The emerging of fungal resistance to first-line empirical monotherapy calls on appropriately evaluates the activity of existing and novel antifungal agents. Creative Biolabs provides you several antifungal pharmacodynamic function analyses, of which in vitro time-kill curve assay is an import service.

In vitro time-kill assay describes the relationship between the concentration of antifungals and the time point of fungal growth, which provides more detailed information than the MIC only. Antifungals with identical MICs but different time-kill curves can have differences in antimicrobial efficacy. Time-kill analysis has the ability to evaluating the efficacy of antifungal drugs and predicting dose for antifungals.

Time-Kill Analysis for Fungi Figure 1. Example of a time-kill plot showing the activity of fluconazole, the echinocandin LY303366, and amphotericin B against an isolate of C. tropicalis. The study was performed with and without shaking of the cultures. Only amphotericin B was fungicidal against this isolate. (Pfaller et al. 2004)

Our Standardized Performance of Antifungal Time-Kill Testing

Time-kill curve assay is a broth-based method, and the rate of killing a fixed inoculum fungus is determined by comparing control group (no drug) and experiment group (antimicrobial agent-containing). The kill curves are constructed by plotting the CFU per milliliter surviving at each time point in the presence and absence of the antimicrobial agent. Kill curve of a single antimicrobial agent is often assessed and constructed by testing several multiples of the MIC. If determining synergy or antagonism effects between two or more antifungal drugs, kill curves are constructed for a fixed concentration of each agent alone and in combination and are compared to that of the no-drug control at each time point.

For fungi, a 99.9%, or 3-log10-unit killing in CFU per milliliter from the starting inoculum is used for evaluating fungicidal activity. The initial inoculum of fungi or fungal conidia is higher than bacteria, which is 1×105 to 5×105 CFU/mL (Figure 2).

Time-Kill Analysis for Fungi Figure 2 Proposed methods for standardized performance of antifungal time-kill testing of yeasts (Pfaller et al. 2004)

Application of Time-Kill Curve

The time-kill curve we built can help you evaluate the efficiency of a new antimicrobial agent. It allows the determination of whether an antifungal agent produces concentration-dependent killing or time-dependent killing and the time-kill assay is used to guide therapy in an individual patient. If the drug is concentration-dependent killing, its extent of killing increases with increased drug concentrations. If it is time-dependent killing, the killing continues only as long as the concentrations are in excess of the MIC.

Several other applications also exist. For instance, time-kill assay is useful in determining tolerance to the lethal activity of antifungals and determining synergy or antagonism effects between two (or more) antimicrobial agents.

Creative Biolabs offers several antifungal pharmacodynamics services. For more detailed information, please feel free to contact us or directly sent us an inquiry.

Reference

  1. Pfaller MA, Sheehan DJ and Rex JH (2004). “Determination of Fungicidal Activities against Yeasts and Molds: Lessons Learned from Bactericidal Testing and the Need for Standardization”. Clinical Microbiology Reviews 17(2): 268–280. DOI: 10.1128/CMR.17.2.268–280.2004
  2. Klepser ME, Malone D, Lewis RE, et al. (2000). “Evaluation of Voriconazole Pharmacodynamics Using Time-Kill Methodology”. Antimicrobial Agents and Chemotherapy 44(7): 1917–1920

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