Congo red dye agar test as an indicator test for detection of invasive bovine Escherichia coli

Congo red dye agar test (CR test) has been used to differentiate invasive and non invasive E. coli in poultry. This simple test was used to detect enteroinvasive E. coli of bovine origin, isolated from cases of neonatal calf diarrhoea. Out of 97 isolates tested 46 showed CR-positive reaction, while 51 were CR negative. Upon confirmation with the Sereny test, a standard test for detection of invasiveness, CR test was found 100% specific and 58.89% sensitive. This test can be used for primary screening of non invasive E. coli from potentially invasive E. coli