Comparison of Plate Count Agar and R2A medium for enumeration of heterotrophic bacteria in natural mineral water

In order to recover as many viable bacteria as possible from natural mineral water, in this study we have compared the counts obtained with the standard method (pour plate procedure with Plate Count Agar (PCA)) and counts with alternative test methods (PCA/spread plates, R2A medium/pour plates and R2A medium/spread plates). The results showed that counts with R2A medium/spread plates at 22 °C and after a 7-day incubation period were more than 343% higher than those obtained with PCA/pour plate method. At 37 °C and after a 3-day incubation period, the R2A pour plate technique gave counts about 368% greater than for the standard method. Moreover, while Pseu- domonas, Comamonas and Acinetobacter species were isolated both from PCA and R2A medium, Flavobacterium spp. and Arthrobacter spp. were isolated only from R2A medium. For its higher productivity, R2A medium should be recommended for heterotrophic plate counts in natural mineral water.