# Antibacterial Effect of Topically Administered Transcamic Acid in Large Joint Arthroplasty
## 4 Discussion
To the best of our knowledge, our study is the most extensive study to date of TXA effects on bacterial growth, assessing 22 bacterial strains obtained from commercially available cell culture collections and the clinical isolates library of our hospital, which belong to 7 different species (6 _S. aureus_ strains, 6 _S. epidermidis_ strains, one _S. lugdunensis_ strain, 2 _P. aeruginosa_ strains, 2 _E. faecalis_ strains, one _E. fecium_ strain, and 4 _E. coli_ strains) and are some of the most common bacterial pathogens responsible for early PJIs [35]. In our study, we compared the results obtained from two different assays: the broth microdilution assay, which is one of the current reference methods for the conventional testing of antimicrobial susceptibility [36], and the kinetic growth assay, by which real-time growth analysis is possible [37]. The first method consisted of endpoint measurements after 24 h of incubation and gave limited results on the TXA's inhibitory action, with only high TXA concentrations (50 and 100 mg/mL) showing growth inhibition on a limited number of bacterial strains. With endpoint growth determination, however, the potential effects of lower TXA concentrations did not become visible. We therefore decided to perform supplementary kinetic growth assays with growth curve analysis, which allowed us to track potential changes in bacterial growth rates in relation to different TXA concentrations. The method enabled the assessment of important growth parameters and TXA's antimicrobial activity through time, which was not addressed in previous studies [27; 28; 29]. Our findings showed that TXA concentrations below 6.25 mg/mL did not affect bacterial growth in any way. At a concentration of 6.25 mg/mL, we observed a decrease in the maximum specific growth rate and an extension of the lag phase only in one _S. aureus_ strain. However, TXA concentrations ranging from 12.5 mg/mL to 50 mg/mL also resulted in partial growth inhibition for other tested bacteria, marked by a decrease in population densities after 24 h of incubation, extended lag phases, and decreased maximum specific growth rates. Only at the highest tested concentrations of 100 mg/mL did TXA completely inhibit the growth of five bacterial strains from four different bacterial species. At TXA concentrations of 12.5 mg/mL or higher, in addition to the observed extended lag phases, bacterial final turbidity values (after 24 h) did not reach those of their respective positive controls. Lower population densities in the plateau phase suggested a bactericidal effect of TXA on some bacterial cells within the population, with the subsequent regrowth of surviving persister bacteria. However, additional research is needed to confirm this hypothesis. The main limitations of our study are the limited assortment of tested bacterial strains, which means that the data cannot be extrapolated to other species, and the static nature of the in vitro model, which overlooks the dynamics of the intraarticular environment, in which the TXA concentration is expected to be influenced by the rate of formation and final volume of periarticular hematoma, followed by resorption into the extra-/intracellular space of periarticular tissues and blood circulation [38; 39]. In other words, concentrations of TXA above 50 mg/mL after standard intraarticular application are unlikely to persist for more than a few hours, given the biological half-life of TXA in the synovial fluid of 2-3 h [38]. This is relevant, since the bacteriostatic effect was observed in susceptible strains only when exposed to the highest tested concentrations in a controlled environment. In order to elucidate further the dynamics of local TXA concentrations after topical application in vivo, additional clinical studies are essential.