Effects of Nitro-Treatment on Salmonella, E. coli and Nitrogen Metabolism during Composting of Poultry Litter

Poultry litter contains appreciable amounts of uric acid which makes it a good crude protein supplement for ruminants whose gut microbes transform the nitrogen in uric acid into high quality microbial protein. However, poultry litter must be treated to kill bacterial pathogens before feeding. Presently, we examined the antimicrobial activity of certain nitrocompounds when administered to early-stage composted poultry litter. The one year-old wood chip litter used in this study had been exposed to 2 to 3 flocks reared without antibiotics. Treatments (ethyl nitroacetate, 3-nitropropionate, ethyl-2 nitropropionate or nitroethane) were applied to 200 g litter by spraying with 100 mL of each nitro-treatment (80 mM in 0.4 M phosphate buffer, pH 6.4) to achieve 25 µmol/g litter. Control litter was sprayed with buffer alone. After application, the litter was distributed (11 g) to 50-mL tubes (in triplicate), inoculated with a novobiocin and naladixic acid-resistant Salmonella Typhimurium (ST_NN) to achieve 3.0 log₁₀ CFU/g. Tubes were closed with caps, sealed with parafilm and incubated at 37^oC for 3 days after which time the tube contents were diluted and plated on 3M E. coli/coliform petri-film and Brilliant Green Agar supplemented with 25 and 20 µg/mL novobiocin and naladixic acid, respectively, for enumeration of wildtype E. coli and ST_NN strain. Ammonia, uric acid and urea were measured colorimetrically. Analysis of variance revealed that all nitrocompound treatments decreased (P < 0.05) ST_NN 1.4 to 1.9 log units compared to controls (6.0 ± 0.2 log₁₀ CFU/g). Escherichia coli was decreased (P < 0.05) compared to controls (6.5 ± 0.2 log₁₀ CFU/g) by 0.5 log units with ethyl nitroacetate but did not differ otherwise. Accumulations of ammonia were decreased (P < 0.05) 21 to 27% by the ethyl-derivatives compared to controls (2.8 ± 0.1 µmol/g). Uric acid concentrations were 3.4 to 4.5-fold higher (P < 0.05) in litter treated with ethyl 2-nitropropinate and nitroethane than in controls (15.5 ± 1.3 µmol/g). Urea (7.9 ± 2.9 µmol/g) was unaffected by nitro-treatment. Results suggest that nitro-treatment may help preserve uric acid in composted litter while aiding in Salmonella control.