One-third of the bacteria in the strain that most commonly causes pneumonia are already resistant to all of the macrolides.

FORBES: Antibiotic Breakthroughs Fall Short

Either the bugs would make a single genetic change to the proteins to which the macrolides bind, or the bacteria would absorb the drug but then pump it out before it could work.

FORBES: Antibiotic Breakthroughs Fall Short

The researchers associated increases in multidrug-resistant MRSA in the hospital with excessive use of two specific classes of antibiotics often prescribed to treat pneumonia (fluoroquinolones) and offered as a substitute for patients allergic to penicillin (macrolides).

FORBES: Private Physicians Drive Up Antibiotic Resistance, Helped Along By Patients

Bacteria learned to get around macrolides in two ways: Either they would make a single genetic change to the proteins to which the macrolides bind, or they would absorb the drug but then pump it out.

FORBES: FDA OKs Aventis Antibiotic

According to Paul Iannini Paul Iannini , chairman of the department of medicine at Danbury Hospital and clinical professor of medicine at Yale University School of Medicine, the bacteria figured out how to get around the macrolides in two ways.

FORBES: Antibiotic Breakthroughs Fall Short

According to Paul Iannini , chairman of the department of medicine at Danbury Hospital and clinical professor of medicine at Yale University School of Medicine, the bacteria figured out how to get around the macrolides in two ways.

FORBES: Antibiotic Breakthroughs Fall Short

Ketek is a modified version of a commonly used class of antibiotics, called macrolides, which includes Pfizer 's (nyse: PFE - news - people ) Zithromax and Abbott Laboratories ' (nyse: ABT - news - people ) Biaxin.

FORBES: Antibiotic Breakthroughs Fall Short