Effect of pH on the antimicrobial susceptibility of planktonic-grown Pseudomonas aeruginosa, Escherichia coli and Staphylococcus aureus ATCC strains

The in vitro susceptibilities of bacteria to antibiotic are traditionally tested in media with a neutral pH. However, in a living organism and particularly in humans, the acidity varies a lot from one place to another. The present study aims to evaluate influence of pH in the expression of in vitro antimicrobial susceptibility among planktonic-grown Pseudomonas aeruginosa, Escherichia coli and Staphylococcus aureus ATCC® strains. Results show that the pH value affect antimicrobial activity differently, depending upon the strain used. Indeed, P. aeruginosa and E. coli are more susceptible to tetracycline under acidic and neutral pH condition whereas S. aureus is equally susceptible to tetracycline in all tested pH condition. Conversely, P. aeruginosa, E. coli and S. aureus are more susceptible to erythromycin, kanamycin and gentamycin under neutral and alkaline pH condition. This preliminary study highlights that pH parameter should be considered in evaluation of antimicrobial effectiveness and this is a point that should be considered by antibiotic prescriber in delivering antibiotic prescription.