Fixed concentrations of Selleckchem Sapitinib 4 mg/L of tazobactam or clavulanic acid were used in combination with piperacillin and cefepime, respectively. The results were interpreted according to the EUCAST breakpoints [17]. Isolates lacking ESBL were selected for this study if resistant to at least three of the following agents: amoxicillin, amoxicillin-clavulanic acid, nalidixic acid, gentamicin or tobramycin and trimethoprim-sulfamethoxazole. E. coli ATCC 25922 and K. pneumoniae ATCC 700603 were used as control strains in susceptibility testing
assays. Phylogenetic grouping of the 200 isolates was determined by multiplex PCR, as described by Clermont et al. [19]. Clonal relationship was determined by Rep-PCR as previously described [20]. Amplicons were run in a 1.5% agarose gel for 100 min, stained with ethidium bromide (Sigma Chemical CO. St. Louis, USA) and photographed. Two isolates were considered to be clonally unrelated when at least two different Selleckchem SC79 bands were observed. Clonal relationship among isolates was also determined by XbaI-PFGE [21]
when ESBL-producing isolates showed the same Rep-PCR pattern than isolates lacking ESBL, these isolates were also analysed by MLST, and this assay was also performed for 40 isolates selected for the conjugation assay representing the most frequent Rep-PCR patterns of each E. coli collection (see below). Detection by PCR and sequencing of 7 housekeeping genes (gyrB, adk, purA, recA, PDK4 icd, mdh and fumC) were performed according to the E. coli MLST database
(http://mlst.ucc.ie/mlst/dbs/Ecoli). Plasmid profile and hybridization experiments After observing that some isolates with the same Rep-PCR pattern presented different clinical categories of at least two antimicrobial agents of different classes, 69 Ec-ESBL isolates and 45 Ec-MRnoB isolates were selected for plasmid analysis and detection of plasmid-mediated genes coding for resistance to β-lactams and quinolones, according to the following criteria: a) all isolates from each Rep-PCR pattern with single isolates, b) one isolate of each antimicrobial susceptibility pattern from Rep-PCR patterns containing >=2 isolates. Plasmid DNA was extracted by the Kado-Liu method [22] and separated on 0.9% horizontal agarose gels electrophoresis. Plasmids R27 (169 kb, Genbank access AF250878), R1 (94 kb, Genbank access NC_003277), RP4 (55 kb, [23]), and ColE1 (6 kb, Genbank access J01566) were used as size standards. Plasmids were also ACY-738 characterized by PCR-based replicon typing (PBRT), as described elsewhere, using the respective PBRT controls [4, 5]. The obtained amplicons were sequenced to confirm their identity. Plasmids were transferred onto nylon membranes by southern blotting (Roche, Mannheim, Germany).