Methicillin-Resistant Staphylococcus Aureus (MRSA)

Introduction

A bacterial pathogen of increasing worldwide concern is Staphylococcus aureus. Staphylococcal infections affect people from all age groups, and recent estimates implicate them in 400,000 hospitalizations and 19,000 deaths annually among hospitalized patients in the United States. Soon after the commercial introduction of methicillin, the first strains of methicillin-resistant Staphylococcus aureus, known as MRSA, were reported, and over the years their prevalence has been increasing in several countries (Aschenbrenner, 8). Historically, MRSA was typically isolated from patients with underlying health conditions or within hospital settings and became known as health care-associated MRSA. However, during the past decade, a major shift has occurred in MRSA epidemiology, as infections are increasingly reported in apparently healthy individuals in the community, in the absence of risk factors; these have become known as community-acquired MRSA. In some hospitals, community-acquired MRSA strains have even started displacing the health care-associated MRSA isolates.

At the same time, MRSA increasingly emerges as a major concern in domestic animals, including dogs, cats, horses, pigs, and chickens. Several authors argue that the surge in community-acquired MRSA, at a time when infections in animals are increasingly reported, is not merely coincidental. Surveys conducted in several countries reveal that pig farmers are colonized with MRSA at higher rates than individuals without occupational exposure to animals, and their families are also at risk (Mody, 1923). For example, MRSA was isolated from farmers' family members who lacked direct contact with farm animals, indicating the possibility of direct human-to-human transmission of zoologically acquired MRSA. Veterinarians and pet owners represent additional at-risk groups for zoonotic infection.

Discussion

Staphylococcus aureus (S. aureus) are gram-positive cocci-shaped bacteria that are commonly found throughout the environment, including on the skin of healthy individuals. S. aureus is essentially benign on the skin, although if allowed to enter the bloodstream or internal tissues, S. aureus can cause a range of potentially serious infections. A person who has had some sort of skin trauma (including a minor cut) may be susceptible to a variety of different skin and soft-tissue infections caused by S. aureus, but the infection can usually be successfully treated with penicillin-derived antibiotics. MRSA, or methicillin-resistant S. aureus, are bacteria that have become highly resistant to many commonly used antibiotics, such as methicillin. MRSA infections are more difficult to treat because traditional antibiotics are ineffective, and patients must therefore be treated with alternative antibiotics. Until the 1990s, identified cases of MRSA were confined primarily to hospitals and healthcare facilities, although MRSA can now be found worldwide in community settings. MRSA infections can range in severity from minor to very serious and even fatal. In 2005, it was estimated that about 20 percent of those MRSA infections categorized as “serious” resulted in the death of the patient (Collins, 56). As a result, MRSA have emerged as very serious nosocomial (hospital-acquired) and community-acquired pathogens.

Methicillin is a semi-synthetic beta-lactamase-resistant penicillin antibiotic that was introduced in 1959 to aid in the fight against bacterial infection. Remarkably, S. aureus strains resistant to methicillin were reported soon after the ...