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Appl. Environ. Microbiol., 09 1995, 3379-3384, Vol 61, No. 9
LT Gribbon and MR Barer
Growing and nonculturable cells of Helicobacter pylori and Vibrio
vulnificus were studied for the capacity to reduce tetrazolium salts in
order to elucidate the possible physiological basis for the proposed
"viable but nonculturable" (VNC) state. Initial difficulties in obtaining
consistent reduction of rho-iodonitrotetrazolium violet (INT) by H. pylori
led us to develop a method for studying the effect of adding exogenous
substrates on these reactions. The established procedure provided a profile
of substrate enhancement of oxidative activity revealed by INT reduction
which was related to both the identity and physiological state of the
organism studied. Representation and interpretation of these enhancement
profiles were facilitated by digital image processing. Nonculturable cells
of H. pylori produced by carbon and nitrogen starvation in air lost all
INT- reducing capacity in 24 h when stored at 37 degrees C, while 99% of
those produced at 4 degrees C retained oxidative activity for at least 250
days when tested in the presence but not in the absence of succinate,
alpha-ketoglutarate, or aspartate. Activity was detected at similar levels
in cells with coccoid and spiral shapes. In contrast, only 1% of
nonculturable cells of V. vulnificus, produced under conditions previously
reported to induce the VNC state in this organism, retained intrinsic
INT-reducing capacity; no substrate- enhanced activity occurred in the
remainder of the population. Thus, there was no common pattern of oxidative
activity indicative of a VNC state in both test organisms. Nonculturable
cells of H. pylori can retain several different oxidative enzyme
activities; whether these indicate viability or the persistence of cells as
"bags of enzymes" remains to be established.
Copyright © 1995, American Society for Microbiology
Oxidative metabolism in nonculturable Helicobacter pylori and Vibrio vulnificus cells studied by substrate-enhanced tetrazolium reduction and digital image processing
Department of Microbiology, Medical School, University of Newcastle upon Tyne, United Kingdom.
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