Drug Susceptibility Profiling of Prototheca Species Isolated from Cases of Human Protothecosis

Prototheca are unicellular, achlorophyllous, yeast-like microalgae that occur in a wide range of natural habitats. At least five species have been implicated as the causative agents of opportunistic infections of men. Human protothecosis typically manifests as cutaneous, articular, or systemic disease. Treatment is largely empirical with poorly predictable and often unsuccessful outcomes. This is largely due to the frequently observed resistance of Prototheca species to conventional antimicrobial agents. This work is the first to perform drug susceptibility profiling exclusively on isolates from human cases of protothecosis. A total of 23 such isolates were tested against amphotericin B and 9 azoles, including efinaconazole and luliconazole, whose activities against Prototheca have never been studied before. Efinaconazole was the most active, with median minimum inhibitory concentration (MIC) and minimum algicidal concentration (MAC) values of 0.031 mg/L and 0.063 mg/L, respectively. Fluconazole and luliconazole had the lowest activity, with median MIC and MAC values of 128 mg/L. To conclude, amphotericin B and most of the azoles showed in vitro activity, with an algicidal rather than algistatic effect, against Prototheca. Still, the activity of individual drugs differed significantly between the species and even between strains of the same species. These differences can be attributed to a species-specific potential for acquiring drug resistance, which, in turn, might be linked to the treatment history of the patient from whom the strain was recovered. The results of this study underscore the potential clinical utility of efinaconazole as a promising therapeutic agent for the treatment of human protothecosis.

Protothecosis in Dogs: A Narrative Review

Protothecosis is a rare and unusual disease that affects both humans and animals, including dogs. The causative agents are unicellular, achlorophyllous, "yeast-like" microalgae of the genus Prototheca (Trebouxiophyceae, Chlorophyta). Although usually saprophytic, Prototheca may, under conditions of immunologic compromise, become pathogenic and even lethal to the host. We present a synthesis of the current literature on protothecosis, with special emphasis on disease features in the dog. Five open-access scientific journal repositories were searched two times by two independent reviewers for original studies (including case reports, standard articles, and conference abstracts) pertaining to cases of protothecosis in dogs. Findings about protothecosis cases in dogs (e.g., animal metrics, type of infection, implemented treatment, and treatment outcome) were synthesized in independent data tables. Eighty studies describing 125 cases of protothecosis in dogs qualified for final analysis. Based on this investigation, protothecosis in dogs can be defined as an emerging disease that poses a serious challenge to the veterinary profession in terms of both diagnosis and management. In general, clinical signs and physical findings most often are referable to the gastrointestinal tract (n = 68; 54.4%). Yet the most common clinical manifestation in dogs is disseminated systemic infection (n = 84; 67.2%), including clinical signs referable to inflammation affecting more than one organ. We emphasize the complexity of Prototheca infection in dogs by summarizing clinical and laboratory findings from 125 cases of Prototheca infection in dogs published over the last half-century.

In Vitro Activity of Quaternary Ammonium in Prototheca Isolated from Clinical Bovine Mastitis Identified by Mass Spectrometry and PCR Sequencing of the cytb Gene Marker

The in vitro algaecide activity of quaternary ammonium (QA) against Prototheca isolated from bovine clinical mastitis was investigated, in which the clinical severity was scored, milk samples were subjected to microbiological culture, and algal species were identified by molecular typing. A total of 4275 milk clinical samples of different cows from ten large dairy farms were used. Forty-four (1%) samples of cows from three dairy farms yielded growth of Prototheca, of which 88.6% (39/44) were identified as Prototheca bovis and 11.3% (5/44) as Prototheca sp. by MALDI-TOF MS, whereas 100% of the isolates were identified as P. bovis using PCR sequencing of the cytb gene. Among cows for which clinical severity scoring was available, 78.8% (26/33) and 21.2% (7/33) had mild and moderate infections, respectively, whereas no animal showed severe clinical signs. The algaecide activity of QA in Prototheca was observed in low concentrations among all isolates, in 20.4% (9/44) at 35 ppm, 36.4% (16/44) at 17 ppm, and 43.2% (19/44) at an 8 ppm, in addition to activity on three reference Prototheca strains. Overall, the study highlights the predominance of P. bovis as the causative agent of algal mastitis in bovines. Prototheca induced abnormalities preponderantly in the milk and mammary gland tissue of cows, and to our knowledge, our study is the first to apply clinical severity scoring in protothecal mastitis. In addition, the study underlines the activity of QA in low concentrations against Prototheca, indicating its potential use as an antiseptic/disinfectant in milking facilities and dairy environments.

Genotyping and drug susceptibility profiling of Prototheca sp. strains isolated from cases of protothecosis in dogs

BACKGROUND

Protothecosis in dogs is a rare, yet emerging disease, distinguished by its often-aggressive clinical course and high fatality rate. Our study was conducted to enhance treatment protocols for affected dogs by better understanding the genetic diversity and drug resistance patterns of Prototheca species.

OBJECTIVES

To identify species and drug susceptibility profiles of an international collection of 28 Prototheca strains isolated from cases of protothecosis in dogs.

ANIMALS

None.

METHODS

Retrospective study. Species-level identification was made for isolates from 28 dogs in 6 countries by molecular typing with the partial cytb gene as a marker. For the determination of minimum inhibitory concentrations (MICs) and minimum algicidal concentrations (MACs), the Clinical Laboratory Standards Institute (CLSI) protocol (M27-A3) was used.

RESULTS

Prototheca bovis was the most prevalent species, accounting for 75% (21/28) of the cases, followed by P. wickerhamii (18%; 5/28) and P. ciferrii (7%; 2/28). Of the 6 drugs tested, efinaconazole (EFZ) was the most potent in vitro, with its median MIC and MAC values equal to 0.125 mg/L. The lowest activity was found for fluconazole (FLU), with MIC and MAC medians of 48 mg/L and 64 mg/L, respectively.

CONCLUSIONS AND CLINICAL IMPORTANCE

Our study identifies P. bovis as the species that most frequently causes protothecosis in dogs, which suggests the possibility of cross-species infection from other animals, especially cows. Additionally, it indicates that EFZ could be used in the treatment of infection in the colon.