salmonellae species

Genus: Salmonella
Description:
Salmonella are typical member of the Enterobacteriaceae, its gram negative bacilli able to grow on a wide range of relatively simple media, they are facultative anaerobic bacteria, and distinguished from other member of the family Enterobacteriaceae by their biochemical characteristics and antigenic structure.
It’s motile, non – spore forming, attack sugar fermentativly, its Oxidase negative and Urease negative.
Normal habitat:
Most of Salmonella are found in the intestinal tract of animal especially of pigs, caws, goats, rodent, ducks and other poultry. Salmonella typhi and Salmonella paratyphi are found only in human and are excreted in faeces and urine of infected patients and are present in the gall bladder of long – term carriers.
Infection is by ingestion of contaminated food or drinking contaminated water. Salmonella typhi is spreading mainly by water and Salmonella paratyphi (A&B) by food. It’s sensitive to heat (killed by proper cooking). Salmonellae are not killed by drying and there fore survive in product such as dried eggs.
In Schistosomasis endemic areas there is a high incidence of chronic Salmonella typhi and Salmonella paratyphi infections and carriers (Salmonella adhere to adult Schistosoma flukes)
Medical important species:
• Salmonella typhi
• Salmonella paratyphi (A,B and C)
• Salmonella typhimurium
• Salmonella enteritis
Antigenic structure:
The typical Salmonella possesses two sets of antigens which are demonstrated by serological reactions in the laboratory.
• Heat – stable polysaccharide which form part of the cell wall lipo – polysaccharide known as O antigen (somatic)
• Flagellar antigen (formed from structural proteins (heat labile) , has a biphasic form (I &II).
• Some strain also produce surface polysaccharide heat – stable antigen known as Vi antigen which found in Salmonella typhi and Salmonella paratyphi (C ) it is associated with the virulence of organism.
• Salmonella are grouped according to their O antigen in to many groups (A – Z) (51 – 61) and (64 – 66).

Pathogenicity:
• Salmonella cause a disease known as salmonellosis or enteric fever or typhoid fever. The infection is transmitted by ingestion of improperly cooked poultry meat and egg also by contaminated milk and milk product. The infected dose is 105 cells, but recently it is 100 cells. The disease characterized by fever with low pulse rates headache, generalized pain, enlargement of spleen (spleenomegally), mental confusion, intestinal hemorrhage and perforation, skin cover by rash (Rose spot), the reaction followed by anemia, TWBS are low, incubation period (7 – 14 days).
• Nephrotyphoid: In those with urinary Schistosomasis, the condition is an immune complex disorder of the kidneys and is characterized by fever, edema, marked albuminouria and haematuria.
• Salmonella paratyphi (A& B): Associated with a disease of paratyphoid, usually mild and characterized by diarrhea and vomiting(less invasive).
• Salmonella paratyphi (C): May cause septicemia, arthritis, and inflammation of gall bladder
• Salmonella typhimurium: cause food poisoning (acute gastroenteritis) characterized by nausea, vomiting, and law grate of fever.
Complication of Salmonellosis:
• Osteomylitis (inflammation of bone)
• Abscesses of spleen
• Typhoid arthritis
• Very rare cause pneumonia and endocarditic



Diagnosis:
• Specimens (depending on the site of infection) include: blood, stool and urine.
• Microscopy: Salmonella are a gram negative usually motile rod. Some strain re capsulated.
• Culture: Salmonella are aerobic and facultative anaerobic optimum temperature for growth is 35-37◦C and pH range from (7 – 7,2)
• Mac conkey agar: Salmonella are non ferments lactose and producing smooth pale yellow colonies.
• On XLD colonies are red black colonies (alkaline)
• DCA : colonies are smaller in size, smooth, pale yellow (NLF), with the black center (except Salmonella paratyphi (A)
• O KIA slope butt gas H2S
R Y + +
Biochemical Test
Primary test:
• Catalase + ve
• Oxidase - ve
• Motility + ve
• Production of acid and gas + ve
• O –F test Fermentative
Secondary test:
• Indole test - ve
• Citrate utilization test - ve
• MR test + ve
• V – p test - ve
• H2S test - ve
• Urease -ve
Serological test:
Widal test:
When culture facilities are not available, the Widal test done to test the presence of salmonella antibodies. Salmonella antigen suspensions were commercially available in about 5 ml amount (stained).

Antimicrobial sensitivity
• Co – trimoxazole
• Ampicillin
• Chloramphenicol
Causes of raised (O) and (H) titer other than active typhoid:
• Previous salmonella infection
• Chronic salmonellosis associated with Schistosoma infection
• Vaccination
• Current infection with other salmonella species
• Chronic liver disease
• Rheumatic arthritis
• Nephritic syndrome
• Rheumatic fever
• Malaria[left]