Effect of variations in heterotrophic plate count methods on bacterial estimation in some sachet water in Calabar Metropolis

Heterotrophic plate count (HPC) or standard plate count is a standardized method for determining the density of aerobic and facultative anaerobic heterotrophic microorganisms in water. In this study, water samples were analyzed to ascertain the effects of temperature, media, and incubation time in HPC methods of bacterial estimation. The samples were analyzed using the membrane filtration and direct plating methods. No faecal coliform was detected in all the samples and at all temperature. However, some coliforms and heterotrophic bacteria were present in the water samples. The organisms were isolated at 4 °C, 28 °C and 37 °C after 24-72 h. The heterotrophic bacterial isolates include: Enterobacter spp., Staphylococcus aureus, S. epidermidis, Bacillus sphericus, B. cereus, Micrococcus roseus, Pseudomonas aeruginosa and Klebsiella pneumonia. It was observed that yeast extract agar gave a higher heterotrophic plate count at 28 °C while EMB agar yielded the highest total coliform count at 37 °C. The result of the physicochemical analysis showed that the water samples met the World Health Organization (WHO) and Standards Organization of Nigeria (SON) standards for drinking water while the bacteriological quality based on the total coliform count result indicates the need for improvement in the treatment systems.