Development and application of isothermal amplification methods for rapid detection of F4 fimbriae producing Escherichia coli

Enterotoxigenic Escherichia coli (ETEC) is the causative agent of a wide range of diseases, which are the important cause of illness and mortality in piglets.ETEC strains expressing F4 fimbriae are frequently associated with post-weaning diarrhea (PWD) and lead to great economic losses in swine production industry worldwide.The aim of this study was to establish a rapid and effective isothermal amplification method for detection of F4 fimbriae.Loop-mediated isothermal amplification (LAMP), Polymerase spiral reaction (PSR) and cross-priming amplification (CPA) were used to develop and optimize the detection method first time.Subsequently, the specificity and sensitivity of these methods were evaluated, and the clinical samples were detected with these methods.All the F4-positive samples could produce ladder-like amplifications products and lead the chromogenic substrate SYBR Green I produce green fluorescence, while in blank control and negative samples lack of this pattern or remained orange.The sensitivity of LAMP and CPA were 10 times higher than PSR method.Meanwhile, these three methods were validated with clinical samples, 7 were found positive, while 125 samples were negative, the testing results were consisted with the real-time PCR method.These findings suggested that the isothermal amplification based on the F4 fimbriae is a rapid, effective and sensitive method under resource constrains.