Antimicrobial susceptibility testing of clinical isolates of Staphylococcus aureus and Enterococcus spp. using two testing systems
Davies, Ann Louise
Cardiff Metropolitan University
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The performance of the BD Phoenix™ system was compared to the Epsilometer test® for a total of 154 non-duplicate gram positive clinical isolates, comprised of 95 Staphylococci and.60 Enterococci.Ttlre Antibiotic Susceptibility Testing values obtained using the Phoenix™ system, were compared with the Minimal Inhibitory concentration values measured using the Epsilometer test® method. The antibiotics investigated included: Daptomycin, Linezolid, Teicoplanin and Vancomycin. The Antíbiotic Susceptibility testing values for Daptomycin against S.aureus obtained via the Phoenix™ are in excellent agreement with the Epsilometer test®. The values obtained for Linezolid, Teicoplanin and Vancomycin against S.aureus produced values that differed by 0.5-1.5 mg/l dependent upon the method used. Nevertheless, this difference did not affect the final result and each isolate of S.aureus was still correctly identified as sensitive to all the test antibiotics with 100% accuracy. The sensitive isolates of Enterococci tested were identified as sensitive with 100% accuracy. The remaining several isolates of Enterococci that demonstrated resistance to the glycopeptide group of drugs Vancomycin and Teicoplanin were identified as resistant with 100% accuracy. The development of resistant Staphylococci and Enterococci to different classes of antimicrobials is increasing worldwide. Notably, glycopeptide resistance is an increasing threat among Enterococcal spp. As such clinical isolates have the potential to cause severe, often life threatening infections, the correct detection of VRE among Enterococci spp. is critical (4), for this reasons this study is of great importance. In addition if a microorganism is sensitive to a particular antibiotic this indicates that the patient should respond to therapy with that antibiotic, using the dosage established from AST, hence the importance of AST. The results of this study indicate that the Phoenix™ system when used in conjunction with the Epsilometer test® provides accurate Antibiotic Susceptibility Testing results, with numerous Staphylococci.and Enterococci isolates tested against various antibiotics. This concludes that both systems prove to be reliable methods for achieving accurate quantitative AST values of both clinical isolates.
BSc (Hons) Applied Biomedical Science
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