Clinical Epidemiological Studies on Methicillin Resistant and Suscepti ble Staphylococci

Abstract

Staphylococcus aureus was discovered for the fi rst ti me in the 1880s [1]. Since then, S. aureus has been shown to be a major pathogenic Gram-positi ve bacterium, causing relati vely mild superfi cial infecti ons (e.g., furuncles or boils, post-operati ve wound infecti ons) to lifethreatening invasive infecti ons (e.g., sepsis, endocarditi s) [2]. In the early 1940s, prior to the introducti on of penicillin, the mortality rate of individuals with a severe S. aureus infecti on was about 80% [3]. The emerge of strains with penicillin resistance was reported for the fi rst ti me in 1948 [4]. Since 1960, approximately 80% of all S. aureus strains became resistant to penicillin. Therefore, methicillin was introduced in 1959 to treat infecti ons caused by this penicillin-resistant S. aureus [5]. In 1961, two years aft er the introducti on of methicillin, there were reports from the United Kingdom of S. aureus isolates that had acquired resistance to methicillin (methicillin-resistant S. aureus, MRSA) [6]. The cause of the development of methicillin resistance was the acquisiti on of the mecA gene [7]. During the last decades, MRSA has become the most prevalent anti bioti c-resistant pathogen in hospitals in many parts of the world and a growing number of reports describe the increasing prevalence in various populati ons in the community [8-10]. In additi on, various healthcareassociated methicillin-resistant S. aureus (HA-MRSA) clones disseminated worldwide [11]. Furthermore, since the 1990s, virulent community-associated MRSA (CA-MRSA) clones, characterized by the presence of the toxin Panton-Valenti ne Leukocidin (PVL), have spread worldwide, fi rst in the community, but now they are also emerging in healthcare faciliti es [11, 12]. The CA-MRSA prevalence worldwide remains low, but an increasing prevalence has been reported [10, 13] and, some people tend to believe that the disti ncti on between CA-MRSA and HA-MRSA is beginning to fade [2, 14]. A CA-MRSA clone which is frequently isolated is the socalled USA-300 strain. This strain has proved to be able to transmit between individuals and causes outbreaks of skin infecti ons and boils.