The misuse of β-Lactam antibiotics results in major problem, microbial resistance against these antibiotics by expression of β-lactamases, facing its use. AmpCs are one of the β-lactamases which confer resistance to penicillins, cephalosporins, cephamycins, and aztreonam, and are not affected by classic β-lactamase inhibitors. Plasmid-mediated AmpC β-lactamases pose a major challenge to infection control because the AmpC gene can be expressed in larger quantities and has a high transmissibility to other bacterial species. This study aimed to detect plasmid mediated AmpC β-lactamases in gram negative isolates in Assiut university hospital. It was performed on 120 cefoxtin resistant isolates obtained from 300-gram negative isolates using the disc diffusion method as a screening test for AmpC production. Since the presence of pAmpC is often associated with the presence of ESBLs, phenotypic detection of ESBL was done using combined disc method and vitek2 compact 15. Phenotypic detection of AmpC was done by disc approximation method and inhibitor-based method using phenyl boronic acid (PBA). Genotypic detection of 5 plasmid mediated AmpC genes families (MOX, CIT, DHA, EBC, and FOX) was done by multiplex PCR. Our result showed that Klebsiella pneumoniae (62.5%) and Escherichia coli (25.8%) were the most frequent isolates. Only 15.8 %, 12.5%, 17.5% resistant isolates to cefoxitin were positive by using disc approximation test, inhibitor-based method using PBA (150 g/mL), and PBA (600 g/mL), respectively. Out of the 120 Cefoxitin-resistant isolates, 22 isolates (18.3 %) were positive by multiplex PCR. CIT and MOX were solely detected in 45.5% and 4.5%, respectively. CIT and FOX together were detected in 45.5%, CIT and DHA together in 4.5%. No isolate was positive for EBC gene. Finally, boronic acid test using 600 μg/mL PBA with 30µg ceftazidime, as phenotypic method for detecting AmpC β- lactamases, was ranked very good for marking negative tests.
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