The minimum inhibitory concentration (MIC) as determined by the MHB microdilution method was used to evaluate the antimicrobial susceptibility of 500 UPEC clinical strains according to the guidelines of the Clinical and Laboratory Standards Institute (CLSI, 2016 ). MDR strains were defined as having acquired no susceptibility to at least one antibiotic in three or more classes. XDR strains were defined as having non-susceptibility to at least one agent in all but two or fewer antibiotic classes (Magiorakos et al., 2012 (link)). The MIC for each antibiotic was compared to the standard values of the CLSI. The antibiotic panel that was used included ampicillin (AM; Sigma-Aldrich, St. Louis, MO, USA), amoxicillin-clavulanate (AMC; Great West Road, Brentford Middlesex, UK), ticarcillin-clavulanate (TIM; Gold Biotechnology, Inc., Ashby Road, St. Louis, MO), piperacillin-tazobactam (TZP; Siemens Medical Solutions USA, Inc., Valley Stream Parkway, Malvern, PA, USA), cephalothin (CF; Eli Lilly and Company, S Harding St, Indianapolis, IN, USA), cefaclor (CEC; Phadia Laboratory Systems, Thermo Scientific, Wyman Street, Waltham, MA, USA), ceftazidime (CAZ; Roselle Rd, Schaumburg, IL, USA), aztreonam (ATM; Bristol-Myers Squibb Corporate, Park Avenue, NY, USA), norfloxacin (NOR), ofloxacin (OFX; MP Biomedicals, Solon, OH, USA), meropenem (MEM), imipenem (IPM; AstraZeneca Pharmaceuticals LP, Wilmington, DE, USA), gentamycin (GM; Schering-Plough Pharmaceuticals, Kenilworth, NJ, USA), ceftriaxone (CRO), trimethoprim-sulfamethoxazole (SXT; Roche, Basel, Switzerland), tetracycline (TE; Heritage Pharmaceuticals Inc., Fieldcrest Avenue, Edison, NJ, USA), and nitrofurantoin (F/M; McKesson Pharmaceutical, One Post Street, San Francisco, CA, USA). E. coli ATCC 25922 and Pseudomonas aeruginosa ATCC 27853 were used as controls.
The extended-spectrum beta-lactamases (ESBLs) were phenotypically detected as previously recommended by CLSI using the double-disc synergy test based on the synergistic effect between clavulanic acid (inhibitor of ESBLs) and β-lactam antibiotics (cefotaxime, CRO, CAZ, cefepime, cefpirome, and ATM). Additionally, ESBLs were detected using an individual disk that was tested with/without clavulanic acid (10 μg/mL) and by the Hodge test using Klebsiella pneumoniae ATCC 700603 (ESBL+) and E. coli ATCC 25922 (ESBL-) as control strains (CLSI, 2016 ).
The extended-spectrum beta-lactamases (ESBLs) were phenotypically detected as previously recommended by CLSI using the double-disc synergy test based on the synergistic effect between clavulanic acid (inhibitor of ESBLs) and β-lactam antibiotics (cefotaxime, CRO, CAZ, cefepime, cefpirome, and ATM). Additionally, ESBLs were detected using an individual disk that was tested with/without clavulanic acid (10 μg/mL) and by the Hodge test using Klebsiella pneumoniae ATCC 700603 (ESBL+) and E. coli ATCC 25922 (ESBL-) as control strains (CLSI, 2016 ).
Free full text: Click here
