Phenotypic profiling of gram-negative bacilli using a new modified sketch of antibiotic disks

Abstract

The aim of the study was to achieve a simple and inexpensive standard routine laboratory phenotypic test, for a reliable detection of multidrug resistance in Enterobacteriaceae, Pseudomonas and Acinetobacter sp., in order to minimize the emergence of antimicrobial resistance in Gram negative bacteria. For this purpose, 89 clinical samples (gram negative bacilli) were collected from Saint Georges Hospital-Beirut (SGH), and (CHN) hospital - Zgharta- Lebanon. The antimicrobial susceptibility test was performed using a new sketch of antibiotics, to determine the resistance profile of each isolated strain and to identify the different betalactamases produced by these isolates. This technique was based on inoculating strains on four Muller-Hinton agar plates; each contains same sixteen different antibiotic disks placed in a certain distances. One agar plate was used as a plain plate that didnt contain any beta lactamase inhibitors. The second agar plate was impregnated with EDTA to confirm the production of MBL. The third agar plate was impregnated with PBA to confirm the production of KPC. The fourth agar plate was embedded with cloxacillin to confirm the production of AmpC. PCR was performed to test specific strains. High level of Antimicrobial resistance was reported among different isolates including Enterobacteriaceae, pseudomonas, and Acinetobacter. Among the 60 Enterobacteriaceae strains, 7 isolates were susceptible to all beta lactams agents, 50 isolates were ESBL producers, 2 isolates were AmpC producers, and one isolate was ESBL and AmpC coproducer. Regarding the 5 Pseudomonas isolates, one strain was susceptible to all beta lactam agents, one strain was KPC producer, one strain was MBL producer, and 2 strains were both MBL and KPC producer simultaneously. . Among the 24 Acinetobacter isolates, 6 strains were found susceptible to all beta lactam agents, 8 strains were found to be KPC producers, 4 strains were found MBL producers, one strain was found MBL and KPC producer simultaneously, 3 strains were ESBL producers, 1 strain was found both AmpC and ESBL producer, and one strain was both AmpC, ESBL and MBL producer. 8 strains out of the 24 Acinetobacter isolates were found to be OXA producers along with other beta lactamases. Our study reported that the phenotypic test evaluated gives reliable results in detecting various beta lactamases. The fact that makes it credible and potential for the standard detection of antimicrobial resistance in routine laboratories.