Comparison of broth microdilution, E-test, and agar disk diffusion methods for antimicrobial susceptibility testing of Lactobacillus acidophilus group members

BOKU - University of Natural Resources and Applied Life Sciences, Dept. of Food Science and Technology, Division of Food Microbiology and Hygiene, Gregor Mendel Straße 33, A-1180 Vienna, Austria; Division of Food Quality Assurance, Muthgasse 18, A-1190 Vienna, Austria; UGent - Ghent University, Faculty of Sciences, Laboratory of Microbiology, K. L. Ledeganckstraat 35, B-9000 Gent, Belgium

^* To whom correspondence should be addressed. Email: konrad.domig{at}boku.ac.at.

	Abstract

In recent years, the absence of acquired antimicrobial resistance has become an important criterion to evaluate the biosafety of lactobacilli used as industrial starter or probiotic cultures. At present, however, standards for susceptibility testing of Lactobacillus strains or approved guidelines for interpreting the test results are not available. Hence, this study was carried out to contribute to the establishment of a standardized procedure for antimicrobial susceptibility testing of lactobacilli. The results obtained by testing 104 strains of the Lactobacillus acidophilus group were compared based on broth microdilution, disk diffusion and Etest. Except for some specific agent-related effects, agreement between MIC values resulting from the broth microdilution method and the Etest was good. In addition, inhibition zone diameters determined with disk diffusion correlated well with MICs of Etest and broth microdilution.