Staphylococcus aureus (Staph)

is a common infectious bacterium, typically encountered on the skin and in the nasal passages of healthy people. Staph can cause serious infections of the bone, soft tissue, eye, respiratory tract and blood stream, and it is one of the most common causes of skin infections. The forms of Staph that are resistant to methicillin and other antibiotics are known as Methicillin-Resistant Staph aureus (MRSA). Vancomycin is generally used to treat resistant Staph infections with some success. However, a new form of resistant Staph, known as Vancomycin-Intermediate-Resistant Staph aureus (VISA) has emerged to further confound treatment. The most troublesome form of antibiotic-resistant Staph is known as Vancomycin-Resistant Staph aureus (VRSA).

MRSA is a formidable bacterial pathogen responsible for a variety of infections commonly seen in patients of all ages. Acquisition of this organism is typically associated with particular settings (such as health care institutions, and especially hospitals and long-term care facilities) and patient groups (such as patients with prolonged hospitalization, past antimicrobial use, indwelling catheters, decubitis ulcers, postoperative surgical wounds, and use of intravenous drugs or treatment with enteral feedings or dialysis). Infections incited by MRSA present a considerable dilemma to clinicians, since therapeutic options are limited and suboptimal dosing contributes to heightened mortality and increased length of hospital stay.

Over the years MRSA strains have gained multiple mechanisms of resistance to the major classes of antimicrobial agents, such as macrolides, aminoglycosides, fluoroquinolones, tetracyclines, and lincosamides like clindamycin. And for the past several decades, glycopeptide antibiotics, such as vancomycin, were considered to be the only agents to which MRSA had not developed resistance. Unfortunately, because of the overuse of glycopeptide antibiotics, MRSA forms have now emerged with reduced or limited susceptibility to these agents as well.

Recent reports of Community-Associated MRSA (CA-MRSA) infections in patients with no known risk factors have serious public health implications. Conventional therapeutic options for these infections are untested, so the potential exists for high morbidity and mortality. Clinical definitions have been established and new molecular approaches have allowed investigators to distinguish CA-MRSA from traditional Nosocomial (hospital-acquired) MRSA strains. There have been several reports of CA-MRSA infections throughout the world, including several outbreaks in the United States. Transmission has occurred by close physical contact in situations involving children in day-care centers, children and adults on Indian reservations, athletes, military personnel, correctional facilities, and men having sex with men. Of concern, these patients are otherwise healthy individuals with no known risk factors for MRSA infection.

staphylococcus

staphylococcus aureus. Electron micrograph from Visuals Unlimited, with permission.