Disk tests incorporating boracic acid inhibitor to detect KPC in Klebsiella pneumoniae

Objective To evaluate the disk tests incorporating boracic acid inhibitor for the detection of Klebsiella pneumoniae carbopenem(KPC)-producing Klebsiella pneumoniae isolates.Methods A total of 36 genetically unrelated KPC-producing Klebsiella pneumoniae isolates were determined.The minimum inhibitory concentrations(MIC) of imipenem,meropenem and ertapenem were determined by agar dilution method.Polymerase chain reaction(PCR) and DNA sequencing were used for the identification of beta-lactamase genotypes.The modified Hodge test(MHT),using both standard and high inoculum of test organisms,was performed to detect carbopenem phenotype.The disk tests consisting of 8 antibiotics with and without boracic acid inhibitor were designed to detect KPC phenotype,and the diameter≥5 mm augmentation of inhibition zone was considered a positive result.Results All 36 KPC-producing Klebsiella pneumoniae isolates were resistant to at least one of the 3 carbopenems.The sensitivity and specificity of MHT were 97.2% and 91.0% for the detection of carbopenems,and they were 100.0% and 87.0% when a high inoculum was employed.For disk tests using cefepime,imipenem or meropenem with and without boracic acid detecting KPC phenotype in Klebsiella pneumoniae,the sensitivity and specificity were 100.0%.Conclusions Disk tests incorporating boracic acid inhibitor in combination with cefepime,imipenem or meropenem may help the phenotypic detection of KPC in Klebsiella pneumoniae,and are very easy to perform and interpret.