Annals of Clinical Microbiology, The official Journal of the Korean Society of Clinical Microbiology

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pISSN 2288-0585 eISSN 2288-6850

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

Original article

Annals of Clinical Microbiology (Ann Clin Microbiol) 1998 December Volume 1, Issue 1, pages 57-62.

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

Eun Gyung Ko, M.D., Chang Jung Kim, M.D., Key Earn Lee, M.D., Jihyun Cho, M.D., and Young Hoe Moon, M.D.

Department of Clinical Pathology, College of Medicine, Wonkwang University, Iksan, Korea

Abstract

Background: In developed countries, food-borne 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 inoculated directly or after enrichment (10^5 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. (Korean J Clin Microbiol 1998;1(1):57-62)

Keywords

Stool culture, Salmonella, Shigella, Vibrio, Yersinia