Mutacin 1140 and nisin A are peptide antibiotics that belong to the lantibiotic family. N-Terminal rings A and B of nisin A and mutacin 1140 (lipid II-binding domain) share many structural and sequence similarities. Nisin A binds lipid II and thus disrupts cell wall synthesis and also forms transmembrane pores. Very little is known about mutacin 1140 in this regard. We performed fluorescence-based studies using a bacteria-mimetic membrane system. The results indicated that lipid II monomers are arranged differently in the mutacin 1140 complex than in the nisin A complex. These differences in complex formation may be attributed to the fact that nisin A uses lipid II to form a distinct pore complex, while mutacin 1140 does not form pores in this membrane system. Further experiments demonstrated that the mutacin 1140-lipid II and nisin A-lipid II complexes are very stable and capable of withstanding competition from each other. Transmembrane electrical potential experiments using a Streptococcus rattus strain, which is sensitive to mutacin 1140, demonstrated that mutacin 1140 does not form pores in this strain even at a concentration 8 times higher than the minimum inhibitory concentration (MIC). Circular complexes of mutacin 1140 and nisin A were observed by electron microscopy, providing direct evidence for a lateral assembly mechanism for these antibiotics. Mutacin 1140 did exhibit a membrane disruptive function in another commonly used artificial bacterial membrane system, and its disruptive activity was enhanced by increasing amounts of anionic phospholipids.

The peptide antibiotic nisin A belongs to the group of antibiotics called lantibiotics. They are classified as lantibiotics because they contain the structural group lanthionine. Lanthionines are composed of a single sulfur atom that is linked to the ␤-carbons of two alanine moieties. These sulfur atoms are vulnerable to environmental oxidation. A mild oxidation reaction was performed on nisin A to determine the relative effects it would have on bioactivity. High-mass-accuracy Fourier transform ion cyclotron resonance mass spectrometry data revealed the addition of seven, eight, and nine oxygens. These additions correspond to the five lanthionines, two methionines, and two histidines that would be susceptible to oxidation. Subsequent bioassays revealed that the oxidized form of nisin A had a complete loss of bactericidal activity. In a competition study, the oxidized nisin did not appear to have an antagonistic affect on the bioactivity of nisin A, since the addition of an equal molar concentration of the oxidized variant did not have an influence on the bactericidal activity of the native antibiotic. Electron microscopy data revealed that the oxidized forms were still capable of assembling into large circular complexes, demonstrating that oxidation does not disrupt the lateral assembly mechanism of the antibiotic. Affinity thin-layer chromatography and fluorescence microscopy experiments suggested that the loss of activity is due to the inability of the oxidized form of nisin to bind to the cell wall precursor lipid II. Given the loss of bioactivity following oxidation, oxidation should be an important factor to consider in future production, purification, pharmacokinetic, and pharmacodynamic studies.

Occidiofungin is a non-ribosomally synthesized cyclic lipopeptide, which possesses broad spectrum antifungal properties at sub-micromolar concentrations. This report explores multiple routes of administration, formulation, and toxicity of occidiofungin in mice. Further, infection studies were performed in mice to assess the application of occidiofungin for treating a systemic yeast and an intravaginal yeast infection. Formulations for intravenous and intravaginal administration of occidiofungin were prepared. Pharmacokinetic analyses were performed in a murine model, and an LCMS method was developed and used to quantify occidiofungin in the mouse plasma samples. Toxicology and histopathology analysis of two repeat dose studies using occidiofungin were performed. In these animal models, following an intravenous administration, liposomal formulation of occidiofungin improved the half-life and peak plasma concentration compared to liposomal-free formulation. Two long-term repeat dosing toxicity studies of occidiofungin indicated the absence of toxicity in organ tissues. A systemic yeast and vulvovaginal yeast murine models of infection were performed. Findings in the systemic infection study has revealed limitations in occidiofungin's use that may be alleviated with the development of novel structural analogs or with further formulation studies. The gel formulation of occidiofungin demonstrated improved efficacy in a vulvovaginal candidiasis study as compared to the commercial product Monistat 3™. This report outlines the optimal routes of administration of occidiofungin and demonstrates minimal toxicity following chronic exposure. Further, the results from these studies provides a clear indication for the use of occidiofungin towards the treatment of recurrent vulvovaginal candidiasis (RVVC), which is a serious and clinically relevant issue.