Evaluation of Colilert-18 for the detection of coliforms and Escherichia coli in tropical fresh water

Department of Microbiology, Soochow University, Shih Lin, Taipei, Taiwan.
Letters in Applied Microbiology (Impact Factor: 1.66). 03/2006; 42(2):115-20. DOI: 10.1111/j.1472-765X.2005.01814.x
Source: PubMed


To evaluate the suitability of Colilert-18 in detecting Escherichia coli and total coliforms in tropical freshwater samples.
Target organisms were isolated from yellow-fluorescent and yellow wells of Colilert-18/Quanti-Tray using m-TEC agar and m-ENDO LES agar respectively. All the selected isolates were first identified based on their fatty acid methyl ester profile. Isolates showing contradictory results to that of the Colilert-18 procedure were re-identified using API 20E strips. A total of 357 isolates, 177 from yellow-fluorescent wells and 180 from yellow wells, were identified.
The false-positive and -negative rates for E. coli detection using Colilert-18 were 36.4% and 11%, respectively, while for coliform detection the false-positive rate was 10.3%.
The high false-positive rate of Colilert-18, tempers its value for E. coli detection when used for tropical freshwater samples.

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    • "E. coli was isolated from the Idexx Quanti-Trays as described by Chao (2006). A 10 μl aliquot of liquid culture from each sampled fluorescent well was streaked onto modified mTEC agar (Becton Dickinson, Sparks, "
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    • "However, other studies have disputed the degree of accuracy for E. coli detection owing to the risk of obtaining false-positive (or negative ) results, but the accuracy varies extensively according to the types and locations of water tested (Pisciotta et al. 2002; Chao et al. 2004). Notably, Chao (2006) reported a high false-positive rate (36AE4%) for E. coli detection using Colil- ert-18 with tropical freshwater. Similarly, a large percentage (27AE3%) of the isolates obtained from the yellow and fluorescent wells, inoculated with marine waters from Florida, were not E. coli (Pisciotta et al. 2002). "
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    ABSTRACT: To assess levels of faecal contamination in the Qu'Appelle River (Saskatchewan, Canada) and its suitability for irrigation, by using the Colilert-18/Quanti-Tray technology. Various sites located along the Qu'Appelle River were sampled weekly from May to August 2005-2007. A total of 594 freshwater samples were collected and analysed for enumeration of Escherichia coli using the Colilert-18. The false-positive rate for E. coli detection using Colilert-18 was at most 1.5%. Throughout the irrigation period (June to August), up to 85% of the water samples collected from one of the irrigation water-pumping sites exceeded the recommended limit of 100 CFU per 100 ml. Spikes in E. coli counts were generally concomitant with the sudden rise in river flows. A sub-sample of confirmed E. coli isolates were typed by randomly amplified polymorphic DNA (RAPD). RAPD analysis revealed a high degree of genetic diversity among E. coli isolates. A significant association between RAPD patterns and the month of E. coli isolation was demonstrated. Colilert-18 provides an effective means for assessing microbial quality of irrigation water. Qu'Appelle River is subject to variability of faecal contamination during irrigation times and monitoring throughout irrigation season is important for ensuring safe production practices.
    Journal of Applied Microbiology 12/2008; 106(2):442-54. DOI:10.1111/j.1365-2672.2008.04012.x · 2.48 Impact Factor
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    • "Only a small fraction of false positives were found in Cuban freshwaters . This is contrary to what was observed by Pisciotta et al. (2002) and Chao (2006) in other tropical environments using the Colilert-18-Quanti-Tray method. Based on these results, we concluded that the use of CC agar was suitable for the enumeration of E. coli in freshwater samples from Cuba. "
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    ABSTRACT: The specificity of a method for the enumeration of Escherichia coli (chromocult agar, CC) was tested using freshwater samples from a tropical area (Cuba Island) by isolating colonies and identifying them with API (Appareillage et procédé d'identification) strips. Enumerations of E. coli by the most probable number (MPN) microplate method were compared with counts on chromogenic and fluorogenic agar media [CC, rapid E. coli (REC), fluorocult] in tropical and temperate freshwater samples. A high percentage of specificity (95.7%) for the CC agar enumeration of E. coli was observed. High regression coefficients (log-log linear regressions) were found between E. coli counts on agar media and by the MPN method. In the tropical environment, counts with REC medium were significantly different from those obtained with the other methods. MPN counts were found to be significantly higher than those obtained using the plate counts methods in the temperate environment. Escherichia coli enumeration methods based on glucuronidase activity appear to be suitable for the evaluation of microbiological quality in the tropical environment featured in this study. The methods for the enumeration of E. coli tested in this study should help improve the evaluation of microbiological contamination of Cuban freshwaters.
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