[Detection of the viable but nonculturable Escherichia coli O157:H7 in aquatic microcosm]

Abstract

Objectives: This study is to monitor the survival of E. coli O157:H7 in the aquatic microcosm from Han River and explore the feasibility of fluorescence staining, heterotrophic plate count and ELISA in detection of viable but nonculturable E. coli O157:H7.

Methods: E. coli O157:H7 were added into aquatic microcosm from Han River and cultured with low temperature and oligo-nutrition. Then the survival of E. coli O157:H7 were real-time monitored by acridine orange direct count (AODC), direct viable count (DVC)-CTC staining, DVC-nalidixic acid (NA) staining, heterotrophic plate count (HPC) and ELISA.

Results: E. coli O157:H7 can be converted to a viable but nonculturable state in the aquatic microcosm from Han River 58 days after cultured at 4°C with oligo-nutrition. The amount of viable E. coli O157:H7 was measured as 1.2 × 10(5) CFU/ml by DVC-CTC and 9.0 × 10(4) CFU/ml by DVC-NA, whereas the amount of culturable bacterial determined by HPC is 0. The amounts of bacteria determined by ELISA are basically stable within 58 days around 10(6) CFU/ml.

Conclusion: E. coli O157:H7 can be converted into a viable but nonculturable state in Han River water at 4°C with oligo-nutrition, and ELISA combined with fluorescence staining and heterotrophic plate count can be used in quantitative detection of the viable but nonculturable E. coli O157:H7.