Activity of Novel Ultrashort Cyclic Lipopeptides against Biofilm of Candida albicans Isolated from VVC in the Ex Vivo Animal Vaginal Model and BioFlux Biofilm Model-A Pilot Study

In recent years, clinicians and doctors have become increasingly interested in fungal infections, including those affecting the mucous membranes. Vulvovaginal candidiasis (VVC) is no exception. The etiology of this infection remains unexplained to this day, as well as the role and significance of asymptomatic vaginal Candida colonization. There are also indications that in the case of VVC, standard methods of determining drug susceptibility to antifungal drugs may not have a real impact on their clinical effectiveness-which would explain, among other things, treatment failures and relapse rates. The aim of the study was to verify the promising results obtained previously in vitro using standard methods, in a newly developed ex vivo model, using tissue fragments of the mouse vagina. The main goal of the study was to determine whether the selected ultrashort cyclic lipopeptides (USCLs) and their combinations with fluconazole at specific concentrations are equally effective against Candida forming a biofilm directly on the surface of the vaginal epithelium. In addition, the verification was also performed with the use of another model for the study of microorganisms (biofilms) in vitro-the BioFlux system, under microfluidic conditions. The obtained results indicate the ineffectiveness of the tested substances ex vivo at concentrations eradicating biofilm in vitro. Nevertheless, the relatively most favorable and promising results were still obtained in the case of combination therapy-a combination of low concentrations of lipopeptides (mainly linear analogs) with mycostatic fluconazole. Additionally, using BioFlux, it was not possible to confirm the previously obtained results. However, an inhibiting effect of the tested lipopeptides on the development of biofilm under microfluidic conditions was demonstrated. There is an incompatibility between the classic in vitro methods, the newer BioFlux method of biofilm testing, offering many advantages postulated elsewhere, and the ex vivo method. This incompatibility is another argument for the need, on the one hand, to intensify research on the pathomechanism of VVC, and, on the other hand, to verify and maybe modify the standard methods used in the determination of Candida susceptibility.

An efflux-susceptible antibiotic-adjuvant with systemic efficacy against mouse infections

Scarcity of effective treatments against sepsis is daunting, especially under the contemporary standpoints on antibiotics resistance, entailing the development of alternative treatment strategies. Here, we describe the design and antibiotic adjuvant properties of a new lipopeptide-like pentamer, decanoyl-bis.diaminobutyrate-aminododecanoyl-diaminobutyrate-amide (C₁₀BBc₁₂B), whose sub-maximal tolerated doses combinations with inefficient antibiotics demonstrated systemic efficacies in murine models of peritonitis-sepsis and urinary-tract infections. Attempts to shed light into the mechanism of action using membrane-active fluorescent probes, suggest outer-membrane interactions to dominate the pentamer's adjuvant properties, which were not associated with typical inner-membrane damages or with delayed bacterial growth. Yet, checkerboard titrations with low micromolar concentrations of C₁₀BBc₁₂B exhibited unprecedented capacities in potentiation of hydrophobic antibiotics towards Gram-negative ESKAPE pathogens, with an apparent low propensity for prompting resistance to the antibiotics. Assessment of the pentamer's potentiating activities upon efflux inhibition incites submission of a hitherto unreported, probable action mechanism implicating the pentamer's de-facto capacity to hijack bacterial efflux pumps for boosting its adjuvant activity through repetitive steps including outer-membrane adhesion, translocation and subsequent expulsion.

Mechanistic Studies of Antibiotic Adjuvants Reducing Kidney's Bacterial Loads upon Systemic Monotherapy

We describe the design and attributes of a linear pentapeptide-like derivative (C_14(ω5)OOc₁₀O) screened for its ability to elicit bactericidal competences of plasma constituents against Gram-negative bacteria (GNB). In simpler culture media, the lipopeptide revealed high aptitudes to sensitize resilient GNB to hydrophobic and/or efflux-substrate antibiotics, whereas in their absence, C_14(ω5)OOc₁₀O only briefly delayed bacterial proliferation. Instead, at low micromolar concentrations, the lipopeptide has rapidly lowered bacterial proton and ATP levels, although significantly less than upon treatment with its bactericidal analog. Mechanistic studies support a two-step scenario providing a plausible explanation for the lipopeptide’s biological outcomes against GNB: initially, C_14(ω5)OOc₁₀O permeabilizes the outer membrane similarly to polymyxin B, albeit in a manner not necessitating as much LPS-binding affinity. Subsequently, C_14(ω5)OOc₁₀O would interact with the inner membrane gently yet intensively enough to restrain membrane-protein functions such as drug efflux and/or ATP generation, while averting the harsher inner membrane perturbations that mediate the fatal outcome associated with bactericidal peers. Preliminary in vivo studies where skin wound infections were introduced in mice, revealed a significant efficacy in affecting bacterial viability upon topical treatment with creams containing C_14(ω5)OOc₁₀O, whereas synergistic combination therapies were able to secure the pathogen’s eradication. Further, capitalizing on the finding that C_14(ω5)OOc₁₀O plasma-potentiating concentrations were attainable in mice blood at sub-maximal tolerated doses, we used a urinary tract infection model to acquire evidence for the lipopeptide’s systemic capacity to reduce the kidney’s bacterial loads. Collectively, the data establish the role of C_14(ω5)OOc₁₀O as a compelling antibacterial potentiator and suggest its drug-like potential.

Sub-inhibitory membrane damage undermines Staphylococcus aureus virulence

We investigated antibacterial properties of a recently described membrane-active lipopeptide, C₁₀OOc₁₂O (decanoyl-ornithyl-ornithyl-dodecanoyl-ornithyl-amide) against Gram-positive bacteria (GPB). Minimal inhibitory concentrations (MICs) and kinetics were compared in culture media and plasma. Chemo-sensitization to antibiotics was determined using the checkerboard assay. Membrane damages were estimated using diverse membrane potential sensitive dyes. ATP levels and relevant enzymes activities were measured using commercial bioassay kits. While relatively weakly active in simple culture media, sub-MIC levels (~ten-fold) of C₁₀OOc₁₂O have significantly improved the antibacterial function of Human plasma. Mechanistic studies indicated that C₁₀OOc₁₂O-treated bacteria have sustained mild membrane damage(s) in association with rapid (within 2 min) but low (<10%) dissipation of the trans-membrane potential; Intracellular ATP levels were transiently reduced (~20%) whereas extracellular ATP increased only at MIC values; Sub-inhibitory concentrations were sufficient for inhibiting major agr-regulated virulence factors (lipase and α-toxin) and for sensitizing MRSA USA300 to the antibiotic oxacillin to the point of reverting the bacteria status from oxacillin-resistant to oxacillin-sensitive (i.e., oxacillin MIC was reduced from 32 to 0.1 mg/l). These findings argue that by means of mild depolarization, C₁₀OOc₁₂O affects the quorum sensing regulator in a manner that transiently weakens bacterial defenses, thereby enforcing studies that support the potential usefulness of fighting S. aureus (and possibly other GPB) infections, by targeting its virulence.