**2. Epidemiological aspects**

Oxacillin resistance in CoNS is a problem in hospitals around the world, and there are reports of oxacillin-resistant samples in all continents (Witte, 1999). The use of methicillin, a semisynthetic penicillin, commenced in 1959, and only two years after its first use, the first report of a methicillin-resistant *Staphylococcus* spp. sample was published (Hiramatsu et al., 2001).

Oxacillin resistance rates vary among various studies, but they are usually high, above 50%. Chaudhury & Kumar (2007) reported that, in a study conducted in a tertiary Indian hospital, 64.6% of the CoNS samples were oxacillin resistant. The most prevalent species was *S. haemolyticus*, isolated from urine samples. Another study also performed in India, described resistance levels of approximately 63% (Jain et al., 2008).

In the European continent, several reports described high oxacillin resistance levels in hospital wards. In a study analyzing samples collected from various hospitals in Eastern Europe in 2005, Sader et al. (2007) reported oxacillin resistance levels in CoNS which varied from 54.8% in Sweden to 83.3% in Greece. A study conducted at a university hospital in Turkey found 54.4% of resistant samples from a total of 158 isolated samples (Ercis et al., 2008). The rates found by a multi-center study conducted in the USA in 2007 and 2008 were of 74% of CoNS oxacillin-resistant samples (Sader & Jones, 2009).

Nevertheless, in the last few years, resistance levels have stabilized. In Spain, a multi-center study on 146 hospitals detected oxacillin resistance in 61.3% of the samples in 2002 and 66.7% in 2006 (Cuevas et al., 2008). In Brazil, recent studies showed resistance rates of 69% (Caierão et al., 2004), 78.4% (Perez & d'Azevedo 2007) and even 88.1% (Antunes et al., 2007). In the case of non-*epidermidis* CNS, Secchi et al. (2008) reported 71% of resistant samples.

Based on the described reports, it is clear that oxacillin resistance is prevalent in hospital in all continents, a fact that reinforces the importance of good antibiotic therapy practices and of infection control measures in hospitals.
