Development and validation of a colorimetric antifungal susceptibility testing method for the dimorphic fungus Talaromyces marneffei

Antifungal drug resistance is an emerging cause of treatment failure in invasive fungal infections, and antifungal susceptibility testing (AFST) may inform treatment decisions. Currently, there are no established AFST guidelines for Talaromyces marneffei (Tm) or other dimorphic fungi. We developed a colorimetric AFST method using a fluorescent redox indicator alamarBlue, which changes from blue to pink in proportion to cellular metabolic activity. We determined the optimal time for alamarBlue addition to be 24 h post-inoculation and for MIC reading to be 72 h post-inoculation. Our method allows three ways to determine minimum inhibitory concentration (MIC): visual inspection of color change, optical density, and fluorescence intensity. We validated the assay by determining the MICs for seven antifungals against 32 Tm clinical isolates and assessed the essential agreement (EA) and inter-rater reliability between our alamarBlue and the Clinical Laboratory Standard Institute (CLSI) broth microdilution methods. The MIC ranges (from low to high) were: 0.008-0.025 μg/ml for itraconazole, 0.004-0.13 μg/ml for voriconazole, 0.03-0.13 μg/ml for posaconazole, 0.06-0.5 µg/ml for flucytosine, 0.5-1 µg/ml for amphotericin B, 0.5-4 µg/ml for caspofungin, and 0.5-16 µg/ml for fluconazole. The EAs were 100% between all three MIC readouts of the alamarBlue method, and 94%-100% between the alamarBlue and CLSI methods. Our alamarBlue method had substantially higher inter-rater agreement and offers a more reliable method that can be standardized across laboratories in both high- and low-resource settings compared to the established CLSI methodology.

Impact of pathogen genetics on clinical phenotypes in a population of Talaromyces marneffei from Vietnam

Talaromycosis, a severe and invasive fungal infection caused by Talaromyces marneffei, is difficult to treat and impacts those living in endemic regions of Southeast Asia, India, and China. While 30% of infections result in mortality, our understanding of the genetic basis of pathogenesis for this fungus is limited. To address this, we apply population genomics and genome-wide association study approaches to a cohort of 336 T. marneffei isolates collected from patients who enrolled in the Itraconazole vs Amphotericin B for Talaromycosis trial in Vietnam. We find that isolates from northern and southern Vietnam form two distinct geographical clades, with isolates from southern Vietnam associated with increased disease severity. Leveraging longitudinal isolates, we identify multiple instances of disease relapse linked to unrelated strains, highlighting the potential for multistrain infections. In more frequent cases of persistent talaromycosis caused by the same strain, we identify variants arising over the course of patient infections that impact genes predicted to function in the regulation of gene expression and secondary metabolite production. By combining genetic variant data with patient metadata for all 336 isolates, we identify pathogen variants significantly associated with multiple clinical phenotypes. In addition, we identify genes and genomic regions under selection across both clades, highlighting loci undergoing rapid evolution, potentially in response to external pressures. With this combination of approaches, we identify links between pathogen genetics and patient outcomes and identify genomic regions that are altered during T. marneffei infection, providing an initial view of how pathogen genetics affects disease outcomes.

Clinical features of Talaromyces marneffei infection in HIV-positive and HIV-negative individuals: A retrospective study in southern China

Talaromyces marneffei (TSM) is a temperature-dependent dimorphic fungus endemic to Southeast Asia and southern China. As the number of people at risk of TSM infection continues to increase, the clinical manifestations are becoming increasingly complex, posing challenges for clinical management. In this study, we analyzed the medical records of 99 patients (71 human immunodeficiency virus [HIV]-positive and 28 HIV-negative) diagnosed with TSM infection from January 1, 2017, to December 31, 2022, in southern China and compared the clinical manifestations in HIV-positive and HIV-negative patients. Most patients (83/99, 84%) were male. The incidence of skin and soft tissue involvement (48% vs. 21%, P = .016); disseminated infection with blood circulation, hematopoietic, lymphatic, alimentary, or central nervous system involvement (69% vs. 36%, P = .002); and gastrointestinal bleeding (33% vs. 9%, P = .023) was higher in the HIV-positive group than the HIV-negative group. The HIV-positive group also had significantly higher alanine aminotransferase (ALT) levels (31 [26-42] vs. 14 [11-16] U/l, P < .001) and ALT/aspartate transaminase ratio (1.9 [1.5-2.2] vs. 1.3 [1.1-1.6], P = .006) than the HIV-negative group. The time to diagnosis (5.5 ± 1.1 vs. 5.1 ± 1.4 days, P = .103), antifungal regimen (P = .278), case fatality rate (20% vs. 21%, P = .849), and relapse/reinfection rate (11% vs. 19%, P = .576) did not differ significantly between the HIV-positive and HIV-negative groups. Poor antiretroviral therapy adherence (OR = 26.19, 95%CI 3.26-210.70, P = .002), advanced age (OR = 1.13, 95%CI 1.03-1.23, P = .010), and Epstein-Barr virus co-infection (OR = 37.13, 95%CI 3.03-455.64, P = .005) were independent risk factors for all-cause mortality from TSM infection in HIV-positive patients. Overall, the predominant infection sites, clinical manifestations, and complications of TSM infection differed by HIV status. However, with prompt diagnosis and appropriate treatment, HIV-positive patients with TSM infection can have similar outcomes to HIV-negative patients.

Talaromyces marneffei isolated from nasal swabs in Portugal

Mycobiota are essential to the health of any living being, creating a balanced and complex interaction between bacteria, the immune system and the tissue cells of the host. Talaromyces marneffei (also known as Penicillium marneffei) is a dimorphic fungus, endemic in South Asia, that often causes a life-threatening systemic fungal infection (called penicilliosis), particularly in immunocompromised hosts. Nasal swabs from 73 healthy volunteers were analysed to characterise their mycobiota, through its cultural characteristics, morphology and molecular methods (PCR). All volunteers were also asked to answer to an anonymous questionnaire. Three women were positive (and asymptomatic) for T. marneffei. One of them was reported to have lupus. This study contributes to improving our knowledge about human normal mycobiota, identifying mycotic agents that may cause complicated systemic infections (as T. marneffei), especially in immunosuppressed patients, as well as other possible risk factors of exposure or prognosis.

Superiority of a Novel Mp1p Antigen Detection Enzyme Immunoassay Compared to Standard BACTEC Blood Culture in the Diagnosis of Talaromycosis

BACKGROUND

Talaromycosis is an invasive mycosis endemic in Southeast Asia and causes substantial morbidity and mortality in individuals with advanced human immunodeficiency virus (HIV) disease. Current diagnosis relies on isolating Talaromyces marneffei in cultures, which takes up to 14 days and is detectable only during late-stage infection, leading to high mortality.

METHODS

In this retrospective case-control study, we assessed the accuracy of a novel Mp1p antigen-detecting enzyme immunoassay (EIA) in stored plasma samples of 372 patients who had culture-proven talaromycosis from blood or sterile body fluids (reference standard) and 517 individuals without talaromycosis (338 healthy volunteers; 179 with other infections). All participants were recruited between 2011 and 2017 in Vietnam.

RESULTS

Of cases and controls, 66.1% and 75.4%, respectively, were male; the median age was 33 and 37, respectively. All cases were HIV infected; median CD4 count was 10 cells/μL. At an optical density cutoff of 0.5, the specificity was 98.1% (95% CI, 96.3%-99.0%); the sensitivity was superior to blood culture (86.3% [95% CI, 82.3%-89.5%] vs 72.8% [95% CI, 68.0%-77.2%]) (P < .001, McNemar test). The time to diagnosis was 6 hours vs 6.6 ± 3.0 days for blood culture. Paired plasma and urine testing in the same patients (n = 269) significantly increased sensitivity compared to testing plasma alone or testing urine alone (P < .001 and P = .02, respectively, McNemar test).

CONCLUSIONS

The Mp1p EIA is highly specific and is superior in sensitivity and time to diagnosis compared to blood culture for the diagnosis of talaromycosis. Paired plasma and urine testing further increases sensitivity, introducing a new tool for rapid diagnosis, enabling early treatment and potentially reducing mortality.

Prognosis and treatment effects of HIV-associated talaromycosis in a real-world patient cohort

Talaromycosis is a leading cause of AIDS-associated opportunistic infections and death in Southeast Asia. We have recently shown in the Itraconazole versus Amphotericin for Talaromycosis (IVAP) trial that induction therapy with amphotericin B reduced mortality over 24 weeks, but not during the first 2 weeks. Antifungal treatment effects in real-world settings have not been rigorously evaluated. Using data obtained from patient records at the Hospital for Tropical Diseases, Ho Chi Minh City, Vietnam from 2004 to 2009, we first developed a prognostic model using Bayesian logistic regression to identify predictors of death. Second, we developed a causal model using propensity score matching to assess the treatment effects of amphotericin B and itraconazole. Our prognostic model identified intravenous drug use (odds ratio [OR] = 2.01), higher respiratory rate (OR = 1.12), higher absolute lymphocyte count (OR = 1.62), a concurrent respiratory infection (OR = 1.67) or central nervous system infection (OR = 2.66) as independent predictors of death. Fever (OR = 0.56) was a protective factor. Our prognostic model exhibits good in-sample performance and out-of-sample validation, with a discrimination power of 0.85 and 0.91, respectively. Our causal model showed no significant difference in treatment outcomes between amphotericin B and itraconazole over the first 2 weeks (95% credible interval: 0.62, 2.50). Our prognostic model provides a simple tool based on routinely collected clinical data to predict individual patient outcome. Our causal model shows similar results to the IVAP trial at 2 weeks, demonstrating an agreement between real-world data and clinical trial data.