To our knowledge, this is the first case of invasive pulmonary aspergillosis after liver transplantation in China caused by A. lentulus. In 2004, Balajee first reported a distinct variant of A. fumigatus that causes invasive infection in four HSCT recipients and demonstrated decreased susceptibilities to multiple antifungal drugs. The isolates sporulated slowly and needed prolonged incubations to be similar to typical isolates. Sequencing showed the mitochondrial cytochrome b gene sequences of all the new isolates were unique, which suggested the potential presence of a genetically unique. Phenotypic methods revealed that the variant isolate has smaller conidial heads with diminutive vesicles compared to A. fumigatus and is not able to survive at 48°C, which was then designated A. lentulus. From then on, this new species has been found in soil, environmental samples and was reported in patients in America, Japan, Spain, Brazil and some other countries, described as a new sibling species of A. fumigatus due to their morphological resemblance.
According to the literature, approximately 4-5% of “A. fumigatus” isolated from patients have later turned out to be the related species, due to their morphological resemblance, which makes the accurate identification of A. lentulus difficult for clinical microbiology laboratories. Therefore, the reported prevalence of A. lentulus might be underestimated. Hence, molecular analysis is required for the identification of A. lentulus. Tamiya and his colleagues used liquid chromatography/time-of-flight mass spectrometry to identify the secondary metabolites secreted as virulence factors by A. lentulus. Among all the secondary metabolites, auranthine in conidia and culture filtrate was only found in A. lentulus, but not in A. fumigatus or the other related species. In culture filtrate, the A. fumigatus isolates produced significantly higher amounts of gliotoxin compared with other species including A. lentulus.
Since the first documented description, only 11 cases (except the present one) of IA caused by A. lentulus have been reported around the world, related to 17 patients. The characteristics and details of the cases in the literature are shown in Table 1. (see Additional file Table_1)
The median age at diagnosis was 50 years (range, 12-82 years). Except two cases with incomplete information, nine patients (77.8%) were male in the remaining 9 cases. Among the 17 patients, 8 (47%) had a history of HSCT, 5 (29.4%) experienced SOT, and 4 patients had other underlying diseases (COPD, cystic fibrosis, refractory nephrotic syndrome, ANCA-associated vasculitis). A. lentulus and A. fumigatus were isolated simultaneously in one patient with COPD. All SOT patients received immunosuppressive therapy and three patients with no history of transplantation, also received immunosuppressive therapy including glucocorticoids. 6 (35.2%) patients had a history of antifungal drug usage before diagnosis.
Except two cases with incomplete information, voriconazole and amphotericin B (including amphotericin B liposomes) were used in four (4/9, 44.4%) and four (4/9, 44.4%) cases as primary antifungal treatment, respectively. However, 6 patients (6/9, 66.6%) showed a fatal clinical outcome.
As we all know, A. fumigatus are intrinsically sensitive to azoles and amphotericin B, but A. lentulus isolates usually have higher MIC values for these drugs and caspofungin, and even show primary resistance to azole drugs. Nowadays, the most common acknowledged mechanism concerning azole resistance in A. lentulus is mutations in the cyp51A gene. Mellado performed heterologous expression in an A. fumigatus cyp51A deficient strain, confirming that cyp51A is responsible for the differences in A. lentulus-azole drug resistance. Since there is no breakpoint for A. lentulus according to CLSI and EUCAST, and the breakpoint of A. fumigatus cannot be referred to, so we did some therapeutic drug monitoring to keep the voriconazole trough concentration above 1.0 mg/L.
According to other researches, Tamiya tested drug susceptibility for A. fumigatus and all three related species including A. lentulus, revealed that amphotericin B was effective against all four species. In contrast, A. lentulus had higher MICs to azoles such as voriconazole and itraconazole. Environmental isolates had decreased susceptibility to voriconazole and itraconazole than clinical isolates. As pointed out by Mortensen, susceptibility tests indicated that A. lentulus demonstrates higher MICs to amphotericin B, itraconazole and voriconazole but a MIC of 0.5 for posaconazole. Interestingly, the susceptibility characteristics of the isolates in our case are slightly different from the susceptibility reported in the published literature. It showed higher MICs to amphotericin B (MIC, 8 mg/L), but normal MICs to voriconazole (MIC, 1.0 mg/L), itraconazole and posaconazole (MIC, 0.5 mg/L). This highlights the importance of microorganism identification and antimicrobial susceptibility testing. However, it should be understood that high in vitro MICs may not only necessarily consist with decreased susceptibility in vivo, clinicians and laboratories should also take notice of patients’ poor condition, drug dose, frequency and so on. In our present case, we administered voriconazole (LD 0.4g q12h, MD 0.2g q12h) plus caspofungin (LD 70mg once,MD 50mg qd), and kept the voriconazole plasma concentration within the recommended range (1.0-5.5mg/L) by therapy drug monitoring. Finally, his sputum culture turned negative and laboratory tests reduced gradually, repeated CT scan showed a reduction of the lesions, and the patient improved eventually.
In conclusion, here we reported the first case of probable invasive aspergillosis caused by A. lentulus after liver transplantation in our country, which showed a good clinical response to voriconazole and caspofungin. We exemplify the important role of accurate species identification and antimicrobial susceptibility testing due to the differential MICs of Aspergillus-related species. More clinical features and treatment of infection with A. lentulus should be discussed in the future.