Comparison of Four Methods for the in vitro Susceptibility Testing of Dermatophytes

Development of an agar-based screening method for terbinafine, itraconazole, and amorolfine susceptibility testing of Trichophyton spp

Resistance in dermatophytes is an emerging global public health issue. We, therefore, developed an agar-based method for screening Trichophyton spp. susceptibility to terbinafine (TRB), itraconazole (ITC), and amorolfine (AMF) and validated it using molecularly characterized isolates. Α total of 40 Trichophyton spp. isolates, 28 TRB wild type (WT) (13 T. rubrum, 10 T. mentagrophytes, 5 T. interdigitale) and 12 TRB non-WT (7 T. rubrum, 5 T. indotineae) with different alterations in the squalene epoxidase (SQLE) gene, were used. The optimal test conditions (inoculum and drug concentrations, incubation time, and temperature) and stability over time were evaluated. The method was then applied for 86 WT Trichophyton spp. clinical isolates (68 T. rubrum, 7 T. interdigitale, 6 T. tonsurans, 5 T. mentagrophytes) and 4 non-WT T. indotineae. Optimal growth of drug-free controls was observed using an inoculum of 20 µL 0.5 McFarland after 5-7 days of incubation at 30°C. The optimal concentrations that prevented the growth of WT isolates were 0.016 mg/L of TRB, 1 mg/L of ITC, and 0.25 mg/L of AMF, whereas 0.125 mg/L of TRB was used for the detection of Trichophyton strong SQLE mutants (MIC ≥0.25 mg/L). The agar plates were stable up to 4 months. Inter-observer and inter-experimental agreement were 100%, and the method successfully detected TRB non-WT Trichophyton spp. strains showing 100% agreement with the reference EUCAST methodology. An agar-based method was developed for screening Trichophyton spp. in order to detect TRB non-WT weak and strong mutant isolates facilitating their detection in non-expert routine diagnostic laboratories.

Dermatophytic Biofilms: Characteristics, Significance and Treatment Approaches

Microbes are found in the environment, possibly more often as biofilms than in planktonic forms. Biofilm formation has been described for several important fungal species. The presence of a dermatophytoma in a dermatophytic nail infection was the basis for the proposal that dermatophytes form biofilms as well. This could explain treatment failure and recurrent dermatophytic infections. Several investigators have performed in vitro and ex vivo experiments to study the formation of biofilms by dermatophytes and their properties. The nature of the biofilm structure itself contributes to fungal protection mechanisms against many harmful external agents, including antifungals. Thus, a different approach should be carried out regarding susceptibility testing and treatment. Concerning susceptibility testing, methods to evaluate either the inhibition of biofilm formation, or the ability to eradicate it, have been introduced. As for treatment, in addition to classical antifungal agents, some natural formulations, such as plant extracts or biosurfactants, and alternative approaches, such as photodynamic therapy, have been proposed. Studies that connect the results of the in vitro and ex vivo experimentation with clinical outcomes are required in order to verify the efficacy of these approaches in clinical practice.

Comparison of Hyphal Fragments and Spores to Evaluate the Pathogenicity of the Eucalyptus Leaf and Shoot Pathogen Calonectria pseudoreteaudii

The genus Calonectria includes many aggressive plant-pathogenic species with a worldwide distribution. Calonectria leaf blight is one of the most prominent diseases of Eucalyptus trees in Southeast Asian and South American plantations. Inoculation trials to evaluate pathogenicity of Calonectria spp. typically use conidial suspensions but this is not possible for species that do not sporulate sufficiently in culture. Calonectria pseudoreteaudii is one of the species that is most aggressive to Eucalyptus in China but most isolates fail to produce conidia in culture, requiring an alternative procedure for artificial inoculation. This study compared inoculations utilizing conidial and hyphal fragment suspensions. Two Eucalyptus genotypes were used, and these were inoculated with different concentrations of hyphal fragments or conidia of three C. pseudoreteaudii isolates. Three days after inoculation, the treated Eucalyptus plants displayed similar disease symptoms, regardless of whether they had been inoculated with conidia or hyphal fragments. This was consistent for all C. pseudoreteaudii isolates and also the different Eucalyptus genotypes. The results demonstrate that hyphal fragment suspensions can be used to provide a reliable indication of C. pseudoreteaudii isolate pathogenicity when conidia are not available for inoculation studies.

Elucidating the clinical, microbiological and molecular diagnostic aspects of Macrophomina phaseolina keratitis

This study reports the clinico-microbiological features of Macrophomina phaseolina keratitis. Clinically diagnosed as microbial keratitis, six patients underwent microbiological evaluation. Fungal culture isolates from cornea were subjected to DNA sequencing of the ITS region, phylogenetic analysis and reconfirmation by polymerase chain reaction (PCR). Minimum inhibitory concentrations (MICs) of six antifungal drugs were determined by microbroth dilution method against the six isolates. All patients were treated with antifungals. Failed medical therapy necessitated therapeutic penetrating keratoplasty (TPK). Corneal buttons were processed for histopathology. In all patients, the corneal scraping showed septate hyaline fungal filaments. The BLAST analysis for ITS sequences of all six fungal isolates suggested M. phaseolina, however, when limited to sequences from type material, they matched M. pseudophaseolina. Phylogenetic analysis could not differentiate between these two species and clustered in a single clade. PCR assay of specific gene sequence [MpCal (calmodulin)] reconfirmed all isolates as M. phaseolina. The MICs of voriconazole and posaconazole were lowest (0.03 to 2 and 0.1 to 2µg/mL respectively) and all isolates were susceptible to natamycin. Except for case 1, which healed with a scar on treatment, all other cases worsened, despite medical treatment, necessitating TPK. Histopathology of 3 out of 4 buttons showed the presence of fungal filaments. While direct microscopic examination of corneal scrapings is helpful in diagnosis, identification of M. phaseolina in culture is challenging. Although MICs of commonly used antifungals are low response to medical therapy is not encouraging; patients may require TPK for resolution of infection in M. phaseolina keratitis.

Honokiol and Magnolol: Insights into Their Antidermatophytic Effects

Dermatophyte infections represent a significant public health concern, with an alarming negative impact caused by unsuccessful therapeutic regimens. Natural products have been highlighted as a promising alternative, due to their long-standing traditional use and increasing scientific recognition. In this study, honokiol and magnolol, the main bioactives from Magnolia spp. bark, were investigated for their antidermatophytic activity. The antifungal screening was performed using dermatophyte standard strains and clinical isolates. The minimal inhibitory concentration (MIC) and the minimal fungicidal concentration (MFC) were determined in accordance with EUCAST-AFST guidelines, with minor modifications. The effects on ergosterol biosynthesis were assessed in Trichophyton rubrum cells by HPLC-DAD. Putative interactions with terbinafine against T. rubrum were evaluated by the checkerboard method. Their impact on cells' viability and pro-inflammatory cytokines (IL-1β, IL-8 and TNF-α) was shown using an ex vivo human neutrophils model. Honokiol and magnolol were highly active against tested dermatophytes, with MIC and MFC values of 8 and 16 mg/L, respectively. The mechanism of action involved the inhibition of ergosterol biosynthesis, with accumulation of squalene in T. rubrum cells. Synergy was assessed for binary mixtures of magnolol with terbinafine (FICI = 0.50), while honokiol-terbinafine combinations displayed only additive effects (FICI = 0.56). In addition, magnolol displayed inhibitory effects towards IL-1β, IL-8 and TNF-α released from lipopolysaccharide (LPS)-stimulated human neutrophils, while honokiol only decreased IL-1β secretion, compared to the untreated control. Overall, honokiol and magnolol acted as fungicidal agents against dermatophytes, with impairment of ergosterol biosynthesis.

Apiaceae Essential Oils: Boosters of Terbinafine Activity against Dermatophytes and Potent Anti-Inflammatory Effectors

Dermatophyte infections represent an important public health concern, affecting up to 25% of the world's population. Trichophyton rubrum and T. mentagrophytes are the predominant dermatophytes in cutaneous infections, with a prevalence accounting for 70% of dermatophytoses. Although terbinafine represents the preferred treatment, its clinical use is hampered by side effects, drug-drug interactions, and the emergence of resistant clinical isolates. Combination therapy, associating terbinafine and essential oils (EOs), represents a promising strategy in the treatment of dermatophytosis. In this study, we screened the potential of selected Apiaceae EOs (ajowan, coriander, caraway, and anise) to improve the antifungal activity of terbinafine against T. rubrum ATCC 28188 and T. mentagrophytes ATCC 9533. The chemical profile of EOs was analyzed by gas chromatography. The minimal inhibitory concentration (MIC) and minimal fungicidal concentration (MFC) of EOs/main compounds were determined according to EUCAST-AFST guidelines, with minor modifications. The checkerboard microtiter method was used to identify putative synergistic combinations of EOs/main constituents with terbinafine. The influence of EOs on the viability and pro-inflammatory cytokine production (IL-1β, IL-8 and TNF-α) was determined using an ex vivo human neutrophils model. The binary associations of tested EOs with terbinafine were found to be synergistic against T. rubrum, with FICI values of 0.26-0.31. At the tested concentrations (6.25-25 mg/L), EOs did not exert cytotoxic effects towards human neutrophils. Anise EO was the most potent inhibitor of IL-1β release (46.49% inhibition at 25 mg/L), while coriander EO displayed the highest inhibition towards IL-8 and TNF-α production (54.15% and 54.91%, respectively). In conclusion, the synergistic combinations of terbinafine and investigated Apiaceae EOs could be a starting point in the development of novel topical therapies against T. rubrum-related dermatophytosis.

Predicting a therapeutic cut-off serum level of itraconazole in recalcitrant tinea corporis and cruris-A prospective trial

BACKGROUND

With rising resistance to terbinafine, and consistently high MICs to fluconazole and griseofulvin, itraconazole is being increasingly used as a first line drug for tinea corporis/cruris. However, inadequate clinical responses are often seen with it in spite of in vitro susceptibility. This is possibly related to a variable pharmacokinetic profile of itraconazole. The drug serum levels associated with the therapeutic outcome have not been defined in dermatophytic infections.

METHODS

Forty treatment naïve patients with tinea corporis/cruris were randomised to one of the three dose groups (100, 200 and 400 mg/day) of itraconazole. The drug serum levels of 21 of these patients were obtained after 2 weeks of treatment and correlated with the final clinical outcome and in vitro antifungal susceptibility data.

RESULTS

Trichophyton indotineae was identified by sequencing of ITS region of rDNA and TEF1α. All isolates were sensitive to itraconazole (Minimum Inhibitory Concentration (MICs) range: 0.06-0.5 µg/ml), while MICs to terbinafine were uniformly high (range 8-32 µg/ml). Thirty-seven patients (92.5%) achieved complete cure, while three failed treatment. Serum levels achieved with 400 mg/day were significantly higher than levels with 100 or 200 mg dose. All patients with itraconazole serum levels of >0.2 µg/ml were cured, while two out of the 10 patients with serum levels <0.2 µg/ml failed treatment.

CONCLUSIONS

Therapeutic failures are uncommon with itraconazole, and the prevalent strain in India has low itraconazole MICs. Treatment failure is likely with itraconazole serum levels of <0.2 µg/ml, while levels >0.2 µg/ml are consistently associated with a positive therapeutic outcome.

Do essential oils from plants occurring in the Brazilian Caatinga biome present antifungal potential against dermatophytoses? A systematic review

The Caatinga is an exclusively Brazilian biome where semiarid climatic conditions promote singularities in adaptive biodiversity. Many aromatic species are found in this region possessing antifungal properties, which are attributed to their essential oils. Thus, we questioned whether essential plant oils found in the Caatinga present anti-dermatophytic potential. Dermatophytes are keratinophilic fungi that cause one of the most prevalent mycoses globally, skin infections known as dermatophytoses (tineas). Here, we provide a comprehensive report of the available published information, analyzing the methods used to evaluate the antifungal activity, verifying the quality of the evidence and possible clinical applications, and discussing research trends in this area. The plants studied concentrated in the genera Croton (Euphorbiaceae), Lippia (Verbenaceae), Piper (Piperaceae), and Mentha (Lamiaceae). All of the studies used in vitro tests to analyze antifungal potential, and little evidence was ascertained concerning the mechanism of antifungal action. In addition, the essential oils also evidenced drug modifying activity of conventional antifungal drugs (Ketoconazole and Terbinafine). We believe that the anti-dermatophyte potential of plant essential oils occurring within the Caatinga is underestimated and that this review will encourage future chemical-pharmacological investigations into the plants within this biome.Key points• The essential oils from plants occurring in the Caatinga Biome present unknown anti-dermatophyte potential.• The studies against dermatophyte fungi concentrate on the families Lamiaceae and Verbenaceae.• In vitro assays were used to assess the anti-dermatophyte potential of the essential oils.

Comparison of the Sensititre YeastOne® and CLSI M38-A2 microdilution methods in determining the activity of nine antifungal agents against dermatophytes

BACKGROUND

Dermatophytes are the most common fungal pathogens causing superficial infections in humans with a high prevalence worldwide. The treatment of these infections is based on the use of topical and systemic antifungal agents. A convenient method with a high predictive value for testing the susceptibilities of dermatophytes is necessary.

OBJECTIVE

To evaluate the ability of the Sensititre YeastOne^® in testing the activity of nine antifungal agents against dermatophytes.

METHODS

We compared Sensititre^® with reference procedure for anidulafungin (ANID), micafungin sodium (MCF), caspofungin acetate (CAS), 5-fluorocytosine (5FC), posaconazole (PCZ), voriconazole (VCZ), itraconazole (ITZ), fluconazole (FLZ) and amphotericin B (AMB) against 79 dermatophyte isolates, the essential agreement (EA) and categorical agreement (CA) between the two methods were obtained.

RESULTS

The MICs or MECs obtained by the Sensititre^® were usually lower than those obtained by the M38-A2. The overall EA between the two methods of nine antifungals was best for 5FC (100%), followed by MCF (94.9%), PCZ (84.8%), AMB (67.1%), FLZ (65.8%), VCZ (63.3%), ANID (29.1%), ITZ (20.3%) and CAS (2.5%). The overall CA between the two methods for all drugs was 100% except for ANID (97.4%), MCF (95%) and PCZ (92.5%). Substantial discrepancies were observed with all drugs except for VCZ and 5FC. The results of M38-A2 in terms of GMIC (or GMEC) and MIC90 (or MEC90) were, in increasing order, as follows: MCF, PCZ, VCZ, ANID, ITZ, CAS, AMB, FLZ and 5FC.

CONCLUSIONS

The Sensititre YeastOne^® shows poor EA with the reference method for dermatophytes; therefore, M38-A2 should remain the reference procedure for antifungal susceptibility testing against dermatophytes.