Microbiology

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Microbiology
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1

MSA (Mannitol Salt Agar)

;(Selective & differential) pink in color.

-promotes growth of staphylococci, and other organisms inhibited by NaCl

in medium. Also, differentiates between pathogenic and non pathogenic.

Pathogenic ferment mannitol produces an acid end product, which raises

Ph, changes color from pink to yelllow.

2

CNA (Columbia colistin nalidixic agar)

Selective for gram positive cocci.Color of medium is agar.

Colistin and nalidixic acid inhibit growth of gram negative and rods.

3

Blood agar

(differential) medium contains sheep RBC's (red in color)

Hemolysis occurs in blood agar due to production of hemolysins by bacteria. Three categories of hemolysis......

1.)-Beta(B) - Complete lysis of RBC's transparent clearings around colonies.

2.)Alpha(a) hemolysis- Partial hemolysis,greenish coloration under colonies.

3.) Gamma (Y) hemolysis; No hemolysis.

4

Starch Agar

Color of agar(pale color) Amylase hydrolyzes starch(uses water to split complex molecules)

Bacteria produces amylase,the enzyme diffuses into the medium,

as a result starch in surrounding colonies are broken down. Iodine applied reacts w/starch causing brown/black color change.

* where no starch no color change.

5

Bile Esculin agar

Medium contains esculin and 40% bile.

Medium pale yellow/green in color. Only bacteria capable of growing in presence of bile will grow on this medium.

EX; Entercoccus.

Entercoccus produces intracellular enzyme esculinase breaks dowm esculin, causes black/brown color change.

6

Phenol Red (PR) w/raffinose broth

Broth ;

RED- Neutral

Yellow-Acid

Pink-Alkanine

Carbohydrate source and Ph indicator.

Can be prepared w/different carbohydrates(raffinose,lactose.sucrose)

Used to detect ability of an organism to ferment different carbohydrates.

Can be used to distinguish diff. species of bacteria.

Tubes of PR broth contain small inverted Durham tube to trap gas produced.

7

Coagulase test

Rabbit plasma as the reagent. Used to detect the presence of the enzyme coagulase in bacteria cells.

-If the cells contain coagulase the plasma will become solid.

POSITIVE RESULT (Staphylococcus)

If the remains liquid -

NEGATIVE RESULT

8

Catalase Test

Uses hydrogen peroxide as the reagent. The enzyme catalase is present in the cells of bacteria that conduct aerobic respiration. used to break down toxic hydrogen peroxide, that is generated as a by-product of areobi metabolism. hydrogen is released as bubbles of gas.

Bubbles with hydorgen peroxide.- Positive for catalase+aerobic organism

No bubbles-negative for catalase.

9

Oxidase test

Uses colorless 1% Klovacs oxidase reagent..

Tests for presence of enzyme cytochrome oxidase final step in electron transport chain.

If presence of enzyme, the reagent is oxidized resulting of purple change.

Purple color change -10-30 sec. -strong positive for oxidase=aeobic organism.

Purple color change in 30-60 sec- weak positive

No purple color change-Negative for oidase.