Ultrasonic bacterial treatment of mineral waters: a study on S. epidermidis, S. warneri, P. aeruginosa and P. mirabilis

The objective of this work is to evaluate the effects of ultrasound waves on the viability of bacteria that usually occur in mineral waters such as spa thermal waters. The study was carried out at a constant temperature of 309.65 K on two Gram-positive bacteria (Staphylococcus epidermidis, Staphylococcus warneri) and two Gram-negative bacteria (Pseudomonas aeruginosa, Proteus mirabilis) with a concentration of 106 CFU mL−1. A commercial ultrasonic bath was used. The effects of the ultrasounds were analysed using a microcalorimetric technique. The microcalorimetric bacterial growth curves were obtained and, stemming from said curves, the heat released by microorganisms during a culture time of 24 h was calculated. The values of the heat released in the samples treated and untreated with ultrasounds were compared. The ultrasound treatment appears to be effective in inhibiting the growth of the two Gram-positive bacteria, but not in the case of the Gram-negative, which presented greater resistance at the same experimental conditions. This study also shows microcalorimetry as an efficient technique to determine the effect of ultrasound waves on bacterial growth.