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.
Biofilms are communities of microorganism enclosed in an extracellular matrix attached to various surfaces. Biofilms and motilities may represent negative impacts in health and industrial sectors, however they also play crucial ecological role. The main objective of this study was to estimate biofilm formation and motilities abilities of three common bacteria under different culture condition (media of growth and pH). Results show that pH variation (from 5 to 8) and composition of media growth (minimum and complex media) have little influence on biofilm formation by Staphylococcus aureus ATCC 25923 and Escherichia coli ATCC 25922. However, biofilm formation by Pseudomonas aeruginosa ATCC 27853 is inhibited at pH 5 and 6 in both complex and minimum media. P. aeruginosa swimming, swarming and twitching motilities are not affected by pH variation whereas S. aureus and E. coli are only able to twitch in complex media. This preliminary study demonstrated that pH may influence bacterial behavior formation particularly for P. aeruginosa