Although we’re all naturally concerned about the possibility our joint implants (of any sort) can become infected, here’s something to consider: Our bodies are ALREADY occupied by all kinds of bacteria. Bacteria are living inside us and more get in every day. We breathe them in and eat them in and they enter through tiny breaks in our skin. All the time. There's no avoiding this.
Bacteria find a way into our bodies every day.
Our new joints are only slightly more at risk from these new bacteria than most of the rest of our body parts and at much less risk than some parts. The skin is most at risk. Our guts are more at risk as are our mouths and nasal passages. It comes down to common sense precautions.
Small cuts in the skin aren't very risky for knees or other joints. If that were the case, we would have to freak out over mosquito bites, kitchen nicks, and paper cuts. Treat as usual and move on. Bigger cuts elsewhere on the body are not big problems either. Our immune systems kill most invaders and those that do get in aren't likely to be headed straight for our knees. Treat as usual. Our bodies will take care of them, too.
A big wound or deep gash on the knee, of course, you might be concerned about. In that case, call the OS and ask about whether you need to take precautions. Chances are such wounds won't hurt your knee either.
Needles introduced into the knee DO carry risk (not just for TKR, but ANY knee), so unless those are really needed, it's best not to inject a knee replacement or use a needle to drain the knee. Physicians who do this are aware of the risk, so they will take precautions.