Killing Kinetics of Carvacrol against Fluconazole-Susceptible and -Resistant Isolates of Candida tropicalis

Overuse and misuse of antibiotics in the agricultural and healthcare sectors have led to the emergence of antibiotic-resistant strains. Therefore, finding alternative antimicrobial compounds, such as phytochemicals, is of great importance. This study evaluated the feasibility of carvacrol as an antifungal agent in suppressing the planktonic and hyphal growth of clinical isolates of fluconazole-susceptible and -resistant Candida tropicalis.

Clinical isolates of fluconazole-resistant C. tropicalis were identified using the CLSI guidelines and the World Health Organization's WHONET software. The inhibitory effect of carvacrol on planktonic cells was assessed by determining the minimum inhibitory concentration (MIC) and time-kill profile. The inhibitory effect of carvacrol on hyphal growth was studied by using light field microscopy.

The findings indicated that 50% of clinical isolates of C. tropicalis were resistant to fluconazole. The MIC90 and MIC50 of carvacrol against clinical isolates of fluconazole-susceptible and -resistant C. tropicalis were 25.00-300.00 µg/ml and 12.50-100.00 µg/ml, respectively. The time-kill analysis indicated that carvacrol exhibited fungicidal activity against the fluconazole-susceptible and -resistant C. tropicalis isolates 2-48 hours after exposure. Moreover, planktonic and hyphal growth of the isolates decreased significantly after exposure to carvacrol.

The findings revealed that carvacrol exhibits inhibitory effects on the planktonic and hyphal cells of fluconazole-susceptible and -resistant C. tropicalis isolates. Therefore, the antifungal potential of carvacrol as a natural antifungal could be further exploited for the treatment of resistant C. tropicalis infections