A conductance method for the assay and study of bacterial trimethylamine oxide reduction

Abstract

Bacterial growth and trimethylamine oxide (TMAO) reduction were measured by following the change in conductance of the growth medium. The method was used as a reliable taxonomic test for the ability of bacteria to reduce TMAO. Conductance measurements were also applied to assaying the enzyme TMAO reductase in resting cells of the marine alteromonad NCMB 400: the enzyme was only active under anaerobic conditions with pyruvate, lactate and formate being good donors; the KmTMAO was 93 ± 16 μmol/1; TMAO reductase activity was inhibited by several N‐oxides including nitrite and nitrate, and was relatively resistant to cyanide. The relevance of conductance measurements and the significance of TMAO reduction are discussed.

Rapid and automated detection of salmonella by electrical measurements

“…This was improved by increasing the pH from 5 0 to 5 9, but above pH 6-0 some precipitation occurred, resulting in reduced selectivity. The poor conductance response of S. typhimurium in RV/T was probably due to the inhibition of TMAO reduction at pH 6-0 or less (Easter, Gibson & Ward, 1982;Kim & Chang, 1974), and the poor ionization of TMA at pH values below 7-0.…”

“…Strains listed in Table 1 were inoculated into Wood & Baird's medium in Malthus conductance ampoules, and tested in the TMAO reduction assay of Easter, Gibson & Ward (1982).…”

“…The conductance assay described by Easter, Gibson & Ward (1982) was used to screen bacteria for their ability to reduce TMAO to TMA in the medium of Wood & Baird (1943).…”

“…TMAO is generally present in marine fish and is reduced to TMA during post-mortem bacterial spoilage. Easter, Gibson & Ward (1982) have described an automated assay for TMAO reduction utilizing modern instruments for measuring the conductance changes during the growth of microbial cultures. The reduction of TMAO, an uncharged neutral molecule, to the highly basic TMA yields a large change in conductance.…”

Shewanella putrefaciens Adhesion and Biofilm Formation on Food Processing Surfaces

“…The disks with a mixed biofilm were transferred to Malthus glass tubes containing 8 ml of a nutrient broth containing 1 g of trimethylamine oxide (TMAO) per liter (42). S. putrefaciens reduces the neutral TMAO to ionized trimethylamine by anaerobic respiration and causes an increase in conductance (11,35). Pseudomonads, which do not respire using TMAO, cause no change in electrical properties of the medium.…”