Intro to Microbio Lab

Why do we use aseptic technique?

For safe handling and to avoid contamination.

What is the purpose of doing a four-quadrant streak

It allows for the isolation of single colonies of bacteria

Nutrient agar (NA) & Tryptic Soy Agar (TSA) plates

Support the growth of a wide range of organisms.

Gram Postive

purple, thick peptidoglycan layer

Gram Negative

pink, thin peptidoglycan layer

Monotrichous

single flagellum

Amphitrichous

flagella at both ends of cell

Lophotrichous

cluster of flagella at one or both ends

Peritrichous

flagella distributed over the entire cell

Motility Test Medium (MTM)

use of semi solid agar media to detect bacterial motility

Mesophiles

moderate temperature loving microbes. (20C-45C)

Psychrophiles

cold loving bacteria (-20C-20C)

Thermophiles

heat loving microbes (41C-122C)

Prodigosin pigment

Produced by Serratia marcesens

Pyocyanin pigment

Produced by Pseudomonas aeruginosa

Canthaxanthin pigment

Produced by Micrococcus roseus

Violacein pigment

Produced by Chromobacterium violaceum

Phases of bacterial growth curve

Lag Phase, Exponential/Log Phase, Stationary Phase, and Death Phase

Lag Phase

The organisms are not dividing because they are adjusting

Exponential/Log Phase

The organism will start dividing and reproduce exponentially

Stationary Phase

As resources are reduced, growth levels off (Bacteria growth and Bacteria death balanced out)

Death Phase

As limiting factors intensify, bacteria start dying faster than reproducing.

Nutritive Media

Media types that provide sufficient nutrients to support the growth of a wide range of microorganisms.

EX: TSA and NA plates

Selective Media

Media types that promote the growth of "select" microbes, while preventing the growth of others

Differential Media

Media types that distinguish between organisms with unique characteristics due to difference in growth or appearance

Staphylococci

Steptococci

Sheep Blood Agar (SBA)

Differential Medium of Hemolysis

Mannitol Salt Agar (MSA)

Selective and Differential Medium. Staphylococci can grow on it and Streptococci cannot

Eosin Methylene Blue Agar (EMB)

Selective and Differential Medium. Distinguish organisms that can ferment lactose and organisms that can't

MacConkey Agar (MAC)

To isolate and identify enteric pathogens or non-pathogenic enteric bacteria. Can also distinguish lactose fermenters and non-lactose fermenters

Triple Sugar Iron Agar (TSIA)

Differential: Ability to ferment glucose/lactose/sucrose, reduce sulfur

Yellow Slant/Yellow Butt = carbohydrate fermentation

Red Slant/Yellow Butt = glucose fermentation only

Red Slant/Red Butt = no fermentation

Red Slant/No Change in Butt = no fermentation

Black Precipitate = sulfur reduction (requires acidic conditions)

Cracking or lifting of agar = Gas prodution

Citrate Utilization Test

Determines the ability of bacteria to use citrate as a sole carbon source for their energy needs

Positive - Blue
Negative - Green

Urease Test

Determines the ability of microorganisms to degrade urea by means of the enzyme urease.

Carbohydrate Fermentation

Determines if the microorganisms can metabolize that sugar

MRS Agar (De Man, Rogosa, and Sharpe)

Selective growth for bacteria from the genera: Lactobacillus, Streptococcus, Pediococcus, and Lenconostoc

Horizontal Gene Tranfer

passes genetic information between cells by a process independent of cell division and separate from reproduction

Three possible mechanisms of lateral gene transfer

1. Conjugation

2. Transformation

3. Transduction

Conjugation

In bacteria, the direct transfer of DNA between two cells that are temporarily joined.

Heat shock

A method that involves rapidly increasing and decreasing the temperature to increase membrane permeability in order to enhance the likelihood of bacterial transformation

Antibiotics

Substances that inhibit or kill bacteria

Disk diffusion/Kirby-Bauer method

-antibiotic embedded in filter disk diffuses into agar medium

-creates a concentration gradient, greatest near disk

Zone of inhibition

The zone where bacteria can't grow around a given antibiotic.

Mueller-Hinton agar

A common agar medium used for anti-microbial susceptibility testing.

Bacteriostatic

inhibits bacterial growth

Bactericidal

kills bacteria

Narrow spectrum antibiotics

Effective against specific bacteria like only for gram negative or only for gram Postive bacteria.

Broad spectrum antibiotics

antibiotics that affect a broad range of gram-positive or gram-negative bacteria