Clinical challenges in addressing resistance to antimicrobial drugs in the twenty-first century.

It has been more than 60 years since Alexander Fleming discovered the drug that came to be known as penicillin. Antibiotics are now one of the most frequently used medications in the United States and are prescribed by medical professionals in almost every specialty. The past decade has seen an alarming increase in the number of pathogens that are resistant to antimicrobial drugs, in the hospital as well as in the community.(1) Among the gram-positive pathogens, methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus species are the biggest threats. The situation is even more alarming with respect to gram-negative pathogens, especially because there are currently no late clinical trials involving new anti-infective drugs that are active against these pathogens.