Salmonella bacteria

Salmonella enterica

salmonella salmonella

Four different serotypes of Salmonella enterica ssp. enterica on Endo agar with biochemical slope (see here). Glucose degradation is accompanied with formation of acid compounds (red slope) and gas production (serotype Typhi without gas). All strains are lactose negative and conspicuous is strongly positive reaction around mannitol tablet and hydrogen sulphide production with formation of black precipitate under the glass and in the area of loop punctures. Serotype Typhi and Typhimurium isolated from hemocultures. Highly mucoid strain of serotype Enteritidis isolated from a patient with urinary infection.

Salmonella enterica is a rod shaped, flagellated, aerobic, Gram-negative bacterium, and a member of the genus Salmonella. S. enterica has an extraordinarily large number of serotypes (over 2500 have been described). The biomedically most relevant subspecies is called S. enterica ssp. enterica, whose following Serovars have special clinical significance in human disease:

  • Salmonella enterica serovar (serotype) Typhi (historically elevated to species status as S. Typhi) is the disease agent in typhoid fever.
  • Salmonella enterica serovar (serotype) Typhimurium (also known as S. Typhimurium) can lead to a form of human gastroenteritis sometimes referred to as salmonellosis.
  • Salmonella enterica serovar (serotype) Paratyphi A is associated with paratyphoid fever.

Most cases of salmonellosis are caused by food infected with S. enterica, which often infects cattle and poultry, though also other animals such as domestic cats and hamsters have also been shown to be sources of infection to humans. However, investigations of vacuum cleaner bags have shown that households can act as a reservoir of the bacterium; this is more likely if the household has contact with an infection source, for example members working with cattle or in a veterinary clinic. Raw chicken and goose eggs can harbor S. enterica, initially in the egg whites, although most eggs are not infected. As the egg ages at room temperature, the yolk membrane begins to break down and S. enterica can spread into the yolk. Refrigeration and freezing do not kill all the bacteria, but substantially slow or halt their growth. Pasteurizing and food irradiation are used to kill Salmonella for commercially-produced foodstuffs containing raw eggs such as ice cream. Foods prepared in the home from raw eggs such as mayonnaise, cakes and cookies can spread salmonella if not properly cooked before consumption.

Abbreviated from Wikipedia

Salmonella enterica basic characteristics


Identification of Salmonella enterica

  • MacConkey growth: +
  • Indole production: -
  • Methyl red: +
  • Voges-Proskauer: -
  • Citrate; Simmons (depends on serotype!! e.g., serotype Typhi = "-"): +
  • Hydrogen sulfide; TSI(depends on serotype!!): +
  • Urea hydrolysis: -
  • Lysine decarboxylase (serot. Paratyphi A: negative): +
  • Arginine dihydrolase: D
  • Ornithine decarboxylase (depends on serotype!!; e.g., serotype Typhi = "-"): +
  • Motility (36 °C) (depends on serotype!!): +
  • D-glucose/gas (depends on serotype!! e.g., serotype Typhi "+/-"): +/+
  • D-mannitol fermentation: +
  • Sucrose fermentation: -
  • Lactose fermentation: -
  • D-sorbitol fermentation (depends on serotype!!): +
  • Cellobiose: -
  • Esculin hydrolisis: -
  • Acetate utilization: -
  • ONPG test: -

  • + positive ( > 90% of strains are positive)
  • D most positive (51 - 89%)
  • d most negative (11 - 50%)
  • - negative (0 - 10%)

Antibiotic treatment of Salmonella infections

Usually no ATB treatment necessary for uncomplicated diarrheal illness.
Should be always guided by in vitro susceptibility tests!! Often antibiotic resistant!!
Selection of appropriate antibiotics depends on diagnosis!!


  • ampicillin
  • amoxicillin
  • trimethoprim-sulfamethoxazole
  • ciprofloxacin
  • chloramphenicol
  • ceftriaxone

Typhoid fever

  • chloramphenicol
  • ampicillin
  • amoxicillin
  • trimethoprim-sulfamethoxazole
  • fluoroquinolones (e.g., ciprofloxacin)
  • cefotaxime
  • ceftriaxone

Salmonella enterica on agar plates

blood agar plate with salmonella colony morphology of salmonella on blood agar salmonella colonies MacConkey agar plate with salmonella streaked MacConkey plate with Samonella and E.coli salmonella, klebsiella, e.coli on MacConkey salmonella and klebsiella growth on MacConkey salmonella and e.coli on MacConkey salmonella enterica on MacConkey colony appearance of salmonella and e.coli on MacConkey comparison of salmonella and e.coli on endo mucoid colonies of salmonella colony appearance of salmonella and e.coli on endo colonies of salmonella on Endo agar salmonella on desoxycholate citrate agar desoxycholate citrate agar, salmonella and klebsiella colonies salmonella on DX agar salmonella on desoxycholate agar growth of salmonella on DX agar hydrogen sulfide positive, black colonies of salmonella salmonella colonies with black centers on desoxycholate citrate salmonella growth on salmonella-shigella agar bacterial colonies on SS agar salmonella colony appearance on SS agar (salmonella shigella agar) salmonella colonies on SS agar salmonella and e.coli growth on CLED agar salmonella cultivation on CLED agar colony appearance of salmonella on CLED salmonella growing on XLD salmonella and e.coli on XLD salmonella colonies close-up, XLD agar XLD agar plate with salmonella Enteritidis hand holding XLD agar plate with salmonella

Salmonella enterica tests for identification

salmonella on Endo with biochemical slope identification of Salmonella enterica salmonella biochemical tests various serotypes of salmonella salmonella hydrogen sulfide test

biochemical identification of salmonella salmonella growth on TSI (triple sugar iron agar) salmonella slide agglutination

Salmonella enterica Gram stain

salmonella morphology under the microscope

Salmonella enterica SEM

salmonella typhimurium SEM

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