salmonella part 1

Who discovered Salmonella typhi, and what was it originally called?

Eberth observed it in 1880, Gaffky isolated it in 1884; it was called Eberth-Gaffky bacillus or Eberthella typhi.

What was the first Salmonella species isolated from animals and who discovered it?

Salmonella choleraesuis by Salmon and Smith in 1885, believed to cause hog cholera.

How many Salmonella serotypes exist and how many are potentially pathogenic?

About 2400 total, around 50 are pathogenic.

What is the natural habitat and main reservoir of Salmonella?

Intestinal tract of warm- and cold-blooded animals.

How is Salmonella typically spread from animals to the environment and humans?

Through subclinical carriers contaminating water, food, and surroundings.

How can Salmonella enter the human food chain through poultry?

Some serotypes like S. enteritidis infect ovaries and are transmitted via eggs.

How long can Salmonella survive in the environment and under what conditions?

Up to 9 months in moist soil, feces, water, and feed (especially blood, bone, fish meal).

Describe the morphology and motility of Salmonella.

Gram-negative, non-spore forming rods; motile with peritrichous flagella except S. gallinarum and S. pullorum.

What type of fimbriae do most Salmonella possess and what is their function?

Type 1 fimbriae with mannose-sensitive adhesion; S. gallinarum/pullorum have non-adhesive type 2 fimbriae.

What are the growth conditions and optimal temperature/pH for Salmonella?

Aerobic/facultative anaerobe, grows at 37°C and pH 6.8.

Name the main selective enrichment media for Salmonella and their special considerations.

Tetrathionate broth, selenite broth, and Rappaport-Vassiliadis (preferred for host-adapted serotypes).

What media are used after enrichment for Salmonella identification?

MacConkey, Brilliant Green Agar, XLD, and Salmonella-Shigella (SS) agar.

How does Salmonella appear on MacConkey, Brilliant Green, XLD, and SS agars?

Pale colonies (MacConkey), red colonies (BGA), red colonies with black centers (XLD), colorless with black centers (SS).

What is the characteristic TSI reaction for Salmonella?

Alkaline slant/red, acid butt/yellow, with H₂S production (R/Y/H₂S+).

Which biochemical tests are used to identify Salmonella and what are their results?

IMViC − + − −; urease negative; lysine decarboxylation positive.

What sugars are fermented by Salmonella and which are not?

Ferments glucose, mannose, mannitol, maltose; does not ferment lactose, sucrose, salicin.

Which Salmonella strains do not produce H₂S?

S. choleraesuis and S. paratyphi A.

What sugars are fermented by S. pullorum and S. gallinarum?

S. pullorum ferments glucose and rhamnose; S. gallinarum ferments dulcitol and maltose.

What temperature and chemicals effectively kill Salmonella?

55°C (1 hr) or 60°C (15 min); killed by boiling, chlorination, 5% phenol, or 1:500 mercuric chloride

What are the three major antigens of Salmonella and their properties?

H (flagellar, heat-labile, immunogenic), O (somatic, heat-stable, endotoxin), Vi (capsular, masks O, poorly immunogenic).

What is Boivin antigen and how is it obtained?

O antigen extracted with trichloroacetic acid from bacterial cells.

What is the significance of Vi antigen in S. typhi and its diagnostic impact?

Masks O antigen; causes failure to agglutinate with O antisera but agglutinates with Vi antisera.

What are H-O variations and how are they induced?

Temporary loss of flagella (phenotypic); induced using phenol agar; reversible using Craigie’s tube.

What is phase variation in Salmonella and how are phases designated?

Alternation of two flagellar antigens : phase 1 (specific, a–z, Z1…), phase 2 (shared, 1, 2...).

What do diphasic and monophasic strains mean in terms of flagella?

Diphasic strains express both phases; monophasic express only one.

What is V-W variation in S. typhi?

V form has Vi antigen (O masked); W form has no Vi (O visible); VW form shows both.

What is S-R variation and its consequence?

Smooth to rough change; loss of O antigen and virulence; colonies become large, irregular.

How can S-R variation be prevented in cultures?

By lyophilization (freeze-drying).

How can lysogeny affect Salmonella antigens?

Phage infection can alter O antigen structure and change serotype.

How is Salmonella classified and named in modern taxonomy?

Two species : S. enterica and S. bongori; S. enterica has six subspecies; serovars named by Kauffmann-White scheme using O and H antigens.