Brucell Weil Felix test Widal test. By: Mr. Wael Laithi. 23/09/2013. Brucell. Gram negative small coccobacilli . Non- motile. None encapsulated. Fastidious, need special media with CO 2 and anaerobic condition for growth these media called as Castenada media .
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By: Mr. WaelLaithi
SEROLOGICAL TESTS such as
On a solid surface (glass slide, tile, card), a small amount (50–100 μL) of the patient’s serum is placed.
A single drop of the desired antigen is added, and the resulting suspension is mixed and then rotated for one minute.
Visible agglutination is indicative of a positive result, and corresponds roughly to a titre of 1:20.
Positive results can be further titrated using the tube method, which is more labour-intensive.
Using 0.25% phenol saline as a diluent, a series of tubes containing twofold dilutions of patient serum are made with a final volume of 1 mL.
A drop of antigen suspension is added to each tube
The mixture is incubated at 50–55 °C for 4–6 hours.
A positive tube would show visible flocculation or granulation, which is accentuated when the tube is gently agitated.
The titre corresponds to the most dilute tube in the series that still shows positivity.
Generally, a titre of ≥1:320 is considered diagnostic.
O (somatic) antigens
Vi (Virulence) capsular polysaccharide antigens
Antigenic structure of Salmonella
Patients suffering from enteric fever would possess antibodies in their sera which can react and agglutinate serial doubling dilutions of killed colored Salmonella antigens in a tube agglutination test.
A slide widal test is more popular among diagnostic laboratories as it gives rapid results.
Qualitative test: One drop each of undiluted patients’ serum samples for the four antigens are placed on the circled card and one drop of each of the four Salmonella antigens are added separately and gently rotated for one minute. Appearance of agglutination gives qualitative results. To know the titer for each of the antigens, the test is repeated with dilutions of serum.
specimen, one drop of specific antigen is added to each, mixed and rotated for one minute. Agglutination in each of these is noted.
80 μl corresponds to 1/20 dilution, 40 μl to 1/40, 20 μl to 1/80, 10 μl to 1/160 and 5 μl corresponds to 1/320 titre.
Incubated in water bath at 370C overnight
The control tubes must be examined first, where they should give no agglutination.
The agglutination of O antigen appears as a “matt” or “carpet” at the bottom.
Agglutination of H antigens appears loose, wooly or cottony.
The highest dilution of serum that produces a positive agglutination is taken as titer.
The titers for all the antigens are noted.