Boronic acid disk diffusion for the phenotypic detection of polymerase chain reaction-confirmed, carbapenem-resistant, gram-negative bacilli isolates

Background: The Middle East is regarded as a secondary reservoir for OXA-48 and New Delhi metallo-beta-lactamase (NDM) carbapenemases. One of the main challenges in clinical microbiology diagnostics is the detection of carbapenemases. For this reason simple screening methods have been sought to detect carbapenemase producers to determine appropriate therapeutic measures and implement infection control interventions. The present study aimed to evaluate the efficacy of the modified Hodge test (MHT) and a boronic acid-based combined disk test using carbapenems as substrates for the phenotypic determination of OXA-48 and NDM type carbapenemases in 45 epidemiologically unrelated carbapenem-resistant clinical isolates of Klebsiella pneumoniae (13 isolates), Acinetobacter baumanii (20 isolates), and Pseudomonas aeruginosa (12 isolates). Results: Boronic acid disk test using meropenem as substrate and 600 mu g of 3-aminophenylboronic acid (APB) was the most sensitive method (83.33 %) for detection of OXA-48, while the most specific method was MHT (100 %). As regards NDM carbapenemase, boronic acid disk tests using imipenem and 600 mu g of APB per disk, and meropenem with 300 or 600 mu g of APB were the most sensitive methods (87.50 %), while the most specific method was the MHT (100 %). Conclusions: The results of the present study indicate that phenotypic screening with the MHT and the boronic acid disk test may be used to detect OXA-48 and NDM carbapenemases in Gram-negative bacilli clinical isolates, and that these tests can be easily applied in tertiary care settings with minimal infrastructure.