E strips

For initial screening, antimicrobial susceptibility testing was performed with 16 antimicrobial agents (HiMedia Laboratories Mumbai, India) namely; norfloxacin (10 μg), cefotaxime (30 μg), imipenem (10 μg), meropenem (10 μg), ceftazidime (30 μg), aztreonam (30 μg), nalidixic acid (30 μg), amoxicillin (20/10 μg), gentamicin (10 μg), ciprofloxacin (5 μg), ampicillin (10 μg), amikacin (30 μg), polymixin B (300 units/disc), cefotaxime + clavulanic acid (30/10 μg), ceftriaxone (30 μg) and Piperacillin+tazobactam (100/10 μg) on Mueller-Hinton agar plates by the Kirby Bauer disc diffusion method as per CLSI guidelines (CLSI, 2012 ) and later minimum inhibitory concentration (MIC) by E-strips (HiMedia Laboratories Mumbai, India) was performed for confirmation. Multidrug resistant (MDR) isolates show resistance to ≥3 antibiotic classes (Magiorakos et al., 2012 (link)). Escherichia coli (ATCC) strain 25922 was included as a quality control.

In this study the strains WT, ΔkpnGH, ΔkpnGHΩkpnGH were examined for resistance to ampicillin: AMP (10 µg/ml), azithromycin: AZM (15 µg/ml), chloramphenicol: CHL (30 µg/ml), carbencillin: CAR (100 µg/ml), ciprofloxacin: CIP (5 µg/ml), colistin: CST (10 µg/ml), cefepime: CPM (30 µg/ml), ceftriaxone: CTR (30 µg/ml), cephalothin: CTX (10 µg/ml), ceftazidime: CAZ (30 µg/ml), doxycycline: DOX (10 µg/ml), doripenem: DOR (10 µg/ml), ertapenem: ETP (10 µg/ml), linezolid: LZD (10 µg/ml), levofloxacin: LVX (10 µg/ml), oxacillin: OXA (10 µg/ml), polymyxin B: PMB (300 µg/ml), streptomycin: STR (10 µg/ml), tetracycline: TET (30 µg/ml), tigecycline: TGC (10 µg/ml), ticarcillin: TIC (75 µg/ml), tobramycin: TOB (10 µg/ml) and trimethoprim: TMP (5 µg/ml) by using commercial discs (Hi Media, Bombay, India) as described previously according to the interpretation criteria recommended by the Clinical and Laboratory Standards Institute CLSI. E. coli ATCC 25922 was used as a reference strain (control) as recommended [23] (link), [24] . MIC of antibiotics was tested using E-strips (Hi Media, Bombay, India). Interpretation was done as per the criteria approved by the CLSI [25] .