ABSTRACT
Background: The recent emergence of pan-drug-resistant (PDR) K. pneumoniae strains hinders the success rate of treatment procedures for patients. High mortality, extended duration of hospitalization with high costs is associated with such infections. Discovery and identification of new drugs are inevitable to combat PDR clinical pathogens. We aim to identify and evaluate new compounds in vitro against a PDR clinical K. pneumoniae isolate using compounds of Pathogen Box and Pandemic Response Box from Medicines for Malaria Venture (MMV). Methods: The PDR strain was initially screened with the 601 compounds from both Boxes at 10 âµM concentration. Formation of dormant cells against the drug activity was assessed using persister assay. MIC was determined for the drugs inhibiting PDR K. pneumoniae during initial screening. Results: Five compounds were identified to inhibit the test strain. MMV1580854 (94.60 â%), MMV1579788 (94.65 â%), MMV1578574 (eravacycline; 93.13 â%), MMV1578566 (epetraborole; 95.29 â%) and MMV1578564 (96.32 â%) were able to exhibit a higher percentage of growth inhibition. Persisters were found to be growing in a range from 104 to 107 âCFU/ml. Minimum inhibitory concentrations (MIC) of all compounds were ≥ 2 âµM except for MMV1579788, which had a MIC of ≥ 5 âµM. Conclusion: Five novel compounds were identified against the highly evolved pan-drug-resistant K. pneumoniae. Among the five, epetraborole andMMV1578564 were identified as highly potent based on the persister frequency and MICs. The pan-drug resistant clinical isolate used in this study was found to be acting differently from the reference or wild type strains against the test compounds in a previous study.
ABSTRACT
BACKGROUND: Tolerance of gram negative pathogens toward last resort colistin is mediated by mcr genes and alterations in chromosomal mgrB via modification of lipopolysaccharide through the PmrAB and PhoPQ component system. Proteus sp., Morganella sp., Neisseria sp., Burkholderia sp. and Providencia sp. are intrinsic resistant to colistin drug. Recent reports have shown that colistin intrinsic resistant organisms harbor and act as reservoirs for mcr genes. AIM: To evaluate the presence of mcr-1 to mcr-5 genes and alterations in mgrB gene in intrinsic colistin-resistant gram negative bacteria isolated from chicken meat samples in Coimbatore district, Tamil Nadu, India. METHODS: One hundred chicken meat samples were collected during 2019-20. Samples were enriched and plated on MacConkey agar supplemented with colistin (2 µg/ml). The bacterial isolates were then identified using biochemical tests. DNA were extracted from isolates using the thermal lysis method. mcr-1 to mcr-5 and mgrB genes was detected using conventional PCR and agarose gel electrophoresis methods. RESULT AND CONCLUSION: The presence of mcr-1 to mcr-5 genes was found to be 23 % (23/100). mcr-1 and mcr-5 genes were not detected in sample isolates. 17/23 samples positive for mcr genes were also found to be carrying alterations in mgrB gene. Phenotypic characterization of these isolates revealed that these bacteria were belonging to colistin intrinsic resistant gram negative bacteria such as Proteus sp., Providencia sp., and Morganella sp. Intrinsic resistant bacteria could act as a potential reservoir and disseminate mcr genes to the colistin sensitive non-intrinsic pathogens of clinical importance in the environment.
