Effects of short-chain nitrocompounds against Campylobacter jejuni and Campylobacter coli in vitro

Campylobacter is an important human pathogen that colonizes the gut of food producing animals. In this study, the effects of 2-nitro-1-propanol, 2-nitroethanol, nitroethane, and 2-nitro-methyl-propionate (0, 10, and 20 mM) on growth of Campylobacter jejuni were tested during culture in Bolton Broth adjusted to pH 5.6, 7.0, or 8.2. The effects of the nitrocompounds were also tested against C. coli in Bolton Broth but adjusted to pH 8.2 only. Viable cell counts of samples taken at intervals during incubation revealed main effects (P < 0.05) of nitroethane, 2-nitro-1-propanol, 2- nitroethanol, and 2-nitro-methyl-propionate as evidence by reduced survivability of C. jejuni. A marked effect of pH on the survivability of C. jejuni during incubation with all compounds was observed, with greater activity observed at pH 8.2 than at pH 5.6 or 7.0 for nitroethane, 2-nitro-1-propanol, 2-nitroethanol, but not for 2-nitro-methyl-propionate. In the case of 2-nitro-methyl-propionate, survivability of C. jejuni was reduced most at pH 5.6. Except for 2-nitro-methyl-propionate, which was ineffective, all nitrocompounds elicited similar effects on C. coli when cultured at pH 8.2. The effect of nitroethane and 2-nitro-1-propanol (10 mM) on naturally-occurring Campylobacter was further investigated during incubation of a porcine fecal suspension. Campylobacter concentrations decreased more rapidly (P < 0.05) during incubation of porcine fecal suspensions supplemented with 2-nitro-1-propanol than unsupplemented control suspensions or suspensions supplemented with nitroethane thus reiterating the superior inhibitory effect of 2-nitro-1-propanol.