Zygomycetes in human disease

In vitro susceptibilities of zygomycetes to combinations of antimicrobial agents

Combinations of antimicrobial agents were tested against 35 strains of zygomycetes. The interaction between amphotericin B and rifampin was synergistic or additive. Flucytosine alone was inactive and, upon combination with amphotericin B, synergy was not achieved. The combination of amphotericin B with terbinafine was synergistic for 20% of strains, and the interaction between terbinafine and voriconazole was synergistic for 44% of strains. Antagonism was not observed.

In vivo activity of posaconazole against Mucor spp. in an immunosuppressed-mouse model

The in vivo activities of posaconazole, itraconazole, and amphotericin B in neutropenic mice with zygomycosis were compared. The in vitro MICs of posaconazole and itraconazole for the strains of Mucor spp. used in this study ranged from 0.125 to 8 microg/ml and 0.25 to 8 microg/ml, respectively. The in vitro MIC range for amphotericin B is 0.125 to 0.25 microg/ml. At twice-daily doses of >or=15 mg/kg of body weight, posaconazole prolonged the survival of the mice and reduced tissue burden.

Efficacy of antifungal therapy in a nonneutropenic murine model of zygomycosis

Three isolates of zygomycetes belonging to three different genera (Rhizopus microsporus, Absidia corymbifera, and Apophysomyces elegans) were used to produce a disseminated infection in nonimmunocompromised mice. The therapeutic efficacy of amphotericin B, given intraperitoneally at doses ranging from 0.5 to 4.5 mg/kg of body weight/day, oral itraconazole at 100 mg/kg/day, and oral terbinafine at 150 mg/kg/day was evaluated in this model. The markers of antifungal efficacy were the median survival time, the mortality rate, and the percentage of infected organs. Organ culture was performed along with microscopic direct examinations of tissues to assess the presence of an active infection. An acute and lethal infection was obtained in untreated mice challenged with each of the three strains. The data obtained for direct examinations and qualitative cultures indicate that, due to the nonseptate nature of the hyphae, each technique gives different information and should be used together with the others. Against all three strains, amphotericin B yielded a 90 to 100% survival rate. Itraconazole was inactive against R. microsporus but significantly reduced mortality in mice infected with A. corymbifera or A. elegans. Terbinafine had no beneficial effects against R. microsporus and A. corymbifera despite documented absorption of the drug. Overall, only limited correlations were observed between MICs determined in vitro and in vivo efficacy of the drugs. The efficacy of itraconazole in these models of zygomycosis suggests that this drug, as well as the new azole compounds presently under development, warrants close evaluation.

In vitro activities of posaconazole, itraconazole, voriconazole, amphotericin B, and fluconazole against 37 clinical isolates of zygomycetes

In vitro antifungal susceptibility testing results of a new antifungal triazole, posaconazole (POS), were compared to results with amphotericin B (AMB), itraconazole (ITC), voriconazole (VRC), and fluconazole (FLC) against clinical agents of zygomycosis. The MICs of POS at which 50% and 90% of the isolates were inhibited were 0.25 and 4 microg/ml, respectively. POS was significantly more active than VRC and FLC and slightly more active than ITC. The results suggest that POS has significant potential for clinical development against the zygomycetes.

Animal models of zygomycosis--Absidia, Rhizopus, Rhizomucor, and Cunninghamella

Infections caused by zygomycetes, which have been increasing in recent years, are known for their difficulty of diagnosis and treatment. Because little is known about this fungus and its infection, vigorous research is now in serious demand. As in many other systemic mycoses, animal model studies are essential in the investigation of zygomycosis, particularly for the study of pathogenesis, diagnosis and treatment. Unfortunately, such studies have been limited when compared with those of aspergillosis. To help investigating the disease, here in this review article, the profile of human zygomycosis is briefly described, followed by a review of the heretofore used animal models of zygomycosis. Among clinically important zygomycetes causing human infection, animal models are available for Absidia corymbifera, Rhizopus oryzae, R. microsporus var. rhizopodiformis, Rhizomucor pusillus and Cunninghamella bertholletiae. Mice are the most commonly used animals, but models using guinea pigs and rabbits are also available. Pretreatment of animals with cyclophosphamide, corticosteroid, alloxan or streptozocine is frequently done to create an immunocompromised state. Treatment with desferrioxamine, an iron chelator, is also used to make animal models. In terms of the route of infection, the airborne route is used for pathophysiological studies in pulmonary infection models, but sometimes intravenous injection is preferred, particularly for antifungal drug studies. When pathophysiological analysis is the purpose of the study, the animals must be cautiously examined both histopathologically and mycologically. For the most part, zygomycosis model studies can be performed in a similar manner to those of aspergillosis. However, Aspergillus spp. and zygomycetes are completely different fungi, and researchers should be aware of the specific, critical aspects when handling zygomycosis models, such as homogenization of infected organs and staining of pathological samples.

Soft tissue infection with Absidia corymbifera in a patient with idiopathic aplastic anemia

We describe a case of primary cutaneous mucormycosis (zygomycosis) in a patient with idiopathic aplastic anemia which responded to surgical debridement and therapy with liposomal amphotericin B. The tissue removed at surgery showed dense infiltration with fungal hyphae on histopathological examination. Primary cultures of tissue on solid media were negative, but Absidia corymbifera was isolated from unprocessed tissue placed in brain heart infusion broth.

Basidiobolus ranarum as an etiologic agent of gastrointestinal zygomycosis

Basidiobolus ranarum is a known cause of subcutaneous zygomycosis. Recently, its etiologic role in gastrointestinal infections has been increasingly recognized. While the clinical presentation of the subcutaneous disease is quite characteristic and the disease is easy to diagnose, gastrointestinal basidiobolomycosis poses diagnostic difficulties; its clinical presentation is nonspecific, there are no identifiable risk factors, and all age groups are susceptible. The case of gastrointestinal basidiobolomycosis described in the present report occurred in a 41-year-old Indian male who had a history of repair of a left inguinal hernia 2 years earlier and who is native to the southern part of India, where the subcutaneous form of the disease is indigenous. Diagnosis is based on the isolation of B. ranarum from cultures of urine and demonstration of broad, sparsely septate hyphal elements in histopathologic sections of the colon, with characteristic eosinophilic infiltration and the Splendore-Hoeppli phenomenon. The titers of both immunoglobulin G (IgG) and IgM antibodies to locally produced antigen of the fungus were elevated. The patient failed to respond to 8 weeks of amphotericin B therapy, and the isolate was later found to be resistant to amphotericin B, itraconazole, fluconazole, and flucytosine but susceptible to ketoconazole and miconazole. One other noteworthy feature of the fungus was that the patient's serum showed raised levels of Th2-type cytokines (interleukins 4 and 10) and tumor necrosis factor alpha. The present report underscores the need to consider gastrointestinal basidiobolomycosis in the differential diagnosis of inflammatory bowel diseases and suggests that, perhaps, more time should be invested in developing standardized serologic reagents that can be used as part of a less invasive means of diagnosis of the disease.

Maxillary sinusitis caused by Actinomucor elegans

We report the first case of maxillary sinusitis caused by Actinomucor elegans in an 11-year-old patient. Histopathological and mycological examinations of surgical maxillary sinuses samples showed coenocytic hyphae characteristic of mucoraceous fungi. The fungi recovered had stolons and rhizoids, nonapophyseal and globose sporangia, and whorled branched sporangiophores and was identified as A. elegans. After surgical cleaning and chemotherapy with amphotericin B administered intravenously and by irrigation, the patient became asymptomatic and the mycological study results were negative.