Hypothesis / aims of study
Urinary tract infections (UTIs) are common in females. After menopause, the rates of UTI increase, and there is a greater probability that the UTI will become recurrent. Antibiotics are routinely used to treat UTIs, however the overuse of antibiotics can lead to unintended consequences such as antibiotic resistance and changes in host microbiome. Therefore, methods and strategies other than antibiotics for UTI management is needed. The urothelial layer of the bladder is crucial to host defense against UTIs, and a granular understanding of urothelial host defense mechanisms would advance the field.
We created a transgenic mouse model that overexpresses estrogen receptor β (ERβ) restricted to the bladder urothelium (uERβ-OE+). We previously showed that the normal estrous uERβ-OE+ female mice cleared UPEC significantly faster than two control groups (uERβ-OE- and C57BL/6 wildtype) when the 3 groups of animals were inoculated with with 2x10^8 CFU of uropathogenic E. coli (UPEC). This finding suggested that urothelial ERβ overexpression augmented defense against UTIs. In this experiment, we measured whether urinary and tissue clearances of uropathogenic E. coli (UPEC) differed between ovariectomized (OVX) uERβ-OE+, uERβ-OE- and C57BL/6 wildtype mice.
Study design, materials and methods
Bilateral ovariectomies (OVX) were performed. Surgeries were done on 3 groups of female 5-7 month old mice via dorsal vertical midline incision on the same day. The presence of ovaries was confirmed by histopathology of removed specimens. The three groups include: (1) uERβ-OE+ (n=6), (2) negative littermates uERβ-OE- (n=5), and (3) wild type (WT) (n=6). The mice were given 4 weeks of recovery after OVX was performed. This time period was chosen because it allowed time for recovery from surgery and for potential biologic changes from OVX to occur.
Thereafter, the three groups of mice were inoculated transurethrally with 2x10^7 CFU UPEC (UTI89). Urine was collected on 4 consecutive days for cultures to quantify bacterial counts. On the fourth day, the mice were sacrificed and the bladders and kidneys were homogenized for culture to quantify bacterial counts.
The Mann–Whitney U test was used to compare differences in CFU between groups for each day of urine collection, as well as bladder and kidney CFU counts. The geometric mean of daily urine, bladder and kidney bacterial count was used in figures to best illustrate and capture the central tendency.
Interpretation of results
OVX did not alter clearance of UPEC in the 3 cohorts of animals. However, there are limitations to our study. We did not use a group of non-OVX mice in this experiment to control for OVX exposure in this experiment. Therefore, in this experiment, we can only compare how OVX affected the 3 groups of mice used, but we cannot conclude whether estrogen is important in UTI defense though this has been shown in a prior publication (1).