Optimization of isolation and culture method of Shigella spp. from stool samples

  Objective  To optimize the isolation method of Shigella spp. from stool samples.

  Methods  A total of 129 stool samples were cultured with Escherichia coli broth and Shigella enrichment broth. The ipaH gene was detected by PCR. Different selective media, including Xylose Lysine Desoxycholate agar, MacConkey agar, and SS medium, were used for the isolation of Shigella spp. The reference strains of Shigella spp. were used for simulated enrichment culture. Real-time PCR was used as detection method.

  Results  The positive rate of EC broth enrichment samples with anaerobic condition was 38.76% and 34 ipaH gene positive strains were isolated (26.36%). The positive rate of Shigella enrichment broth samples with anaerobic condition was 55.81%, which was significantly higher than that of EC broth (P<0.01), and 48 ipaH gene positive strains were isolated (37.21%). The isolation rate of Shigella spp. could be improved with other selective media such as MAC medium and SS medium except XLD medium. Anaerobic condition could increase the content of Shigella flexneri (Ct value decreased), but it had no obvious influence on Shigella sonnei.

  Conclusion  Enrichment with 2–3 different selective culture media in combination with molecular biological method might be an effective way to improve the isolation rate of Shigella spp. in stool samples.