Endotoxin as a Marker for Water Quality

Abstract

Background: Water quality testing is vital to protect human health. Current testing relies mainly on culture-based detection of faecal indicator organisms such as Escherichia coli (E.coli). However, bacterial cultures are a slow process, taking 24-48 h and requiring specialised laboratories and trained personnel. Access to such laboratories is often sparse in developing countries and there are many fatalities deriving from poor water quality. Endotoxin is a molecular component of Gram-negative bacterial cell walls and can be used to detect their presence in drinking water.

Method: The current study used a novel assay (BacterisK) to rapidly detect endotoxin in various water samples and correlate the results with E. coli content measured by culture methods. The data generated by the BacterisK assay are presented as an 'endotoxin risk' (ER).

Results: The ER values correlate with E. coli and thus endotoxin can be used as a marker of faecal contamination in water. Moreover, the BacterisK assay provides data in near real-time and can be used in situ allowing water quality testing at different spatial and temporal locations.

Conclusion: We suggest that BacterisK can be used as a convenient risk assessment tool to assess water quality where results are required quickly or access to laboratories is lacking.

Keywords: BacterisK; LAL assay; drinking water; endotoxin; faecal contamination; water testing.

Figure 1

A Pearson correlation between the endotoxin units (EU/mL) and ER. Endotoxin unites were calculated using the Kinetic-QCL™ assay and compared to ER as calculated using BacterisK. n = 64, p < 0.0001, R² = 0.929.

Figure 2

Relationship between E. coli (CFU/100 mL) and ER in various freshwater samples. E. coli CFU were enumerated using the standard Membrane filtration method. ER was obtained using the BacterisK assay. Each bar represents the mean ER + SEM for each group of E. coli CFU/100 mL. A total of 69 independent samples were analysed. The 0–10 group consisted of 23 samples, the 11–100 group consisted of 14 samples and the >100 group consisted of 32 samples. The negative control represents pyrogen-free water and the positive control represents purified endotoxin from E. coli O55:B5. * p < 0.05 and *** p < 0.001 as calculated using an unpaired t-test.