Assessment of ultrasound irradiation on inactivation of gram negative and positive bacteria isolated from hospital in aqueous solution

Microbial contamination of water poses a major threat to public health. With the emergence of microorganisms resistant to multiple antimicrobial agents, there is increased request for promotion of disinfection methods. Since ultrasound wave (US) exhibits antibacterial activities on bacteria, the aim of this study was to evaluate the antimicrobial effect of low frequency (37 kHz) ultrasound on Pseudomonas aeruginosa and Staphylococcus aureus as a model for gram-negative and gram-positive bacteria, respectively. Sonolysis experiment was carried out in a laboratory-scale batch sonoreactor equipped with plate type transducer at 400 W of acoustic power in the presence and absence of ampicillin as an antibiotic on the both Pseudomonas aeruginosa and Staphylococcus aureus. All of the bacteria were affected by the ultrasound and an increase in percent kill for both bacteria occurred with increasing duration of exposure and intensity of ultrasound. It was found that gram-negative bacteria were more susceptible to the ultrasonic treatment rather than gram-positive bacteria. In addition, the combination of US with an antibiotic (ampicillin) enhanced killing of both bacteria over the use of US alone. The rate of bactericide effect of US wave was increased in samples containing ampicillin. This process was influenced by the chemical and microbiological characteristics of aqueous media. Therefore, with further research about its practicality for treatment of wastewater, it may become a possible substitute process for wastewater disinfection.