Minimum inhibitory concentration of vancomycin to methicillin resistant Staphylococcus aureus isolated from different clinical samples at a tertiary care hospital in Nepal

S. aureus is a flexible pathogen, which may be responsible for causing community acquired as well as nosocomial infections [1]. Despite the years of efforts to develop the new antibiotics for the eradication of MRSA, it has established itself as the commonest cause of skin and soft tissue infections [16, 17]. The prevalence of MRSA in our study was 47/125(37.6%), which was consistent with the results reported by Sanjana et al. (39.6%) [18] and Juayang et al. (40.6%) [19]. However, lower prevalence of MRSA in comparison to our study were reported by Subedi et al. (15.4%) [20], Baral et al. (26%) [21], Pandey et al. (26.12%) [22] and Kumari et al. (26.14%) [23]. While higher prevalence of MRSA were reported by Arora et al. (46%) [24], Dibah et al. (46.3%) [25], Khanal et al. (68%) [26] and Tiwari et al., (69.1%) [27]. The difference in the prevalence of MRSA among different studies may be due to difference in the location and time period of the study. The prevalence of MRSA may differ from one hospital to another hospital, depending upon the types of the patients it receives, hygienic condition of the hospital and the health care workers. If the hospital is a referral center then the prevalence of the MRSA among the patients may be very high, as the chance of getting antimicrobial therapy before reaching the referral center is very high and due to selective pressure the bacteria may acquire drug resistance. Healthcare workers may be not only the important source of transmission of MRSA to patients or among patients but also to the community [28]. Strict implementation of hand hygiene and decolonization of the MRSA carriers will be helpful to control the transmission of MRSA [11]. In addition, maintaining good (environmental as well as personal) hygiene in the hospital, among healthcare workers and patients will be more beneficial [11]. Due to the availability of limited treatment options for infections caused by MRSA, the treatment of such infections is often difficult leading to prolonged hospital stay and longer course along with higher cost of treatment sometimes leading to treatment failure resulting into fatal outcome [28]. Further, the higher rate of isolation of MRSA from clinical specimens of patients suggests the more attention to be given for infection control and surveillance, which may increase the overall infection control cost in the hospital [29].

In our study no strains of MRSA were found to be vancomycin resistant or vancomycin intermediate sensitive and the minimum inhibitory concentrations of vancomycin to the strains of MRSA ranged from 0.125 ?g/ml to 1 ?g/ml. As in our study, in a research from Nepal; Amatya et al. also did not note any strains of MRSA to be VISA or VRSA but higher MIC (i.e., 0.5 ?g/ml to 2 ?g/ml) of vancomycin to MRSA (in comparison to our study) was reported [11]. In contrast, in another study from Nepal; Pahadi et al. reported the four isolates of the MRSA to be VISA, with MIC of vancomycin to all the MRSA, ranging from 0.5 ?g/ml to 4 ?g/ml [13]. The discrepancy seen in results of different studies conducted in Nepal, may be because of the involvement of the patients with previous history of exposure to vancomycin in some studies. No VRSA has yet been reported from Nepal [13]. Decreased susceptibility of S. aureus to vancomycin was reported first from Japan in 1997 [30]. And the first strain of VRSA was isolated in 2002 from Michigan, USA [31]. Since then the VISA and VRSA have been reported frequently by many researchers [32–36].

The mechanism behind the resistance of Staphylococcus aureus to vancomycin may be the thickening of cell wall [37]. In addition; prior exposure to vancomycin increases the chances of the isolation of the strains of Staphylococcus aureus with reduced susceptibility [11] and the reason for emergence of VRSA/VISA may be the selective pressure due to the haphazard use of the antibiotic (vancomycin) [11]. The morbidity and mortality due to infection caused by VRSA are very high because of limited treatment options available [33]. At present when the infections due to MRSA have become a serious public health concern; the development and rapid spread of resistance of S. aureus to the reserve drug (vancomycin) is very fearsome and immediate actions should to be taken by the responsible authorities to halt it [11].

Due to haphazard use of antibiotics, there is increasing trend of development of drug resistance among the bacteria and the condition is more critical in poorer countries [38, 39]. To prevent the situation of the drug resistance from worsening; the use of antibiotic for the treatment of the patients should be based on culture and sensitivity report [40].