Abstract
Membrane filtration and Colilert assays are commonly used to quantify Escherichia coli levels in agricultural water. These methods have not been evaluated in test agricultural water (TAW), a formulation used for assessing chemical sanitizer effectiveness. Quantitative recovery of E. coli in TAW may be affected by turbidity levels. TAW was formulated with a pH value of 6.5 at two turbidity levels (0 and 50 NTU). Pan-susceptible and cefotaxime-resistant E. coli strains were added separately to TAW (200 CFU/100 mL). Inoculated TAW was either (1) filtered using a 0.45 μm membrane filter (MF) and placed onto Tryptone Bile X-Glucuronide (TBX) agar or CHROMagar ECC (ECC), or (2) tested by IDEXX Quanti-Tray/2000 Colilert. Recovery percentages of E. coli at both turbidity levels were similar on TBX and ECC, but pan-susceptible E. coli ARS C101 in TAW at 50 NTU on TBX was not quantifiable. For Colilert assays, the recovery percentages of E. coli from 0 NTU and 50 NTU TAW were between 93.4 ± 4.4% and 127.0 ± 10.5%. Overall, ECC and Colilert provided quantifiable results for recovery of pan-susceptible and cefotaxime-resistant E. coli from artificial agricultural water at different turbidity levels. Higher levels of turbidity affected the ability to quantify E. coli by MF with TBX and recovery by Colilert.