Fungal growth is more likely to be affected by hormones in equine uterine isolates compared to isolates from nonreproductive sites

Fungal endometritis is an important cause of infertility in mares. Studies indicated that whereas estradiol may have a stimulatory effect on fungal growth, progesterone may have an inhibitory effect. However, both studies only examined 1 fungal isolate. Hormone responsiveness of fungal isolates from mare reproductive tract has not been evaluated. Objective was to determine if clinical fungal isolates from mare uteruses are hormone responsive; if so, are uterine isolates more likely to be hormone responsive compared to fungal isolates from nonreproductive sites. We hypothesized that estradiol has stimulatory effects whereas progesterone has inhibitory effects on fungal growth and that fungal isolates from mare uteruses are more likely hormone responsive compared to fungal isolates from nonreproductive sites. Fungal isolates from mare uteruses (n = 7) and isolates from nonreproductive sites (n = 5) were evaluated for hormone responsiveness after being cultured in RPMI media for 48 hours at 30C in 96-well plates. Absorbance was read at 600 nm at seeding times, 24 and 48 hours. Correlation between absorbance and fungal concentration was determined by hemocytometer. Dependent variable was percent change in fungal concentration from initial seeding. Estradiol treatment groups were: ethanol (vehicle) control and 10, 150, and 1,000 ng/ml whereas progesterone treatment groups were: ethanol control and 0.1, 5, and 100 g/ml. Data were not normally distributed and nonparametric analyses were used. Effects of hormone treatment and site on fungal growth were determined by Kruskal-Wallis test and treatment effects were determined using multiple comparison rank sum Steel test with ethanol group as the control in JMP Pro v. 14 (SAS Institute, Cary, NC). Estradiol affected growth (p = 0.0004) at 48 hours with increased growth (p = 0.0189) in 10 ng/ml compared to control. Progesterone affected growth at 24 (p < 0.0001) and 48 hours (p < 0.0001) with decreased growth in 5 g/ml (p < 0.0001) and 100 g/ml (p < 0.0001) groups compared to controls. Estradiol affected growth (p < 0.0001), with 3/7 (at 24 and 48 hours) isolates from uterus and 0/5 (at 24 hour) and 1/5 (at 48 hour) isolates from nonreproductive sites affected by estradiol. Progesterone affected growth (p < 0.0001), with 6/7 (at 24 and 48 hour) isolates from mare uterus and 1/5 (24 hour) and 3/5 (48 hour) isolates from nonreproductive sites affected. Majority of fungal isolates from mare uteruses were hormone responsive to estradiol (that increased growth rates) and progesterone (that decreased growth rates) whereas most nonreproductive isolates were not hormone responsive. This study highlighted potential interactions between hormone status and fungal infectivity in equine uterus.

Keywords: Fungal, hormone responsiveness, horses

Acknowledgement Part of this work was supported by Theriogenology Foundation

This manuscript was originally published in the journal Clinical Theriogenology Vol 12(3) Sept 2020.  Clinical Theriogenology is the official journal of the Society for Theriogenology (SFT) and the American College of Theriogenologists (ACT).  This content has been reproduced on the IVIS website with the explicit permission of the SFT/ACT.