It sounds like that was a painful fall. A skinned knee in medical terms is a superficial abrasion. These types of injuries can get infected from bacteria that you pick up on the surface of anything that touches it, or from bacteria that already exist on the surface of the skin. A staph infection is a bacterial infection in which the main culprit is the bacteria staphylococcus (Staph for short). There are different species of Staph and many of them do live on the skin. Most of the time, these abrasion infections like the one you have consist of many different bacteria. Usually keeping the wound clean and using antibiotic ointment is enough to ward off any major infection. If your injury
was bad enough, sometimes bacteria can make it deeper into your tissues causing an abscess if this has happened, then the a Staph infection is more likely and you will need to seek attention from a doctor
who can do an incision and drainage. If you knee is getting better with the above measures, then you will never know what type of bacteria caused the infection.
If you are worried about this, then I would suggest that you schedule an appointment with your primary care physician
. He or she can take a close look at your knee and determine if any additional treatment is needed. I hope it gets better.