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.
Salmonella enterica basic characteristics
- GRAM-NEGATIVE RODS
- CATALASE: POSITIVE
- OXIDASE: NEGATIVE
- FACULTATIVELY ANAEROBIC
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 infectionsUsually 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!!
- fluoroquinolones (e.g., ciprofloxacin)
Salmonella enterica on agar plates
Salmonella enterica tests for identification
Salmonella enterica Gram stain
Salmonella enterica SEM
CENTERS FOR DISEASE CONTROL AND PREVENTION (CDC)
- What is Salmonellosis?
- Typhoid fever
- Typhoid fever FAQ
- ANTIGENIC FORMULAE OF THE SALMONELLA SEROVARS