Other antibiotics included cefepime (FEP, 30 μg), aztreonam
(AZT, 30 μg), and cefoxitin (FOX, 30 μg). β-lactam/β-lactamase LXH254 inhibitor combinations included amoxicillin/clavulanic acid (AMC, comprising amoxicillin 20 μg and clavulanic acid 10 μg), ampicillin/sulbactam (AMS) combinations in rations of 20 μg and 10 μg respectively, and piperacillin/tazobactam (TZP) in potency ratio of 100/10 μg respectively. Trichostatin A purchase Imipenem (IM 30 μg) was used to test susceptibility to carbapenems. Detection and Interpretation of β-lactamase phenotype Two strategies were used for detection of β-lactamase phenotypes as detailed in the CLSI guidelines , and in other related studies . The first strategy MEK162 cell line was the double-disc synergy test (m-DDST) in which the β-lactam antibiotics were placed adjacent to the amoxicillin/clavulanic (AMC) disc at inter-disc distances (centre to centre) of 20 mm. A clear extension of the edge of the disc zones towards the AMC (ghost zones or zones of synergy) was interpreted as positive for ESBL production. In the combined
disc method (CDM), tests were first done using β-lactam antibiotics and then repeated using discs containing combinations of β-lactam/β-lactamase inhibitors. A result indicating a ≥ 5 mm increase in zone diameter for the β-lactam/β-lactamase inhibitor disc was interpreted as production of ESBLs [45, 46]. The results from the m-DDST and CDM methods were also used for empiric categorization of strains into NSBL-, IRT-, ESBL- CMT- and pAmpC-like β-lactamase phenotypes as detailed before . PCR detection of β-lactamase genes Preparation of DNA used as template in PCR reactions was obtained by boiling bacteria suspension from an 8 hr culture at 95 °C for 5 minutes. The supernatant was stored at -20o C until further use. Subsequent PCR amplifications were carried out in a final volume of 25
μL or 50 μL. A minimum of 5 μL of template DNA and 1 μL of 10 mM concentration of both forward and reverse primers were used in PCR reactions. Isolates from Decitabine our collection that had been found to carry various bla genes in past studies [24, 27, 47], were used as positive controls in PCR screening for genes of interest. Sterile distilled water or E. coli strains susceptible to all β-lactam antibiotics were used as negative controls. PCR products were analyzed using electrophoresis in 1.5 % agarose gels and stained with ethidium bromide. Visualization of the PCR products was done under UV light and the image recorded with the aid of a gel documentation system (Bio-Rad Laboratories, Hercules, CA, USA). Selection of isolates for further analysis Isolates from each phenotype were selected for further analysis using PCR and sequencing strategies. For phenotypes with a high number of isolates (i.e. more than a hundred strains), at least 56% of the isolates were selected for further analysis.