PE - Agar preparation / types

Question 1

Answer 1

Bouillon (broth, fluid)

• Liquid, basis = bouillon (meat soup)
• Liquid + nutrients for bacterial growth

Question 2

Answer 2

Slant agar

• bouillon + agar 3%
• Slant (dehydration is slower)
• * more surface area

Question 3

Answer 3

Tube (high agar)

• bouillon + agar 3%
• agar-agar = acidic polysaccharide, extracted from certain red algae hygroscopic
• in water dissolves at 100°C ( clear solution )
• gels at 45°C

Question 4

Answer 4

cooked meat (CM):

(Enrichment meida)

• Chopped meat bouillon: bouillon + chopped cow meat
• Serum bouillon

Definition of enrichment media: liquid media containing chemical (or organic) constituents to promote growth of some bacteria.

Question 5

Answer 5

Solid (rigid) media:

Composed of polysaccharide extracted from red algae (seaweed)
in water dissolves at 100 C ( clear solution ) gels at 45 C

Question 6

Answer 6

Blood agar plates

blood agar culture media = agar culture media + 5 % sheep blood
- better nutrition, neutralization of toxic fatty acids

Haemolysis on blood agar:

• Alfa-haemolysis: partial clearing of blood around colonies with green discoloration of the medium; outline of red blood cells intact
• Beta-haemolysis: zone of complete clearing of blood around colonies due to lyses of the red blood cells
• Gamma-haemolysis: no haemolysis

Question 7

Answer 7

Chocolate agar plates

chocolate agar culture media = warming up the blood agar culture media (slowly to 80)

• for more demanding bacteria

Both factors X (hemin) and V (nicotinamide adenine dinucleotide [NAD]) are present, supplying the special growth factor requirements of Haemophilus influenzae and, when incubated in CO2, of Neisseria meningitidis and Neisseria gonorrhoeae.

Question 8

Answer 8

Clauberg medium (K-tellurit medium)

Selective differential medium for the isolation of C. diphteriae

Contains: potassium-tellurite and blood glycerinate

Organisms which grow on this medium reduce the potassium tellurite to tellurium; resulting in black to greyish colonies three biotypes: gravis, mitis, intermedium, + garlic smell

Question 9

Answer 9

Loeffler’s medium ( Loeffler’s serum medium/slope )

Selective differential medium for the isolation of C. diphteriae

Contains: clotted serum

The morphology of organisms is typical in smears (The medium enhances the development of metachromatic granules)

Question 10

Answer 10

Löwenstein-Jensen, Sula

(Selective and differentiating media)

• growth rate is quite slow (cell division~18 hrs)

Löwenstein-Jensen (solid, slant, egg-based):

• malachite-green for selecting
• glycerol, asparagines, egg, potato-extract - antibiotics
• rough: dry growth.
• tough: difficult in lifting the colony from the surface.
• buff: pale-yellow granules, (like bread-cramps)

Sula (broth):

• malachite-green
• ascites or serum
• clumps in the bottom

Question 11

Answer 11

Eosin methylene blue (EMB)

(Selective and differentiating media)

G - bacteria, differentiating based on lactose frementors

• fermenters of lactose appear dark purple to black. (E.coli, klebsiella)
• Non-fermenters of lactose colourless colonies (proteus, salmonella)

Question 12

Answer 12

Bismuth-sulphite

(Selective and differentiating media)
Contains brilliant-green, bismuth- and sodium-sulphite (to detect H2S-production)
Colonies of Salmonellae appear to be black

Convert sulphite into H2S in the presence of heavy metal.

Question 13

Answer 13

Brillant-green

Contains brilliant-green (partially inhibits growth of Proteus sp. and E. coli), brilliant-sugar (lactose, dextrose, and sucrose), and Andrade-indicator

Colonies of Salmonellae appear to be colourless

Colonies of E. coli appear to be red if grown

Question 14

Answer 14

Deoxycholate-citrate

(Selective and differentiating media)

Contains deoxycholic acid, sodium citrate, lead acetate, iron-ammoniac sulphate, lactose and neutral red indicator

• Colonies of Shigellae appear to be colourless.
• Colonies of E. coli appear to be red if grown.

Question 15

Answer 15

TCBS - Thiosulfate-citrate-bile salts-sucrose agar

(Selective and differentiating media)

• bromthimol-blue indicator
• pH near 9.0; 37 C; 18 hours

Used for: Vibrio species

Colonies: convex, smooth, round shaped yellow.

Question 16

Answer 16

Transport swabs (e.g. Stuart)

• it is used if a clinical specimen cannot be cultured immediately
• it preserves the relative balance of any microorganisms present
• it prevents the overgrowth of contaminants during transit and sustain the pathogen
• No organic growth factors for growth

Question 17

Answer 17

Transport growth media (e.g. Uricult)

• microorganisms can grow immediately
• save time

Question 18

Answer 18

Blood culture

• Before antibiotic treatment
• Done before temp spike
• 20-30 ml
• collect several (6) (different times)
• aerobic + anaerobic

If bacteria is present => Gram stain and culture is done

Question 19

Answer 19

Virus transport medium

• Stored at 4°C