History OF Salmonella
Salmonella Typhi is also knowan as Eberth-Gaffkey or Eberth Typhi. Eberth (1880) observed Salmonella into mesenteric lymph node and spleen of typhoid patient. Gaffkey isolated this organisms in 1884.
Introduction of Salmonella
Family : Enterobacteriaceae
Gram negative bacilli, non-sporing, non-encapsulated, aerobic or facultative anaerobes, 2 to 4 × 0.6 µm, most strains are motile except Salmonella gallinarum and pullorum.
Salmonella Typhi and Paratyphi
2 to 3 µm Χ 0.6 µm
Gram negative bacilli
Motile due to peritrichous flagella
Aerobic or facultative anaerobes
Optimal temperature 37°C
Nutrient broth : Uniform turbidity
Blood agar: Colonies 2 to 3 mm, circular, low convex, smooth, translucent and non hemolytic
MacConkey agar: Non- lactose fermenter ( colorless colonies)
Deoxycholate Citrate agar (DCA): Non lactose fermenter colonies
Wilson and Blair bismuth sulfite medium: Jet black colonies with sheen
Enrichment media like selenite F broth or tetrathionate broth: Uniform turbidity
Methyl red positive, Voges-Proskauer test negative , non lactose fermenter, urea hydrolysis test negative , glucose fermenter and citrate utilization test variable. Lysine decarboxylase test positive , motile and hydrogen sulphide (H2S) variable
Serotyping : With the use of polyvalent and monovalent antisera
KauffmanN and White Scheme of serological classification of Salmonella works on the use of theses antisera.
Antigens of Salmonella
O antigen (somatic): Phospholipid protein polysaccharide complex, heat stable, alcohol stable, acid stable and less immunogenic
H antigen (flagellar) : Heat labile protein, alcohol labile, withstand formaldehyde and strongly immunogenic
Vi antigen and K antigen are capsular antigen. Vi antigen: glycolipid, surface antigen, heat labile, virulent to mice, persistent antibodies against it indicate carrier state.
F antigen (fimbrial): Preserved in 0.1 or 0.2 formaldehyde
M antigen: Loose extracellular polysaccharide slime consisting of colinic acid
R antigen : In S R mutation due to the loss of O antigens
Mode of transmission
10 bacilli through ingestion
Enteric fever/typhoid fever
Food poisoning /gasteroenteritis
Pathogenesis of Salmonella
Ingestion of Salmonella
Enter into body through lymphoid of pharynx.
In gut organisms attach with epithelial cells of intestinal villi and penetrate lamina propria, submucosa
Bacilli phagocytosed by macrophages or polymorphonulcear cells.
Enter mesesnteric lymph nodes and multiply there.
Enter thoracic duct and then blood stream.
It may affect liver, spleen, bone marrow, lung , kidney and heart.
Special features of Salmonella
Ability to withstand phagocytosis ( intra-cellular multiplication)
Resistance to bile
Symptoms due to endotoxin
step ladder fever
Congestion of mucus membrane
In first week
Serology ( Widal test)
In four week
Media available for Salmonella are-
Salmonella-Shigella (SS) agar
Enrichment media are-
Tetra thionate broth
Selenite F broth
Discharge from lesion
Transfer patient blood into blood culture medium (i.e. liquid medium like BHI broth, tryptone soy broth, bile broth etc.).
Incubate medium into incubator at 37°C for 5 days. ( If you are using Bactec ,no need of blind sub-culturing because positive vial indicated by this instrument via siren).
Check turbidity and subculture on solid media like blood agar and MacConkey agar.
After over night incubation at 37°C , check growth of the organisms and colony morphology.
Non -lactose fermenter colonies on MacConkey agar.
Inoculate stool in selenite F broth or tetrathionate broth and incubate.
Later, subculture in XLD agar or deoxycholate agar or MacConkey agar or Wilson and Blair medium.
Non lactose fermenter colonies on MacConkey agar or XLD (For Salmonella Typhi -black colonies) or DCA or Wilson and Blair medium ( For Salmonella Typhi -black colonies with sheen against green background) .
Urine culture ( positive in second and third week)
Non lactose fermenter colonies on MacConkey agar.
Culture using pus, rose spots, lymph nodes, CSF and bone marrow
Slide agglutination test
using polyvalent and grouping cum factor antisera
Widal test : Widal test is an agglutination test employed in the serological diagnosis of enteric fever. It also applicable in febrile agglutinins tests. The test is named after Georges Fernand Isidore Widal, a French physician and bacteriologist. Salmonella antibody starts appearing in the serum at the end of first week and rises sharply during the third week of enteric fever. This test measures agglutinating antibody levels against O and H antigens.
Diagnosis of carrier
Vi agglutination test
It contains Salmonella Typhi 1000million/ ml, Salmonella Paratyphi A 750 million/ ml and Salmonella Paratyphi B 750 million/ ml.
Streptomycin dependent strain vaccine
Ty21a (oral vaccine)
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