In vitro activity of fidaxomicin and combinations of fidaxomicin with other antibiotics against Clostridium perfringens strains isolated from dogs and cats.

BACKGROUND: Previous studies have demonstrated that fidaxomicin, a macrocyclic lactone antibiotic used to treat recurrent Clostridioides difficile-associated diarrhea, also displays potent in vitro bactericidal activity against Clostridium perfringens strains isolated from humans. However, to date, there is no data on the susceptibility to fidaxomicin of C. perfringens strains of animal origin. On the other hand, although combination therapy has become popular in human and veterinary medicine, limited data are available on the effects of antibiotic combinations on C. perfringens. We studied the in vitro response of 21 C. perfringens strains obtained from dogs and cats to fidaxomicin and combinations of fidaxomicin with six other antibiotics. RESULTS: When tested by an agar dilution method, fidaxomicin minimum inhibitory concentrations (MICs) ranged between 0.004 and 0.032 µg/ml. Moreover, the results of Etest-based combination assays revealed that the incorporation of fidaxomicin into the test medium at a concentration equivalent to half the MIC significantly increased the susceptibility of isolates to metronidazole and erythromycin in 71.4% and 61.9% of the strains, respectively, and the susceptibility to clindamycin, imipenem, levofloxacin, and vancomycin in 42.9-52.4% of the strains. In contrast, » × MIC concentrations of fidaxomicin did not have any effect on levofloxacin and vancomycin MICs and only enhanced the effects of clindamycin, erythromycin, imipenem, and metronidazole in ≤ 23.8% of the tested strains. CONCLUSIONS: The results of this study demonstrate that fidaxomicin is highly effective against C. perfringens strains of canine and feline origin. Although fidaxomicin is currently considered a critically important antimicrobial that has not yet been licensed for veterinary use, we consider that the results reported in this paper provide useful baseline data to track the possible emergence of fidaxomicin resistant strains of C. perfringens in the veterinary setting.

Susceptibility testing of Prototheca bovis isolates from cases of bovine mastitis using the CLSI reference broth microdilution method and the Sensititre YeastOne colorimetric panel.

A total of 62 Prototheca bovis isolates from cases of bovine mastitis were tested for susceptibility to different antifungal compounds by the Clinical and Laboratory Standards Institute (CLSI) reference microdilution method and a commercial colorimetric microdilution panel (Sensititre YeastOne). All isolates displayed low susceptibility to echinocandins (MICs > 8 µg/ml for anidulafungin, caspofungin, and micafungin), flucytosine (MIC > 64 µg/ml), and the azoles enilconazole and fluconazole (MICs > 4 and > 64 µg/ml, respectively). Moreover, 45.2, 32.3, and 1.6% of isolates had MICs > 4 µg/ml for ketoconazole, terbinafine, and voriconazole, respectively, when tested by the CLSI method. In contrast, all isolates were more susceptible to the polyene compounds amphotericin B and nystatin, and itraconazole, posaconazole, and ravuconazole (MICs ≤ 2 µg/ml, in all cases). Comparison of the results obtained in the CLSI and Sensititre methods showed excellent essential agreement (EA) for azoles (98.4% for itraconazole and posaconazole, and 100% for voriconazole) and moderate EA for amphotericin B (72.6%), when MICs were read after 48 and 24 h of incubation, respectively. In contrast, much lower EA values were obtained in some cases when the MICs for both techniques were determined after 48 h of incubation (e.g., 9.7% for amphotericin B and 69.4% for posaconazole). Therefore, the CLSI broth microdilution method and the Sensititre YeastOne panel can be used indistinctly for susceptibility testing of P. bovis isolates against azoles but not against amphotericin B until further optimization of the test conditions. LAY SUMMARY: The antifungal susceptibility of Prototheca bovis isolates was analyzed. All tested isolates displayed low susceptibility to echinocandins, flucytosine, and some azoles. Excellent agreement of the results of two different test methods was obtained for azoles, but not for the polyene amphotericin B.

Searching for Peptide Inhibitors of T Regulatory Cell Activity by Targeting Specific Domains of FOXP3 Transcription Factor.

(1) Background: The ability of cancer cells to evade the immune system is due in part to their capacity to induce and recruit T regulatory cells (Tregs) to the tumor microenvironment. Strategies proposed to improve antitumor immunity by depleting Tregs generally lack specificity and raise the possibility of autoimmunity. Therefore, we propose to control Tregs by their functional inactivation rather than depletion. Tregs are characterized by the expression of the Forkhead box protein 3 (FOXP3) transcription factor, which is considered their "master regulator". Its interaction with DNA is assisted primarily by its interaction with other proteins in the so-called "Foxp3 interactome", which elicits much of the characteristic Treg cell transcriptional signature. We speculated that the disruption of such a protein complex by using synthetic peptides able to bind Foxp3 might have an impact on the functionality of Treg cells and thus have a therapeutic potential in cancer treatment. (2) Methods: By using a phage-displayed peptide library, or short synthetic peptides encompassing Foxp3 fragments, or by studying the crystal structure of the Foxp3:NFAT complex, we have identified a series of peptides that are able to bind Foxp3 and inhibit Treg activity. (3) Results: We identified some peptides encompassing fragments of the leuzin zipper or the C terminal domain of Foxp3 with the capacity to inhibit Treg activity in vitro. The acetylation/amidation of linear peptides, head-to-tail cyclization, the incorporation of non-natural aminoacids, or the incorporation of cell-penetrating peptide motifs increased in some cases the Foxp3 binding capacity and Treg inhibitory activity of the identified peptides. Some of them have shown antitumoral activity in vivo. (4) Conclusions: Synthetic peptides constitute an alternative to inhibit Foxp3 protein-protein interactions intracellularly and impair Treg immunosuppressive activity. These peptides might be considered as potential hit compounds on the design of new immunotherapeutic approaches against cancer.