الفهرس 
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Abstract
Metallo-β lactamases have recently emerged as one of the most worrisome resistance mechanisms owing to their capacity to hydrolyze with the exception of aztreonam, all β-lactams including carbapenems. Their genes are carried on highly mobile elements, allowing easy dissemination and are difficult to detect, posing significant risks due to their ability to participate in horizontal MBL gene transfer. There are no standardized methods for detecting MBLs carrying organisms and despite PCR being highly accurate and reliable, its accessibility is often limited to reference laboratories. Several non molecular techniques have been studied, all taking advantage of the enzyme’s zinc dependence by using chelating agents, to inhibit its activity.
The present study aimed to evaluate imipenem- EDTA CDT and imipenem -EDTA DDST (in comparison to MBLs E-test) as simple reliable inexpensive methods for phenotypic detection of MBLs production by Gram negative bacilli.
This study included 115 isolates of Gram negative bacilli obtained from various clinical samples including urine, pus from wounds, LRT samples, burn exudates, blood, vaginal discharge, purulent ascitic fluid, purulent pleural effusion and ear discharge. The most common isolated pathogen was Ps. aeruginosa (39%), followed by A. baumanni (19%), then E.coli (15.7%), Klebsiella (13%), Proteus (12%) and Serratia (1%).
Out of the 115 Gram negative isolates, 31 (27%) showed resistance to imipenem (16 isolates of Ps. aeruginosa, 12 A. baumannii, 2 E.coli spp. and 1 Klebsiella spp.). The most common samples from which the imipenem resistant isolates were isolated were pus from wounds (29%), followed by urine and LRT samples (22.6%) then burn exuadate (16%), blood samples (6.5%) and finally purulent pleural effusion sample (3.2%).
The imipenem resistant isolates showed high resistance to piperacillin (96%), followed by piperacillin/tazobactam, amikacin, cefepime and gentamycin (84%). Imipenem resistant isolates of Ps.aeruginosa in this study showed maximum resistance to piperacillin (100%), followed by ceftazidime (94%), amikacin (87.5%), piperacillin/ tazobactam (81%), then cefepime (75%) and finally ciprofloxacin (56%), while imipenem resistant A.baumannii showed 100% resistance to ceftazidime, ceftriaxone and ciprofloxacine, 92% resistance to both piperacillin and cefepime, 83.3% resistance to both gentamycin and piperacillin/tazobactam, 75% resistance to amikacin, ampicillin/sulbactam and tobramycin. The least resistance was observed to both tetracycline and trimethoprim/ sulfamethoxazole (58.3%).
Phenotypic detection of MBLs production among imipenem resistant isolates was done by imipenem-EDTA CDT, imipenem-EDTA DDST and MBL E-test. The present study found that all the 31 imipenem resistant isolates gave positive results with both imipenem-EDTA CDT and MBL E-test (100% sensitivity), while DDST gave positive results in 14 out of the 31 isolates (45.2% sensitivity) (all were Ps. aeruginosa isolates). None of the imipenem resistant A.baumannii and Enterobacteriacae isolates gave positive results by DDST.
The study found that CDT was more sensitive than DDST.CDT gave same results when compared to MBL E-test, but given the cost constraints of the E-test, CDT is more convenient as a routine screening method for MBLs detection in microbiology laboratories.