Ceftriaxone

The antimicrobial susceptibility of the isolates to 17 antimicrobial agents was determined on Mueller–Hinton agar (Oxoid, UK) using the Kirby Bauer disc diffusion method, according to the guidelines of the Clinical and Laboratory Standards Institute (CLSI, 2020). The tested antimicrobial agents (Bioanalyse, Turkey) included Amoxicillin/clavulanate (30 µg), cefepime (30 µg), cefotaxime (30 µg), cefoxitin (30 µg), ceftriaxone (30 µg), ceftazidime (30 µg), aztreonam (10 µg), imipenem (10µg), amikacin (30 µg), gentamicin (10 µg), ciprofloxacin (5 µg), tetracycline (30 µg), trimethoprim 1.25 µg/sulphamethoxazole 23.75 µg (SXT, 25 µg), chloramphenicol (30 µg), nitrofurantoin (300 µg), and tigecycline (15 µg). The broth microdilution assay was used to determine the minimum inhibitory concentrations (MICs) of colistin. The breakpoints proposed by the European Committee on Antimicrobial Susceptibility Testing [34 ] were used for interpreting the antimicrobial susceptibility tests of tigecycline and colistin. MDR and XDR phenotypes were inferred according to the definitions of Magiorakos et al. [35 (link)].

Altogether n = 155 identified uropathogenic E. coli (UPEC) were collected during the period of August 2012 to August 2014, from Pakistan Institute of Medical Sciences. Ethical Review Board (ERB) of Pakistan Institute of Medical Sciences approved this study. Ethical Review Board approved verbal consent taken from all the patients. Important patient data such as name, age, gender, location was recorded and unique identification number were assigned to each patient. Samples were from community-acquired urinary tract infections. Antibiotic testing and phenotypic detections of ESBL were performed by disc diffusion methods according to the guidelines CLSI, 2014 [13 ]. Isolates were tested for the susceptibility to 12 different classes of antibiotics including β-lactamase inhibitors (piperacillin tazobactam, amoxicillin-clavulanic acid), cephalosporins (ceftazidime, cefotaxime, ceftriaxone), fluoroquinolone (ciprofloxacin, levofloxacin), aminoglycosides (amikacin), trimethoprim sulfonamides, nitrofurantoin, and fosfomycin (BIOANALYSE, Turkey). Control strain E. coli ATCC 25922 was used in this assay.

The susceptibility of the confirmed E. coli isolates to thirteen antibiotics was examined according to the Kirby–Bauer disk diffusion method [27 ]. The antibiotics were obtained from Bioanalyse (Ankara, Turkey) and included ampicillin (10 μg), amoxicillin (25 μg), amoxicillin-clavulanic acid (30 μg), cephalexin (30 μg), ceftriaxone (30 μg), gentamicin (10 μg), kanamycin (30 μg), tetracycline (30 μg), chloramphenicol (30 μg), ciprofloxacin (5 μg), levofloxacin (15 μg), trimethoprim-sulphamethoxazole (25 μg), and nitrofurantoin (300 μg). For the test, fresh culture suspensions were standardised to 0.5 McFarland (equivalent to 8 log cfu/mL). Using sterile cotton swabs, sterile prepoured plate count agar (PCA) (Laboratorios CONDA, Madrid, Spain) plates were swabbed with standardised culture suspensions and incubated at 37°C for 1 h. Antibiotic discs were then placed on the agar surface and incubated at 37°C for 24 h. The diameter of the inhibition zone was measured in mm (Figure 1). Isolates were categorized as resistant, intermediate, or susceptible according to the guidelines of the Clinical and Laboratory Standard Institute [27 ]. The multiple antibiotic resistance (MAR) index was computed as a/b, where a is the number of antibiotics the isolate was resistant to and b is the total number of antibiotics to which the isolate was exposed [28 (link)].