Comparative study for Isolation of Yersinia pseudotuberculosis from Water

Cho, Chong Rae; Um, Tae Hyun; Paik, In Ki

Abstract

BACKGROUND
Yersinia pseudotuberculosis is recognized throughout the world as a cause of water-or food born infections in human and animals. Although many attempts have been made to define optimal conditions for the isolation of the organism from water, their isolation yields remain low; therefore, we tried to find an effective method for the recovery of Y. pseudotuberculosis from water.
METHODS
Water samples were deliberately contaminated with Y. pseudotuberculosis at various levels and then processed by the following three isolation METHODS: centrifugation, direct filtration, and intracellular culture. For the centrifugation method, the water samples were centrifuged at 5000 rpm for 1 hr and the final precipitates were inoculated in cefsulodin-irgasan-novobiocin(CIN) media. For the filtration method, the water samples were filtered by negative pressure and the filter papers were put directly on CIN media. For the intracellular culture method, the organisms were extracted from the HeLa cells that had been infected with Y. pseudotuberculosis and inoculated on CIN media. We also examined the efficacy of the filtration method after cold enrichment with a mixture of Y. pseudotuberculosis, Escherichia coli, and Citrobacter freundii.
RESULTS
With the concentration of 3x10(2)/100 mL, Y. pseudotuberculosis was isolated only by the filtration method; however, none of the culture methods were good enough to recover the organism from the water sample when the concentration was 3x10/100 mL. With cold enrichment, however, the recovery was much more efficient; the organism grew after direct inoculation or after filter inoculation when the starting concentrations were 3x10(2)/100 mL or 3x10/100 mL, respectively.
CONCLUSION
A combined use of direct filtration and filter inoculation after cold enrichment is the most effective method to yield Y. pseudotuberculosis isolation. The introduction of effective methods for the isolation of Y. pseudotuberculosis from untreated drinking water would increase the awareness by the public of the health hazard of spring water.