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- Al-Farsi, Hissa M., et al.
(författare)
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Effects of the Antimicrobial Peptide LL-37 and Innate Effector Mechanisms in Colistin-Resistant Klebsiella pneumoniae With mgrB Insertions
- 2019
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Ingår i: Frontiers in Microbiology. - : FRONTIERS MEDIA SA. - 1664-302X. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- Background Colistin is a polypeptide antibiotic drug that targets lipopolysaccharides in the outer membrane of Gram-negative bacteria. Inactivation of the mgrB-gene is a common mechanism behind colistin-resistance in Klebsiella pneumoniae (Kpn). Since colistin is a cyclic polypeptide, it may exhibit cross-resistance with the antimicrobial peptide LL-37, and with other innate effector mechanisms, but previous results are inconclusive. Objective To study potential cross-resistance between colistin and LL-37, as well as with other innate effector mechanisms, and to compare virulence of colistin-resistant and susceptible Kpn strains. Materials/Methods Carbapenemase-producing Kpn from Oman (n = 17) were subjected to antimicrobial susceptibility testing and whole genome sequencing. Susceptibility to colistin and LL-37 was studied. The surface charge was determined by zeta-potential measurements and the morphology of treated bacteria was analyzed with electron microscopy. Bacterial survival was assessed in human whole blood and serum, as well as in a zebrafish infection-model. Results Genome-analysis revealed insertion-sequences in the mgrB gene, as a cause of colistin resistance in 8/17 isolates. Colistin-resistant (Col-R) isolates were found to be more resistant to LL-37 compared to colistin-susceptible (Col-S) isolates, but only at concentrations >= 50 mu g/ml. There was no significant difference in surface charge between the isolates. The morphological changes were similar in both Col-R and Col-S isolates after exposure to LL-37. Finally, no survival difference between the Col-R and Col-S isolates was observed in whole blood or serum, or in zebrafish embryos. Conclusion Cross-resistance between colistin and LL-37 was observed at elevated concentrations of LL-37. However, Col-R and Col-S isolates exhibited similar survival in serum and whole blood, and in a zebrafish infection-model, suggesting that cross-resistance most likely play a limited role during physiological conditions. However, it cannot be ruled out that the observed cross-resistance could be relevant in conditions where LL-37 levels reach high concentrations, such as during infection or inflammation.
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| 2. |
- Al-Farsi, Hissa M
(författare)
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Multidrug-resistant Enterobacterales in Oman : molecular epidemiology and therapeutic insights
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The spread of antibiotic resistance is a concerning issue causing limited treatment options for bacterial infections, particularly with Gram-negative bacteria. Surveillance and epidemiological studies help to determine the magnitude of the problem as well as to establish early measures to slow down the spread of resistance and consequently increase antibiotic lifespan. Currently, there is a visible paucity of published data about resistance from the Arabian Peninsula. In this thesis, we studied a collection of carbapenem nonsusceptible E. coli (n=35) and K. pneumoniae (n=237) isolated in 2015 from various hospitals in Oman. We aimed at identifying resistance mechanisms, mapping the bacterial population structure, investigating bacterial fitness, and studying potential treatment options available to tackle infections caused by such multidrug-resistant strains. These aims were addressed in five papers as discussed below. NDM and OXA-48 were the only carbapenemases we found in this collection, both among E. coli (Paper I) and K. pneumoniae (Paper II). The pattern of resistance among the isolates from Arabian Peninsula mimics the pattern reported from the Indian subcontinent, most likely due to the close socioeconomic interactions between them. Both regions lack KPC enzymes, which are commonly seen in China and the US from strains belong to ST11 and ST258, respectively. Despite ST11 being predominant in this collection, we did not detect KPC. Yet, we detected a high-risk clone of E. coli, ST131-H30Rx-CTX-M-15. Additionally, we identified newly emerging clones of K. pneumoniae and E. coli such as ST231 and ST1193-H64RxC, respectively. Nearly 10% of the K. pneumoniae isolates in our collection were colistin resistant which prompted us to study the mechanisms of colistin resistance (Paper III). MgrB-inactivation by insertion elements was seen in 8 isolates while other mutations were seen in other chromosomal genes known to be involved in colistin resistance e.g. pmrB, phoPQ and crrB. However, we did not detect mcr genes. Collectively, the genetic alterations are thought to reduce the net negative charge in bacterial cell wall, hence lowering the binding affinity of colistin. Our data underscores that there is no reduction in the surface charge in colistinresistant K. pneumoniae, due to the MgrB-insertion (Paper IV). The genetic alteration might lead to other structural changes in the cell wall such as altering hydrophobicity, which required further investigation. Also, our data shows no difference in the survival rates of colistin resistant and susceptible strains in blood, serum and zebrafish model. Thus, gaining resistance against colistin does not infer a fitness cost in K. pneumoniae with MgrB-insertion (Paper IV). Additionally, colistin and LL-37 share similar binding mechanism which suggest there might be a cross-resistance between them. Our data supported this hypothesis, but only at high concentrations of LL-37 ( ≥ 50 mg/L) (Paper IV). Finally, we studied available options to treat infections caused by multidrug-resistant strains. Combining colistin and rifampicin showed good in vitro activity against multidrug-resistant strains of E. coli (Paper V) and K. pneumoniae (Paper III). To summarise, we conducted comprehensive genomic analysis of E. coli and K. pneumoniae isolates from Oman to reveal the resistance mechanism, their impact on bacterial cell structural and if there is a fitness cost inferred by the resistance mechanisms. Finally, we studied combination therapy as an available option at hand for tackling infections caused by multidrug-resistant strains.
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