In vitro antimicrobial susceptibility of Prototheca spp. isolated from bovine mastitis in a Portugal dairy herd

New Approaches for risk assessment and management of bovine protothecosis

Protothecosis is a potential zoonosis related to bovine mastitis. In several countries, a higher incidence of protothecal bovine mastitis that is being recorded and the resistance of Prototheca species to various factors (chlorine, high temperatures, antimicrobial and antiseptic treatments, pH variations), make it difficult to control its spread among farms. The authors aim to describe the infection caused by microalgae, focusing on the problems within cattle farms and proposing new approaches to farm management, based on Regulation (EU) No 2016/429 on transmissible animal diseases. This new flexible approach, based on risk analysis, is a further tool in protecting against Prototheca species. The list of transmissible animal diseases under Regulation (EU) No 2016/429 includes those caused by microorganisms resistant to antimicrobials, which can have important implications for human and animal health, feed and food safety. This approach would involve a series of changes to the rules used for Official Controls (Regulation (EU) No 2017/625) moving from the concept of the food chain to that of the agri-food chain.

Preliminary Results, Perspectives, and Proposal for a Screening Method of In Vitro Susceptibility of Prototheca Species to Antimicrotubular Agents

Microorganisms belonging to the genus Prototheca are achlorophyllous microalgae, occasionally behaving as environmental pathogens that cause severe mastitis in milk cows, as well as localized or systemic infections in humans and animals. Among the different species belonging to the genus, Prototheca zopfii genotype 2 (recently reclassified as P. bovis) and P. blaschkeae are most commonly associated with bovine mastitis. To date, no pharmacological treatment is available to cure protothecal mastitis, and infected animals must be quarantined to avoid spreading the infection. The few antibiotic and antifungal drugs effective in vitro against Prototheca give poor results in vivo This failure is likely due to the lack of specificity of such drugs. As microalgae are more closely related to plants than to bacteria or fungi, an alternative possibility is to test molecules with herbicidal properties, in particular, antimicrotubular herbicides, for which plant rather than animal tubulin is the selective target. Once a suitable test protocol was set up, a panel of 11 antimicrotubular agents belonging to different chemical classes and selective for plant tubulin were tested for the ability to inhibit growth of Prototheca cells in vitro Two dinitroanilines, dinitramine and chloralin, showed strong inhibitory effects on P. blaschkeae at low micromolar concentrations, with half-maximal inhibitory concentrations (IC₅₀) of 4.5 and 3 μM, respectively, while both P. zopfii genotype 1 (now reclassified as P. ciferrii) and P. bovis showed susceptibility to dinitramine only, to different degrees. Suitable screening protocols for antimitotic agents are suggested.

The in vitro efficacy of SunSmile® Fruit & Vegetable Rinse against pathogenic strains of Prototheca algae that cause mastitis in cows

The research concerns algae of the genus Prototheca. They are found in the natural environment and they can cause a disease in animals and humans called protothecosis. The aim of the study was to evaluate the in vitro activity of the fruit and vegetable rinse agent SunSmile^® Fruit & Vegetable Rinse (Sunrider International) against P. zopfii isolates. The materials consisted of ten P. zopfii strains isolated from the milk of cows with mastitis. The following antifungal chemotherapeutic agents were also used in the study for comparison: nystatin, ketoconazole, amphothericin B, miconazole, clotrimazole, econazole, fluconazole, and flucytosine. The tube dilution method were used to evaluate the effect of a fruit and vegetable rinse agent and the disc-diffusion method to evaluate the effect of antifungal chemotherapeutic agents on P. zopfii strains. All tested strains of P. zopfii were susceptible to the action of the SunSmile^® agent. The MMC was in the range of 0.0024-0.0190%. The SunSmile^® Fruit & Vegetable Rinse can be used in prevention of mastitis in cows and in human protothecosis due to its safe, natural composition and efficacy.

Molecular typing and differences in biofilm formation and antibiotic susceptibilities among Prototheca strains isolated in Italy and Brazil

Bovine mastitis caused by Prototheca is a serious and complex problem that accounts for high economic losses in the dairy industry. The main objective of this study was to identify and characterize at genetic level different Prototheca strains and provide the most complete data about protothecal antibiotic resistance. The study involves 46 isolates from Italian (13 strains) and Brazilian (33 strains) mastitic milk. These strains were identified by multiplex PCR and single strand conformation polymorphism analysis and characterized by randomly amplified polymorphic DNA (RAPD)-PCR. Moreover, biofilm production and antibiotic susceptibility were evaluated. Forty-two strains resulted as Prototheca zopfii genotype 2, whereas 4 isolates could belong to a potential new Prototheca species. The RAPD-PCR, performed with 3 primers (M13, OPA-4, and OPA-18), showed a notable heterogeneity among isolates and grouped the strains according to the species and geographical origin. Biofilm production was species-dependent and P. zopfii genotype 2 strains were classified as strong biofilm producers. In vitro antibiotic susceptibility tests indicated that Prototheca strains were susceptible to antibacterial drugs belonging to aminoglycosides group; the highest activity against Prototheca strains was observed in the case of colistin sulfate, gentamicin, and netilmicin (100% of susceptible strains). It is interesting to note that all the Italian P. zopfii genotype 2 strains showed lower minimum inhibitory concentration values than the Brazilian ones. Nisin showed more efficacy than lysozyme and potassium sorbate, inhibiting 31% of the strains. Results obtained in this study confirmed that RAPD-PCR is a rapid, inexpensive, and highly discriminating tool for Prototheca strains characterization and could give a good scientific contribution for better understanding the protothecal mastitis in dairy herd.

Induction of oxidative stress in Prototheca zopfii by indole-3-acetic acid/HRP or 2,4-pentanedione/HRP systems and their oxidation products

We investigated the toxic effects on Prototheca zopfii of indole-3-acetic acid (IAA) and 2,4-pentanedione (PD) combined with horseradish peroxidase (HRP) alongside the oxidation products of 3-methyl-2-oxindole (MOI) and indole-3-carbinol (I3C) from the IAA/HRP system and methylglyoxal (MGO) from the PD/HRP system. The microorganism was incubated in the absence (control) or presence of IAA, PD, IAA/HRP, PD/HRP, MOI, I3C and MGO and determined: (1) cytotoxicity by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium) assay; (2) growth inhibitory concentration by resazurin assay and (3) antioxidant enzymes activities of: catalase (CAT), glutathione reductase (GR) and superoxide dismutase (SOD). P. zopfii was more susceptible to IAA at 40 mM than PD at the same concentration, which seems to indicate that IAA was more effective at initiating cell death. These data corroborate results from the resazurin assay. Concentrations of 40 mM of IAA, IAA/HRP and PD/HRP, 20 mM of PD/HRP, 10 mM of MOI, 2 mM of I3C and 8 mM of MGO inhibited the growth of P. zopfii. With sub-inhibitory concentrations of IAA and IAA/HRP at 30 mM, MOI at 8 mM and I3C at 1 mM, the activities of CAT and GR increased, whereas no statistical difference was observed for CAT activity with IAA/HRP. Thus, PD at 30 mM and MGO at 6 mM increased the activities of CAT and GR, whereas PD/HRP system at 15 mM decreased CAT activity and PD/HRP and MGO showed no statistical difference for SOD activity. In conclusion, IAA/HRP or PD/HRP systems and their oxidation products exert cytotoxic effects on P. zopffi; however, I3C and MGO appear to exert greater microbicidal effect on P. zopfii.

Short communication: Dairy bedding type affects survival of Prototheca in vitro

Protothecae are algal pathogens, capable of causing bovine mastitis, that are unresponsive to treatment; they are believed to have an environmental reservoir. The role of bedding management in control of protothecal mastitis has not been studied. The purpose of this study was to evaluate the growth of either environmental or mastitis-associated Prototheca genotypes in dairy bedding materials that are commonly used in Maine. Prototheca zopfii genotypes 1 and 2 (gt1 and gt2) were inoculated into sterile broth only (control ), kiln-dried spruce shavings, "green" hemlock sawdust, sand, or processed manure-pack beddings with broth, and incubated for 2 d. Fifty microliters of each isolate was then cultured onto plates and the resulting colonies counted at 24 and 48 h postinoculation. Shavings were associated with significantly less total Prototheca growth than other bedding types. Growth of P. zopfii gt1 was significantly higher than that of gt2 in the manure-pack bedding material. Spruce shavings, compared with manure, sand, or sawdust, may be a good bedding type to prevent growth of Prototheca. Based on these in vitro findings, bedding type may affect Prototheca infection of cattle in vivo.

Treatment with gentamicin on a murine model of protothecal mastitis

The aim of this study was to establish a murine protothecal mastitis model and to evaluate the treatment efficiency of gentamicin. Challenge routes were determined with a pathogenic Prototheca zopfii genotype 2 (P. zopfii) strain. 25 BALB/c mice were inoculated in mammary glands with graded dosages (10(3), 10(4), 10(5), 10(6), 10(7) CFU of P. zopfii) and killed on the 7th day. Another 25 animals were also killed at 1, 3, 5, 7, and 9 days after inoculation of 1 × 10(6) CFU of P. zopfii, the milk somatic cell counts, pathological section of mammary glands, and P. zopfii burden were observed. The antimicrobial activity was tested using disc diffusion test and minimum inhibitory concentrations. Gentamicin was given intramuscularly to analyze the therapeutic effect. The results showed that the best infection route was intra-mammary gland, and the mastitis model was established with 1 × 10(6) CFU of P. zopfii. After infection, the somatic cell counts increased significantly. The pathological reaction mainly consisted of infiltration of inflammatory cells, destruction of acini, accumulation of lymphocyte cells and the severity of the changes was dosage and time-dependent. The P. zopfii burden revealed that P. zopfii continuously replicated. In vitro susceptibility tests indicated that the Prototheca strains were antimicrobial susceptible to gentamicin at concentrations between 0.03 and 4 μg/ml. In vivo therapeutic assay demonstrated that high concentrations of gentamicin (≥20 mg/kg) could inhibit the growth of P. zopfii. We conclude that the murine model of protothecal mastitis was established successfully and gentamicin may be an effective choice for treatment of P. zopfii.

Comparative activity and mechanism of action of three types of bovine antimicrobial peptides against pathogenic Prototheca spp

The yeast-like algae of the genus Prototheca are ubiquitous saprophytes causing infections in immunocompromised patients and granulomatous mastitis in cattle. Few available therapies and the rapid spread of resistant strains worldwide support the need for novel drugs against protothecosis. Host defence antimicrobial peptides inactivate a wide array of pathogens and are a rich source of leads, with the advantage of being largely unaffected by microbial resistance mechanisms. Three structurally diverse bovine peptides [BMAP-28, Bac5 and lingual antimicrobial peptide (LAP)] have thus been tested for their capacity to inactivate Prototheca spp. In minimum inhibitory concentration (MIC) assays, they were all effective in the micromolar range against clinical mastitis isolates as well as a Prototheca wickerhamii reference strain. BMAP-28 sterilized Prototheca cultures within 30-60 min at its MIC, induced cell permeabilization with near 100% release of cellular adenosine triphosphate and resulted in extensive surface blebbing and release of intracellular material as observed by scanning electron microscopy. Bac5 and LAP inactivated Prototheca following 3-6 h incubation at fourfold their MIC and did not result in detectable surface damage despite 70-90% killing, suggesting they act via non-lytic mechanisms. In circular dichroism studies, the conformation of BMAP-28, but not that of Bac5 or LAP, was affected by interaction with liposomes mimicking algal membranes. Our results indicate that BMAP-28, Bac5 and LAP kill Prototheca with distinct potencies, killing kinetics, and modes of action and may be appropriate for protothecal mastitis treatment. In addition, the ability of Bac5 and LAP to act via non-lytic mechanisms may be exploited for the development of target-selective drugs.

Identification of Candida species isolated from bovine mastitic milk and their in vitro hemolytic activity in Western Turkey

In this study, identification of 207 Candida isolates, previously isolated from mastitic bovine quarter milk samples at the level of genus, was made using API 20 C AUX system. The most frequently isolated species were Candida krusei (34.8%), followed by Candida rugosa (16.4%), Candida kefyr (12.6%), Candida albicans (10.1%), and Candida tropicalis (9.2%). Less common isolates were Candida zeylanoides (5.8%), Candida parapsilosis (4.3%), Candida guilliermondii (3.4%), Candida famata (1.9%), and Candida glabrata (1.5%). Additionally, in vitro hemolytic activity of all Candida strains were also examined in the present study. C. krusei (72 isolates), C. kefyr (26), C. albicans (21), C. tropicalis (19), C. zeylanoides (12), and C. glabrata (3) demonstrated both alpha and beta hemolysis at 48-h postinoculation. Only alpha hemolysis was detected in C. rugosa (34), C. guilliermondii (7), and C. famata (4), while C. parapsilosis (9) did not show any hemolytic activity after incubation for 72 h. Statistically significant difference (P < 0.001) was determined between the beta-hemolytic activities of Candida strains. The hemolytic activities of C. zeylanoides, C. albicans and C. kefyr were higher than other strains. This is the first study to describe variable hemolysis types exhibited by different Candida strains isolated from bovine mastitic milk in Turkey.