Effect of Environmental Factors on Survival of Salmonella typhimurium in Soil1
- L. M. Zibilske and
- R. W. Weaver2
Salmonellae have a wide host range that includes cattle and humans. Appoximately 10% of the cattle excrete this microorganism in their manure. Most manure is ultimately disposed of on soil with little pretreatment. The survival times of salmonellae in soils varies greatly. This investigation was undertaken in the laboratory to determine how accurately salmonella survival can be predicted when environmental conditions are known. Salmonella typhimurium was inoculated into two Texas soils, a clay and a fine sandy loam, using cattle manure slurry and saline as inoculum carriers. Soil samples were incubated in the laboratory at three temperatures and moistures: 5, 22, and 39°C; and 0, 0.5, and >22 atm tension, respectively. Survival was monitored for 12 weeks by direct spread plating of soil dilutions onto dulcitol-iron thiosulfate (DIT) medium developed for this experiment. The DIT medium restricted growth of normal soil microflora but allowed growth and differentiation of S. typhimurium. Statistical evaluation of treatment effects was complex because of three factor interactions. Soil moisture and temperature interacted as did soil moisture and inoculation method. Time as a factor strongly interacted with moisture, soil, and temperature. S. typhimurium died within 1 week in dry soil incubated at 39°C. For some treatment combinations incubated at 39°C, interactions occurred that resulted in survival to 42 days. Survival at 5 and 22°C was comparable and usually longer than at 39°C. Salmonella populations increased in some samples at 3 days but declined afterward.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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