3rd Year MBBS Microbiology Slides & Tests

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Blood Agar

 Chocolate Agar

Nutrient Agar


RBCs in Urine

Hyphae

Slide of Stool

Gram positive Cocci


Mycobacerium Tuberculsis (Ziehl-Neilsen stain)

Ziehl Neelson Staining:

• 1. Cover with tissue paper
• 2. Flood slide with carbolfuchsin, the primary stain, for 2 minutes while heating with steam.
• 3. Remove paper cover, decolorize slide with a mixture of hydrochloric acid and ethanol.
• 4. Counter stain with methylene blue.

Urease Test:

Indicator --- Phenol Red

Urease producing org. will convert urea in test tube to ammonia, pH becomes alkaline, the indicator becomes red.

Urease +ve --- Red --- H.pylori, Proteus, Klebsiella, Yersinia, Enterocolitica

Urease -ve --- Yellow --- Salmonella, Shigella.

Triple Sugar Iron:

contains Ferous Sulfate, 3 sugars(glucose, lactose, sucrose) (glucose in 1 tenth the conc. Of other sugars)

Butt – poorly oxygenated area

Slant – inclined well oxygenated area

In the presence of (A)cid the indicator will turn --- yellow (sugar fermented acid produced)

in the prescense ofAl(K)aline the indicator will remain --- pink

if lactose is not fermented but the glucose is... butt will be yellow(no O2) but on slant the acid will be oxidised so it will be red.

H2S production--- black

Interpretation

(slant/deep/gas/H2S) (organisms)

A A + - Klebsiella, Enterobacter, E.Coli

K A - - Shigella, Serratia

K A + + Salmonella, Proteus

K K - - Pseudomonas

A A - - Vibrio

A A + + Citrobacter

K A - + S. typhi

Oxidase Test:

It is used to differentiate aerobic n facultative aerobes from anaerobes based on the formers oxygen utilization ability n the presence of oxidase enzyme.

Phenylene diamine dihydrochloride(subd. 4 oxidase) acts as an electron receptor and gets oxidized to produce purple or black colour.

Oxidase +ve --- Purple --- P.aeru, vibrio, nisseria, brucella n pasturella

Oxidase -ve --- E.coli, salmonella, shigella

Specimen/Slide --- filter paper showing purple colour.

Motility Test:

semisolid agar --- 0.4% conc. Of agar is used

medium is made in an upright position

a straight wire is used to innoculate at centre of medium

Interpretation

motile org. produce haze --- E.coli n Salmonella, Proteus

non motile org. produce discrete line --- Klebsiella, Shigella

DNAse test:

is used to identify S.Aureus that produces deoxyribonuclease enzymes

Contains

• Dnase

• NaCl

• Agar

+ve is seen as a clearing around the colonies

Citrate Test:

differentiates family of enterobacter based on their utilization of citrate as a source of carbon.

Contents :

Sodium Citrate --- Source of carbon

Ammonium Phosphate --- source of nitrogen

org. that extract carbon also extract nitrogen, turn medium alkaline

Indicator --- Bromothymol Blue (blue at alkaline pH, green at acidic)

Simmons Citrate agar is used 4 culture, slope of medium streaked, incubated at 37 deg 4 24 hrs.

Interpretation

Citrate Test +ve --- Blue --- Citrobacter, Klebseilla, Salmonella

Citrate Test -ve --- Green --- E.Coli