Detection of Microorganisms in Clinical Sonicated Orthopedic Devices Using Conventional Culture and qPCR.

Objective  To evaluate the sensitivity and specificity of the quantitative real-time polymerase chain reaction (qPCR) for 16S rDNA gene screening using sonicated fluid from orthopedic implants. Methods  A retrospective study was conducted on 73 sonicated fluids obtained from patients with infection associated with orthopedic implants. The samples were subjected to conventional culture and molecular testing using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and qPCR for 16S rDNA . The cycle threshold values were used to define a cut-off of the qPCR of the 16S rDNA for negative and positive cultures. Results  No statistical differences were observed between the positive and negative culture groups based on the time from the first surgery to infection ( p  = 0.958), age ( p =  0.269), or general comorbidities. Nevertheless, a statistical difference was found between the mean duration of antibiotic use before device removal (3.41 versus 0.94; p =  0.016). Bacterial DNA was identified in every sample from the sonicated fluids. The median cycle thresholds of the positive and negative cultures were of 25.6 and 27.3 respectively ( p  < 0.001). As a diagnostic tool, a cycle threshold cut-off of 26.89 demonstrated an area under the curve of the receiver operating characteristic of 0.877 ( p  ≤ 0.001). Conclusion  The presence of antimicrobial agents for more than 72 hours decreased culture positivity, but did not influence the qPCR results. Despite this, amplification of the 16S rDNA may overestimate infection diagnosis.