Bacteria Culture Media Flashcards
What are The 2 States of Bacterial Culture Media?
- Liquid Culture
- Solid Culture
Describe the 2 Liquid Culture Media Types.
Growth Media:
Allows Growth of most organisms
Differential media:
Distinguishes between different organisms
Describe the 4 Solid Culture Types.
Non-Selective
Used for growth of most organisms
Differential
Used to distinguish between different organisms
Selective
For the growth of specific organisms
Chromogenic
Colorful plates for specific organisms
What is the Typical composition of a Nutrient Agar?
5g Peptone
3g Beef extract/Yeast extract
15g Agar
8g NaCl
1000ml Distilled Water
What is Haemolysis? What Are the Different Types?
Haemolysis:
The breakdown of RBCs, causing Haemoglobin release into surrounding fluid
3 types:
α-Haemolytic
Reduction of Haemoglobin to Methaemoglobin
β-Haemolytic
Complete/True lysis of Red Blood Cells
γ-Haemolytic
Lack of Haemolysis
What is An Elective Agent?
A nutrient or compound that encouraging growth of desired organism
What Are Differential Agents?
Components added in Culture media
Help to visually distinguish between micro-organisms
Based on Biochemical/Metabolic properties
(pH, Metabolism)
What is A Selective Agent?
Compound inhibiting growth of unwanted micro-organisms, while allowing growth of target organism
Examples:
- Bile Salts (For Coliforms)
- Antibiotics
Work by exploiting differences such as:
- Cell Wall Structure
- Metabolic Vulnerabilities
- Resistance Genes
Describe the Differential media-XLD Agar.
- Selective and differential medium
- Used to isolate + differentiate Salmonella and
Shigella from clinical samples
Composition:
- Lactose
- Sucrose
- Sodium Thiosulfate
- L-lysine
- Xylose
- Yeast Extract
- Agar
- Phenol Red
- Sodium Deoxycholate
- Ferric Ammonium Citrate
Sodium Thiosulfate: Prevents growth of Gram
positive bacteria
Xylose + Lysine fermenters: Appear Black
Lactose + Lysine Fermenters: Appear Yellow
Describe the Sorbitol MacConkey Agar SMaC Agar
Differential Media based on lactose fermentation
Used to Isolate + Differentiate E. Coli
More selective for Gram- bacteria (due to presence of crystal violet + Bile Salts)
Composition:
- Peptone
- NaCl
- Bile Salts
- Sorbitol
- Crystal Violet
- Neutral red
- Agar
Describe Salt Agar Selective + Differential Media.
Used to Identify + isolate Staphylococci
Selective Component
- High Salt Concentrations
- Selects organisms tolerant of high salt levels
Differential Component: Mannitol + Phenol red
Allow medium to differentiate bacteria based on ability to ferment mannitol
Describe CHROMagar MRSA.
Chromogenic Culture media
Used for Detection + Differentiation of Methicillin Resistant Staphylococcus Aureus (MRSA)
Differentiates MRSA from Methicillin-Sensitive S. Aureus (MSSA)
Presence of MRSA: Mauve/Pink
Other Bacteria: Blue/Colourless/Inhibited
Describe UTI Brilliance Agar.
- Chromogenic
- Designed to Detect Differentiation of UTIs
- Identified using Colony Colour + Morphology
Components:
Rose-Gal: Detects β-galactosidase activity
E. Coli: Dark pink coloured colonies
Staphylococcus aureus: Light pink colonies
X-Glu: Detects β-glucosidase activity
Klebsiella aerogenes: Dark blue colonies
Enterococcus faecalis: Blue-green coloured colonies
Tryptophan: Detects Tryptophan deaminase activity
Pseudomonas aeruginosa: Brown colonies
Proteus vulgaris: Straw coloured colonies; brown halo.
How is a Culture Media Prepared?
- Dissolve 28g of Agar in 1L Distilled Water
- Mix well, distribute into final containers
- Autoclaving at 121°C for 15 minutes
- Cool to 50°C, pour into plates
- Solidify, label, and store at 4°C
What happens in the Autoclaving Stage?
- Used to Sterilize sample
- Done at 121°C for 15-20 mins
Mechanism:
- Autoclave Sterilizer Chamber Closed
- Vacuum pump removes air inside device/
forces it out by pumping in steam - Sterilizer pumped with high pressured
Steam to raise Internal Temperature - During sterilizing process, steam
continuously enters autoclave to kill all
microorganisms - Internal temp reaches 121°C & 15 psi above
atmospheric pressure. - Once required time of sterilization has
elapsed, chamber will be exhausted of
pressure and steam - Door opens to cool + dry contents
What happens In the Plate Pouring Phase?
- Autoclaved agar cooled at 50°C
- Additional Antibiotics/Enrichments are
added e.g. Blood - Agar Poured into petri dishes aseptically
What Is The Streak Plate Technique?
- Streak done in 1 direction
(Loop Flamed after completion) - Plate turned 90°C, streak made in 1 direction
(Loop Flamed after completion) - Plate turned 90°C, streak made in direction
(Loop Flamed after completion) - Final Streak In Centre of Plate
(Loop Flamed Upon Completion)
Describe MALID-TOF Mass Spectrometry.
Matrix-Assisted Laser Desorption/Ionization-
Time Of Flight
Mechanism:
- Bacterial culture in saline added to plate
Matrix added according to protein size - Bacteria ionized with laser, releasing a
“cloud” of proteins - Proteins accelerated using electric charge,
time of flight is recorded
(Light proteins travel fast, heavy proteins travel slow)
- At the end of their travel, proteins are
detected with sensor, creating a spectrum
representing protein makeup of each
sample - Spectrum compared against large database
of spectra from precisely characterized
bacteria and fungi - Database used to make identifications at
species, genus and family level.
Advantage:
Sample acquisition process takes less than a minute
Workflow to prepare samples is easy and fast
