Preparation of simulated stool specimens for proficiency testing scheme on the detection of Salmonella and Shigella

Abstract

Objective To prepare simulated stool specimens for proficiency testing (PT) by mixing lentils with Salmonella, Shigella and Escherichia coli strains and to establish an assessment scheme for the detection of Salmonella and Shigella in clinical samples. Methods Salmonella, Shigella and Escherichia coli strains were respectively spiked to lentils in Cary-Blair transport medium to create simulated stool specimens. Various ratios of Escherichia coli to Salmonella strains were spiked to lentils to prepare mixed simulated stool specimens. The accuracy and stability of prepared stool samples for PT were tested in-house. Results of sample detection were collected from participating laboratories for further external quality assessment. Results The Escherichia coli and Salmonella strains mixed at ratios of 100∶1 to 106∶1 could be efficiently isolated from the media. Enrichment was needed in order to effectively isolate Salmonella strains from the media when the ratios of Escherichia coli to Salmonella strains were 104∶1 to 106∶1. Of the16 participating laboratories, 14 laboratories (87.5%) received a grade of and the other 2 laboratories (12.5%) received a grade of mainly satisfactory . Conclusion The simulated stool specimens and the PT procedures designed in this study were suitable for proficiency testing program on the detection of Salmonella, Shigella and other similar microbes. Key words: Proficiency testing; Salmonella; Shigella; Escherichia coli