Determination of Fungicidal Activities against Yeasts and Molds: Lessons Learned from Bactericidal Testing and the Need for Standardization

Abstract

In certain unique clinical settings, the ability of the antimicrobial agent administered to kill the pathogen outright may be quite important. These situations invariably involve infection of a site not easily accessed by host defenses and/or of a structure with essential anatomic or physiologic function such as the heart (endocarditis), central nervous system (meningitis), or bone (osteomyelitis). Likewise, infections in immunosuppressed hosts, especially those who are neutropenic, are often thought to require microbicidal therapy. Proof of the cidal nature of an antimicrobial agent in vitro is tedious, complex, and fraught with error. Although several methods for assessing in vitro bactericidal activity have been standardized (NCCLS M26-A and M21-A), the clinical relevance of these determinations is questionable and the tests are performed infrequently in most laboratories. Most of the clinical data supporting the need for microbicidal therapy and testing have focused on bacterial infections. However, given the fact that most serious fungal infections occur in profoundly immunosuppressed individuals, it is generally assumed that a cidal regimen would be preferable in that setting as well. In view of this clinical concern and the perceived need to assess the fungicidal activity of a variety of agents, we considered that it would be useful to review what is known about the issues and problems in assessing bactericidal activity and the clinical utility of such measurements. Following this review, we discuss the issue of how one defines fungicidal activity in vitro and in vivo and how feasible it might be to determine the fungicidal activity of organism-drug combinations for purposes of both drug development and clinical care. Proposed methods for fungal time-kill determinations and minimal fungicidal concentration determinations are also discussed

In vitro antifungal activity and cytotoxic effect of essential oils and extracts of medicinal and aromatic plants against Candida krusei and Aspergillus fumigatus

“…This makes it possible to determine if the agent has a fungistatic or fungicidal effect, and if the killing process is concentration or time-dependent (Pfaller et al, 2004). Analysis of the time-kill curves of oil from C. ambrosioides L. with C. krusei did not have a significant effect at 0.5 x and 1 x MIC, whereas a fungicidal effect (CFU /mL >3 log units) was detected at 4 x MIC, after 4 h (Figure 1a).…”

In vitro antifungal activities of amphotericin B in combination with acteoside, a phenylethanoid glycoside from Colebrookea oppositifolia

“…These fungal suspensions were further diluted in Penassay broth and a 100 ml volume of this diluted inoculum was added to each well of the plate, resulting in a final inoculum concentration of 0.5610 4 -2.5610 4 c.f.u. ml -1 for yeasts (Pfaller et al, 2004) and 0.4610 4 -5610 4 c.f.u. ml -1 for Aspergillus species (CLSI, 2008b).…”

“…The MIC (minimum inhibitory concentration) of Candida species was determined by using higher range of inoculum (Pfaller et al, 2004). Three clinical isolates of each species were also tested and no statistically significant changes were observed (data not shown control (P,0.001).…”

UPC2 Is Universally Essential for Azole Antifungal Resistance in Candida albicans

“…T he increased frequency of invasive fungal infections in recent decades is directly related to an expansion in the immunocompromised patient population, including those with HIV/AIDS, cancer chemotherapy patients, neutropenic patients, recipients of transplants with indwelling catheters, and patients receiving antibiotics (1)(2)(3). Candida species collectively are the fourth leading cause of nosocomial infections in the United States, and such infections are associated with unacceptably high rates of mortality (2,(4)(5)(6).…”