Hydrophobicity Test and DNA Probe Hybridization Assay in the Detection of Enterotoxigenic Escherichia coli

ABSTRACT

The hydrophobicity assay and DNA probe hybridization assay were compared for analysis of enterotoxigenic Escherichia coli(ETEC), heat-labile enterotoxin(LT) and heat-stable enterotoxin (ST). The ETEC isolated from diarrheal patients were serotyped and investigated for the presence of colonization factor antigens CFA/1, CFA/II, CFA/III and CFA/IV with the expression of mannose-resistant hemagglutination(MRHA) and the levels of surface hydrophobicity. The following results were obtained. 1. Out of these 48 strains, 34 strains were found to be positive for LT production by DNA probe hybridization assay. Out of 34 strains, 1 strain was ST producer, 25 strains were LT producers, and 8 strains were produced both ST+LT producers by DNA probe hybridization assay. 2. Out of 34 strains of positive DNA probe hybridization test, 31 strains was positive in the hydrophobicity test. Among strains of positive hydrophobicity test, 20, 1, and 7 strains produced only LT, only ST and both ST-LT, respectively. Screening efficiency for identifying ETEC by salting out test was 82.4% in sensitivity and 78.6% in specificity. For ETEC detection, the hydrophobicity assay was the least sensitive but was simple, rapid and a good substitute for the DNA probe hybridization assay. 4. CFAs were identified in 43.8% of ETEC strains; 2.1% of the CFAs strains with CFAs harbored CFA/I, 29.2% carried CFA/II, 16.7% carried CFA/III and CFA/IV. And 35.4% expressed none of these CFAs. CFA/I was found in ETEC of serotype 0128 K67, CFA/II was 0128 K67, 0142 K+ and 0159 K+, CFA/III was 086a K15 and 0128 K67, CFA/IV was 0 86a K15, 0128 K67, 0125 K70 and 0148 K+.