BACTERIAL IDENTIFICATION METHODS

CHAPTER 3

Contentpurification of culturesmorphological and pureculture studiesbiochemical tests

Purification of culturesThe only way to purified culture are by

getting a pure culture.Have a control procedure in collecting

specimen, preparing media, microbiological tecniques, staining and reagents and equipment used.

Collecting specimenSterile procedure using a correct media for

transportation and stock.Main source for bacteria should be microbial

food. Which are??The transport media used to preserve and

ensure the viability of bacteria during the transportation period

Besides also provide a particular temperature for the viability of bacteria

Crucial for cerebrospinal fluid, blood culture and fecal specimens, etc.

Preparation of mediaThe media should be packed well to prevent

from leakage and breaks, protected from moisture and sunlight and excessive heat

The expiry date should be noted and the instruction of storage should be followed

The mix bacterial colonies should be sub cultured until the culture are purified

the bacterial colony characteristic should only derive from a single colony

Pure colony

Morphological and pure culture studies

In nutrient agar

In MacConkey agar

In MacConkey agar

In Blood agar

3 types of hemolysis

Biochemical testsCatalase testOxidase testCoagulase testSugar fermentation testMRVP testIndole testCitrate testMotility testH2S test

Catalase testProduce bubble just

after attaching the bacteria to the reagent

To differentiate staphylococci and streptococci

Oxidase testHave 2 methods:Filter paper/Sterile swabTo help identify Vibrio, Neisseria, Pasteurella

and Pseudomonas sp.Oxidase enzymes oxydize phenylenediamine.Deep purple colour on reagent paper

Oxidase test

Coagulase testTo identify S.aureusThe enzyme

coagulase clots plasma

Tube : fibrin clotSlide: clumping of

bacterial cells

Sugar fermentation testGlucose testMaltose testSucrose testLactose testSome will appear

with gas production

Voges-Proskauer testTo differentiate

enterobacteriaOrganism ferments

glucose with acetoin production. Acetoin is oxidised to diacetyl which reacts with creatine

Brick red colour develop slowly

Methyl Red testTo differentiate

enterobacteriaOrg. ferment

glucose, producing sufficient acidity in buffered medium to give a colour change of indicator

Brick red medium

Indole testUsing Kovac reagent.To differentiate Gram

negative rods, especially E.coli

Tryptophan is broken down wt the release of indole which reacts wt dimethylaminobenzaldehyde

Reddening of strip or medium

Indole test using other reagent

Citrate testTo differentiate

enterobacteria from other bacteria

Org uses citrate as its only source of carbon, producing an alkaline reaction wt colour change indicator

Blue and turbid medium

Motility test

The endPlease do revision for your 1st test..next week!!