SALMONELLA

 

Characteristics

´Rod shaped.

´Gram negative bacteria.

´Causes infection in humans and vertebrates.

´Motile by peritrichous flagella except S. gallinarum pullorum.

´Non-spore forming and non-capsulate.

´May be aerobic or facultative anaerobes.

 


CULTURAL CHARACTERS: -

´Grow on ordinary culture media.

´Small circular, translucent, non lactose fermenting colonies are formed.



BIOCHEMICAL REACTION: 

´Do not ferment lactose or sucrose.

´Do not produce indole.

´    Ferment glucose, mannitol, maltose with production of acid and gas.

 


TAXONOMY: -

´The genus salmonella belongs to the family Enterobacteriaceae.

´The genus comprises two species;

´S. bongori and S. enterica which is divided into 6 subspecies.

´The taxonomic group contains more than 2500 serotypes.

´Salmonella have been clinically categorized as invasive (typhoidal) or non-invasive (non-typhoidal) based on host preference and disease manifestations in humans.




CLASSIFICATION

´Based on DNA-DNA hybridization there are 2 species;

1) Salmonella bongori

2) Salmonella enterica

      S. Enterica has 6 sub species.

 


Diseases caused by salmonella:

´Salmonella causes the following clinical diseases in human beings;

1) Enteric fever

2) Gastroenteritis

3) Septicaemia

 

 

1)ENTERIC FEVER:

Typhoid fever caused by S. typhi and paratyphoid fever caused by S. Paratyphi A, B and C.

 The name of typhoid was given by Louis who distinguished it from typhus fever.

 It is systemic disease characterized by fever and abdominal pain.

 

 

MECHANISM OF INFECTION: -

´The infection is caused by ingestion of contaminated food.

´Inside the gut bacilli attached to microvilli of ileal mucosa and penetrate the submucosa.

´Phagocytosed by macrophages.

´Their ability to resist intracellular killing and to multiply within the cells.

´They enter the Mesenteric lymph nodes where they multiply and via thoracic duct enter the blood stream causing bacteraemia.

´The incubation period is usually 7-14 days may range from 3-56 days.

 



2. GASTROENTERITIS: -

´Zoonotic disease.

´Caused by ingestion of contaminated food like poultry, milk, meat and eggs with salmonella.

´Characterized by nausea, vomiting and diarrhea.

´Fever and abdominal cramps are common.

 

 



3. SEPTICAEMIA:

´Commonly caused by S. choleraesuis and S. paratyphi C.

´ Infection occurs through oral route.

´Incubation period is short.

 




TRANSMISSION: -

´Close contact with acutely infected individuals or chronic carriers.
Infection occurs through oral route.
Most human infection caused by eating food or drinking water that has been contaminated by feces.
Food most commonly infected are;

          ◉uncooked Seafood, meat and poultry.

          ◉Uncooked eggs, vegetables and fruits.

 



DIAGNOSIS: -

´Testing blood and urine samples.

´    In chronic salmonellosis it may be bone marrow rather than blood.

 



TREATMENT:

´Because salmonella infection can be dehydrating, treatment focuses on replacing fluids and electrolytes.

´Severe cases may require hospitalization and fluids delivered directly into a vein.

´Anti-diarrheal and Antibiotics are also recommended

 



PREVENTION:

´Proper sewage disposal.

´Correct handling of food.

´Personal good hygiene.

 

 



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