Watch out for that gleaming stethoscope around your doctor's neck. The diaphragm (the round part that touches your skin) was found in a new study to be a hot spot for MRSA (staph), the dreaded drug-resistant bacteria people pick up in hospitals.  
There are no MD guidelines for disinfecting scopes between patients.  You would be well within reason to suggest a wipe-down before your checkup begins.

Source: Mayo Clinic Proceedings
Quoted from Prevention Magazine