Question

Describe one advantage of using The Most Probable Number Procedure (MPN) method with PRLB (Phenol Red Lactose Broth with a Durham tubes) and describe one limitation of this procedure

Answer 1

• The most important advantage is the method is easy to interpret. The interpretation is made by observing the colour change in phenol red lactose broth and gaseous production in durham's tube. Colliforms are vigourous fermentors of lactose there fore there presence is indicated by conversion of media from red to yellow which indicate acid production and gas production in durham's tube ( either tube get lifted up or airbubble in tube) indicate presence of colliforms. Hence easy interpretation of result is possible. There is no additional equipment or skill is required for result interpretation.
• Disadvantage is that generation of false positive. It require long incubation sometime interference non colliforms may generate positive result . Eg. Interference with aeromonas, vibrio etc. So accuracy decreases in generation of result.