# Antibacterial Effect of Topically Administered Transcamic Acid in Large Joint Arthroplasty
## 3 Results
### Kinetic Growth Assay  
To assess potential initial inhibitory or bactericidal effects of TXA's sub-MICs, that may not be maintained during the total 24 h incubation time, a kinetic growth assay was performed analyzing the growth time-dependent susceptibility of 22 clinically relevant bacterial strains. Figure 1: Effects of different TXA concentrations on the proliferation of 22 clinically relevant bacterial strains after 24 h incubation. Growth analysis showed various susceptibilities of the tested bacterial strains to different TXA concentrations at different growth stages. Microbial growth patterns for _E. faecalis_ OBV 11/850 and _S. aureus_ ATCC 43300 presented in Figure 2 are examples of different TXA-specific dynamic growth profiles. Growth curves for the other 20 tested bacterial strains are presented in Figures S1-S20 in the Supplementary Material. At a concentration of 100 mg/mL, no growth was observed for strains _S. aureus_ ATCC 43300 (Figure 2b), _S. epidermidis_ ATCC 28319 (Figure S6), _P. aeruginosa_ DSM 21385 (Figure S13), and _P. aeruginosa_ OBV 19/662 (Figure S14). For _S. lugdunensis_ OBV 20/143, the culture's OD started to increase slightly after 21.5 h of incubation with 100 mg/mL of TXA. However, the culture still showed a 94% reduction in population density compared with its reference control after 24 h of incubation (Figure S12). At a concentration of 100 mg/mL, a substantial reduction in bacterial growth was observed in cultures of _S. aureus_ OBV 17/104, _S. epidermidis_ DSM 3269, _S. epidermidis_ ATCC 12228, _S. epidermidis_ OBV 14/175-3, _E. faecalis_ ATCC 29212, _E. faecalis_ OBV 11/850 (Figure 2a), and _E. facoium_ OBV 11/549-b. For _E. facoium_ OBV 11/549-b and _S. epidermidis_ DSM 28319, the same was also observed at a concentration of 50 mg/mL. For the mentioned strains, a 50-90% decrease in population density was observed after 24 h of incubation compared with their reference controls (Figure 3). To describe and compare the growth of bacteria, two key growth parameters--the lag time (\(\lambda\)) and specific growth rate (\(\mu\))--were obtained by curve-fitting procedures. Parameters for all bacterial cultures at different tested TXA concentrations are reported in Table S1. Extended lag phases (>1 h longer than the reference controls) were observed in 14 out of 22 tested bacterial strains at TXA concentrations equal to or higher than 6.25 mg/mL (Figure 4). However, longer lag phases that extended 8 to 16 h over the reference control's lag phases were observed only in cultures for which TXA concentrations of 50 mg/mL (_S. aureus_ ATCC 43300, _S. aureus_ ATCC 25923, _S. epidermidis_ DSM 28319, and _S. lugdunensis_ OBV 20/143) and 100 mg/mL (_S. aureus_ OBV 17/104 and _S. aureus_ ATCC 25923) were applied. Cultures with a lag phase that exceeded the 16 h difference compared with their reference control did not grow during the 24 h incubation period, except for _S. lugdunensis_ OBV 20/143, which started to show some growth after 21.5 h of incubation, as already mentioned. Figure 2: Representative examples of growth curves for bacteria exposed to different (12.5–100 mg/mL). TXA concentrations for 24 h: (**a**) _E. faecalis_ OBV 11/850; (**b**) _S. aureus_ ATCC 43300. The curves represent OD\({}_{600\text{nm}}\) values as a function of time. TXA concentrations equal to or higher than 6.25 mg/mL showed some effect on the maximum specific growth rate of the tested bacterial cultures, decreasing it by more than 20% (Figure 5). Cultures with a more than 90% decrease in the maximum specific growth rate compared with their reference control were _S. epidermidis_ ATCC 12228 and cultures that did not grow during the 24 h incubation period at a TXA concentration of 100 mg/mL. At the same concentration, eight additional bacterial strains (_S. aureus_ ATCC 25923 and OBV 17/104, _S. epidermidis_ 14/175-3 and DSM 3269, _S. lugdunensis_ OBV 20/143, _E. faecalis_ OBV 11/850, _E. faecium_ OBV 11/549-b, and _E.