PPT 模板下载： www.1ppt.com/moban/

LAB EXERCISE 5

Identification of Unknown Bacteria

（ Enteric Gram Negative Rods ）

Enterobacteriaceae Infections

EnterobacteriaceaeLactose fermenters

(LF)E. coli

Klebsiella

Enterobacter

……

Non-lactose fermenters (LNF)

Salmonella

Shigella

Proteus

……

Classification of Enterobacteriaceae• There are several selective and

differential media used to isolate distinguishes between LF & LNF.

• The most important media are:– MacConKey agar– Eosin Methylene Blue (EMB) agar– Salmonella Shigella (SS) agar– Triple Sugar Iron (TSI) agar

• Kligler Iron Agar (KIA)

Differentiate between LF & LNF by Growth on SS agar • SS agar is selective & differential

medium for Enterobacteriaceae.

Differentiate between LF & LNF by Growth on KIA slant

Unpathogenic

Pathogenic

SOME IDENTIFICATION TEST

• Biochemical test–Carbohydrate Fermentation–Indole test (Enzyme test)

• Other–Motility

KIA (Kligler Iron Agar) Test

• The indicator is RED at alkaline pH, and YELLOW at acidic pH.

• Interpretation:– Red slant /yellow butt → only glucose is

fermented.– Yellow slant /yellow butt →glucose and

lactose both are fermented.– Bubbles or crack present → gas production.– Black precipitate present → H2S production.

ControlLF Gases produced

LNF H2S produced LNF

Carbohydrate Fermentation • Aim: To determine the ability of

microbe to ferment a specific carbohydrate with or without the production of gas.

• Material:Carbohydrate Carbohydrate

Glucose (Red cap) /golden Mannitol (White cap)

Lactose (Yellow cap) Sucrose (Black cap) /green

Maltose (Blue cap)

* Indicator: Phenol Red (acid → yellow)

Carbohydrate Fermentation • Interpretation:

– Acid production: Changes the medium into yellow color- organism ferments the given carbohydrate and produce organic acids there by reducing the pH of the medium into acidic.

– Acid and Gas production: Changes the medium into yellow color. Gas production can be detected by the presence of small bubbles in the inverted Durham tubes.

– Absence of fermentation: No change observed in the colour of medium. The organism cannot utilize the carbohydrate but the organism continues to grow in the medium using other energy sources in the medium.

Indole Test• Aim: To determine the ability of microbe

to degrade the amino acid tryptophan.

• Interpretation:– Development of cherry red colour at the

interface of the reagent and the broth, within seconds after adding the Kovacs’ reagent indicates the presence of indole and the test is positive.

– If no colour change is observed, then the test is negative and so organisms are not capable of producing tryptophanase.

Motility

• Aim: To determine the ability of microbe to migrate (motile).

• Interpretation:– Organism growing only in line of

inoculation → non-motile.– Organism appears as haze beyond

line of inoculation → motile

Serological test

• Object of study : – Use known antiserum (antibodies) to

identify unknown antigens.

• Materials and equipment ： • 1:20 Typhoid serum• 1:20 Shiga serum

Serological test• Practise ：

– Using a wax marker, draw 3 circles on 2 clean glass slides. Label the circles A, B, and C.

– Add 1 drop of NS to the “A” circle, 1 drop of known Typhoid serum to the “B” circle, and 1 drop of known Shiga serum to the “C” circle.

– Emulsify one or two colonies on each drop to make a smooth suspension.

Serological test• Interpretation:

– Agglutination of the bacteria indicates a positive reaction.

– No agglutination is negative.

Widal test• Object of study :

– This is a tube agglutination test employed in the serological diagnosis of enteric fever.

• Materials and equipment ： • S.TYPHI "O" antigen• S.TYPHI "H" antigen• S.PARATYPHI "AH" antigen• S.PARATYPHI "BH" antigen• Patient serum (1:10 dilution)• 200μL pipettor, Pipettor tips, 40-well Immunoplate

Widal test• Practise ：

– An immunoplate having 40 wells in 4 rows is taken. The rows are labeled as O, H, AH, BH.

– Using a micropipettor add 50μL normal saline to all the wells in the 40-well immunoplate.

– Add 50μL diluted patient serum (1:10) into well O1 containing 50μL saline, mixed by sucking and pumping the fluid with tip for 3 times.

Widal test• Practise ：

– Transfer 50μL from well O1 to O2 , mixed by gently pipetting. Use the same tip to transfer 50μL from well O2 to O3. Avoid bubbles. Using the same tip, repeat these twofold dilution down the entire row, discarding 50μL from A9 so that it ends up with 50μL of diluted serum. The dilution from well A1 to A9 is 1:20, 1:40……1:1280.

Widal test• Practise ：

– Add 50μL antigen S.TYPHI "O" to each well (from “9” to “1”), mix well. The final dilution from well O1 to O9 is 1:40, 1:80……1:2560; Well “10” is the control tube.

– Repeat this doubling dilution with different antigen (H /AH /BH) in defined rows.

– Mix each well and incubate for 1h at 45℃. And place the plate at RT standing for 15 minutes to wake up.

Widal test• Practise ：

– Observe the results and determine the titer of the serum ( + + ) .The highest dilution of serum causing obvious agglutination of bacteria ( + + ) is defined as the titer of the serum.

Widal test• Results ：

– First observe the control well 10. They should show a uniform turbidity in contrast to the aggregates seen in the wells containing the serum dilutions . it is represented as “ - ”.

– The agglutination is represented as“+”:• “+ + + +”represents all of the bacteria

agglutinated. Big agglutin appears at the bottom of the tube, while the supernatant is clear.

• “+ + +”represents part of the bacteria agglutinated. Middle agglutin appears at the bottom of the tube, while the supernatant is a little turbid.

• “+ +” represents small part of the bacteria agglutinated. Half of the supernatant is turbid.

Widal test• Results ：

– The agglutination is represented as“+”:• “+”represents very small amount of the

bacteria agglutinated, while the supernatant is turbid.

• “ - ”represents no agglutination. The phenomenon is same as that of the control tube.

• Attentions– Gently manipulate the pipettes. Do not break the

test tubes with the pipettes. Be careful when you add and transfer the samples one by one, to avoid confusion.

– Do not shake the test tubes when you observe the results , to avoid the spreading of the agglutinates during observation.

O<1:80,TH<1:160,

PH<1:80

Normal value

O ≥1:80 & TH ≥1:160 or

O ≥1:80 & PH ≥1:80

Typhoid fever

Paratyphoid fever

O ≥1:80 & TH <1:160 or

O ≥1:80 & PH <1:80

Early infection or other

salmonella infections

O <1:80 & TH ≥1:160 or

O <1:80 & PH ≥ 1:80

Vaccination or nonspecific

memory reaction

Interpretation of results