Antimicrobial efficacies for metal ions and graphene-based compounds against klebsiella pneumoniae, acinetobacter baumannii and enterococcus faecium in the absence and presence of conditioning films

Vaidya, Misha Yogeshchandra (2019) Antimicrobial efficacies for metal ions and graphene-based compounds against klebsiella pneumoniae, acinetobacter baumannii and enterococcus faecium in the absence and presence of conditioning films. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

The occurrence and transmission of antimicrobial resistant (AMR) bacteria in the health-care and community settings is rising. With the lack of newer antibiotics in the pipeline and increasing resistance for the existing antibiotics and biocides that are available, it is estimated that the mortality rate due to non-treatable infections might rise to 10 million by 2050. This AMR related problem can be in part controlled by the discovery of novel antimicrobial sources. This study investigated the use of metal ions and graphene-based compounds (GBCs) singularly and in combination as potential antimicrobial agents against three medically related pathogens (Klebsiella pneumoniae, Acinetobacter baumannii and Enterococcus faecium). In order to determine the compounds efficacy in conditions that resembled those more found in vivo, the antimicrobials were also tested in the presence of 10 % bovine plasma conditioning films (CF). Moreover, the antimicrobial efficacies of the compounds were evaluated against two bacterial phenotypes, planktonic and biofilm. The preliminary antimicrobial efficacy screening was performed for fifteen metal ions and fourteen graphene based compounds (GBCs) using zone of inhibition, minimum inhibitory concentration and minimum bactericidal concentration assays in the absence and presence of 10 % plasma CF. Five metal ions (Ag, Cu, Pt, Au and Pd) and four GBCs (GO, AgGO, AuGO and PdGO) were selected for physical, chemical and elemental analysis using scanning electron, Raman and electron dispersive X-ray microscopy respectively. The antimicrobial agents were combined to determine synergistic effects using fractional inhibitory and bactericidal concentration assays. A crystal violet biofilm assay was used to analyse the antibiofilm efficacies. A biotoxicity evaluation using skin fibroblast cell lines was tested using an MTT assay. The results demonstrated that overall, the most active antimicrobial agents were Ag, Pt, Pd and Au ions amongst tested metal ions and AgGO amongst tested GBCs, but their antimicrobial activity was dependent on whether the form of the bacteria was planktonic or biofilm. In some cases, the presence of a CF had an adjuvant effect on the antimicrobial activity of the metal ions or GBCs. Palladium ions amongst the metal ions and PdGO amongst the GBCs demonstrated the least cell toxicity. Enterococcus faecium was the most resistant bacteria in all the tests. These results suggest that metal ions, and metal ion combinations with GO, or other metal ions possess the potential to be used as biocides or in topical applications as antimicrobials, however the effect of tested samples on cell toxicity is a significant concern.