Objective: The coexistence of ESBLs and pAmpCs enzymes in the same Klebsiella strain may result in false-negativetests for the detection of ESBLs as pAmpCs resist inhibition by clavulanic acid so masking ESBL presence. This study wasto highlight the detection rates of ESBLs and pAmpCs by using phenotypic method; MAST 4-disc test and multiplexpolymerase chain reaction (PCR) method. In addition, it aimed to evaluate the sensitivity of the phenotypic method indetection of these enzymes.Methods: Klebsiella isolates were collected from clinical samples in different wards in Zagazig University Hospitals. Theantibiogram of these bacteria was determined by disc diffusion method. The presence of ESBLs and pAmpCs within theisolates was determined using the phenotypic MAST 4-disc test followed by a multiplex PCR method.Results: In total, 38 Klebsiella pneumoniae strains were evaluated. Among these isolates, 65.8% were ESBL producers,2.6% were pAmpC producers, and 31.6% were neither ESBL nor pAmpC producers. The most frequent genotype of ESBLwas CMY (84%); followed by CMY (44%) before pAmpC producers were of CMY genotype. The distribution of differentESBL genotypes was CMY, CMY and CTX-M II genotype (28%) and followed by CMY and CTX-M IV genotype (24%). Usingmultiplex PCR as a reference method, MAST 4-disc test was of 92% sensitivity and 86.7% specificity.Conclusion: A rising alarm of ESBL producing strains among K. pneumoniae isolates. The exact detection of ESBLs inisolates that produce both enzymes is important for both treatment and epidemiology. J Microbiol Infect Dis 2013; 3(1):24-30Key words: ESBL, pAmpC, Β-Lactasmases, Nosocomial, Klebsiell

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