What are the antigens of Salmonella typhi?
The antigenic structure of S typhi is [Vi], 9, 12:d,1 and infection with this organism may result in the production of serum antibodies to the O=9,12 somatic, the H=d flagellar, and the “Vi” capsular antigens. Classically, the Widal agglutination test has been used to detect patients’ antibodies to these antigens.
What is the morphology of Salmonella typhi?
MORPHOLOGY OF SALMONELLA TYPHI (S. TYPHI) Shape – Salmonella typhi is a rod shape (bacillus) bacterium. Size – The size of Salmonella typhi is about 1–3 µm × 0.5–0.6 µm (micrometer).
What are the differences between O and H antigen?
The key difference between O and H antigen is that O antigen is the outermost portion of the bacteria’s surface covering while H antigen is the slender threadlike structure that is part of the flagella.
What is phase and antigenic variation?
Phase variation or phenotypic switch allows the expression of a given phenotype to be switched ON or OFF. Antigenic variation refers to the expression of a number of alternative forms of an antigen on the cell surface, and at a molecular level, shares common features with phase variation mechanisms.
What are the basic morphological characteristics of Salmonella?
MICROSCOPIC APPEARANCE
Gram Stain: | Negative. |
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Morphology: | Straight rods. |
Size: | 0.7-1.5 micrometers by 2.0-5.0 micrometers. |
Motility: | Usually motility by peritrichous flagella, however non-motile mutants do occur, and one type ( Salmonella gallinarum / Salmonella pullorum ) is always non-motile. |
Capsules: | None. |
What is the selective media for Salmonella typhi?
The most commonly used media selective for Salmonella are SS agar, bismuth sulfite agar, Hektoen enteric (HE) medium, brilliant green agar and xylose-lisine-deoxycholate (XLD) agar.
What is antigen O and antigen H?
The O antigens are distinguished by their different chemical make-up. The H antigens are distinguished by the protein content of the flagella. Each O and H antigen has a unique code number. Scientists determine the serotype based on the distinct combination of O and H antigens.
What is the meaning of O antigen and H antigen?
O antigen and H antigen are two types of antigens used to determine the different serotypes of bacterial species. O antigen is a lipopolysaccharide found on the cell wall. H antigen is a proteinaceous antigen which is a part of the flagella.
Why O antigens of Salmonella Paratyphi A and B are not included in widal test?
Serologic and Molecular Diagnosis Widal’s test is not sufficiently sensitive, specific or reliable enough to be an optimal diagnostic assay for typhoid fever and it does not aid in the diagnosis of paratyphoid fever, as these antibodies are not cross-reactive against S. Paratyphi A, B and C antigens.
Is Salmonella typhi Gram positive or negative?
gram-negative bacterium
Salmonella enterica serotype typhi is a gram-negative bacterium that is responsible for typhoid fever and has been a burden on developing nations for generations.