Key words: Salmonella Typhi, Water borne infection.

Key words: Salmonella Typhi, Water borne infection.

Table 1. Characteristics of water samples tested.

Fig. 1. Survival of Salmonella typhi, Salmonella Fig. 2. Survival of Salmonella typhi, Salmonella cells (107 in 0.1ml suspension) were, immediately after collection of water samples (Feb. 5, 1973), added to 100ml of each sample and incu- when collected). Viable cells of the test organisms were enumerated daily. Phosphate buffer- cells (107 in 0.1ml suspension) were, immediately after collection of water samples (June 25, 1973), added to 100ml of each sample and incubated at 23 Ž (=mean temperature of samples when collected). Viable cells of the test organisms were enumerated daily. Phosphate buffer- Salmonella typhi (E11) Salmonella typhi (53) Salmonella typhi (E11) Salmonella typhi (53) Salmonella paratyphi B Shigella sonnei Salmonella paratyphi B Shigella sonnei

Washed cells were, immediately after collection of water samples, added to 100ml of each sample and incubated at indicated temperature (mean temperature of each set of samples when collected). Sets of samples were collected on (A) Feb. 4, 1974, (B) Dec. 17, 1973, (C) May 21, 1973, and (D) Aug. 20, 1973, respectively. Phosphate Fig. 4. Correlation between water temperature and survival time index (T 1/10) in Salmonella typhi (Ell). Survival time index was enumerated as the time (days) for reduction of initial population (105/ml) to 1/10. Table 2. Comparison of survival time index in Salmonella typhi (E11) in relation to temperature of sewage, river water, estuarine water, and sea water. a) Upper figure indicates the mean temperature of water samples when collected, and lower figure indicates the temperature changed from the mean temperature of the samples. b) Survival time index (T 1/10) was enumerated as the time (days) for reduction of initial population (105/ml) to 1/10.

Fig. 5. Correlation between water temperature and survival time index (T 1/10) in Salmonella paratyphi B. Survival time index was enumerated as the time (days) for reduction of initial population (105/ml) to 1/10. Fig. 6. Correlation between water temperature and survival time index (T 1/10) in Shigella sonnei. Survival time index was enumerated as the time (days) for reduction of initial population (105/ ml) to 1/10. Table 3. Comparison of survival time index in Salmonella typhi (E11) in relation to inoculum size in sewage, river water, estuarine water, and sea water. a) Washed cells (0.1m1 of cell suspensions of 105/ml, 106/ml, 107/ml, and 108/ml, respectively) were, immediately after collection of water samples, added in duplicates of 100ml of water samples and incubated at 12 Ž. Viable cells of S. typhi were enumerated daily. b) Survival time index was enumerated as the time (days) for reduction of initial population to 1/10 (T 1/10) and 1/100 (T 1/100).

Fig. 7. Survival of Salmonella ty phi, Salmonella paratyphi B, and Shigella sonnei in untreated (U) and membrane-filtered (F) water samples from llection of water samples and membrane-filtration, added to 50m1 of each sample and incubated at 10 Ž. Mean temperature of samples when collected (Feb. 4,1974) was 10 Ž. Panels c and d demonstrate survival of S. typhi in temperature- Fig. 8. Survival of Salmonella typhi, Salmonella paratyphi B, and Shigella sonnei in untreated (U) and membrane-filtered (F) water samples from collection of water samples and membranefiltration, added to 50ml of each sample and incubated at 25 Ž. Mean temperature of sampl-

Fig. 9. Effects of temperature and ph on survival of Salmonella typhi and Salmonella paratyphi B. Washed cells (107 in 0.1ml suspension) were added in duplicates of 50m1 of 1/20M phosphate

4) Nabbut, N. H. and Kurayiyyah, F.: Survival of Salmonella typhi in sea-water. J. Hyg. Camb., 70: 223-228, 1972.

7) McFeters, G. A. and Stuart, D. G.: Survival 9) Conn, N. K., Heymann, C. S., Jamieson, A., of coliform bacteria in natural waters: field McWilliam, J. M. and Scott, T. G. Waterborne typhoid fever caused by an unusual and laboratory studies with membrane-filter chambers. Appl. Microbiol., 24: 805-811, Vi-phage type in Edinburgh. J. Hyg. Camb., 1972. 70: 245-253, 1972. 8) Lendon, N. C. and Mackenzie, R. D.: Trac- ing a typhoid carrier by sewage examination. Mon. Bull. Minist. Health, 10: 23-27, Survival of Salmonella typhi in Urban Water System and Coastal Sea Water Takamasa NISHIO and Junzo NAKAMORI Hiroshima Prefectural Institute of Public Health, Hiroshima 734 Laboratory model experiments were made with the object of clarifying the vital states of Salmonella typhi in urban water system and coastal sea water, in comparison with those of Salmonella paratyphi B and Shigella sonnei, by adding washed cells of these organisms at a ratio of 10-/ml to samples of sewage, river water, estuarine water and sea water. when collected were then observed. Their survival rates at the mean temperature of the samples Viable cells of S. typhi decreased in number as the time proceeded in each of the water samples. Almost no V-W and S-R variations were found during the period of survival. When the time (days) for reduction of initial population to 1/10 (T1/10) was used as the survival time,index T1/10 at temperatures below 15 Ž(2.37.8) was significantly (P<0.01) greater than those at temperatures above (0.4 `2.2) in each of the water samples used, and it became apparent that T1/10 is inversely correlated closely with water temperature. Correlation coefficients between water temperature and T1/10 were in sewage, -0.96 in river water, -0.90 in estuarine water and-0.77 in sea water, respectively. It was difficult to ascertain any unique relation between survival and variety of water samples or ph, BOD, COD, C1-concentration, and the number of coliforms and other culturable bacteria, unlike with the temperature of the samples. Growth or considerable prolongation of the period of survival was found in membrane-filtered water samples. Thus, the decrease of viable cells of S. typhi in untreated water samples is considered to be mostly due to a competition with-and predation by those micoorganisms normally living therein, and intensity of these bactericidal actions is considered to be proportional to water temperature. These findings suggest that survival of S. typhi in urban water system is the greatest in the winter season and the most brief in summer, and that in winter when S. typhi is discharged in sewage the organism may enter the coastal sea and may survive sufficiently long in sea water. With Salmonella paratyphi B and Shigella sonnei, also, approximately similar results were obtained as with S. typhi, although the test organisms showed a tendency for prolonged survival in the order of S. paratyphi B>S. S. sonnei. Possibility of transmission of S. typhi to man through shellfish which has been exposed to it in the sea was discussed.