Comparison of Isolation rate of the Pathogenic Microorganisms According to Stool Culture Methods

Ko, Eun Gyung; Kim, Chang Jung; Lee, Key Earn; Cho, Jihyun; Moon, Young Hoe

Abstract

BACKGROUND: In developed countries, food-born diseases have decreased and hospital laboratory have taken more simple method rather than complex enrichment-selective methods. But detection rate of pathogenic bacteria in stool culture was not so high.
METHODS
We mixed 4 pathogenic bacteria (S. typhi, S. flexneri, V. cholerae and Y. enterocolitica) with 3 stool specimens from healthy persons (for Y. enterocolitica, 5 specimens) and innoculated directly or after enrichment (105 bacteria/plate). After proper incubation, we counted suspected colonies and calculated true positive rate after identification of each colonies.
RESULTS
For S. typhi, in the case of direct innoculation on the MacConkey, XLD and SS agar, positive rate of selected colonies were below 36.6%. After enrichment in SF broth for 8 hours, the rate were 80.0%, 83.0% and 70.0% respectively. For S. flexneri, the rates were 86.7%, 100%, 93.3% in direct innoculation, and were highest after enrichment in GN broth for two hours (93.3% in MacConkey and 100.0% in both XLD and SS agar). For V. cholerae, inspite of screening by catalase and oxidase tests, positive rate of selected colonies were 0% (0/7 colonies) in direct innoculation on the MacConkey. After enrichment in APW about 1 day and on TCBS agar, the rate were 100%. For Y. enterocolitica, after incubation at room temperature for 2 days, most selected colonies were Y. enterocolitica on CIN media.
CONCLUSION
For more efficient detection of pathogenic bacteria in stool culture, combination of direct innoculation on MacConkey agar and on one or two selective media after proper enrichment process, should be considered.