Antibacterial activity of polyunsaturated fatty acids related to chronic wound infections

Eshlak, MS 2019, Antibacterial activity of polyunsaturated fatty acids related to chronic wound infections , PhD thesis, University of Salford.

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Wound infections present major health problems worldwide. It has been revealed that bacterial biofilm communities frequently colonise chronic wounds.Biofilms with Multidrugresistant organisms (MDRO) such as Methicillin Resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa are increasingly implicated in chronic wound infections. The limited therapeutic options are further compromised by the fact that wound-infecting bacteria often co-exist within a polymicrobial biofilm community, which enhances bacterial tolerance or resistance to antimicrobials. The polyunsaturated fatty acid (PUFA) compounds including Docosahexaenoic acid (DHA) and Eicosapentaenoic acid (EPA) offer both immunomodulatory and antimicrobial properties that could enhance wound healing.

This study evaluated the activity and efficiency of these compounds against wound pathogens and compared them to common antibiotics Linezolid (LZD) and vancomycin (VAN). Standard antibiotic sensitivity assays were used to determine the ability of PUFAs to inhibit growth and biofilm formation. Most activity was observed against S. aureus strains. The bacteriostatic activity (minimum inhibitory concentration - MIC) of DHA and EPA for S. Aureus SA3 and P. aeruginosa PA01 was 65 and 117 μgml-1 respectively. Meanwhile, the bacteriocidal activity required higher concentrations (MBC) of 260 and 468 μgml-1 respectively. The antibiotic LZD was most active against Gram positive bacteria (MIC range from 1.9 µg ml-1 to 3.9 µg ml-1). However, vancomycin was the most potent biofilm disrupter, with MBECs ranging from 5-12.5 µg ml-1. These concentrations were 35-fold lower than the MBECs recorded for linezolid (125 -500 µg ml-1). Considerably higher concentrations of PUFA compounds were required to disrupt biofilms. The MBECs of DHA ranged between 750 and 3125 µg ml-1. EPA was found to be more disruptive than DHA (MBECs ranging between 500 and 2250 µg ml-1), while the MBECs of combination treatment with both PUFAs (DHA+EPA) ranged from 750 - 1500 µg ml-1.

The antimicrobial activity of different concentrations of PUFAs was further Assessed by monitoring inhibition of growth of a clinical wound isolate of S. aureus (SA3)for 24 h. PUFAs were shown to differentially affect expression of global gene regulators using RT-qPCR. DHA and EPA were found to upregulate agrA and icaA but downregulate sarA at the same concentrations and exposure times.

Two different infection models were used to assess the activity of PUFAs in vivo (Galleria mellonella) and on ex-vivo skin compared to common antibiotics (LZD and VAN). PUFAs reduced virulence of SA3 in G.mellonella, protecting the larvae from death. Furthermore, prolonged exposure to sub-inhibitory concentrations affected growth Efficiency of SA3 in vivo. Whole genome sequencing of parent vs PUFA and antibiotics adapted strains of S. aureus SA3 revealed some common mutations in sarA and clfB genes, that may contribute to altered virulence and susceptibility to treatment. Preliminary studies with the ex-vivo skin model suggested that this may be a useful system for testing the efficacy of antimicrobial compounds for wound-treatment. Differences in SA3 survival and growth were measurable in the presence of PUFAs or absence of PUFAs.

In conclusion, PUFAs (DHA and EPA) showed weak antimicrobial activity compared to common antibiotics against common wound-associated bacteria. However, this study shows evidence that PUFAs have additional desirable properties, including disruption of global gene regulation, reduction of virulence and low potential to promote development of resistance.

Item Type: Thesis (PhD)
Contributors: James, C (Supervisor)
Schools: Schools > School of Environment and Life Sciences
Depositing User: Dr Mohamed Eshlak
Date Deposited: 07 May 2019 11:15
Last Modified: 27 Aug 2021 21:23

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