Background: New prophylactic and therapeutic tools are needed for the treatment of herpes simplex virus infections. Several essential oils have shown to possess antiviral activity in vitro against a wide spectrum of viruses. Aim: The present study was assess to investigate the activities of the essential oil obtained from leaves of Artemisia arborescens against HSV-1 and HSV-2 Methods: The cytotoxicity in Vero cells was evaluated by the MTT reduction method. The IC₅₀ values were determined by plaque reduction assay. In order to characterize the mechanism of action, yield reduction assay, inhibition of plaque development assay, attachment assay, penetration assay and post-attachment virus neutralization assay were also performed. Results: The IC₅₀ values, determined by plaque reduction assay, were 2.4 and 4.1 μg/ml for HSV-1 and HSV-2, respectively, while the cytotoxicity assay against Vero cells, as determined by the MTT reduction method, showed a CC₅₀ value of 132 μg/ml, indicating a CC₅₀/IC₅₀ ratio of 55 for HSV-1 and 32.2 for HSV-2. The antiviral activity of A. arborescens essential oil is principally due to direct virucidal effects. A poor activity determined by yield reduction assay was observed against HSV-1 at higher concentrations when added to cultures of infected cells. No inhibition was observed by attachment assay, penetration assay and post-attachment virus neutralization assay. Furthermore, inhibition of plaque development assay showed that A. arborescens essential oil inhibits the lateral diffusion of both HSV-1 and HSV-2. Conclusion: This study demonstrates the antiviral activity of the essential oil in toto obtained from A. arborescens against HSV-1 and HSV-2. The mode of action of the essential oil as antiherpesvirus agent seems to be particularly interesting in consideration of its ability to inactivate the virus and to inhibit the cell-to-cell virus diffusion.

The activities of six derivatives of a new class of isonicotinoylhydrazones were investigated in vitro against Mycobacterium tuberculosis H37Rv ATCC 27294, isoniazid-resistant M. tuberculosis ATCC 35822, rifampicin-resistant ATCC 35838, pyrazinamide-resistant ATCC 35828, streptomycin-resistant ATCC 35820 and 16 clinical isolates of M. tuberculosis. Several compounds showed interesting antimycobacterial activity against both ATCC strains and clinical isolates, but were less active against isoniazid-resistant M. tuberculosis. Combinations of five isonicotinoylhydrazone derivatives and rifampicin, ethambutol, para-aminosalicylic acid, isoniazid and clofazimine were also investigated against M. tuberculosis H37Rv ATCC 27294 and against ATCC drug-resistant strains. Addition of sub-MICs of some isonicotinoylhydrazone derivatives resulted in a four- to 16-fold reduction in MICs of ethambutol, para-aminosalicylic acid and rifampicin with fractional inhibitory concentrations (FICs) ranging between 0.17 and 0.37, suggesting a synergic interaction against M. tuberculosis H37Rv. Increased activity was also observed with other combinations (FICs 0.53–0.75), including isoniazid, and a synergic interaction between one of the isonicotinoylhydrazone derivatives and isoniazid (FIC 0.26) was shown against isoniazid-resistant M. tuberculosis ATCC 35822, whereas no effects were observed on combining the isonicotinoylhydrazones with clofazimine. The ability of isonicotinoylhydrazones to inhibit specifically the growth of M. tuberculosis, the high selectivity index and their ability to enhance the activity of standard antituberculous drugs in vitro indicate that they may serve as promising lead compounds for future drug development for the treatment of M. tuberculosis infections.

Objectives: The aim of this study was to investigate the in vitro antifungal activity of an isothiosemicarbazone cyclic analogue against isolates of Candida spp. including fluconazole-resistant Candida albicans. Methods: We investigated the activity of 2-cyclohexylidenhydrazo-4-phenyl-thiazole (EM-01D2) against 114 clinical isolates of Candida spp., representing five different species, by microdilution, according to the NCCLS method 27-A. The activity against C. albicans biofilms was also investigated. Toxicity in vitro was evaluated by MTT reduction assay. Results: EM-01D2 demonstrated low toxicity, broad spectrum, fungicidal activity and was active against C. albicans and Candida krusei at concentrations lower than those shown by amphotericin B and fluconazole (P < 0.05). It maintained potent in vitro activity against fluconazole-resistant C. albicans isolates. Fungicidal activity occurred at concentrations 1–2 doubling dilutions greater than the corresponding MICs, and time–kill analysis indicated that a 99.9% loss of C. albicans viability occurred after 6 h of incubation in the presence of EM-01D2 at concentrations equal to four times the MIC. EM-01D2 was also active in inhibiting the growth of C. albicans ATCC 10231 biofilms, even though such inhibition occurred at concentrations higher than the MICs determined under planktonic growth conditions. However, when C. albicans biofilms were pre-exposed to subinhibitory concentrations of EM-01D2, a reduction of MIC₅₀ of amphotericin B was observed. Conclusions: Based on these results, EM-01D2 could represent a template for the development of novel fungicidal agents.