BACTERICIDAL TESTING

Purification and identification of bovine cheese whey fatty acids exhibiting in vitro antifungal activity

Milk lipids contain several bioactive factors exhibiting antimicrobial activity against bacteria, viruses, and fungi. In the present study, we demonstrate that free fatty acids (FFA) derived from the saponification of bovine whey cream lipids are active in vitro at inhibiting the germination of Candida albicans, a morphological transition associated with pathogenicity. This activity was found to be significantly increased when bovine FFA were enriched in non-straight-chain FFA. At low cell density, this non-straight-chain FFA-enriched fraction was also found to inhibit in a dose-dependant manner the growth of both developmental forms of C. albicans as well as the growth of Aspergillus fumigatus. Using an assay-guided fractionation, the main components responsible for these activities were isolated. On the basis of mass spectroscopic and gas chromatographic analysis, antifungal compounds were identified as capric acid (C10:0), lauroleic acid (C12:1), 11-methyldodecanoic acid (iso-C13:0), myristoleic acid (C14:1n-5), and gamma-linolenic acid (C18:3n-6). The most potent compound was gamma-linolenic acid, with minimal inhibitory concentration values of 5.4 mg/L for C. albicans and 1.3 mg/L for A. fumigatus, in standardized conditions. The results of this study indicate that bovine whey contains bioactive fatty acids exhibiting antifungal activity in vitro against 2 important human fungal pathogens.

Effect of increasing inoculum sizes of Aspergillus hyphae on MICs and MFCs of antifungal agents by broth microdilution method

In order to investigate the influence of different hyphal inoculum sizes on minimal inhibition concentrations (MICs) and minimum fungicidal concentrations (MFCs) of amphotericin B (AMB), voriconazole and itraconazole, five isolates each of Aspergillus fumigatus, Aspergillus flavus, Aspergillus niger and Aspergillus terreus were studied using a broth microdilution method. Three inoculum sizes were used: 1 x 10(3)-5 x 10(3), 1 x 10(4)-5 x 10(4) and 1 x 10(5)-5 x 10(5) cfu/ml. MICs and MFCs were read at 24 and 48 h at 35 degrees C. For all species tested, AMB MICs and MFCs were minimally affected by inoculum size on. However inoculum size significantly affected MICs and MFCs of voriconazole and itraconazole; there was an increase of up to 6-fold in MICs and MFCs for the various aspergilli when the inoculum increased from 10(3) to 10(5) cfu/ml (P<0.05). Thus azoles showed significant inoculum effects, while AMB showed comparatively minimum inoculum effects against Aspergillus spp.

Synergy of an investigational glycopeptide, LY333328, with once-daily gentamicin against vancomycin-resistant Enterococcus faecium in a multiple-dose, in vitro pharmacodynamic model

The pharmacodynamics of an investigational glycopeptide, LY333328 (LY), alone and in combination with gentamicin, against one vancomycin-susceptible and two vancomycin-resistant Enterococcus faecium strains were studied with a multiple-dose, in vitro pharmacodynamic model (PDM). Dose-range data for the PDM studies were obtained from static time-kill curve studies. In PDM experiments conducted over 48 h, peak LY concentrations of 0.1x and 1x the MIC every 24 h and peak gentamicin concentrations of 18 micrograms/ml every 24 h (Gq24 h) and 6 micrograms/ml every 8 h (Gq8 h) were studied alone and in the four possible LY-gentamicin combinations. Compared to either antibiotic alone, LY-gentamicin combination regimens produced significantly higher apparent killing rates (KRs) calculated during the initial 2 h postdosing. The mean KRs for LY or gentamicin alone versus those for the LY-gentamicin combination regimens were 0.35 +/- 0.55 log10 CFU/ml/h (95% confidence interval [CI95%], 0 to 0.70) and 1.46 +/- 0.71 log10 CFU/ml/h (CI95%, 1.01 to 1.91), respectively (P < 0.0001). Bacterial killing at 48 h (BK48), which was calculated by subtracting the bacterial counts at 48 h from the initial inoculum, with a negative value indicating net growth, was also significantly greater. The mean BK48S were -0.69 +/- 0.44 log10 CFU/ml (CI95%, -0.41 to -0.97) and 3.72 +/- 2.28 log10 CFU/ml (CI95%, 2.28 to 5.17) for LY or gentamicin alone versus LY-gentamicin combination regimens, respectively (P < 0.0001). None of the 12 regimens with LY or gentamicin alone but 75% (9 of 12) of the LY-gentamicin combination regimens were bactericidal. Eighty-three percent (10 of 12) of the LY-gentamicin combination regimens also demonstrated synergy. No significant differences between the pharmacodynamics of LY-gentamicin combination regimens containing Gq24 h versus those containing Gq8h were detected.