Comparison of PetrifilmTM AC and Pour plate techniques used for the heterotrophic aerobic bacterial count in water

Heterotrophic bacteria (HPC) are commonly found in water samples. While these bacterial counts do not necessarily indicate a health hazard, high counts provide a good indication of the efficiency of water disinfection and integrity of distribution systems. The aim of this study was to compare the PetrifimTM AC method to the Pour Plate technique for the testing of HPC in water samples. Artificially contaminated (192 samples) and natural water samples (25) were processed using two methods. Both methods accurately detected high, medium and low counts of HPC, producing average Z scores between -2 and + 2. Paired-wise student t-test and correlation coefficient showed nonsignificant differences between the results of two methods. Acceptable repeatability and reproducibility was obtained using both the methods. Uncertainty of measurement for PetrifilmTM AC and Pour Plate method was found to be 2.9% and 5.4% respectively. PetrifilmTM AC proved to be robust at 33 °C and 37 °C. In conclusion, PetrifimTM AC, which is easy to process, read and less time consuming, proved to be comparable to the conventional Pour Plate method in establishing HPC in water. In addition, PetrifimTM AC requires less space for the processing and incubation, generate small volume of waste for disposal and requires no equipment, except for the incubator.