Detection of carbapenem resistance due to outer membrane porin alteration in non carbapenemase producing E. coli and K. pneumoniae isolates from Mulago National Referral Hospital, Uganda
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Antimicrobial resistance is a global public health concern which compromises the use of antibiotics in the fight against microbes. Carbapenems are the most effective antibiotics for the treatment of clinical infections caused by Enterobacteriaceae, especially multi-drug-resistant strains. However, the emergence of carbapenem-resistant Enterobacteriaceae has become a major public health problem worldwide leading to limited treatment alternatives resulting in increased morbidities, mortalities and healthcare costs. This prompts for a need to clarify the resistance mechanisms as well as rapid and accurate detection of resistance if effective control is to be achieved. This study aimed at determining molecular mechanisms of carbapenem resistance in Escherichia coli and Klebsiella pneumoniae that are carbapenemase negative. A total of 87 isolates (47 E. coli and 40 K. pneumoniae) were screened for antimicrobial susceptibility by disc diffusion method. The 61 meropenem non-susceptible isolates were then screened for the production of carbapenemases, Extended Spectrum Beta Lactamases and AmpC enzymes phenotypically. The 28 carbapenemase negative isolates were then screened for outer membrane porin genes, followed by sequencing to detect mutations in the outer membrane porins. Out of 87 isolates, 28 (32.2%) were resistant to meropenem and 33 (37.9%) were intermediate. Among the 61 meropenem non-susceptible isolates, 36 (59%) were Extended Spectrum Beta Lactamase producers, 8 (13.1%) were AmpC producers, 23 (41.4%) were producing carbapenemases and 28 (45.9%) were carbapenemase negative. All the 28 carbapenemase negative isolates had at least one mutation in their outer membrane porin gene sequence that either resulted into a frame shift, deletion, insertion or substitution that led to early termination and production of truncated and non-functional protein, and/or produced an extended spectrum beta lactamase or AmpC enzyme. There is a high prevalence of carbapenem resistance in Mulago National Referral Hospital. Alteration of outer membrane porin proteins associated with production of extended spectrum beta lactamases and/or AmpC enzymes could have conferred carbapenem resistance in some of E. coli and K. pneumoniae isolates. There is need for the government to sensitize the public on proper antibiotic use. Healthcare workers should also prescribe appropriate antibiotics for effective treatment of carbapenem resistant infections.