Meropenem

Antimicrobial susceptibility testing was performed using the Kirby-Bauer disk diffusion method, adhering to Clinical and Laboratory Standards Institute (CLSI) guidelines [26 ]. The selection of antibacterial disks was based on CLSI 2022 recommendations and availability. The bacterial inoculum, equivalent to 0.5 McFarland standards, was uniformly spread onto Mueller–Hinton agar plates (Himedia India) using a sterile cotton swab applicator. Antibiotic disks for gram-positive bacteria were penicillin G (10 μg), nitrofurantoin (300 μg), ciprofloxacin (5μg), trimethoprim-sulfamethoxazole (1.25/23.75 μg), gentamicin (10 μg), cefoxitin (30 μg), and clindamycin (30 μg) (Himedia, India).
The antimicrobial disks for Enterobacteriaceae included piperacillin-tazobactam (100/10 μg), ampicillin (10 μg), nitrofurantoin (300 μg), amoxicillin-clavulanate (20/10 μg), gentamicin (10 μg), cefotaxime (30 μg), ciprofloxacin (30 μg), meropenem (10 μg), piperacillin (100 μg), cefepime (30 μg), amikacin (30 μg), trimethoprim-sulfamethoxazole (1.25/23.75 μg), ceftazidime (30 μg), and ceftriaxone (30 μg) (Himedia, India). Antimicrobial disks for Pseudomonas spp and Acinetobacter were gentamicin (10 μg), meropenem (10 μg), ceftazidime (30 μg), piperacillin-tazobactam (100/10 μg), ciprofloxacin (5 μg), and amikacin (30 μg) (Himedia, India).

Isolated yeast strains were tested against 30 antibiotics with different modes of actions such as amikacin (MD001), amoxycillin (MD002), azithromycin (MD004), benzyl penicillin (MD062), cefalexin (cephalexin) (MD014), cefepime (MD070), cefotaxime (cephotaxime) (MD064), chloramphenicol (MD016), ciprofloxacin (MD017), erythromycin (MD022), gemifloxacin (MD076), gentamicin (MD061), kanamycin (MD026), levofloxacin (MD027), methicillin (MD031), moxifloxacin (MD033), neomycin (MD036), norfloxacin (MD038), ofloxacin (MD039), pefloxacin (MD040), polymyxin-B (MD043), rifampicin (MD045), roxithromycin (MD046), streptomycin (MD048), sulphadiazine (MD050), sulphamethizole (MD052), teicoplanin (MD055), vancomycin (MD060), tetracycline (MD056), meropenem (SD727) (Himedia, Mumbai, India) with standard antibiotic concentration previously determined by testing against pathogens [17 (link)]. The diameter of the inhibition zone was measured after 48 h of incubation at 30 °C.

Antibiotic susceptibility tests of all isolates were performed using Kirby Bauer disc diffusion method on Mueller-Hinton Agar with recommended antibiotics by CLSI 2020 guidelines [14 ].The antibiotics used were gentamicin (GEN,30 µg), amikacin (AK, 10 µg), ciprofloxacin (CIP, 5 µg), ceftazidime (CAZ, 30 µg), cefepime (CPM, 30 µg), aztreonam (AT, 30 µg), imipenem (IPM, 10 µg), piperacillin (PI,30 µg), piperacillin-tazobactam (PIT), meropenem (MRP, 10 µg), ofloxacin (OF, 30 µg), Levofloxacin (LEV, 30 µg) and colistin (CL,10 µg) from Hi-Media, Laboratories Pvt. Ltd. India.
Isolates that were non-susceptible to at least one agent in ≥ 3 antimicrobial categories have been categorized under MDR [15 (link)].

The isolates positive for at least one virulence marker gene by PCR were subjected to antimicrobial susceptibility test against the selected antimicrobials (ampicillin-10 μg, amikacin-10 μg, chloramphenicol-30 μg, ceftriaxone-10 μg, cephalexin-30 μg, ciprofloxacin-10 μg, co-trimoxazole-25 μg, cefoperazone-tazobactam-75 + 10 μg, meropenem-10 μg, norfloxacin-10 μg, gentamicin-10 μg, cefixime-5 μg, doxycycline hydrochloride-10 μg and ofloxacin-5 μg) (HiMedia, India) by disc diffusion method in Mueller–Hinton agar [18 (link)]. The performance of this test was checked by employing E. coli ATCC 25922 as a standard quality control strain. The results were expressed as sensitive, intermediate and resistant as per standard CLSI guidelines [19 ]. MDR was defined as “acquired non-susceptibility to at least one agent in three or more antimicrobial categories” [20 (link)].