Staphylococcus aureus gain access to the epidermis through cracks in the skin, abrasions, cuts, burns, surgical incisions and intravenous catheters causing wide spectrum of infections, from localized skin lesions such as abscesses, folliculitis to deep seated infections. In the present study, of 306 isolates of Staphylococcus aureus, 27% were from pus sample, which signifies their important role in abscess formation.
Antimicrobial resistance has been noticed as one of the paramount microbial threats of the twenty-first century . The multidrug resistance to most of the antibiotics used in infections caused by staphylococci is an increasing problem. The emergence of methicillin resistance among Staphylococcus aureus strains led to difficulties in the treatment of infections caused by this organism . Therefore, surveillance on the antimicrobial susceptibility patterns of Staphylococcus aureus is of utmost importance in understanding new and emerging resistance trends as well as in the management of both hospital and community-acquired infections.
This study demonstrated that overall rates of susceptibility to commonly prescribed antibiotics in Staphylococcus aureus isolates were below 70%, with the exception of clindamycin, amikacin, teicoplanin, and vancomycin. Despite the considerable progress in antimicrobial therapy, resistance in Gram-positive pathogens continues to increase, mainly in relation to the drugs commonly used in medical practice. A high proportion of isolates (94.7%) were resistant to penicillin in this study. This was expected as it has been recognized that only a small proportion of the Staphylococcus aurues lineages do not produce beta-lactamases [23–26].
Erythromycin has been used extensively for the treatment of both minor and more serious staphylococcal infections. As a consequence, its role today is increasingly limited due to increasing resistance, which poses a great therapeutic challenge. One third (32.7%) of our isolates were resistant to erythromycin, compared to previous similar studies in Nepal which have round resistance rates of 7.1% in 2010, 11% in 2011, 63.6% in 2013 [24, 27, 25]. Similarly, trimethoprim-sulfamethoxazole (co-trimoxazole) can be an alternative treatment choice, particularly for non-multi-resistant MRSA infections, although emergence of resistance has been previously observed. This may be due to excessive use of this drug for many other infections and over-the-counter availability of antimicrobials in the developing world for the treatment of many other infections. 81.7% of our isolates were resistant to co-trimoxazole, compared with 42.96% in 2009 , 12.5% in 2010 , 64% in 2011 , and 72.7% in 2013  in Nepal.
While ciprofloxacin is predominantly a Gram-negative drug, it does have activity against Staphylococcus aureus. As a consequence of low cost and easy availability, there has been indiscriminate use of ciprofloxacin in Nepal. We identified resistance rate of 63.7%, much higher than previous studies (26% in 2009 , 12% in 2011 ). The same trend is seen with gentamicin, with 60.4% of our isolates being resistant compared with 46.98% in 2009 , 32.73% in 2010 , 11% in 2011 , and 54.5% in 2013 . Fortunately, rate of resistance to amikacin remains low.
All of our isolates had retained susceptibility to vancomycin and teicoplanin, consistent with previous studies [23, 25–27, 29], confirming that glycopeptides should be used as empiric therapy for serious staphylococcal infections while waiting for susceptibility testing results to come through . This is likely related to low usage of these agents in Nepal due to high cost. Concerningly, however, lineages with increased resistance to teicoplanin have been observed overseas [31–34].
Clindamycin is one of the drugs of choice in MRSA infections. Macrolide-resistant isolates of Staphylococcus aureus may have constitutive or inducible resistance to clindamycin (due to methylation of the 23S rRNA encoded by the erm gene also referred to as MLSB i.e., Macrolide, Lincosamide and type B Streptogramin resistance) or may be resistant only to macrolides (due to efflux mechanism encoded by the msrA gene) . As the presence of an erm gene encoding for inducible resistance may result in treatment failure , it is important to perform its testing. We found 38 (12.4%) D-test positive isolates, indicating inducible resistance to clindamycin.
Today the concern of MRSA has reached the pinnacle. It is noteworthy that MRSA can cause both community and hospital acquired infections. Prior antibiotic use is the most common risk factor for colonization and infection with MRSA. In our study, 43.1% of Staphylococcus aureus isolates were found to be MRSA which is higher as compared to other studies conducted in Nepal. The incidence of MRSA was reported to be 20% in 2001 , 15.4% in 2005 , 26.14% in 2008 , 39.6% in 2010  and 42.4% in 2013  in Nepal.
Two different methods were employed for the detection of MRSA. The cefoxitin disk method detected 132 (43.1%) MRSA cases while the oxacillin disk method missed 12 cases and detected only 120 (39.2%) Staphylococcus aureus as MRSA. According to CLSI , the cefoxitin disk test is comparable to the oxacillin disk test for the prediction of mecA-mediated resistance to oxacillin. The cefoxitin disk test is easier to read and thus is the preferred method. Besides, cefoxitin is an inducer of the mecA gene.
There are a number of factors contributing to increasing rates of resistance in Staphylococcus aureus in Nepal. Firstly, regulation of antibiotics is poor with their easy and over the counter availability without prescription. Some health care workers and pharmacists are often paid incentives by the pharmaceutical companies to prescribe or sell unnecessary antibiotics. Medical practice by unqualified personnel, who often prescribe unnecessary antibiotics, is yet other common problem in Nepal. Locally produced antibiotics are of questionable quality; and compliance of the patients is also often poor. Many antibiotics are prescribed without culture and sensitivity due to lack of laboratory facilities in most of the areas. Moreover, infection control policies are yet to be instituted properly in most of the hospitals and medical institutions of Nepal.
Thus, regular surveillance of hospital associated infections and antibiotic sensitivity pattern of MRSA; and formulation of definite antibiotic policy may be helpful for reducing the incidence of MRSA infection. Furthermore, healthcare workers should be trained to control hospital infection and infection control program should be conducted effectively in all health care centers.