Culture medium influences detectability of antimicrobial effects of autologous platelet concentrates against anaerobic periodontal pathogens.

BACKGROUND

Autologous platelet concentrates (PRP, PRF, i-PRF) represent blood-derived biomaterials that have been reported to exhibit antimicrobial activity against oral microorganisms in vitro. In diffusion-based assays, visualization of inhibitory effects depends not only on bacterial growth but also on matrix-dependent diffusion behavior within the surrounding culture medium, particularly those complex media used for fastidious anaerobic species. However, it remains unclear whether commonly used agar media provide comparable assay environments for evaluating APC-derived antimicrobial effects. This feasibility study therefore investigated whether PRP, PRF and i-PRF generate measurable inhibition zones on different agar matrices and whether medium selection influences inhibition detectability and measurable zone expression in diffusion-based assays.

METHODS

Inhibitory effects of PRP, PRF and i-PRF against Porphyromonas gingivalis and Prevotella intermedia were tested on Brucella blood agar (BBA), Mueller-Hinton blood agar and Tryptic Soy Agar supplemented with blood (TSASB). Only measurable inhibition zones were included in quantitative analyses, while detectability outcomes were assessed separately.

RESULTS

BBA produced significantly larger measurable inhibition zones for P. gingivalis compared with TSASB (p = 0.0006; Cliff's δ = 0.92). For P. intermedia, BBA and MHB showed comparable inhibition patterns (p = 0.77), whereas TSASB yielded no measurable inhibition zones. Inhibition effects were detectable for all investigated platelet preparations. Exploratory comparisons between PRP, PRF and i-PRF across culture media did not reveal statistically significant differences under the present experimental conditions.

CONCLUSION

Agar composition represents an active experimental matrix in diffusion assays and critically shapes inhibition zone expression, particularly for strict anaerobic periodontal pathogens. Culture medium selection therefore constitutes a key methodological variable in antimicrobial evaluation of APCs, and negative findings in diffusion assays should be interpreted cautiously within the context of the underlying assay environment.