Chapter 6 : Culturing Microorganisms ONLY

Microbial growth

Increase of amount of microbial cells

Not size

What is Medium/ Media ?

The nutrient material prepared to support microbial growth in a laboratory

What is Culture?

Microorganisms that grow or reproduce in the presence of medium

2 Requirements for Medium ?

1. A medium must provide an energy source, sources of carbon, nitrogen, sulfur, phosphorus, organic growth factors, and vitamins in order to support microbial growth.

2. Medium itself must initially be sterile, in other words, it must initially contain no living microorganisms.  The medium can be sterilized by an instrument called autoclave, which provides steam under pressure (high heat and high pressure) in order to kill all microorganisms.

What are the 2 major forms of medium ?

Liquid and solid

What is a Broth ?

liquid form of any type of medium

What is a Solid media ?

when a solidifying agent called agar is added to the liquid medium. 

What is Agar ?

Polysaccharide ( polymer of sugar molecules)

What can the Solid form of a medium come as ?

• test tube as a deep.

• in a test tube held at an angle, this is called a slant.

• in a Petri dish, this is called an agar plate.

What are 3 advantages of using agar medium ?

(1) Agar has a fragile texture.  Microorganisms DO NOT break down the structure of agar. 

(2) It is much easier to observe microbial growth on the solid surface of agar medium than liquid medium. 

3) Solid medium provides increased surface area for microbial growth.

Define Colony

a visible mass of microbial cells grown on the surface of solid medium belonging to a single microbial species.

What is fastidious bacteria ?

are difficult to culture in the lab because they require special media, longer incubation time, or anaerobic condition (i.e., NO oxygen).

 

What are the 4 types of Media ?

Complex , Enriched , Selective , Differential

What is Complex media ?

most commonly used media in the lab

What is the purpose of complex media ?

to cultivate bacteria in the lab on a regular basis AND also used to cultivate microbial samples collected from the environment such as water fountain, your shoes (soil), door knob, computer keyboard, etc.

Examples of Complex media ?

Tryptic Soy Broth (liquid form, abbreviated as TSB) OR Tryptic Soy Agar (solid form, abbreviated as TSA)
- Nutrient Broth (liquid form, abbreviated as NB) OR Nutrient Agar (solid form, abbreviated as NA)

What is Enriched media ?

is a rich medium supplemented with animal blood usually 5-10% sheep, rabbit, or horse blood.

What is an example of enriched media ?

Blood Agar

What is Enriched media’s purpose

to culture human pathogens from patients' clinical samples such as blood, urine, sputum, nose, stool samples, etc.

Why use such rich media to culture human pathogens from patients' clinical samples

Because human clinical samples tend to contain MIXED populations of microbial species , so enriched media is used to encourage the growth of a particular microbial species of interest from a MIXED population

What are the chemical components of Blood Agar ?

What is Selective Media’s purpose

used to select for the growth of a particular microbe OR a particular type of bacteria while suppressing or inhibiting the growth of others.

What are the 4 examples of Selective Media?

• Sabouraud dextrose agar

• MacConkey Agar

• Eosin- Methylene Blue

• Hektoen Enteric agar

What does Sabouraud dextrose agar select ?

Fungi

What does MacConkey Agar, Eosin- Methylene Blue, and Hektoen Enteric agar Select for ?

Gram Negative bacteria

Why does Sabouraud dextrose agar select for Fungi Only ?

Due to its Acidic pH and presences of Antibiotics

What are MacConkey chemicals that are inhibitors for gram positive ?

Crystal Violet and Bile Salt

Examples of Gram negative bacteria

• E. coli

• Klebsiella pneumoniae

• Proteus mirabilis

• Salmonella typhimurium

• Shigella flexneri

Examples of gram positive bacteria?

any bacterial species belong to genus Staphylococcus and genus Streptococcus

What are Eosin- Methylene Blue chemicals that are inhibitors for gram positive ?

Eosin and Methylene Blue

What are Hektoen Enteric Agar chemicals that are inhibitors for gram positive ?

Bile Salt

List the Examples of Differential Media

• MacConkey Agar,

• Eosin- Methylene Blue,

• Hektoen Enteric agar

• And Blood Agar

Why does Lactose Fermenting gram negative bacteria turn pink on MacConkey Agar ?

Because MacConkey agar contains an pH indicator called neutral red as part of his chemical ingredients.

• Neutral red is colorless at neutral pH.

• Neutral red turns pink at acidic H Lactose fermenting gram-negative bacteria are able to ferment sugar lactose and produce lactic acid. Lactic acid will turn neutral, red pink on MacConkey agar

How does HE Agar differentiate bacteria belonging from genus salmonella from bacteria belonging to genus Shigella ?

Sulfur to Sulfide Conversion

What does Sulfur to Sulfide Conversion do ?

differentiate bacteria belonging from genus salmonella from bacteria belonging to genus Shigella

What are some examples of lactose fermenting gram-negative bacteria?

E.Coli and genus Klebsiella

What are some examples of non lactose fermenting gram-negative bacteria

Genus Salmonella , Proteus , and Shigella

How does blood agar differentiate bacteria?

Blood Hemolysis

What is Blood Hemolysis ?

Break down of red blood cells on blood agar

What can Alpha-hemolytic do?

can ONLY partially break down red blood cells on blood agar.

Alpha-hemolytic example

Streptococcus pneumoniae

What can beta-hemolytic bacteria do ?

can completely break down red blood cells on blood agar.

Beta-hemolytic example

Staphylococcus aureus and Streptococcus pyogenes

What can gamma-hemolytic bacteria do ?

CANNOT break down red blood cells on blood agar.

Gamma-hemolytic example

Staphylococcus epidermidis