Abstract
Acquired metallo-β-lactamases (MβL) are emerging determinants of resistance in Pseudomonas aeruginosa . The objectives of this study were to phenotypically detect MβL in P. aeruginosa collected in urology ward from Skikda hospital Algeria. A total of seventeen P. aeruginosa isolates were identified using API 20NE and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALD-TOFMS). Antibiotic susceptibility was performed using disk diffusion method on Muller-Hinton agar. The minimum inhibitory concentrations (MIC) of imipenem were determined by Etest method. Positively screened isolates were further subjected to four different methods phenotypic; Modified Hodge test (MHT), Imipenem-EDTA combined disk test (CDT), Imipenem-EDTA double-disk synergy test (DDST) and new biochemical method Modified Carba NP test (MCNP). Out of 32 (45.71%) isolates were resistant to imipenem; 20 (62,5%) isolates were MβL producing, 5 (15.62%) were carbapenemase class A or D producing, and 7 (21.87%) isolates were detected as negative test. Rapid detection of MβL-producing P. aeruginosa may help inappropriate antimicrobial therapy and avoid the development and dissemination of these strains. Thus far, the validation of a simple and accurate MβL detection method such as CDT, DDST and MCNP test, can be easily incorporated into the daily routine of a clinical laboratory. Key words: Phenotypic detection, Pseudomonas aeruginosa, Metallo-β-lactamases.  
Highlights
Pseudomonas aeruginosa is a well-known isolate in hospital settings, and has been frequently associated with nosocomial outbreaks among susceptible patients (Paterson, 2006)
Screened isolates were further subjected to four different methods phenotypic; Modified Hodge test (MHT), Imipenem-ethylenediaminetetraacetic acid (EDTA) combined disk test (CDT), Imipenem-EDTA double-disk synergy test (DDST) and new biochemical method Modified Carba NP test (MCNP)
Of the 70 isolates of P. aeruginosa, 37 (52.85%) were resistant to aztreonam, 45 (64.28%) to ceftazidim, 32 (45.71%) to cefepim, 40 (57.14%) to ticarcillin, 65 (92.85%) to ticarcillin/clavulanic acid, 27 (38.57%) to piperacilin, 32 (45.71%) to imipenem, 18 (25.71%) to amikacin, 40 (57.14%) to gentamicin, 33 (47.14%) to tobramicin, 27(38.57%) to nitilmicin, 49 (70 %) to nalidixic acid, 23 (32.85%) to ciprofloxacin, and all isolates were susceptible to colistin (Table 1)
Summary
Pseudomonas aeruginosa is a well-known isolate in hospital settings, and has been frequently associated with nosocomial outbreaks among susceptible patients (Paterson, 2006). Resistance to this novel antibiotic is increasing worldwide (Touati et al, 2013; Sefraoui et al, 2014; Hammami et al, 2011). Many carbapenemases have been identified in P. aeruginosa, including (1) KPC and GES variants of Ambler class A, (2) IMP-, VIM-, SPM-, GIM-, NDM-, and FIM-type metallo-β-lactamases (MβLs) of Ambler class B, and (3) OXA variant enzymes of Ambler class D (Poirel et al, 2010; El et al, 2011)
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