Browsing by Author "Pitt, William G."

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Effect of low-intensity ultrasound upon biofilm structure from confocal scanning laser microscopy observation
(1996-10) Qian, Z.; Stoodley, Paul; Pitt, William G.
Ultrasonic irradiation at 500kHz and 10 mW cm−2 of a 24 h old biofilm of P. aeruginosa enhanced the killing of bacteria by gentamicin. To determine whether this bioacoustic effect was caused by ultrasonic-induced changes in the biofilm morphology (biofilm breakup or disruption), the biofilms were examined by confocal scanning laser microscopy (CSLM). Such disruption would be undesirable in the possible ultrasonic treatment of implant infections. The CSLM results showed that the biofilm is a partial monolayer of cells with occasional aggregates of cells, non-cellular materials and extracellular spaces. The aggregates contained large amounts of exopolysaccharide. The structure of biofilm was not changed when the biofilm was exposed to continuous ultrasound at 500 k Hz and 10 mW cm−2, the same irradiation parameters that increased cell killing by nearly two orders of magnitude. The observation that low-intensity ultrasound does not disrupt biofilm or disperse the bacteria has significance in the possible use of ultrasound to enhance the action of antibiotics against biofilms.
Effects of ultrasonic treatment on the efficacy of gentamicin against established pseudomonas aeruginosa biofilms
(1996-05) Huang, Ching-Tsan; James, Garth A.; Pitt, William G.; Stewart, Philip S.
The effect of simultaneous ultrasonic treatment on the efficacy of gentamicin against planktonic and established biofilm cells of Pseudomonas aeruginosa was investigated. Planktonic cells were treated with 6 or 12 μg ml−1 of gentamicin for 4 h with ultrasonic treatment at three levels of power density (0.2, 2 and 15 mW cm−2). Biofilm cells grown on stainless steel slides in a continuous flow reactor were treated with 30 μg ml−1 of gentamicin and ultrasound. Ultrasound itself at these power levels did not cause cell killing or lysis in planktonic and biofilm cultures. Concentrations of 6 and 12 mg ml−1 gentamicin led to 2.65- and 2.75-log reductions of the surviving fraction in planktonic cultures in the absence of ultrasound. The addition of ultrasound did not show further reduction compared with those without ultrasonication. Gentamicin (30 μg ml−1) caused variable killing in biofilms which ranged from 0.83- to 2.86-log reductions of the surviving fraction without ultrasonication. Gentamicin efficacy measured by the surviving fraction was improved by 0.28-, 1.12- and 0.58-log when coupled with 0.2, 2 and 15 mW cm−2 ultrasonic treatments, respectively. Experimental results indicated that ultrasound modestly improved the efficacy of gentamicin against established P. aeruginosa biofilms.
Removal of oral biofilm by sonic phenomena
(2005) Pitt, William G.
Purpose: To investigate the role of sonic acoustic waves and related phenomena in removing a model plaque from a surface, and to determine if there was an optimal frequency for sonic-type toothbrushes. Methods: A mechanical system was built in which submerged biofilms of Streptococcus mutans were exposed to sonic energy in the range from 80 to 1,000 Hz. The system was calibrated by an accelerometer and pressure transducer, and biofilm removal was measured by optical techniques. Results: The results showed that the removal was strong function of the acoustic intensity, but there was no significant dependence upon frequency. Biofilm was removed in very small amounts (up to 2% in 10 minutes) due to acoustic energy in the absence of convective fluid flow, even at high acoustic intensities. When the acoustic action was coupled with convective fluid flow, caused by the piston and well geometry, up to 80% of a bioflim was removed at a calculated acoustic intensity of 27 W/cm2 in 2 minutes. When gas bubbles were entrained in the fluid, the removal approached 100% under intense sonic conditions. With respect to removal of plaque on teeth, the vigorous action of flowing fluid and bubbles is expected to remove plaque, and a maximum fluid velocity is recommended rather than a particular frequency.