Staphylococcus aureus: An Invincible Bug

Staphylococcus aureus is a bacterium of significant importance because of its ability to cause a wide range of diseases and capacity to adapt to diverse environmental forms [1,2]. The organism causes infections both in human and animals such as rashes, inflammations of bones and the meninges as well as septicaemia [3]. It is now the most frequently identified drugresistant pathogen in a hospital. Penicillin and its derivatives, including methicillin have been used for the treatments of infections caused by S. aureus [4]. However, certain strains of S. aureus developed resistance known as methicillin resistant Staphylococcus aureus (MRSA). Penicillinase producing S. aureus was first reported in 1944. The ensuing years have witnessed a slow and persistent rise in penicillin-resistant S. aureus. By the late 1940s, UK and USA hospitals reported ~50% of S. aureus resistant to penicillin. A comprehensive epidemiologic study of 2000 blood isolates of S. aureus in Denmark during 1957-66 confirmed 85-90% penicillin-resistance for hospital isolates and 65-70% for community isolates [5]. In the 1950s, resistance of S. aureus to chloramphenicol, erythromycin, and tetracyclines emerged. Six months after the first semisynthetic penicillinase resistant penicillin, methicillin, was introduced for clinical use, three isolates of MRSA were identified in England. It gradually spread and by 1967, multidrug resistant MRSA was reported in Europe, Australia and India. By late the 1970s, MRSA isolates had spread worldwide in hospitals and communities. In USA hospitals, MRSA as a cause of nosocomial infections rose from 2.4% in 1975 to 29% in 1991. Sharp differences in prevalence of MRSA between the various countries have been reported. In the early 1980s, gentamicin-resistant MRSA was reported from several countries. Epidemic multiresistant MRSA was reported from Australia, England and Central Europe [6]. S. aureus are colonized in anterior nares, perineum, skin or skin glands of humans and animals. The carriage rates vary from 25-50% in the general population. It is higher in diabetics, in patients with intravascular lines, in health care workers, and in drug users. Colonisation may be transient or persistent and can last for years. The efficacy of methods to reduce MRSA recurrence and transmission by decolonising carriers has not been documented. However, it may be advisable to do so in patients with recurrent MRSA infections and if there is an ongoing transmission in close contacts. S. aureus including MRSA has been isolated from various animals both infected and carriers. Transmission to man has been reported from dogs, horses, pigs and cows, as evidenced by phenotyping and genotyping of the isolates [7].