Question

How many bacterial cells will remain after an antimicrobial treatment of 3 minutes, an initial microbial load of 106 cells, and a DRT of 1 minute?​

Answer 1

Answer:

The land application of agricultural residues can have a direct impact on bacterial concentrations in groundwater, surface water and soil, where leachate from manure-amended fields reaching subsurface tile drains has been shown to have concentrations exceeding background levels (Abu-Ashour et al., 1994; Jamieson et al., 2002; Unc and Goss, 2004; Goss and Richards, 2008). The survival of enteric bacteria can be influenced by several factors, including soil moisture, soil type, pH, temperature and nutrient availability (Abu-Ashour et al., 1994; Goss et al., 2001; Jamieson et al., 2002).

The survival of enteric bacteria in manure-amended soils increases with high moisture content, where moisture retention is linked to soil particle size distribution and organic matter content (Jamieson et al., 2002). Abu-Ashour et al. (1994) explain that there is an increased survival of bacteria with increased organic matter content in soils. Furthermore, finer soils (e.g. clay and humic substances) increase water retention, which ultimately increases bacterial survival. Chandler and Craven (1980) found E. coli cells were able to survive dry loam soil conditions but proliferated once moisture was restored. Bacterial survival is also favoured by cooler temperatures and neutral pH, with pH of 6 to 7 being optimum (Abu-Ashour et al., 1994; Jamieson et al., 2002). Goss et al. (2001) reported that E. coli O157:H7 can survive for up to 100 days under cold soil temperatures (< 5°C). It should be noted that freezing and thawing of soils reduces bacterial survival.