Yes, if the right bacteria gets in the right place! But it's not going to be the only contributing cause...
Our own bacteria should ensure this doesn't happen or at least doesn't happen often, so I don't think sex would be the whole and only cause - there would be other things predisposing the woman to the UTIs. Like her own flora not fighting off the bacteria. Or hormonal changes making it easier for the bacteria to get in... and so on.
So lack of estrogen, really, can make UTIs more likely.
