Sonication – method, principle and advantages
Sonication – a new diagnostic method
After removal in the operating room, implants are placed in the air-tight container and transported to the microbiological laboratory. After addition of Ringer’s solution, the implant is processed by vortexing (30 seconds) and sonication (1 minute) to dislodge (planktonize) microorganism into the surrounding fluid (sonicate). The sonication fluid is cultured on aerobic and anaerobic agar plates and inoculated in broth media.
Principle of sonication
High acoustic intensity of conventional ultrasound baths kills microorganisms (especially gram-negative and anaerobic bacteria). Sonication in the specially designed ultrasound bath BactoSonic® uses low frequency and low intensity ultrasound at the threshold of microbubble formation (cavitation). Due micro-currents of sonication fluid, shear forces and oscillating cavitation bubbles biofilm is removed and the bacteria are disaggregated.
The resulting cavitation energy is reduce to the level, that no significant cell destruction occurs, enabling culture of viable microorganisms.
Advantages of sonication
• High accuracy
With low-intensity sonication, microorganisms are dislodged from the implant but not killed, enabling high sensitivity of conventional cultures (Fig. 4).
Particularly difficult to detect microorganisms (including small-colony variants), individual morphotypes and mixed infections can be better detected. The sensitivity is particularly improved in patients receiving previous antibiotics, due to better survival of bacteria in biofilm. Ultrasound reaches through surrounding fluid the whole implant surface, which is associated with high specificity.
• Rapid result
Sonication increases microbial growth by inducing micro-currents in the sonication fluid, thereby shortening the microbial detection time.
• Quantiative biofilm assessment
Since bacteria survive, but not replicate in the sonication fluid, quantitative assessment of removed biofilm is possible. The microbial density is expressed as number of colony-forming units (CFU) per ml of sonication fluid.
• Additional investigations
The sonication fluid contains high density of bacteria, making it suitable for further microbial (e.g. PCR, MALDI-TOF, microcalorimetry) and immunological analyses (e.g. determination of biomarkers, gene expression).
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