METABOLIC-ACTIVITY OF PATHOGENIC BACTERIA DURING SEMICONTINUOUS ANAEROBIC-DIGESTION

In natural environments such as anaerobic digesters, bacteria are freq uently subjected to the stress of nutrient fluxes because of the conti nual changes in the flow of nutrients, and to survive, they must be ca pable of adapting readily to nutrient changes. In this study, the meta bolic activities of Escherichia coli, Salmonella typhimurium, Yersinia enterocolitica, Listeria monocytogenes, and Campylobacter jejuni were studied within culture bags (Versapor-200 filters, 0.22-mu m pore siz e) in laboratory anaerobic digesters. The metabolic activity of these bacteria was indicated by their adenylate energy charge (EC) ratios an d their ability to incorporate [H-3]thymidine, which was related to th e respective changes in viable numbers within the culture bags during anaerobic digestion. Fluctuations in the adenylate EC ratios, the upta ke of [H-3]thymidine, and the viable numbers of E. coli, S. typhimuriu m, Y. enterocolitica, and L. monocytogenes cells were probably due to constant changes in the amount of available nutrients within the anaer obic digesters. The viability of S. typhimurium increased quickly afte r a fresh supply of nutrients was added to the system as indicated by the uptake of [H-3]thymidine and an increase in the adenylate EC ratio s. The viable numbers of E. coli, S. typhimurium, Y. enterocolitica, a nd L. monocytogenes organisms declined rapidly from 10(7) to 10(8) CFU /ml to 10(3) to 10(4) CFU/ml and remained at this level for an indefin ite period. The decimal reduction time calculated during the period of exponential decline ranged from 0.8 to 1.2 days for these bacteria. C . jejuni had the greatest mean decimal reduction time value (3.6 days) . This bacterium had adenylate EC ratios of less than 0.5 during anaer obic digestion, although the adenylate nucleotide concentrations in th e cells were much greater than those in the other enteric cells. The r esults show that the enteric bacteria investigated probably exist in t ransient states between different stages of growth because of fluctuat ing nutrient levels during anaerobic digestion.