Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 5/25/2016
Publication Date: N/A
Technical Abstract: Formate contributes to virulence of Escherichia coli and Salmonella via induced expression of invasion genes and enhanced fitness and acid resistance during anaerobic growth. Ethyl nitroacetate (ENA) inhibits methane production by ruminal microbes, reportedly by inhibiting formate and hydrogen metabolism. The potential of ENA to inhibit formate metabolism by E. coli O157:H7 and Salmonella Typhimurium DT104 was assessed via 24 h anaerobic growth (CO2) at 37 deg C, in triplicate, in carbonate buffered tryptic soy broth supplemented without or with 16 mM sodium formate and treated with 0 or 9 mM ENA. Total gas volume measurements revealed that O157:H7 and DT104 cultures treated with ENA produced less than or equal to 3.4 mL less gas (P<0.05) than untreated cultures (21.7 and 19.7 mL, respectively). Less hydrogen was produced (P<0.05) in cultures treated with ENA than without ENA (0.97 versus 7.14 µmol/mL for O157:H7) and (0.29 versus 5.98 µmol/mL for DT104), thus indicating a potent effect of ENA on formate hydrogen lyase activity. Specific growth rates, estimated from viable cell counts determined at 0, 3, 6, and 24 h, tended to be lowest (P=0.05) for O157:H7 cultures when treated with ENA and supplemented with formate (0.33) but did not differ between ENA-treated O157:H7 cultures grown with formate supplementation (0.52) or untreated O157:H7 cultures grown with or without formate supplementation (0.55 and 0.58). Growth rates for DT104 were less (P<0.05) for cultures treated with ENA than without (0.18 versus 0.46) and were unaffected by formate supplementation. Maximum cell densities (log10 CFU/mL) of O157:H7 and DT104 were less for cultures treated with (8.09 and 7.24) than without ENA (8.91 and 8.92) for O157:H7 and DT104, respectively. We conclude that ENA inhibits bioconversion of formate to hydrogen by O157:H7 and DT104, and this can reduce the fitness of treated cultures as evidenced by reduced rates and extents of growth.