Characterization of Escherichia Coli Isolates from Different Fecal Sources by Means of Classification Tree Analysis of Fatty Acid Methyl Ester (Fame) Profiles

Abstract

Microbial source tracking (MST) methods need to be rapid, inexpensive and accurate. Unfortunately, many MST methods provide a wealth of information that is difficult to interpret by the regulators who use this information to make decisions. This paper describes the use of classification tree analysis to interpret the results of a MST method based on fatty acid methyl ester (FAME) profiles of Escherichia coli isolates, and to present results in a format readily interpretable by water quality managers. Raw sewage E. coli isolates and animal E. coli isolates from cow, dog, gull, and horse were isolated and their FAME profiles collected. Correct classification rates determined with leaveone-out cross-validation resulted in an overall low correct classification rate of 61%. A higher overall correct classification rate of 85% was obtained when the animal isolates were pooled together and compared to the raw sewage isolates. Bootstrap aggregation or adaptive resampling and combining of the FAME profile data increased correct classification rates substantially. Other MST methods may be better suited to differentiate between different fecal sources but classification tree analysis has enabled us to distinguish raw sewage from animal E. coli isolates, which previously had not been possible with other multivariate methods such as principal component analysis and cluster analysis.

Ab Initio and in Situ Comparison of Caffeine, Triclosan, and Triclocarban as Indicators of Sewage-Derived Microbes in Surface Waters

“…Microbial assays relying on culturing techniques typically take from 18 to 96 h , , whereas biomolecular and chemical analyses can be completed in hours or even minutes , . Targeting chemical markers is beneficial since many microbial indicator organisms extant in raw sewage also are common to wildlife and sources other than wastewater , . In addition, chemical markers consistently occur at the highest levels at the source and at relatively lower concentrations in receiving streams , , whereas microbial indicators potentially can multiply in surface waters or become temporally inactive, i.e., viable but nonculturable .…”

Microbial Source Tracking

“…Fatty acid methyl ester (FAME) profiling for source tracking is at an early stage of testing (39,73,123,143). Serotyping and FAME have not been compared with other methods, nor have they been tested using blind samples.…”

Detection and Occurrence of Indicator Organisms and Pathogens

“…None of the isolates were classified as of human origin, and 81% of the isolates were correctly classified as originating from wildlife. A FAME profile analysis method was developed for classification of E. coli isolates by implementation of classification tree analysis to group fecal isolates (Seurinck et al, 2006a). Using this approach, the authors successfully discriminated between raw sewage and animal E. coli isolates with a correct classification rate of 85%.…”