Abstract
Members of the order Mucorales are emerging invasive molds that cause infections in immunocompromised patients. However, little is known about the relation between different species of Mucorales and their virulence in invasive pulmonary mucormycosis. Based upon our earlier epidemiological studies, we hypothesized that Cunninghamella bertholletiae would demonstrate increased virulence. Therefore, we studied the relative virulence of C. bertholletiae (CB), Rhizopus oryzae (RO), R. microsporus (RM), and Mucor circinelloides (MC) in experimental invasive pulmonary mucormycosis in persistently neutropenic rabbits in relation to the fungi in vitro sporangiospore germination rate and hyphal metabolic activity. Rabbits infected with CB demonstrated (1) higher lung weights in comparison to RM (P ≤ 0.05), RO and MC (P ≤ 0.001), (2) pulmonary infarcts in comparison to RO and MC (P ≤ 0.001), (3) tissue fungal burden (CFU/g) vs. MC (P ≤ 0.001), and (4) the lowest survival of 0% (0/18), in comparison to 16% (3/18, P ≤ 0.01) of RM, 81% (21/26) of RO, and 83% (15/18) of MC-infected rabbits (P ≤ 0.001). Serum PCR concentration-time-curve showed the greatest amplitude for CB. Virulence correlated directly with sporangiospore germination rate at 4 h among species, i.e., CB (67–85%) > RM (14–56%) > RO (4–30%) > MC (0%), and hyphal metabolic activity, i.e., CB (1.22–1.51) > MC (0.54–0.64) = RM (0.38–0.41) = RO (0.37–0.59). C. bertholletiae was significantly more virulent in experimental invasive pulmonary mucormycosis than R. microsporus, R. oryzae, and M. circinelloides. In vivo virulence correlated with species-dependent differences of in vitro germination rate and hyphal metabolic activity.
Declaration of interest: The authors have no conflicts of interest for this subject matter. The authors alone are responsible for the content and writing of the paper.
This paper was first published online on Early Online on 12 June 2012.