Cairn Persistant Bladder Infection/UTI

Question
Hi.  I have a 6 year old Cairn Terrier that I rescued when she was 7 mo's old.  Last year July of 2006) she got a UTI (for the very first time)... she was peeing blood, straining, not able to control her urine, etc.  I took her to the Vet and we did anitibiotic's, etc.. and it cleared up.  About May of this year, she got another one.  Same symptoms, I took her to the Vet we did two weeks of Clamavox and then about 2 weeks after she finished it... she had another one.  I took her back, we did a month's worth of the Clamavox and two weeks after that, she now has another one.  I'm being told "Well some dogs are prone to UTI's" but she never had any until now and honestly, I'm concerned about just continuing to give her antibiotic's and having her get it again 2 weeks after finishing them.  We did have it cultured and it was e coli type bacteria.  They have put her back on Clamavox and want me to give her Royal Cannin Urinary SO (uh? Isn't this one of the recalled pet foods?  I'm not too keen on this idea.)
Here's my question... the ONLY thing different in her life was her food.  I used to feed her a formula from Purina One.  Then I went and they were out (around the time of the pet food recall) so I decided to try a "natural" brand by Avoderm.  Could she have a food allergy that's causing some of this?  Since I was nearing the end of her food, I stopped at a pet store and asked about more nutrious food choices.  They suggested Kor Wellness because it doesn't have any grains in it.   They have checked her thyroid and it was normal.  I'm not sure the Vet has any more idea's on why this wont seem to go away.  Have you ever encountered this?

Answer
Jennifer -

Let me give you the legalese caveat first - I am NOT a vet, and any opinions I express are only that....

Cairns are prone to food allergies, and food allergies can cause all kinds of compromises in their immune system.  I have also had a dog who had repeated UTIs that the vets couldn't figure out that were resolved with some vitamins containing Vit C (because it lowered the pH of the urine, which in turn killed the buggies).

I do NOT recommend Royal Canin. Their list of ingredients does not pass my fussy test.  I'm not worried about grains per se, but I would avoid corn at all costs, and probably wheat and soy as well.  Many of the better kibbles use barley or oats.

I would also recommend trying a different protein - Fish being the one most dogs with allergies tolerate well.  Good brands are Wellness, Eagle Pack Holistic Select, Wysong and California Natural.  I feed By Nature, but it's a regional brand you may not have access to.

I would suggest a change to a top notch fish based food - see what happens.... It can't hurt and it might solve the problem.

Best wishes, and I am so darned sorry to not be able to give you additional idea.

-Beth