Urine is a wonderful culture medium and a single bacterium multiplies to become 100,000 bacteria in two hours time. This is the basis of culture where colony count of more than 100,000 is considered significant of infection, since urine sample obtained at time of active infection in bladder should be able to provide that number of bacteria. It is impossible to pass urine without contaminating it with bacteria from urethral meatus. If urine even in absence of infection thus obtained is cultured, the colony count obtained will depend upon the time it is left outside the body at room temperature. A common mistake people do is to collect urine in morning and send to lab after couple of hours, results thus obtained are bound to be fallacious. Another factor could be that urine provided by you at sample collection may have been left out for some time in lab itself, accounting for 75,000 bacterial count. You must thus realise that only a sterile or insignificant count from a urine culture is correct, while a positive culture for bacteria may result from an active infection as well as wrong collection or processing.
You must have urinary protein-creatinine ratio, and DTPA scan study for GFR to know the status of your single kidney if you are keen to know your renal health, and consult a urologist/nephrologist in person.