Food microbiology: Biochemical tests – presumptive identification and confirmation of coliform bacteria!
After growing bacteria on a selective media such as violet red bile agar (VRBA) for identification of coliforms it is of essence to carry out some further tests to confirm if the bacteria growing on the agar media are trully coliforms. In this case, one such test is done using 10 representative colonies from VRBA. These are transferred to a sterile brilliant green lactose broth tube and incubated at 35°C for 24 h. Gas positive tubes that show a pellicle from these tubes are further subjected to gram staining so as to eliminate Gram-positive, lactose-fermenting bacilli.
