Intra- and Interlaboratory Performances of Two Commercial Antimicrobial Susceptibility Testing Methods for Bifidobacteria and Nonenterococcal Lactic Acid Bacteria

Abstract

In a small-scale harmonization study involving nine laboratories in eight European countries, the intra-and interlaboratory performances of two commercially available systems, i.e., the VetMIC microplate system and Etest, for antimicrobial susceptibility testing of nonenterococcal lactic acid bacteria (NELAB) and bifidobacteria were analyzed. In addition, one laboratory also performed standard broth microdilution as a reference method. MICs of tetracycline, erythromycin, ampicillin, gentamicin, clindamycin, and streptomycin for the type strains of 25 species of NELAB and bifidobacteria and MICs of vancomycin for a selection of relevant taxa were determined. The previously described lactic acid bacterium susceptibility test medium (LSM) and related mixed-medium formulations, all including Iso-Sensitest broth as a basic component, were used as test media. The overall agreement of median MIC ranges ؎ 1 log 2 dilution determined by the VetMIC and Etest methods with the median MICs determined by the reference method was very good for tetracycline, ampicillin, and streptomycin (92.3 to 100%) but low for erythromycin (19.5 to 30.7%) and clindamycin (50.0 to 80.8%). There was a consensus among the participating laboratories that VetMIC was preferred over Etest because of its lower cost, better growth support, and more uniform criteria for MIC end point reading. With the range for acceptable intralaboratory reproducibility being defined as the median MIC ؎ 1 log 2 dilution, VetMIC results (with 69.2% of all data sets in the acceptable range) were shown to display greater reproducibility than Etest results (with 58.8% of all data sets in the acceptable range). Also at the interlaboratory level, the proportion of MIC values obtained with VetMIC that belonged to the complete agreement category (60.0%) was higher than the proportion of such values obtained with Etest (47.0%), which indicates a higher degree of interlaboratory reproducibility for the former method. Apart from some agent-specific effects, the majority of VetMIC and Etest replicate data sets were situated within a 1-to 2-log 2 dilution range, suggesting that the two methods can be considered to be equivalent for recognizing resistance phenotypes. This multicenter study has further validated the standard use of LSM and related mixed-medium formulations with commercially available systems and formed the basis for the ongoing development of the ISO 10932/IDF 223 standard for susceptibility testing of NELAB and bifidobacteria.

Functional Properties (Acid and Bile Tolerance) and Antibiotic Susceptibility of Lactic Acid Bacteria Isolated from Newborn Calves for the Design of a Probiotic Product

“…The standardization of the method for the assessment of antibiotic susceptibility and its interpretation was determined by different research groups [16,19,21,25,28,41,42], in order to generate a data base to establish and compare susceptibility profiles in different hosts and areas. Moreover, the selection of the technique is essential to determine the resistance criteria, as suggested by Mayrhofer et al [21], who compared the procedures of CLSI and ISO/ IDF Standard guides.…”

Human gut microbiota: does diet matter?

“…In addition, individual human responses may be different. Bifidobacteria are typically susceptible to the majority of clinically relevant antibiotics such as penicillins (β-lactam antibiotics), cephalosporins and macrolides (101)(102)(103)(104)(105)(106) , and most of the commensal gut bacteria (e.g. bifidobacteria, Bacteroides spp.)…”

Antimicrobial resistance of lactobacilli isolated from food

“…Klare et al (2005) developed lactic acid bacterium susceptibility test medium (LSM), a mixed formulation of IST broth (90% v/v) and MRS broth (10% v/v). This medium was used by Huys et al (2010) for antimicrobial susceptibility testing of non-enterococcal lactic acid bacteria (NELAB) and bifidobacteria in eight European countries and this study has further validated the standard use of LSM and formed the basis for the ISO 10932/IDF 223 from 2010 (standard for susceptibility testing of NELAB and bifidobacteria). Our study had begun before the publication of the International Standard, so the applied method is different from the ISO 10932:2010.…”