Salmonella and shigella

• Organisms in the Enterobacteria group

  • Salmonella
  • Shigella
• Salmonella

  • Complex with many serogroups
  • Reservoirs include several animals & humans
• Shigella

  • Not so complex with only 4 serogroups
  • Reservoirs include only humans
• Serogroups of Shigella

  • S. dysenteriae
  • S. flexneri
  • S. boydii
  • S. sonnei
• Examples of Salmonella

  • S. Typhimurium
  • S. Typhi
  • S. Choleraesuis
• Kauffmann-White scheme


  Serotypes based on ‘O’ and ‘H’ antigens
• ‘O’ antigens

  Determined by somatic antigens
• There are over 6 ‘O’ groups
• ‘H’ antigens

  Determined by flagella antigens
• There are 2 flagella proteins (phase 1 & 2)
• Phase variation occurs
• K antigen

  capsule
• Some Salmonella are non-typeable
• Salmonella classification (Present)

  • S. enterica subsp. enterica
  • S. enterica subsp. salamae
  • S. enterica subsp. arizonae
  • S. enterica subsp. diarizonae
  • S. enterica subsp. houtenae
  • S. enterica subsp. indica
  • S. bongori
• Total number of Salmonella genus is 2,501
• Shortened classification of Salmonella

  • Salmonella Typhi
  • Salmonella Paratyphimurium
• Salmonella infections are acquired by ingestion of contaminated food or water
• Enteric fever


  Infection source is humans
• Salmonellosis

  Infection source is various animals
• Factors affecting likelihood of infection/severity

  • Infective dose
  • Strain type
  • Status of host defense mechanism
• Most infections range from asymptomatic self-limiting gastroenteritis to severe systemic illness
• Pathogenesis of Salmonella infections

  1. Attach to M cells

  2. Invade deeper tissues

  3. Infect cells of the R/E system

  4. Penetrate ileal mucosa
• Clinical syndromes of Salmonella infections

  • Enteric fever
  • Gastroenteritis
  • Septicaemia
  • Metastatic lesions
  • Asymptomatic/carrier state
• Causes of Enteric Fever

  • S. Typhi
  • S. Paratyphi A
  • S. Paratyphi B
  • S. Paratyphi C
• Clinical signs of Enteric Fever

  Incubation Period: 7-21 days<|>Fever with relative bradycardia<|>Hepatosplenomegaly<|>Abdominal distention<|>Intestinal perforation<|>Intestinal haemorrhage<|>Toxaemia<|>Mortality 20% if untreated
• Lab diagnosis specimens for Salmonella

  • Blood cultures
  • Stools
  • Urine
  • Bone marrow
• Bone marrow is the most sensitive of all tests
• bone marrow testing

  Inconvenient for diagnosis
• ELISA


  More sensitive and specific for diagnosis
• Treatment options for Salmonella infections

  • Ciprofloxacin
  • 3rd generation cephalosporin
  • Amoxycillin
  • Cotrimoxazole
  • Chloramphenicol
• Organism is increasingly resistant to treatment options with the alternatives mentioned (ACC)
• Duration of treatment is 10-14 days
• Sources of infection for Enteric fever

  • Contaminated foods
  • Contaminated water
• Four percent of convalescing patients continue to shed organisms in stools 1 year after infection
• Chronic carriers are associated with carriage in gall bladder
• Control measures for Salmonella

  • Health education on personal hygiene
  • Improvement of water and sewage engineering
  • Vaccination
• Common serovars associated with salmonellosis

  • Typhimurium
  • Enteritidis
  • Virchow
  • Agona
  • Hadar
• Frequency of other serovars depends on geographical location
• Carrier states for Salmonella

  • Subclinical
  • Convalescent
  • Chronic
• Serology


  Detection of ‘O’ and ‘H’ antigens