Microbicidal Action of Indole-3-Acetic Acid Combined with Horseradish Peroxidase on Prototheca zopfii from Bovine Mastitis

The activity of silver nanoparticles against microalgae of the Prototheca genus

AIM

To investigate the in vitro activity of silver NPs (AgNPs) against pathogenic microalgae of the Prototheca genus.

MATERIALS & METHODS

The antialgal potential of AgNPs against Prototheca species of both clinical and environmental origin was assessed from minimum inhibitory (algistatic) and algicidal concentrations. The in vitro cytotoxicity of AgNPs against bovine mammary epithelial cell line was evaluated by means of the standard MTT assay.

RESULTS

AgNPs showed a strong killing activity toward Prototheca algae, as the minimal algicidal concentration (MAC) values matched perfectly the corresponding minimum inhibitory concentration (MIC) values for all species (MAC = MIC, 1-4 mg/l), except P. stagnora (MIC > 8 mg/l). The concentrations inhibitory to pathogenic Prototheca spp. (MIC, 1-4 mg/l) were below the concentrations at which any toxicity in epithelial cells could be observed (CC₂₀ > 6 mg/l).

CONCLUSION

The study emphasizes the potential of AgNPs as a new therapeutic tool for the management of Prototheca infections.

3-Bromopyruvate as an Alternative Option for the Treatment of Protothecosis

Protothecosis is an unusual infection of both humans and animals caused by opportunistically pathogenic microalgae of the genus Prototheca. Until now, no standardized treatment protocols exist for the protothecal disease, boosted by a remarkable resistance of Prototheca spp. to a wide array of antimicrobial agents currently available in clinical use. Consequently, there is an urgent need for new effective drugs against Prototheca algae. In this study, the anti-Prototheca activity of 3-bromopyruvate (3BP), either alone or in combination with amphotericin B (AMB) was assessed in vitro, as well as the cytotoxicity of 3BP toward the bovine mammary epithelial cells and murine skin fibroblasts. The mean minimum inhibitory concentrations (MIC) and minimum algaecidal concentrations (MAC) were 0.85 ± 0.21 and 2.25 ± 0.54 mM for Prototheca wickerhamii, 1.25 ± 0.47 and 4.8 ± 1.03 mM for Prototheca blaschkeae, and 1.55 ± 0.69 and 5.6 ± 1.3 mM for Prototheca zopfii gen. 2, respectively. For all Prototheca strains tested, a synergistic interaction between 3BP and AMB was observed, resulting in about 4-fold reduction of their individual MICs, when used together. The elevated content of intracellular glutathione (GSH) was associated with a decreased susceptibility to 3BP. Both epithelial and fibroblast cells retained high viability upon treatment with 3BP at concentrations equivalent to the highest MIC recorded (3 mM) and 10-fold higher (30 mM), with the mean cell viability exceeding 80%, essentially the same as for the untreated cells. The results from these in vitro studies emphasize the high activity of 3BP against the Prototheca algae, its synergistic effect when used in combination with AMB, and the safety of the drug toward the tested mammalian cells. Along with the advantageous physico-chemical and pharmacokinetic properties, 3BP may be considered an effective and safe novel agent against the protothecal disease.

Biofilm-producing ability and efficiency of sanitizing agents against Prototheca zopfii isolates from bovine subclinical mastitis

The objectives of the present study were to evaluate (1) the capacity of the microalga Prototheca zopfii isolated from subclinical bovine mastitis cases to form biofilms; and (2) the resistance of these isolates to sanitizing agents. Ten isolates of P. zopfii from cows with subclinical mastitis (somatic cell count>200×10(3) cells/mL), distributed in 5 dairy farms, were evaluated for their capacity to form biofilms in polystyrene microplate assays and stainless steel coupons, at 25°C and 37°C±1°C. Prototheca zopfii were isolated from milk samples via microbiological culture and analyzed by 18S rRNA gene sequencing. Biofilm formation on the coupons was observed by scanning electron microscopy. The resistance to sanitizing agents was assessed using the biofilm-forming P. zopfii isolates in stainless steel coupon assays, which were subjected to 3 sanitizers: peracetic acid, sodium hypochlorite, and iodine solution. To evaluate resistance to the sanitizers, the minimum inhibitory concentration (MIC) technique was performed using decreasing concentrations of the sanitizing agents (20, 10, 5, 2.5, 1.25, 0.625, 0.312, 0.156, 0.078, 0.039, and 0.019 g/L). After inoculating the isolates, all concentrations were evaluated at 3 distinct incubation periods (24, 48, and 72 h) to assess the effect of incubation time on the MIC. Using the polystyrene microplate assays, 1 isolate showed weak biofilm production, 5 moderate, and 4 strong, when incubated at 25°C±1. For isolates incubated at 37°C±1, 6 showed weak biofilm production and 4 moderate. All P. zopfii isolates (n=10) had the capacity to form biofilms on stainless steel coupons. The longer the incubation period of the P. zopfii isolates at different dilutions, the greater the concentrations of sanitizer needed to prevent growth of the microalgae under the tested conditions. We detected a significant effect of sanitizer and time of incubation (24, 48, and 72 h) on MIC values against P. zopfii isolates. The isolates were sensitive in vitro to peracetic acid (MIC90≥0.019 g/L), sodium hypochlorite (MIC90≥0.312 g/L), and iodine solution (MIC90≥0.625 g/L), after 24 h of incubation (where MIC90=concentration needed to inhibit 90% of isolates). Of the tested sanitizers, peracetic acid had the greatest efficiency against P. zopfii. We conclude that P. zopfii isolates are capable of biofilm production, which may contribute to their persistence in a milking and dairy environment.

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.