|Year : 2015 | Volume
| Issue : 2 | Page : 69-72
Antimicrobial susceptibility pattern of methicillin-resistant strains of Staphylococcus aureus in a super specialty hospital
Jasmin Halim Hussain, Archana Thakur, Bibhabati Mishra, Vinita Dogra, Tavleen Jaggi
Department of Microbiology, G.B. Pant Hospital, New Delhi, India
|Date of Web Publication||10-Apr-2015|
Jasmin Halim Hussain
Department of Microbiology, G.B. Pant Hospital, J. L. Nehru Marg, New Delhi - 110 002
Source of Support: None, Conflict of Interest: None
Introduction: Staphylococcus aureus is a major cause of infection, and methicillin-resistant strains are increasingly being reported worldwide. This study was carried out to evaluate the antibiotic susceptibility pattern of methicillin-resistant strains of S. aureus, isolated from clinical specimens from a super specialty hospital in Delhi. Materials and Methods: The study comprised of 80 strains of S. aureus isolated from various clinical specimens. From these isolates, methicillin-resistant strains were screened, and their susceptibility pattern to vancomycin, teicoplanin, daptomycin, and linezolid was detected using standard microbiological techniques. Results: Of the 80 strains, 53 strains were found to be methicillin resistant while the rest of the 27 strains were methicillin-susceptible. Four among the 53 strains were linezolid resistant, and eight were vancomycin-intermediate. Of the 8 strains, two were teicoplanin intermediate, and one was teicoplanin resistant. All the 53 strains were sensitive to daptomycin. Conclusion: In the current study, daptomycin was found to be the only drug to which all the isolates were susceptible. However, daptomycin resistance has also been reported from elsewhere. Therefore, all the recommended measures to control the emergence and spread of these strains must be followed strictly in all health-care systems.
Keywords: Antibiotic susceptibility, MRSA, super specialty hospital
|How to cite this article:|
Hussain JH, Thakur A, Mishra B, Dogra V, Jaggi T. Antimicrobial susceptibility pattern of methicillin-resistant strains of Staphylococcus aureus in a super specialty hospital. Int J Health Allied Sci 2015;4:69-72
|How to cite this URL:|
Hussain JH, Thakur A, Mishra B, Dogra V, Jaggi T. Antimicrobial susceptibility pattern of methicillin-resistant strains of Staphylococcus aureus in a super specialty hospital. Int J Health Allied Sci [serial online] 2015 [cited 2022 Oct 5];4:69-72. Available from: https://www.ijhas.in/text.asp?2015/4/2/69/154908
| Introduction|| |
Although Staphylococcus aureus is a commensal organism, persistently or transiently present in up to 80% of healthy individuals,  it is one of the common organisms found to be associated with both nosocomial and community acquired infections.  After the discovery of penicillin, the mortality associated with Staphylococcal infections was reduced dramatically.  However, soon after the introduction of penicillin, penicillinase-producer Staphylococcus spp. strains were described. These penicillin-resistant strains spread into hospitals and years later into the community.  Penicillin-resistant strains became more common than penicillin-susceptible strains, first in hospitals and later in the community, by the late 1970s.  Antibiotics that were effective against penicillinase-producer strains like methicillin became the drugs of choice for treating Staphylococcus spp. related infections. However, soon after the introduction of methicillin, strains of Staphylococcus spp. with a modified transpeptidase that had low affinity for beta-lactam antibiotics were described.  Nowadays, the prevalence of health-care associated methicillin-resistant strains of S. aureus (MRSA) is higher than health-care associated methicillin-susceptible S. aureus in some countries of America and Asia.  The burden of common bacterial infections is higher in low- and middle-income countries, but data about the prevalence of MRSA in these countries are scarce.  While MRSA infections are associated with increased mortality and costs for health-care systems in developed countries,  the spread of MRSA in developing countries can have devastating consequences because of the lack of infrastructure that can provide bacterial identification and antimicrobial susceptibilities and the high cost of antibiotic drugs required to treat severe MRSA infections. 
The aim of the study was to evaluate the incidence of MRSA and their susceptibility pattern to the drugs commonly used for such infections isolated from the clinical specimens in a super specialty hospital in India.
| Materials and methods|| |
0Staphylococcus aureus isolated from various clinical specimens were included in the study. All the specimens were collected aseptically in sterile containers and were inoculated in blood agar and MacConkey agar plates and incubated for 24 h at 37°C. The S. aureus strains were further screened for methicillin resistance using cefoxitin 30 μg disc by Kirby-Bauer disc diffusion method on 5% NaCl Muller Hinton agar and incubated for 24 h at 34°C. A zone of <21 mm was considered as methicillin-resistant.
The susceptibility of the MRSA to daptomycin, vancomycin, teicoplanin, and linezolid was evaluated by detecting minimum inhibitory concentrations (MICs) using E - strips from HiMedia Pvt. Ltd. India as per manufacturer's guidelines. Following Clinical and Laboratory Standards Institute (CLSI) 2014 breakpoints, the susceptibility pattern of the organisms was interpreted from the MICs.
For vancomycin, isolates with MIC ≤2 μg/ml were considered as sensitive, 4-8 μg/ml were considered as intermediate sensitive and ≥16 μg/ml were considered as resistant.
For teicoplanin, isolates with MIC ≤8 μg/ml were considered as sensitive, 16 μg/ml were considered as intermediate sensitive and ≥32 μg/ml were considered as resistant.
For daptomycin, isolates with MIC ≤1 μg/ml were considered as sensitive.
For linezolid, isolates with MIC ≤4 μg/ml were considered as sensitive, and ≥8 μg/ml were considered as resistant.
| Results|| |
Total, 80 strains of S. aureus were isolated from various clinical specimens like pus (34), intravenous catheter tip (20), bile (19), and others (7) received in the Department of Microbiology in a Super Specialty Hospital in Delhi. Of the 80 strains, 53 strains were found to be methicillin resistant while the rest of the 27 strains were methicillin-susceptible.
Minimum inhibitory concentrations of all the 53 methicillin-resistant strains were detected for vancomycin, teicoplanin, daptomycin, and linezolid, and susceptibility pattern was interpreted following CLSI 2014.
Four among the 53 MRSA strains were found to be resistant to linezolid while being susceptible to the rest of the three antibiotics [Table 1].
Eight of the MRSA strains were found to be vancomycin-intermediate. Of these 8 vancomycin-intermediate strains, one was found to be teicoplanin resistant, and two were teicoplanin intermediate [Table 2].
All of the 53 strains were found to be susceptible to daptomycin.
| Discussion|| |
In our study, a very high prevalence of MRSA has been recorded. 66.25% of the isolated S. aureus strains were found to be MRSA. High prevalence of MRSA was also reported in some other previously published Indian studies. ,,
In this study, as many as four strains were found to be linezolid resistant. Linezolid was introduced clinically in the year 2000 and a year later in 2001 the first MRSA strain resistant to linezolid was reported.  Though linezolid resistance was reported from other parts of the world since then,  the first Indian case of linezolid resistance was reported from Kashmir in 2011.  Linezolid resistance is a major concern for all the health-care systems.
In the present study, all the patients from whom the linezolid resistant strains of MRSA were isolated were under linezolid coverage for > 1 week. Therefore, the resistance may be acquired due to overexposure to the drug. Linezolid resistance due to over exposure of the drug has also been reported in some other studies. 
Vancomycin is a recommended drug for MRSA infections. In 1996, the first vancomycin-intermediate clinical isolate of S. aureus was isolated in Japan.  But, unfortunately, decrease in susceptibility of S. aureus and isolation of vancomycin-intermediate and resistant S. aureus have recently been reported from many countries.  In this study, 8 strains were found to be vancomycin-intermediate. Many previously reported studies from various parts of India also recorded the emergence of low level and intermediate vancomycin resistance. ,,,,
Various clinical trials comparing the efficacy and safety of teicoplanin and vancomycin have been carried out worldwide. Available data suggest that teicoplanin is as effective as vancomycin, and it has superior tolerability along with advantages such as once daily bolus administration, intramuscular use, and lack of requirement of routine serum monitoring.  However, in this study, one of the strains is found to be teicoplanin resistant (MIC = 32) while two strains being intermediate (MIC = 16). The patient from whom the strain was isolated was on teicoplanin for more than a week. Hence, this might result due to overexposure to the drug.
In this study, all the strains were found to be susceptible to daptomycin. None of the patients had a history suggestive of previous exposure to the drug. Daptomycin resistance without pre-exposure to the drug is rare, but development of decreased susceptibility to daptomycin during long-term therapy in patients with MRSA infection has been reported in various previously published studies. ,,
| Conclusion|| |
The emergence of drug-resistant MRSA is worrisome in the present therapeutic scenario especially in the developing countries. A regular surveillance of the sensitivity pattern of MRSA is mandatory in all health-care systems. Basic hygienic measures like hand washing and hand sanitizing must be followed strictly in hospital settings to control the spread of such strains among the patients.
In order to control the emergence of resistance strains, proper antibiotic policy is a must in all health-care systems and these policies must be followed strictly so that judicial use of antibiotics can be assured and unnecessary and over exposure to the drugs can be avoided.
In this study, daptomycin was found to be the only antibiotic showing 100% susceptibility. However, the emergence of daptomycin resistance has also been recorded in some studies. Therefore, these drugs should be used very cautiously or else the threat of drug resistance will increase and no longer it will be possible to treat MRSA infections.
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[Table 1], [Table 2]