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. 2011 Jun;49(6):2262-5.
doi: 10.1128/JCM.02585-10. Epub 2011 Mar 30.

Strain-tailored double-disk synergy test detects extended-spectrum oxacillinases in Pseudomonas aeruginosa

Didier Hocquet  1 , Barbara Dehecq, Xavier Bertrand, Patrick Plésiat
Affiliations

Strain-tailored double-disk synergy test detects extended-spectrum oxacillinases in Pseudomonas aeruginosa

Didier Hocquet et al. J Clin Microbiol. 2011 Jun.

Abstract

The prevalence of class D extended-spectrum oxacillinases (ES-OXAs) in ceftazidime-resistant strains of Pseudomonas aeruginosa is often underestimated by double-disk synergy tests (DDST) using clavulanate. A DDST with a customized distance between a disk of ceftazidime or cefepime and inhibitors (clavulanate and imipenem) detected 14 out of 15 different ES-OXAs.

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Figures

Fig. 1.
Fig. 1.
Double-disk synergy test with P. aeruginosa isolates producing the extended-spectrum oxacillinases OXA-16 and OXA-142 (OXA-10 derived), OXA-28 and OXA-183 (OXA-13 derived), or OXA-32 and OXA-161 (OXA-2 derived) or overproducing the cephalosporinase AmpC (AmpC). Distances between the disks were adapted to each strain, based on the inhibition zone diameter around disks containing each compound tested separately. For instance, if no inhibition zone was noticed around clavulanate- and ceftazidime-containing disks, the distance between their two disks is 5 ± 1 mm. Abbreviations: FEP, cefepime (30 μg); AMC, amoxicillin-clavulanate (20/10 μg); CAZ, ceftazidime (30 μg); IMP, imipenem (10 μg). Interpretative results are given (see Table 1).
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