Page 134 - MNUmicrobiology practical 2025

General Microbiology & Immunology (PM 401) second level Semester 4 2024/2025

Widal test

–
An agglutination test, which detects the presence of serum agglutinins antibodies-
against (H and O) antigens in patients’ serum suffering from typhoid and paratyphoid

fever.

• When facilities for culturing are not available, the Widal test is reliable and can be

of value in the diagnosis of typhoid fevers in endemic areas.

• Salmonella antibodies begin to appear in the serum at the end of the first week and

rise sharply during the 3rd week of endemic fever. In acute typhoid fever, O

agglutinins can usually be detected 6–8 days after the onset of fever and H

agglutinins after 10–12 days
.

• The patient’s serum is tested for anti-O and ant-H antibodies (agglutinins) against

the following antigen suspensions (usually stained suspensions)
:
o S. Typhi O antigen suspension

o S. Typhi H antigen suspension

o S. Paratyphi AH antigen suspension

o S. Paratyphi B H antigen suspension

➢ The paratyphoid “O” antigens are not employed as they cross react with typhoid

“O” antigen.

Material: Widal Test Kit, Serum sample, Test tubes

:
Procedure
Slide test

1. Place one drop of positive control on one reaction circle of the slide
.
2. Pipette one drop of isotonic saline on the next reaction circle. (-ve Control)
.
3. Pipette one drop of the patient’s serum onto the remaining four reaction circles.

General Microbiology & Immunology (PM 401) Practical note Page 123