Original scientific paper

Factors affecting the antimicrobial susceptibility testing of bacteria by disc diffusion method

Marina Bubonja ; Department of microbiology and parasitology, School of medicine, University of Rijeka, Rijeka, Croatia
Maja Mesarić ; Department of microbiology and parasitology, School of medicine, University of Rijeka, Rijeka, Croatia
Ante Miše ; Department of microbiology and parasitology, School of medicine, University of Rijeka, Rijeka, Croatia
Marina Jakovac ; Department of microbiology and parasitology, School of medicine, University of Rijeka, Rijeka, Croatia
Maja Abram ; Department of microbiology and parasitology, School of medicine, University of Rijeka, Rijeka, Croatia

Abstract

Aim: The disc diffusion technique is used routinely for antimicrobial susceptibility testing of rapidly growing bacteria. However, in different European countries various national standards for antimicrobial testing are used to determine bacterial susceptibility. The aim of this study was to determine the influence of different conditions, as well as interpretation of results according to Clinical and Laboratory Standards Institute (CLSI) or British Society for Antimicrobial Chemotherapy (BSAC) on antimicrobial susceptibility testing.
Methods: Antimicrobial susceptibility of clinical isolates and quality control ATCC was tested by disc diffusion technique using different temperatures, incubation period, pH of agar medium and the size of bacterial inoculum.
Results: The great variations in the inhibition zone diameters and consequently in the interpretation of results were noticed in the case of Stenotrophomonas maltophilia. Cotrimoxazole susceptibility results varied significantly depending on standard applied. Inoculum density and alteration in pH value of the testing medium had effect on zone inhibition diameters of Staphylococcus aureus and Escherichia coli ATCC strains. The antibacterial activity of all examined antibiotics was affected by the alteration of acidity of the testing medium but aminoglycosides were the most affected by different pH.
Discussion and conclusions: The results of susceptibility testing depend on performance of standardized disc diffusion test method as well as on applied standards and protocols. Continuous quality control is essential in the recognition, resolution and avoidance of errors in used method. In addition, the harmonisation of national standards for antimicrobial susceptibility testing should aid detection and comparison of antibiotic resistance in Europe and elsewhere.

Keywords

antimicrobial susceptibility testing; bacteria; disk diffusion method

Hrčak ID:

31398

URI

https://hrcak.srce.hr/31398

Publication date:

1.12.2008.

Article data in other languages: croatian

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