Inhibition of Hyphal Growth of Azole-Resistant Strains of Candida albicans by Triazole Antifungal Agents in the Presence of Lactoferrin-Related Compounds

Abstract

The effects of bovine lactoferrin (LF) or the LF-derived antimicrobial peptide lactoferricin B (LFcin B) on the growth ofCandida albicans hyphae, including those of three azole-resistant strains, were investigated by a crystal violet staining method. The hyphae of two highly azole-resistant strains were more susceptible to inhibition by LF or LFcin B than the azole-susceptible strains tested. One moderately azole-resistant strain was defective in the formation of hyphae and showed a susceptibility to LF greater than that of the susceptible strains but a susceptibility to LFcin B similar to that of the susceptible strains. The highly azole-resistant strain TIMM3317 showed trailing growth in the presence of fluconazole or itraconazole, while the extent of growth was reduced by the addition of LF or LFcin B at a sub-MIC. Thus, the addition of LF or LFcin B at a sub-MIC resulted in a substantial decrease in the MICs of fluconazole and itraconazole for two highly azole-resistant strains; e.g., the MIC of fluconazole for TIMM3317 was shifted from >256 to 0.25 μg/ml by LF, but the MICs were not decreased for the susceptible strains. The combination effects observed with triazoles and LF-related compounds in the case of the two highly azole-resistant strains were confirmed to be synergistic by the fractional inhibitory concentration index. These results demonstrate that for some azole-resistant C. albicans strains, LF-related compounds combined with triazoles can inhibit the growth of hyphae, an important form of this organism in pathogenesis.

Lactoferricin

“…It is thought that this synergism is due to the membranedisorganizing nature of this peptide, which leads not only to increased permeability through the bacterial cell wall [75] but also to dissipation of the proton-motive force, resulting in decreased activity of ATP-dependent multi-drug effl ux pumps [40,76]. The synergistic nature of Lfcin also extends to a common antiviral drug.…”

“…In addition to a number of bacteria, Lfcin, and particularly LfcinB, is also effective at inhibiting the growth of a number of yeasts, molds and fi lamentous fungi, including the pathogen Candida albicans, as well as dermatophytes (table 1) [8,[39][40][41]. Recent evidence suggests that Lfcin has two antifungal mechanisms, with the fi rst involving a direct fungicidal activity.…”

Periodontitis, periodontopathic bacteria and lactoferrin

“…LF is one of the antimicrobial factors in saliva (Tenovuo 2002). Previously, we studied its effects on the oral pathogen Candida albicans (Wakabayashi et al 1998, Takakura et al 2003. Moreover, LF has been studied for its antimicrobial activity against periodontopathic bacteria and its relationship with periodontal diseases (Kalmar andArnold 1988, Aguilera et al 1998).…”

Identification of a novel antifungal nonapeptide generated by combinatorial approach

“…Since the last decade many studies have been conducted on the interaction of drugs available in the market [1,8,[19][20][21]. Besides these, there are some reports available regarding interaction between N-terminal peptide of human lactoferrin with fluconazole [4,22] and antimicrobial synergism between two peptides magainin 2 and PGLa, discovered in the skin of the African clawed frog [23]. To our knowledge studies on the combination of synthetic peptides with available antifungal drugs have not been carried out before and such a study seems logical, as the mode of action of peptides is quite different from that of known antifungal agents.…”

“…Although the phenomenon of multidrug resistance is better recognized and characterized in the case of cancer and bacteria, it is also an emerging problem in antifungal chemotherapy, thus making worse the already difficult situation resulting from an increasing number of immunocompromised patients, the appearance of new human pathogenic fungi and the very limited number of available antifungal drugs. Long-term antifungal treatment with the commonly used antifungals, such as amphotericin B has toxic effects; ketoconazole, fluconazole and clotrimazole are limited in their spectrum and efficacy and use may result in strain resistance [3,4]. Hence, considerable research is being directed to screening for lead compounds with a defined mechanism of action that can serve as template for further medicinal chemistry modifications [5].…”