Ampicillin

The antibiotic susceptibility profiling of the Salmonella isolates was determined by Kirby-Bauer disk diffusion method [16 (link)]. Seven different antibiotics were used in this study, namely, tetracycline (30 μg), chloramphenicol (30 μg), trimethoprim-sulphamethoxazole (25 μg), ciprofloxacin (5 μg), nalidixic acid (30 μg), ampicillin (10 μg), and ceftriaxone (30 μg) (Mast Group Ltd, Merseyside, UK). Antimicrobial susceptibility was done on Muller Hinton agar (Mast Group Ltd, Merseyside, UK) and Escherichia coli ATCC 25329 control strain was used. The diameter of zonal clearance was measured in millimeters and results were recorded as susceptible (S), intermediate (I), and resistant (R) according to CLSI, performance standards for antimicrobial susceptibility testing [17 (link)].

All isolates were examined for resistance to routine antimicrobial agents by standard disk diffusion method using Staphylococcus aureus (ATCC 25923) and Escherichia coli (ATCC 25922) as control strains (17 ). The antibiotics tested were gentamicin, amikacin, ceftazidime, ceftizoxime, cefotaxime, ceftriaxone, imipenem, ciprofloxacin, co-trimoxazole, chloramphenicol, penicillin, oxacillin, ampicillin, vancomycin, rifampicin and erythromycin (Mast Co, the UK). Isolates showing intermediate levels of susceptibility were classified as nonsusceptible.

Eight K. pneumoniae isolates were received from the Medical Microbiology laboratories of three hospitals in Armenia between January 2019 and August 2019. All isolates were recovered from various clinical specimens (urine, sputum, throat, blood, and stool) of hospitalized patients. The isolates were identified using a matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF-MS) as described previously (59 (link)).
All isolates were tested using a disk diffusion method for susceptibility to a panel of 11 antibiotics, including ampicillin (10 mg), piperacillin-tazobactam (30/6 mg), amoxicillin-clavulanic acid (20 and 10 mg, respectively), ceftazidime (10 mg), cefepime (30 mg), norfloxacin (10 mg), levofloxacin (5 mg), amikacin (30 mg), imipenem (10 mg), meropenem (10 mg), and chloramphenicol (30 mg) (Mast Group, Merseyside, United Kingdom) according to the European Committee on Antimicrobial Susceptibility Testing protocol (EUCAST v.6.0, 2017) (60 ). The antibiotics chosen were those most frequently used in clinical settings in Armenia. Isolates resistant to three or more antibiotic classes were considered multidrug resistant.