Ultrasound frequency of sonication applied in microbiological diagnostics has a major impact on viability of bacteria causing periprosthetic joint infection

Objectives: Sonication of explanted prosthesis constitutes an element of microbiological diagnostics. The aim of performing this procedure is to remove biofilm and to increase sensitivity of diagnostics. Ultrasound used for medical purposes are low-frequency and low-intensity. With this wide range of frequency which can be used in sonication process it is necessary to find the golden mean between biofilm dislodging and planktonic bacteria sparing. Materials and methods: The aim of this study was to determine the least harming low-intensity ultrasound frequency (35 kHz, 40 kHz or 53 kHz) used during sonication process with other parameters constant. Four bacteria species were examined: S. aureus, E. faecalis, E. coli, K. pneumoniae. Number of microbiological studies (n) for each group (g) counted 40 specimens (based on scheme 1 bacteria type – 4 groups, 40 studies each). Results: A detailed analysis of gathered data was conducted. Based on study findings following conclusions were drawn. Sonication has a significant and negative impact on survival of sonicated planktonic bacteria. Part of bacteria in planktonic state are damaged/killed by ultrasound, which is demonstrated by lower CFU count in sonicated samples versus control group. Conclusions: Optimal ultrasound frequencies for sonication of S. aureus, P. aeruginosa and E. coli are 35 kHz and 40 kHz. Ultrasound frequencies used in sonication process (35 kHz, 40 kHz, 53 kHz) of E. coli showed same impact on bacteria survival. It is crucial to perform further assessment of ultrasound parameters on clinical effects of sonication used in PJI diagnostics.