

What factor is NAD also called?

Factor V

What organisms are promoted by chocolate agar?

Haemophilus and other fastidious bacteria

Why is chocolate agar brown?

Heated blood

What organisms can grow on chocolate agar?

H. influenzae and N. gonorrhoeae

What type of medium is alkaline peptone water?

Enriched medium

What is the pH of alkaline peptone water?

9.0

What sodium chloride concentration is used in alkaline peptone water?

0.5–1.0%

What organisms are recovered using alkaline peptone water?

Vibrio and Aeromonas spp.

What organism does sodium chloride favor in alkaline peptone water?

Vibrio

What is the purpose of alkaline peptone water before TCBS inoculation?

Vibrio enrichment

What type of medium is BHI?

Enriched medium

What does BHI with 6.5% NaCl isolate?

Salt

What does BHI with 0.1% agar favor?

Anaerobes

What does BHI with Fildes enrichment support?

Fastidious organisms

What organisms are supported by BHI with Fildes enrichment?

Fastidious organisms (Haemophilus and Neisseria)

What does 6.5% NaCl in BHI create?

High

What organisms can grow in BHI with 6.5% NaCl?

E. faecalis and E. faecium

What does 0.1% agar in BHI do?

Reduces O₂ tension

What organisms are favored by BHI with 0.1% agar?

Clostridium perfringens, Bacteroides fragilis and Fusobacterium spp.

What type of medium is BCYE agar?

Enriched and selective

What organism is BCYE useful for isolating?

Legionella spp.

What component of BCYE provides iron?

Ferric pyrophosphate

What components enhance Legionella growth in BCYE?

Yeast extract, α

What component of BCYE absorbs toxic compounds?

Activated charcoal

What component is essential for Legionella growth?

L

What type of medium is Loeffler's medium?

Enriched medium

What organism does Loeffler's medium support?

Corynebacterium diphtheriae

What type of medium is Loeffler's medium based on?

Serum