I bought 2 kits from HBS and when putting down one can to 11.5L the first yeast was dead, 24 hours later used the yeast from the second can, dead also

I would have thought with my care sanitising it would be OK with a successful yeast pitch at 48hrs, but after my 3rd stubby I am convinced a cat pissed into my fermenter, it is just to sour.
I have lost my brew but now my biggest worry is how careful I need to be with the bottles so as not to infect the next brew that goes into them... a few stubbies from this brew are now mixed in with others. Do I need to quarantine them?
Sadly it seems that the MSB kits don't turn over quickly enough and as a result the quality yeast included is suspect.
