Normal mechanisms that maintain sterility of urine
a. Adequate urine volume
b. Free-flow from kidneys through urinary meatus
c. Complete bladder emptying
d. Normal acidity of urine
e. Peristaltic activity of ureters and competent ureterovesical junction
f. Increased intravesicular pressure preventing reflux
g. In males, antibacterial effect of zinc in prostatic fluid