S. typhi is the causal organism of typhoid (or enteric) fever, representing a more serious form of Salmonella infection than the other salmonellae.
Growth and Control
The characteristics of this species are essentially those of other non-heat resistant Salmonella. Full details are given on the entry for non-typhoid salmonellae. This is the abridged version appears with S. typhi-specific data given where available.
Temperature: Minimum 7°C, growth greatly reduced at <15°C. Maximum 45°C. Optimum 35-37°C.
Water Activity: Minimum 0.94, optimum 0.99, maximum >0.99.
pH: Minimum 3.8, optimum, 7-7.5, maximum 9.5. The minimum pH is influenced by other factors such as the acid present, and the presence of nitrite etc.
Atmosphere: Can grow in the presence or absence of air. Growth under nitrogen is only slightly less than that under air. Grows at 8-11°C in the presence of 20-50% CO2.
Temperature: Survival can be quite good, for example the organism was viable for 190 days when inoculated onto chocolate biscuits, and for 230 days on sweets. S. typhi can survive for 4 days in shellfish stored at 10-13°C, and in ice for in excess of 90 days.
Viable but Non-Culturable (VNC) Cells: This organism is thought to undergo transition to the VNC state in water.
Inactivation (CCPs and Hurdles):
Water Activity: Inactivated within 1 day when exposed to 30% NaCl.
Treatment of S. Typhi contaminated bean sprouts with 200 mg/l sodium hypochlorite only reduced the count by 1.5 log cycles (i.e. ineffective).
Incubation: 7-28 days (average 14)
Symptoms: Fever, malaise, anorexia, spots on trunk. These occur commonly with pea-like diarrhoea or constipation. Patients may become delirious. Recovery is slow, taking from 1 to 8 weeks. Hospitalisation rate estimated at 75%, case fatality rate 0.4%.
Condition: Typhoid, or enteric, fever.
Toxins: Toxins are not produced in foods.
At Risk Groups: In non-endemic areas children between 0-5 years are at the greatest risk.
Treatment: Quinolone and cephalosporin antibiotics may be used. Vaccines are available.
Reservoirs / Sources
Human: Humans are the sole reservoir of this organism. Carriers may harbour the organism in their gall bladders.
Animal: Does not infect animals.
Food: Foods may become contaminated from food handlers or via the use of contaminated water during processing. Shellfish grown in polluted waters may also accumulate the organism within their tissue.
Environment: Water that has been contaminated by human faecal pollution is a transmission route. Survival in seawater for up to 9 days, and in sewage for weeks have been recorded. Survival in groundwater was better than in pond, stream or lake water and this was attributed to less grazing pressure by protozoa.
Transmission Routes: Mainly from water or from human carriers.