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Comparison of minimum inhibitory concentration by broth microdilution testing versus standard disc diffusion testing in the detection of penicillin, erythromycin and ciprofloxacin resistance in viridans group streptococci

Biomedical Sciences Research Institute Computer Science Research Institute Environmental Sciences Research Institute Nanotechnology & Advanced Materials Research Institute

Maeda, Yasunori, Goldsmith, Colin E., Coulter, Wilson A., Mason, Charlene, Dooley, James, Lowery, Colm, Millar, B. Cherie and Moore, John E. (2011) Comparison of minimum inhibitory concentration by broth microdilution testing versus standard disc diffusion testing in the detection of penicillin, erythromycin and ciprofloxacin resistance in viridans group streptococci. JOURNAL OF MEDICAL MICROBIOLOGY, 60 (12). pp. 1782-1786. [Journal article]

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DOI: 10.1099/jmm.0.027573-0

Abstract

The aim of this study was to investigate the reliability of disc diffusion testing with penicillin, erythromycin and ciprofloxacin within the viridans group streptococci (VGS). In total, the antibiotic susceptibilities of 167 VGS isolates were compared by standard disc diffusion and broth microdilution methods, and these phenotypic data were compared to the carriage of the respective gene resistance determinants [ermB and mefA/E (macrolides); QRDR, gyrA, gyrB, parC and parE (quinolones)]. Overall, there were 35 discrepancies [resistant by MIC and susceptible by zone diameter (21.0%)] between MIC and disc diameter when penicillin susceptibility was interpreted by Clinical and Laboratory Standards Institute criteria. Scattergrams showed a bimodal distribution between non-susceptible and susceptible strains when erythromycin susceptibility was tested by both methods. Thirty-four (20.4%) isolates were categorized as resistant by MIC breakpoints, while disc diameter defined these as having intermediate resistance. With ciprofloxacin, three isolates (1.8%) showed minor discrepancies between MIC breakpoints and disc diameter. Isolates non-susceptible to all three antimicrobial agents tested were reliably distinguished from susceptible isolates by disc diffusion testing, except for the detection of low-level resistance to penicillin, where broth microdilution or an alternative quantitative MIC method should be used. Otherwise, we conclude that disc diffusion testing is a reliable method to detect strains of VGS non-susceptible to penicillin, erythromycin and ciprofloxacin, as demonstrated with their concordance to their gene resistance characteristics.

Item Type:Journal article
Faculties and Schools:Faculty of Life and Health Sciences
Faculty of Life and Health Sciences > School of Biomedical Sciences
Research Institutes and Groups:Biomedical Sciences Research Institute
Biomedical Sciences Research Institute > Northern Ireland Centre for Food and Health (NICHE)
ID Code:22141
Deposited By:Professor James Dooley
Deposited On:15 May 2012 13:22
Last Modified:17 May 2012 11:02

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