Biology subjects

Russell, A. C.

Publications and source records attributed to Russell, A. C..

4 recordsLinked to original sources

bioRxiv2025

Virulence of Naegleria fowleri isolates varies significantly in the mouse model of primary amoebic meningoencephalitis

Naegleria fowleri is a small free-living amoeba that causes an acute, fatal disease called primary amoebic meningoencephalitis (PAM). One persisting question is why few people succumb to disease when so many are potentially exposed. We tested the hypothesis that N. fowleri isolates vary in virulence and in the minimum infectious dose required to induce disease by using a mouse model of PAM and intranasally inoculating dilutions of five clinical isolates of N. fowleri. Results showed significant differences in onset of severe disease and mortality rates between isolates. Remarkably, for isolate V596, 100 amoebae produced 100% mortality within 5 days. In contrast, higher numbers of amoebae were required for other isolates and mice survived for >2 weeks. Concurrently, we developed an in vitro virulence assay by comparing feeding rates between amoebae isolates seeded onto Vero cells. We observed a positive correlation between cytopathic effects in vitro and virulence in vivo. Article Summary LineIsolates of Naegleria fowleri vary in virulence, which results in significant differences in minimal infectious concentrations of amoebae that cause primary amoebic meningoencephalitis.

microbiology↗

bioRxiv2025

Secreted small RNAs of Naegleria fowleri as biomarkers for diagnosis of primary amoebic meningoencephalitis

Rapid and accurate diagnostics are needed to effectively detect and treat primary amoebic meningoencephalitis (PAM) caused by the free-living amoeba, Naegleria fowleri. Delayed diagnosis and similarities to other causes of meningitis contribute to a case mortality rate of >97%, and current testing requires a spinal tap to obtain cerebrospinal fluid (CSF). Thus, there is an unmet medical need for a non-invasive liquid biopsy diagnostic method. We sequenced N. fowleri extracellular vesicles (EVs) and identified microRNAs, tRNAs and other small RNAs in N. fowleri-EVs. From these data we selected two prevalent small RNAs as biomarker candidates. We developed an RT-qPCR assay and both small RNAs were detected in N. fowleri-EVs and amoeba-conditioned media. In the mouse model of PAM, both small RNA biomarkers were detected in 100% of mouse plasma samples at the end-stage of infection. Notably, smallRNA-1 was detected in the urine of infected mice at timepoints as early as 24h post infection (18/23 mice) and in the plasma as early as 60h post infection (8/8 mice). Additionally, smallRNA-1 was detected in 100% (n=6) of CSF samples from human PAM cases, and in whole blood samples, but not in human plasma from PAM cases. In this study, we discovered small RNAs as biomarkers of N. fowleri infection--one which can be detected reliably in CSF, urine, and whole blood. The RT-qPCR assay is a highly sensitive diagnostic assay that can be conducted in [~]3h after receipt of liquid biopsy. The data suggest detection of smallRNA-1 biomarker could provide earlier diagnosis of PAM and be used to monitor biomass of amoebae during treatment. One Sentence SummarySmall RNAs of Naegleria fowleri can be detected in liquid biopsies and serve as early diagnostic biomarkers of primary amoebic meningoencephalitis.

microbiology↗

bioRxiv2021

Differential growth rates and in vitro drug susceptibility to currently used drugs for multiple isolates of Naegleria fowleri

The free-living amoeba, Naegleria fowleri, which typically dwells within warm, freshwater environments, can opportunistically cause Primary Amoebic Meningoencephalitis (PAM), a disease with a mortality rate of >98%, even with the administration of the best available drug regimens. The lack of positive outcomes for PAM has prompted a push for the discovery and development of more effective therapeutics, but most studies only utilize one or two clinical isolates in their drug discovery assays. The inability to assess possible heterogenic responses to drugs among isolates from varying geographical regions hinders progress in the field due to a lack of proven universal efficacy for novel therapeutics. Herein we conducted drug efficacy and growth rate determinations for 11 different clinical isolates, including one obtained from a successful treatment outcome, by applying a previously developed CellTiter-Glo 2.0 screening technique and flow cytometry. We found some significant differences in the susceptibility of these isolates to 7 of 8 different drugs tested, all of which comprise the cocktail that is recommended to physicians by the Centers for Disease Control. We also discovered significant variances in growth rates among isolates which draws attention to the dissidence among the amoebae populations collected from different patients. The findings of this study reiterate the need for inclusion of additional clinical isolates of varying genotypes in drug assays and highlight the necessity for more targeted therapeutics with universal efficacy across N. fowleri isolates. Our data establishes a needed baseline for drug susceptibility among clinical isolates and provides a segue for future combination therapy studies as well as research related to phenotypic or genetic differences that could shed light on mechanisms of action or predispositions to specific drugs.

microbiology↗

bioRxiv2020

Discovery of anti-amoebic inhibitors from screening the MMV Pandemic Response Box on Balamuthia mandrillaris, Naegleria fowleri and Acanthamoeba castellanii

Pathogenic free-living amoebae, Balamuthia mandrillaris, Naegleria fowleri and several Acanthamoeba species are the etiological agents of severe brain diseases, with case mortality rates >90%. A number of constraints including misdiagnosis and partially effective treatments lead to these high fatality rates. The unmet medical need is for rapidly acting, highly potent new drugs to reduce these alarming mortality rates. Herein, we report the discovery of new drugs as potential anti-amoebic agents. We used the CellTiter-Glo 2.0 high-throughput screening methods to screen the Medicines for Malaria Ventures (MMV) Pandemic Response Box in a search for new active chemical scaffolds. Initially we screened the library as a single-point assay at 10 and 1 {micro}M. From these data, we reconfirmed hits by conducting quantitative dose response assays and identified 12 hits against B. mandrillaris, 29 against N. fowleri and 14 against A. castellanii ranging from nanomolar to low micromolar potency. We further describe 11 novel molecules with activity against B. mandrillaris, 22 against N. fowleri and 9 against A. castellanii. These structures serve as a starting point for medicinal chemistry studies and demonstrate the utility of phenotypic screening for drug discovery to treat diseases caused by free-living amoebae.

microbiology↗