Background: The paradoxical effect of fungi, (which is a special phenomenon that certain Candida spp. might exhibit augmented growth in the presence of echinocandin at some concentration higher than the minimum inhibitory concentration) would be better illustrated through growth curves.
Materials and methods: We investigated the paradoxical effect of caspofungin and micafungin on the growth and cell viability of 38 clinical isolates of Candida albicans using a microbial sensitivity test and growth curve methodology.
Results: When cells were incubated in the presence of antifungal agents for 48 h, the paradoxical effect was observed in 50% and 47.4% of the isolates incubated with caspofungin and micafungin, respectively. Growth curves indicated the occurrence of the paradoxical effect varied between different echinocandins. Moreover, increased turbidity in the sensitivity test did not correlate with increased fungal cell growth. For caspofungin, the paradoxical effect appeared earlier than in the microbial sensitivity test, while for micafungin, the effect observed in the microbial sensitivity test was not a true paradoxical effect.
Conclusion: The growth curve methodology is more accurate for evaluating the occurrence of the paradoxical effect in comparison with the microbial sensitivity test.