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The bioassays assimilable organic carbon (AOC) and coliform growth response are better indexes than biological oxygen demand to determine water quality and water's ability to support the growth of bacteria. Ozonated (5 mg/liter) and chlorinated tap water were used to wash alfalfa seeds for 30 min. After washing in the ozonated tap water, the AOC concentration increased 25-fold, whereas the dissolved ozone decreased to undetectable levels. The AOC levels for the chlorinated water after washing the seeds also increased. These increases are due to ozone's strong oxidizing ability to break down refractory, large-molecular-weight compounds, forming smaller ones, which are readily used as nutrient sources for microorganisms. This same phenomenon was observed when using ozone in the treatment of drinking water. The AOC value increased from 1,176 to 1,758 micrograms C-eq/liter after the reconditioned wastewater was ozonated. When the ozonated wastewater was inoculated with Salmonella serotypes, the cells survived and increased generation times were observed. The increased nutrients would now become more readily available to any pathogenic microorganisms located on alfalfa seed surface as seen with the increase in the inoculated levels of Salmonella in the ozonated wastewater. If the washing process using ozonated water is not followed by the recommended hypochlorite treatment or continually purged with ozone, pathogen growth is still possible.

Waste wash waters from chicken egg-processing facilities can harbor high densities of bacteria, including salmonellae. For this study, we enumerated total coliforms, Escherichia coli, and Salmonella spp. in the egg wash waters of a large egg producer. We then determined how long these organisms would survive at temperatures of 5, 15, and 25 degrees C. We found that the fraction of salmonellae surviving over time at a given temperature was comparable to the fraction of indicator organisms that survived. We also found that the survival of these organisms varied with temperature, with 16, 8, and < 2 days being required for a 90% reduction of Salmonella in waste wash water held at 5, 15, and 25 degrees C, respectively. Finally, we noted that the response of laboratory-derived cultures to environmental stresses mimics the response of the indigenous microbial population, but individual cells within that population may survive for longer periods than laboratory-cultured strains.

Previous reports indicate that Escherichia coli O157:H7, Salmonella spp., and Vibrio cholerae can grow in nutrient-limited, reconditioned wastewater over the temperature range of 4 to 46 degrees C when the biological oxygen demand of this water is <2, while its coliform growth response (CGR) is >2. In the current study, we investigated the growth response of Vibrio parahaemolyticus, Shigella spp., Vibrio vulnificus, and Pseudomonas aeruginosa in water samples with a CGR of >2 over the temperature range of 4 to 50 degrees C. Both the nonselective media, tryptic soy agar, and the selective media used to identify the pathogen were used for their recovery. The selective media were thiosulfate-citrate-bile-sucrose (TCBS), MacConkey agar (MAC), and Pseudomonas isolation agar (PIA) for the Vibrio, Shigella, and Pseudomonas spp., respectively. V. parahaemolyticus numbers declined rapidly after surviving for 6 days under the nutrient-limiting growth conditions. Shigella spp. did not grow but survived for >28 days at 4 to 25 degrees C. V. vulnificus grew over the narrow temperature range of 12 to 21 degrees C and survived for >21 days at the higher and lower temperature ranges. P. aeruginosa survived and grew during the 14-day test period at 13 to 35 degrees C. Recovery on the nonselective agar gave statistically (P > 0.05) higher numbers than the respective selective media commonly used for these pathogens. These results indicate that caution should be used in attempting direct recoveries using selective media of the four gram-negative bacteria species used in this study from the nutrient-limited water environment.

The pathogen Escherichia coli O157:H7 has been recovered from various water sources and food samples. The growth potential of this bacterium in nutrient-limited, reconditioned wastewater from a pork-processing plant was determined over a temperature range of 4 to 46 degrees C. Even though the biological oxygen demand of the wastewater was <2 mg/liter, results of bioassays for assimilable organic carbon and the coliform growth response of the water suggested that sufficient nutrients were present to support limited bacterial growth. A three-strain mixture of E. coli O157:H7 grew over the temperature range of 10.2 to 29.4 degrees C. Bioassays appear to be a good indicator of the ability of this wastewater to support growth of this pathogen. Statistically higher levels of bacterial growth (P < 0.05) were detected on a nonselective medium (tryptic soy agar) than on a selective medium (sorbitol-MacConkey agar), suggesting that stress or injury of the bacterium occurs when the organism is exposed to the nutrient-limited conditions of the wastewater. These results indicate that E. coli O157:H7 can survive and grow in this particular nutrient-limited wastewater, suggesting a potential hazard if this water becomes contaminated with this pathogen.

Many food-processing plants are looking to increase the use of reconditioned water beyond the currently approved uses for initial cleaning (vegetables) and scalding water (meat and poultry). The preliminary survey showed that the reconditioned water from a local meat plant could support bacterial growth. The growth potential of Salmonella spp. and Vibrio cholerae (starting level of 3 to 4 log CFU/ml) in the reconditioned wastewater from this plant (with and without added thiosulfate) was studied at temperatures from 5 to 42°C. Bioassays for the assimilable organic carbon and coliform growth response suggest that this reconditioned water contained sufficient nutrients to support bacterial growth. Both pathogens grew in the unchlorinated reconditioned and chlorinated reconditioned water containing 10 mg of sodium thiosulfate per ml to neutralize the residual chlorine. Cell counts declined rapidly in chlorinated water without thiosulfate. The results of this study emphasized the importance of maintaining residual chlorine levels (0.2 mg/liter) in both reconditioned and potable waters to prevent pathogen growth.