Factors affecting the survival ofSalmonellaandEscherichia coliin anaerobically fermented pig waste

Abstract

The survival of S. typhimurium was investigated in acidogenic, anaerobically fermented pig wastes and in synthetic media, each containing volatile fatty acids (VFA). S. typhimurium survived at pH 6.8, but not at pH 4.0, when incubated at 37.degree. C for 24 h in fermented or synthetic medium containing VFA. The minimum inhibiting concentration of VFA for S. typhimurium after 48 h incubation at 30.degree. C at pH 4.0 was 0.03 mol/l and for E. coli it was 0.09 mol/l. Fermented pig wastes in a digester, maintained at pH 5.9, were inoculated with S. typhimurium and then incubated at 37.degree. C for 24 h. The pH was adjusted to 4.0 or 5.0. After a further 48 h at 30.degree. C, S. typhimurium survived at pH 5.0 but not at pH 4.0. The pH is thus critical in determining the survival of this organism in acidogenic anaerobically fermented pig waste.