METHIONINE UPTAKE AND CYTOPATHOGENICITY OF VIABLE BUT NONCULTURABLE SHIGELLA-DYSENTERIAE TYPE-1

A pathogenic strain of Shigella dysenteriae type 1 was selected for st udy to elucidate the physiology and potential pathogenicity of organis ms in the viable but nonculturable (VBNC) state in the environment. St udies in our laboratory have shown that S. dysenteriae type 1 survives in laboratory microcosms in the VBNC state for long periods of time, i.e., more than 6 months. VBNC cells of S. dysenteriae type 1 were fou nd to retain cytopathogenicity for cultured HeLa cells. To determine w hether VBNC S. dysenteriae type 1 expressed protein after loss of cult urability, S-35 labelled methionine was added to suspensions of VBNC c ells. Total cellular proteins were extracted and examined by autoradio graphy. Results indicate that VBNC S. dysenteriae type 1 is capable of both active uptake of methionine and incorporation of methionine into protein. Amino acid uptake and protein synthesis substantiate the via bility of cells of S. dysenteriae type 1 in the VBNC state, i.e., alth ough the cells are unable to be cultured on laboratory media by standa rd bacteriological methods, the cells remain metabolically active. Fur thermore, VBNC cells of S. dysenteriae type 1 may pose a potential pub lic health hazard that has not yet been recognized.