New Diagnostic Tool to Tackle Diarrhoea

Scientists from Bangladesh and Japan have developed a cheap and rapid diagnostic technique to identify strains of a common bug that causes diarrhoea.

Scientists had earlier identified over ten genes from five strains of the bacterium Escherichia coli that can cause diarrhoea in humans.

Earlier tests involved identifying each individual gene, a costly process that took four to five hours for each gene.

Two-step or single-step genetic tests were also developed earlier, but these could not detect all the concerned genes. These tests were based on the polymerase chain reaction (PCR) technique that amplifies genes to make their detection easier.

The new PCR test, to be published online in the Journal of Microbiological Methods, identifies ten specific E. coli genes in a single reaction, saving time and money. It was developed by a team of scientists from the University of Hirosaki, Japan, and Dhaka University (DU).

In their report the scientists said the new test would be a valuable contribution to routine diagnostic tests while also providing valuable information for physicians and researchers.

"A physician treating a patient with diarrhoea would be able to find out his ailment much faster and also, it would cost far less than the conventional method of culturing stools for 24 hours," Chowdhury Rafiqul Ahsan, one of the three authors of the report, told SciDev.Net.

Diagnostic laboratories in Dhaka now charge between US$ 23 and US$ 71, depending on how quickly gene matches are obtained. Against this, the new test identifies all ten possible causative genes in a single test that could, on commercialisation, cost less than US$ 7.

Ahsan, a senior academician at the department of microbiology at DU, toldSciDev.Net that the "biggest advantage of the highly reliable technique is (that) it enables us to detect the exact cause of the infection in less than 3–4 hours."

Azharul Islam Khan, head of the diarrhoeal diseases unit at the International Centre for Diarrhoeal Disease Research, Bangladesh, said the development was significant for public health. "Last year we found about 12 per cent of all diarrhoea patients suffering from E. coli infection, considered almost as deadly as cholera."

E. coli infection is characterised by rapid discharge of liquid stools which can be fatal if immediate rehydration therapy is not given, Khan added.

Here is the full reference and abstract:

A novel single-step multiplex polymerase chain reaction assay for the detection of diarrheagenic Escherichia coli.

Miyuki Fujioka^a, Yoshimitsu Otomo^a, Chowdhury Rafiqul Ahsan^b.

^a Hirosaki University, Graduate School of Health Sciences, Hon-cho 66-1, Hirosaki, Aomori, 036-8564, Japan.
^b Department of Microbiology, University of Dhaka, Dhaka-1000, Bangladesh.

Escherichia coli that causes diarrhea in humans is referred to as diarrheagenic E. coli (DEC), and has been categorized into the following 5 groups: shigatoxin-producing E. coli (STEC), enteropathogenic E. coli (EPEC), enteroinvasive E. coli (EIEC), enteroaggregative E. coli (EAggEC), and enterotoxigenic E. coli (ETEC). In this study, we developed a novel one-step multiplex polymerase chain reaction (mPCR) for the rapid detection of 10 pathogenic genes (stx1, stx2, eae, bfpA, invE, aggR, esth, estp, elt, and astA) of DEC. Five categorized strains were used as positive controls for DEC harboring each pathogenic gene, and 828 DEC-like strains, isolated from diarrheal stool samples and assumed to be DEC on the basis of serotyping, were used in the mPCR-based detection of the pathogenic genes. To demonstrate the utility of mPCR, the 828 strains were subjected to our optimized protocol, and the results obtained were compared with those obtained by monoplex PCR. The results showed agreement for all strains. Using mPCR, we also detected 65 DEC and 41 astA-positive E. coli, and 7 of these DEC strains were “O antigen untypable” (OUT). This novel mPCR protocol allowed for rapid, convenient, and economical pathogenicity-based identification of the DEC.