Itis quite customary for a vet to put a dog on a broad spectrum antibiotic such as bioclav when they find a UTI...however when that does not clear it up in less than 10 days, it is time to take a culture and find the exact med to use.
If you indeed asked your vet for a CULTURE, then she/he should have taken the sample and sent it off. Therefore, you should not have to pay another visit ($75) and should be refunded the $45 towards the culture itself (usually $60-70) If your current vet does not agree to this, I would change. I have not run into a vet that woudl not send off a culture when asked to do so. Also when at least 2 antibiotics have been prescribed, and the condition still exists, this is pretty standard practice.
FYI: When they do an "urinalysis" in house, what is generally done, is they use a chemstrip in the urine to find ph, protein, blood etc (they cost about 25 cents), takes about 60 seconds. I use them every wk for my pugs. then if they find a positive reading, they will look under a microscope generally, and try to determine what type of orgnism they are dealing with. Thats it.
so the visit, and rest of the fee is pretty darn good money. Not arguing with that as a business person, but when their attempts fail, it is time to move on and get a culture done by the lab before the condition becoms chronic. JMO