Susceptibility Testing of Anaerobic Bacteria: Evaluation of the Redesigned (Version 96) bioMérieux ATB ANA Device

Abstract

We compared the susceptibility results for 200 clinical anaerobes with nine antibiotics obtained by using a new ATB ANA (bioMérieux) device against those obtained by the National Committee for Clinical Laboratory Standards (NCCLS) standard agar dilution method. For better evaluation of the device, we added some resistant Bacteroides fragilis group strains from our own collection: 3, 6, and 12 strains that were resistant to imipenem, ticarcillin plus clavulanic acid, and co-amoxiclav, respectively, and 2 other strains with decreased susceptibility to metronidazole. For some strains that did not grow on ATB S medium, tests were performed by using West-Wilkins medium supplemented with 1.5% agar. The new ATB ANA device made clinical categorization of the investigated strains possible, according to French (Committee of the Antibiogram of the French Society of Microbiology) or U.S. (NCCLS) breakpoints, with the following respective results: category agreement, 94.3 and 94.9%; minor errors, 4.8 and 3.8%; major errors, 0.4 and 0.8%; and very major errors 4.6 and 4.2%. The ATB ANA device was able to detect low-level metronidazole-resistant B. fragilis strains according to the French breakpoints but not the NCCLS ones. For B. fragilis and β-lactamase-positive Prevotellastrains, the clustering effect of amoxicillin MICs around the French breakpoints led to more frequent minor errors. ATB ANA is a very convenient method to determine the antibiotic susceptibilities of anaerobes. Results obtained by ATB ANA correlated well with those obtained by the reference method.

Anaerobic bacteria in 118 patients with deep-space head and neck infections from the University Hospital of Maxillofacial Surgery, Sofia, Bulgaria

“…In addition, for Gram-positive anaerobes, there is no ampicillin breakpoint. The susceptibility breakpoint for Gram-positive anaerobes should be higher than that for Gram-negative anaerobes (Dubreuil et al, 1999). Therefore, although in the present study three Gram-positive anaerobic strains exhibited amoxicillin MICs of >1 mg ml 21 , they should not be considered as amoxicillin-resistant strains.…”

Incidence of Anaerobic Bacteria in 118 Patients with Deep-space Head and Neck Infections from the People’s University Hospital of Maxillofacial Surgery, Bhopal, India

“…The susceptibility breakpoint for Grampositive anaerobes should be higher than that for Gram-negative anaerobes. 8 Therefore, although in the present study three Gram-positive anaerobic strains exhibited amoxicillin MICs of >1µg ml -1 , they should not be considered as amoxicillinresistant strains.…”

Antimicrobial resistance of clinical isolates of anaerobic bacteria from a regional hospital in Costa Rica

“…Hence empirical therapies are used as treatments in these infections [1,2]. However, the emergence of resistance to antibiotics that are 62 commonly used as first-line therapies and the variations in susceptibility patterns in different countries, geographic areas and even among hospitals in the same area, have shown the need to carry out the AST more often [2][3][4][5]7,8].…”

“…The AST method recommended by the Clinical Laboratories Standards Institute (CLSI) is the agar dilution method, which should be performed to a group of strains isolated in a certain period [1]. Nonetheless, given the need to identify individual susceptibility in some isolates, many laboratories have shifted to the use of simpler methods such as the ATB-ANA (bioMérieux) and the E-test (AB Biodisk), the latter approved by the U.S. Federal Drug Administration [2,7,8].…”