Objective: To identify the isolates of Shewanella spp. from specimens of food poisoning based on biological and biochemical analysis.
Methods: Strains were obtained from the investigation on two food poisoning episodes in September and October, 2007 in Ma'anshan city, Anhui province. In accordance with the national standard protocol (GB/T 4789), all specimens were enriched and isolated on selective medium, and the suspected strains were identified by the VITEK-32 and API20E systems. For Shewanella spp. identified by the biochemical system, more characteristics were analyzed using auxiliary biochemical, growth, hemolytic and drug-resistance tests. DNAs of Shewanella spp. were extracted, 16S rDNA was PCR amplified and sequenced with universal 16S rDNA primers. Phylogenetic tree was constructed with MEGA 4.0.
Results: After enrichment, all specimens were inoculated to selective medium and Shewanella spp. strains were isolated from 8 samples with single colony on both TCBS and BP media. The characteristics of growth in the Triple Sugar Iron (TSI) agar appeared to have had hydrogen sulfide production but no gas production or positive oxidase. No Shewanella spp. strain was detected in WS, SS and EMB media. The 8 strains were identified as Shewanella algae (S. algae) or Shewanella putrefaciens (S. putrefaciens) by VITEK-32, as S. putrefaciens by API20E system. No other enteropathogenic bacteria, including Vibrio cholerae, Salmonella, Vibrio parahaemolyticus, Proteus vulgaris or Staphylococcus aureus, were detected from those 8 samples. From 16S rDNA phylogenetic trees, 7 out of 8 Shewanella spp. were identified as S. algae, 1 as S. putrefaciens.
Conclusion: Strains of Shewanella spp. were isolated from samples of the food poisoning episodes, providing a possible clue to investigate the role of Shewanella spp. on food poisoning.