Microbiology lab quiz 1, Dr. Collins

3 types of media

1. Solid

2. Semi-solid

3. Liquid

2 ways to transfer bacteria

Pipets and inoculating loops

What does aseptic mean?

Free of contamination

3 methods of obtaining isolated colonies

1. Streak plate.

2. Pour plate.

3. Spread plate.

Streak plate method

Bacteria from a culture are transferred to a plate using an inoculating loop.

Spread plate method

Dilute bacterial culture is spread across an agar plate using a sterile hockey stick

Pour plate method

A small volume of dilute bacterial culture is added to a sterile petri dish and and mixed with melted agar

Which two plate methods use DILUTED culture?

Spread and pour

Swarming motility

Movement through a semi-solid surface via the rotation of flagella

Twitching motility

Movement along a solid surface via the extension and retraction of pili

What will swarming motility look like?

A flower

What will twitching motility look like?

A halo

What can we use to identify different types of bacteria?

Differential staining methods

Gram-positive bacteria

Have a thick layer of peptidoglycan in their cell wall

Gram-negative bacteria

Have a thinner layer of peptidoglycan in their cell wall and also have a LPS layer

What color should Gram-positive bacteria stain?

Purple

What color should Gram-negative bacteria stain?

Pink

Characteristics of a proper smear:

• Bacteria are evenly spread on a slide and separated from one another.

• Bacteria are not washed off the slide.

• Bacteria form is not distorted.

Example of a Primary gram stain:

Crystal violet

Example of a Secondary gram stain:

Safranin

What does a Mordant do:

It allows for interaction between dye and cell wall

Example of a Mordant:

Gram’s Iodine

Mycolic acids

Lipids in the cell wall of acid-fast bacteria

Acid-fast bacteria

Bacteria whose cells walls are not readily de-stained with acid-alcohol

A dark red stain indicates:

Acid fast bacteria

A blue stain indicates:

Non acid-fast bacteria

Example of a primary acid-fast stain:

Carbolfuchsin

Example of a secondary acid-fast stain:

Methylene blue

Biofilms

Bacterial species growing as a hydrated community

What substance surrounds the cells in a biofilm?

EPS (extracellular polymeric substances)

What does EPS consist of?

Extracellular DNA, protein, and polysacharides

The ability of an organism to form biofilms can be determined using _______________

crystal violet

The bacteria __________ ___________ commonly forms biofilms on burn victims and individuals with cystic fibrosis

Pseudomonas aeruginosa

One method of measuring bacterial cell populations is…

Standard plate count method

Standard plate count method:

Bacteria is serially diluted and plated onto growth media. Only plates containing 30-300 colonies are used.

Plates containing less than 30 colonies are called:

Too few to count (TFTC)

Plates containing more than 300 colonies are called:

Too numerous to count (TNTC)

The standard plate count method is considered a:

Direct method of quantification

Equation used to quantify bacterial populations:

cfu/ml