Comparison of disc diffusion antibiotic sensitivity pattern and Minimum Inhibitory Concentration for meropenem resistant coliform isolates: can increasing the dosage give more coverage?
Keywords:
Broth micro dilution; coliforms; Enterobacteriaceae; meropenem resistance; MIC.Abstract
Objective Patients with hematological malignancies are vulnerable to Carbapenem Resistant Enterobacteriaceae (CRE) infections. Meropenem is a broadspectrum antibiotic used to treat Enterobacteriaceae infections. Determination of minimum inhibition concentration (MIC) using broth microdilution (BMD) is the gold standard in defining optimal treatment. The objective was to compare the disc diffusion antibiotic sensitivity pattern and MIC for the meropenem resistant coliform isolates at National Cancer Institute Maharagama, Sri Lanka. Materials and methods A total of 977 clinical isolates were collected and susceptibility to meropenem was assessed by the disc diffusion (DD) method. Out of that, 87 resistant coliform isolates were randomly selected and MICs were tested using the BMD method. For the blood culture isolates (n=32), results were also obtained using VITEK2 automated system and were compared with BMD and DD results. Results Out of 494/977 (50.6%) meropenem resistant isolates, majority were resistant to coliforms (67.2%). A total of 87 meropenem resistant coliform isolates by DD method were further analyzed, out of which 85.1% (n=74) were resistant, 13.8% (n=12) were intermediate and 1.19% (n=1) were sensitive by the BMD method. No significance difference between the DD method and the BMD method was observed (P>0.05). Out of 32 blood culture isolates that were resistant by the DD method, one was sensitive and one was intermediate by VITEK2 method. Error analysis of blood culture isolates showed very major errors between BMD and VITEK2 ( 3.13%) in one sample while frequent major errors in DD and VITEK2 compared with the BMD, which ranged from 3.13 % to 18.75% repectively. Conclusion Increasing the dose based on the MICs will result in the susceptibility in few of the isolates which were previously detected as resistant by the DD method. It can be further hypothesized that for the isolates with MICs above the therapeutic dose, alternative strategies such as combination therapy of meropenem and the development of novel antibiotics, are needed for the effective management of meropenem resistant strains.
Bangladesh Journal of Medical Science Vol. 25 No. 04 October’26 Page: 1220-1226
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Copyright (c) 2026 Nishadi Jayathilaka, Chayani Welagedara, Chathurnima Perera, Rukshika Costa, Nadun Kalinga, Varuna Navaratne, Samanmalee Gunasekara, Thamarasi Senaratne
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