Why are the bacteria that cause hospital-acquired infections resistant to many antibiotics?

Question

Why are the bacteria that cause hospital-acquired infections resistant to many antibiotics, and why don't hospital acquired infections exist elsewhere ?

The infections that are caused in hospitals are usually a result of bacteria that are resistant to multiple antibiotics making them difficult to treat, but why are the bacteria resistant to all these antibiotics? I realize that a lot of antibiotics are used in hospitals but the question that comes to my head whenever I read this is "So?". To make my misconception clearer, I will use MRSA as an example . I mean , for the Staphylococcus aureus bacterium to become resistant , the antibiotic has to be used on it , so how can the antibiotics used to treat different infections in difference people act as a selection pressure for Staphylococcus aureus ( the Bacteria that causes MRSA )?

Answer 1

Hospitals have certain features:

• They are full of people immunocompromised in some way (old, exposed tissue, on steriods etc.)
• They are full of people with pathogens
• They are full of doctors who will give antibiotics to people with pathogenic infections

This is a perfect breeding ground for drug resistance in pathogens, with lots of pathogens, lots of places for them to grow (patients) and quite a lot of exposure to antibiotics. You use Staphylococcus aureus as an example, and it is a good one. We all have some of it on us, but it is not generally exposed to antibiotics so it does not develop resistance, and we do not generally have large areas of exposed flesh that would cause it to be pathogenic. In hospital this is not the case, so we get it causing trouble and developing resistance.

These things do occur outside of hospitals, but it does not tend to be as common or frequent.