Detection of methicillin-resistance gene in Staphylococcus epidermidis strains isolated from patients in Al-Zahra Hospital using polymerase chain reaction and minimum inhibitory concentration methods


1 Department of Microbiology, Medical School, Isfahan University of Medical Sciences, Isfahan, Iran

2 Vice chancellor for research, School of medicine, Isfahan University of Medical Sciences, Isfahan, Iran


Background: In recent years, antibiotic resistance of Staphylococcus epidermidis to methicillin has significantly increased, making it essential to study resistance to methicillin, which is a determining factor in the appropriate treatment pattern. The purpose of this study was to identify methicillin-resistant genes in S. epidermidis strains using polymerase chain reaction (PCR) and to determine their mean minimum inhibitory concentration (MIC) to methicillin using E-test method.
Materials and Methods: MIC was determined on 146 samples of S. epidermidis using E-test method. Moreover, all samples were tested for the presence of mecA gene using PCR.
Results: PCR test showed 75.34% of the samples to contain mecA gene. Methicillin resistance test was performed using E-test on all the samples, which showed resistance in different dilutions.
Conclusion: The frequency of mecA gene in S. epidermidis isolates was 75.34%. Among the various applied tests used for determining methicillin resistance, sensitivity and specificity of PCR were the highest and reached 100%. Sensitivity and specificity were found to be 95.3% and 94.7%, respectively, for phenotypic test (E-test) and 86.5% and 80.9%, respectively, for disk diffusion method. Based on the above results, it seems that resistance of S. epidermidis to methicillin is on the rise, and therefore more research is warranted.


1. Forbes BA, Sahm DF, Weissfeld AS. Types of nosocomial infections. In: Shanahan JF, editor. Bailey-Scotts diagnostic microbiology. 12 th ed. Vol. 20. Philadelphia: Mosby; 2002. p. 68-9.  Back to cited text no. 1
2. Lim SM, Webb SA. Nosocomial bacterial infections in Intensive Care Units. I. Organisms and mechanisms of antibiotic resistance. Anaesthesia 2005;60:887-902.  Back to cited text no. 2
3. von Eiff C, Jansen B, Kohnen W, Becker K. Infections associated with medical devices: Pathogenesis, management and prophylaxis. Drugs 2005;65:179-214.  Back to cited text no. 3
4. Barrau K, Boulamery A, Imbert G, Casalta JP, Habib G, Messana T, et al. Causative organisms of infective endocarditis according to host status. Clin Microbiol Infect 2004;10:302-8.  Back to cited text no. 4
5. Ziebuhr W. Staphylococcus aureus and Staphylococcus epidermidis: Emerging pathogens in nosocomial infections. Contrib Microbiol 2001;8:102-7.  Back to cited text no. 5
6. Garrett DO, Jochimsen E, Murfitt K, Hill B, McAllister S, Nelson P, et al. The emergence of decreased susceptibility to vancomycin in Staphylococcus epidermidis. Infect Control Hosp Epidemiol 1999;20:167-70.  Back to cited text no. 6
7. Dickinson TM, Archer GL. Phenotypic expression of oxacillin resistance in Staphylococcus epidermidis: Roles of mecA transcriptional regulation and resistance-subpopulation selection. Antimicrob Agents Chemother 2000;44:1616-23.  Back to cited text no. 7
8. Hebert GA. Hemolysins and other characteristics that help differentiate and biotype Staphylococcus lugdunensis and Staphylococcus schleiferi. J Clin Microbiol 1990;28:2425-31.  Back to cited text no. 8
9. Hebert GA, Crowder CG, Hancock GA, Jarvis WR, Thornsberry C. Characteristics of coagulase-negative staphylococci that help differentiate these species and other members of the family Micrococcaceae. J Clin Microbiol 1988;26:1939-49.  Back to cited text no. 9
10. Kloos WE, Bannerman TL. Update on clinical significance of coagulase-negative staphylococci. Clin Microbiol Rev 1994;7:117-40.  Back to cited text no. 10
11. Mack D, Davies AP, Harris LG, Rohde H, Horstkotte MA, Knobloch JK. Microbial interactions in Staphylococcus epidermidis biofilms. Anal Bioanal Chem 2007;387:399-408.  Back to cited text no. 11
12. Vuong C, Voyich JM, Fischer ER, Braughton KR, Whitney AR, DeLeo FR, et al. Polysaccharide intercellular adhesin (PIA) protects Staphylococcus epidermidis against major components of the human innate immune system. Cell Microbiol 2004;6:269-75.  Back to cited text no. 12
13. Arciola CR, Campoccia D, Gamberini S, Donati ME, Pirini V, Visai L, et al. Antibiotic resistance in exopolysaccharide-forming Staphylococcus epidermidis clinica isolates from orthopaedic implant infevtions. Biomaterials 2005;26:6530-5.  Back to cited text no. 13
14. Koksal F, Yasar H, Samasti M. Antibiotic resistance patterns of coagulase-negative staphylococcus strains isolated from blood cultures of septicemic patients in Turkey. Microbiol Res 2009;164:404-10.  Back to cited text no. 14
15. Hiramatsu K, Cui L, Kuroda M, Ito T. The emergence and evolution of methicillin-resistance Staphylococcus aureus. Trends Microbiol 2001;9:486-93.  Back to cited text no. 15
16. Hiramatsu K, Katayama Y, Yuzawa H, Ito T. Molecular genetics of methicillin-resistance staphylococcus aureus. Int J Med Microbiol 2002;292:67-74.  Back to cited text no. 16
17. Chambers HF. Methicillin resistance in staphylococci: Molecular and biochemical basis and clinical implications. Clin Microbiol Rev 1997;10:781-91.  Back to cited text no. 17
18. York MK, Gibbs L, Chehab F, Brook GF. Comparison of PCR detection o mecA with standard susceptibility testing methods to determine methicillin resistance in coagulase-negative staphylococci. J Clin Microbiol 1996;34:249-53.  Back to cited text no. 18
19. Martins A, Cunha Mde L. Methicillin resistance in Staphylococcus aureus and coagulase-negative staphylococci: Epidemiological and molecular aspects. Microbiol Immunol 2007;51:787-95.  Back to cited text no. 19
20. Mirsalehian A, Jabalameli F, Alizadeh S. Comarison of disk agar diffusion susceptibility testing and PCR in detection of methicillin resistance Staphylococcus aureus. Tabriz Univ Med J 2003;61:420-5.  Back to cited text no. 20
21. Hedin G, Lofdahl S. Detecting methicillin-resistant Staphylococcua epidermidis-disc diffusion, broth breakpoint or polymerase chain reaction? APMIS 1993;101:311-8.  Back to cited text no. 21
22. Olsson-Liljequist B, Larsson P, Ringertz S, Lodhal S. Use of a DNA hybridization method to verify results of screening for methicillin resistance in staphylococci. Eur J Clin Microbiol Infect Dis 1993;12:527-33.  Back to cited text no. 22
23. McDonald CL, Maher WE, Fass RJ. Revised interpretation of oxacillin MICs for Staphylococcus epidermidis based on mecA detection. Antimicrob Agents Chemother 1995;39:982-4.  Back to cited text no. 23
24. Ferreria RB, Iorio NL, Malvar KL, Nunes AP, Fonseca LS, Bastos CC, et al. Coagulase-negative staphylococci: Comparison of phenotypic and genotypic oxacillin susceptibility tests and evaluation of the agar screening test by using different concentrations of oxacillin. J Clin Microbiol 2003;41:3609-14.  Back to cited text no. 24
25. Hussain Z, Stoakes L, Lannigan R, Lango S, Noncekivell B. Evaluation of screening and commercial methods for detection of methicillin resistance in coagulase-negative staphylococci. J Clin Microbiol 1998;36:273-4.  Back to cited text no. 25
26. Perazzi B, Fermepin MR, Malimovka A, Garcia SD, Orgambide M, Vay CA, et al. Accuracy of cefoxitin disk testing for characterization of oxacillin resistance mediated by penicillin-binding protein 2a in coagulase-negative staphylococci. J Clin Microbiol 2006;44:3634-9.  Back to cited text no. 26
27. Rosser SJ, Alfa MJ, Hoban S, Kennedy J, Harding GK. Etest versus agar dilution fpr antimicrobiol susceptibility testing of viridans group streptococci. J Clin Microbiol 1999;37:26-30.  Back to cited text no. 27
28. DeGiusti M, Pacifico L, Tufi D, Panero A, Boccia A, Chiesa C. Phenotypic detection of nosocomial mecA-positive coagulase-negative staphylococci from neonates. J Antimicrob Chemother 1999;44:351-8.  Back to cited text no. 28
29. Vannuffel P, Laterre PF, Bouyer M, Gigi J, Vandercam B, Reynaert M, et al. Rapid and specific molecular identification of methicillin-resistant Staphylococcus aureus in endotracheal aspirates from mechanically ventilated patients. J Clin Microbiol 1998;36:2366-8.  Back to cited text no. 29
30. Caierao J, Superti S, Dias CA, d'Azevedo PA. Automated systems in the identification and determination of methicillin resistance among coagulase negative staphylococci. Mem Inst Oswaldo Cruz 2006;101:277-80.  Back to cited text no. 30
31. Stefani S, Varaldo PE. Epidemiology of methicillin-resistant staphylococci in Europe. Clin Microbiol Infect 2003;9:1179-86.  Back to cited text no. 31
32. Rupp ME, Archer GL. Coagulase-negative staphylococci: Pathogens associated with medical progress. Clin Infect Dis 1994;19:231-43.  Back to cited text no. 32
33. Martins A, Cunha Mde L. Methicillin resistance in Staphylococcus aureus and coagulase-negative staphylococci: Epidemiological and molecular aspects. Microbiol Immunol 2007;51:787-95.  Back to cited text no. 33
34. Oliveira AD, d'Azevedo PA, de Sousa LB, Viana-Niero C, Francisco W, Lottenberg C, et al. Laboratory detection methods for methicillin resistance in coagulase negative Staphylococcus isolated from ophthalmic infections. Arq Bras Oftalmol 2007;70:667-75.  Back to cited text no. 34
35. Nam MH, Woo HY, Lee JH, Lee NY. Comparison of mecA gene detection with susceptibility testing methods in coagulase negative Staphylococcus according to the new NCCLS guidelines. Korean J Clin Microbiol 2000;3:57-61.  Back to cited text no. 35
36. Sharma V, Jindal N, Devi P. Prevalence of methicillin resistant coagulase negative staphylococci in a tertiary care hospital. Iran J Microbiol 2010;2:185-8.  Back to cited text no. 36
37. Tveten Y, Jenkins A, Digranes A, Melby KK, Allum AG, Kristiansen BE. Comparison of PCR detection of mecA with agar dilution and E-test for clinical isolates of coagulase negative Staphylococci. Clin Microbiol Infect 2004;10:459-70.  Back to cited text no. 37
38. Swenson JM. News test for detection of oxacillin resistant Staphylococcus aureus. Clin Microbiol 2002;24:159-62.  Back to cited text no. 38
39. Gerberding JL, Miick C, Liu HH, Chambers HF. Comparison of conventional susceptibility tests with direct detection of penicillin-binding protein 2a in borderline oxacillin-resistant strains of Staphylococcus aureus. Antimicrob Agents Chemother1991;35:2574-9.  Back to cited text no. 39