Regardless of the source of the bacteria that was found, from contamination or not, it was not supposed to any bacteria to be able to survive.
I do not know about the concentration, but based on the quantity of fluids I was drinking, is to expect that at least 10% of the urine was from CS solution (~25 PPM). And the culture was grown for at least 24 hours, that should be more than enough for the CS kill all the bacteria.
I have kidney stone. Seems that it is too large to come out alone and by blocking the ureter it sparks the infection, that may become systemic.