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. 2025 Aug 20;18(1):365.
doi: 10.1186/s13104-025-07423-9.

Evaluating the recovery of pan-susceptible and antibiotic-resistant Escherichia coli in synthetic test agricultural water using membrane filtration and colilert methods

Zirui Ray Xiong  1   2 , Ajani A Brooks  1   3 , Ellen Gabriel  1 , Alan Gutierrez  1 , Shayla B Johnson  1 , Cheryl East  1 , Lisa M Durso  4 , Elica Moss  3 , Manan Sharma  5
Affiliations

Evaluating the recovery of pan-susceptible and antibiotic-resistant Escherichia coli in synthetic test agricultural water using membrane filtration and colilert methods

Zirui Ray Xiong et al. BMC Res Notes. .

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.

Keywords: Agricultural water; Antimicrobial resistance; Colilert assay; Escherichia coli; Membrane filtration; Test methods.

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Conflict of interest statement

Declarations. Ethics approval and consent to participate: Not applicable. Consent for publication: Not applicable. Competing interests: The authors declare no competing interests.

Figures

Fig. 1
Fig. 1
Recovery percentage of E. coli ARS C101 (pan-susceptible) and C301 (cefotaxime-resistant) by membrane filtration on selective media. A total of ca. 200 CFU E. coli was inoculated in 100 mL Test Agricultural Water (TAW) with turbidity of 0 NTU or 50 NTU. The membrane filter was placed onto two selective media (CHROMagar ECC and TBX) and colony counts were compared with the initial inoculum level to calculate recovery percentage
Fig. 2
Fig. 2
Membrane filters placed onto TBX media to recover E. coli ARS C101 in TAW (Test Agricultural Water) at 50 NTU. Growth on membrane filters placed on TBX was not quantifiable because distinct colonies of C101 were not observed
Fig. 3
Fig. 3
Recovery percentage of E. coli ARS C101 and C301 by Quanti-Tray/2000 Colilert assay. A total of ca. 200 CFU E. coli was inoculated in 100 mL TAW with turbidity levels of 0 NTU and 50 NTU. The Most Probable Number/100 mL (MPN/100 mL) values of E. coli was compared with the initial inoculum level to calculate recovery percentage. Turbidity was a significant factor (p = 0.0233, Two-way ANOVA and Tukey HSD test) affecting a higher recovery percentage at 0 NTU compared to at 50 NTU in TAW for the Colilert assay (p = 0.0016, Pairwise t-test with Bonferroni correction)
Fig. 4
Fig. 4
Strain type is a significant factor for recovery by membrane filtration with CHROMagar ECC. P-value is 0.0233 based on two-way ANOVA and Tukey HSD test. Pairwise t-test showed that the difference between recovery percentage of E. coli ARS C101 and C301 was significant (p = 0.03, p-value with Bonferroni correction)
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