Activated lactoferrin and fluconazole synergism against Candida albicans and Candida glabrata vaginal isolates

To evaluate the fungistatic activity of activated lactoferrin (ALF), fluconazole (FCN) individually and in combination against Candida vaginal isolates as well as to measure the time to recovery from the fungistatic effects after exposure in vitro to threshold minimal inhibitory concentrations (MIC).

Fungistasis patterns for ALF (2.5 mg/mL) and FCN (0.25 mg/mL) were tested at threshold MIC against vaginal isolates of C albicans (n = 5) and C glabrata (n = 5) grown in Sabouraud's dextrose broth against 10(5) yeast inoculum at 37 degrees C for 48 hours by microscale optical density (OD) assay according to the following criteria: "Total stasis" indicates that an agent elicited no change or a change in turbidity <0.1 OD unit for >48 hours (complete growth inhibition), "stasis recovery" (SR) is the time point at which turbidity of a previous stasis system shows an upward growth trend for >0.1 OD unit (recovery from growth inhibition), and "partial stasis" (PS) is proliferation after stasis recovery, measured as a percentage relative to growth control at any time (incomplete growth inhibition).

For ALF (2.5 mg/mL), the mean SR time was 15.6 +/- 2 hours for C albicans (n = 5) and 27.5 +/- 2 hours for C glabrata (n = 5). The SR patterns for FCN were strain dependent and showed a wide range of deviation for both Candida species; accordingly, the values were 15.8 +/- 9 hours for C albicans and 25.5 +/- 12 hours for C glabrata. After 48 hours exposure to C albicans, ALF and FCN elicited a mean PS of 27.5 +/- 2% and 24.8 +/- 7%, respectively. The PS values at 48 hours showed a marked variation between C glabrata isolates, 29.1 +/- 24% for ALF and 21.5 +/- 38% for FCN. However, a combination of ALF and FCN at their threshold MIC showed significant drug synergism, causing total stasis of both species of Candida isolates. Thus, no SR for any Candida isolate was detected at or beyond 48 hours. Conversely, native lactoferrin failed to demonstrate such potent synergism with FCN against either Candida species.

The combination of ALF and FCN at the threshold MIC elicited potent synergism, leading to total fungistasis of C albicans and C glabrata vaginal pathogens. ALF is a new class of fungistatic agent with a mode of action distinct from that of azoles.