Prototheca bovis, a unicellular achlorophyllous trebouxiophyte green alga in the healthy human intestine

Abstract

Introduction. Prototheca species are non-photosynthetic trebouxiophyte algae ubiquitously distributed in nature and can be found in sewage and soil. This microbial eukaryote causes human protothecosis in immunocompromised individuals. Thus, Prototheca presence in the stool of individuals without gastrointestinal symptoms has been reported only rarely. Hypothesis/Gap statement. There is an absence of detailed characterization of human Prototheca isolates. Aim. The aim of this study was to perform morphological and molecular characterization of Prototheca isolates obtained from human stool. Methodology. Prototheca was isolated from faecal samples of four individuals living in a rural area in Thailand. A combination of bioimaging along with molecular and bioinformatics tools was used to characterize the four strains. The growth rate was tested using four media and three temperature conditions. Phylogenetic analysis using the small subunit ribosomal RNA (SSU rRNA) and cytochrome b (cytb) was also performed. Results. Static and live microscopy demonstrated the various life stages of Prototheca and its major defining cellular characteristics. An optimized DNA extraction methodology that improves DNA yield is provided. Partial fragments of the SSU rRNA and cytb genes were obtained. Phylogenetic analysis placed all four strains in the clade with Prototheca bovis. More broadly, Prototheca was not monophyletic but split into at least two distinct clades instead. Conclusion. The results represent the first molecular characterization of Prototheca in Thailand. The study provides insight into transmission dynamics of the organism and potential caveats in estimating the global prevalence of Prototheca. These will spearhead further investigations on Prototheca occurrence in rural areas of both industrialized and developing nations.

Identification of Prototheca from the Cerebrospinal Fluid of a Cat with Neurological Signs

“…Overall, protothecosis is considered a rare human disease with an increased incidence in patients with immunosuppression [ 50 ]. Epidemiological investigations based on a One Health approach, including humans, animals, and the environment, would be necessary to better understand the ecology of prototheca [ 51 ].…”

Prototheca spp. in Bovine Infections

“…P. bovis can also be recovered from milking equipment, also [61]. It was isolated from horse feces [62], from the intestine of a patient with troubles after cheese consumption [63], and recently found in a healthy human intestine [64]. Calves fed on mastitic milk containing the microorganisms are considered a further source of environmental contamination in affected herds [65].…”

Prototheca Infections and Ecology from a One Health Perspective

“…In another report, a 2-month-old infant diagnosed with treatment-resistant gastroenteritis provided P. wickerhamii -positive stool cultures in the context of an otherwise usual intestinal flora [ 66 ]. In a recent survey in a rural area in Thailand [ 67 ], P. bovis was detected in the fecal samples of four out of 98 healthy volunteers exhibiting no diarrhea. Participants of this study spent extended periods of time on rice fields (similar to the first human case described by Davies [ 7 ]), and had frequent contact with ruminants and poultry, whose manure was used to fertilize local vegetable gardens.…”

“…Participants of this study spent extended periods of time on rice fields (similar to the first human case described by Davies [ 7 ]), and had frequent contact with ruminants and poultry, whose manure was used to fertilize local vegetable gardens. Since it was not possible to confidently identify the source of protothecal colonization, the authors highlighted the need to apply a comprehensive One Health approach that includes humans, animals and the environment in such future surveys [ 67 ].…”