The use of Colilert-18, Colilert and Enterolert for the detection of faecal coliform, Escherichia coli and Enterococci in tropical marine waters, Trinidad and Tobago

Membrane Filtration (MF) is still widely used in many Caribbean countries for bathing beach water quality analysis. MF is an excellent technique but has a few limitations that restrict the number of samples processed due to the time required and the need for confirmation. Another method Defined Substrate Technology (DST) has overcome these limitations and was investigated as an alternative for faecal coliform, Escherichia coli and enterococci detection. A total of 110 samples were collected from two popular bathing areas in Trinidad, during both wet and dry seasons. IDEXX Colilert-18, Colilert and Enterolert were tested against MF and the data was separated into three water impact groups based on the level of bacteria pollution: low, medium and high. Statistical analysis was performed using ISO 17994:2004 standard as well as Paired t-test to determine whether there were any differences between the DST and MF methods Overall, the DST was more sensitive with higher values obtained compared to the MF. The recovery of enterococci had low relative mean differences for all three water groups 10.3%, 7.6% and 14.3% (low, medium and high). The recovery of E. coli was similar to the recovery of enterococci with 9.3%, 8.8% and 12.6% and the recovery of faecal coliform had the largest percentage difference for all three water groups with 16.7%, 18.9% and 26.1%. The analysis showed the DST recovery had no significant difference (P>0.05) to MF with positive correlation and similar r(2) values obtained. Differences in both methods were also small enough that there was more than 85% agreement to whether the Trinidad and Tobago Water Pollution Rules water quality standards were met or exceeded. In conclusion, the DST will be suitable for water quality monitoring of recreational waters in the Caribbean due to its similarity to MF and its simpler and a faster methodology. (C) 2020 Elsevier B.V. All rights reserved.