Abstract
Staphylococcus aureus and Methicillin-resistant S. aureus (MRSA) remains one of the major concerns of healthcare associated and community-onset infections worldwide. The number of cases of treatment failure for infections associated with resistant bacteria is on the rise, due to the decreasing efficacy of current antibiotics. Notably, Acrophialophora levis, a thermophilous fungus species, showed antibacterial activity, namely against S. aureus and clinical MRSA strains. The ethyl acetate extract of culture filtrate was found to display significant activity against S. aureus and MRSA with a minimum inhibitory concentration (MIC) of 1 μg/mL and 4 μg/mL, respectively. Scanning electron micrographs demonstrated drastic changes in the cellular architecture of metabolite treated cells of S. aureus and an MRSA clinical isolate. Cell wall disruption, membrane lysis and probable leakage of cytoplasmic are hallmarks of the antibacterial effect of fungal metabolites against MRSA. The ethyl acetate extract also showed strong antioxidant activity using two different complementary free radicals scavenging methods, DPPH and ABTS with efficiency of 55% and 47% at 1 mg/mL, respectively. The total phenolic and flavonoid content was found to be 50 mg/GAE and 20 mg/CAE, respectively. More than ten metabolites from different classes were identified: phenolic acids, phenylpropanoids, sesquiterpenes, tannins, lignans and flavonoids. In conclusion, the significant antibacterial activity renders this fungal strain as a bioresource for natural compounds an interesting alternative against resistant bacteria.
Highlights
Staphylococcus aureus is a commensal and opportunistic pathogen known to cause numerous mild to life-threatening infections in both human and animals
The antibacterial activity of all three organic fractions of A. levis IBSD-19 was assessed using the agar well diffusion method by measuring the diameter of growth inhibition zones at a fixed concentration of 1 mg/mL. We found that both S. aureus and methicillin-resistant S. aureus (MRSA) were only sensitive to ethyl acetate fraction with the inhibition zone of 13.2 and 10.1 mm (Fig 3a and 3b) respectively
This study suggests that since the test fraction had strong anti-staphylococcal and anti-MRSA activity by probably acting on the cell surface, it could present a low risk of developing drug resistance, and this fraction might be thought as an alternative to traditional antibiotics, especially those used for the treatment of skin and mucosal infections
Summary
Staphylococcus aureus is a commensal and opportunistic pathogen known to cause numerous mild to life-threatening infections in both human and animals. S. aureus remains one of the leading causative agents of morbidity and mortality worldwide [1]. This is to a large extent due to antibiotic-resistant strains, in particular methicillin-resistant S. aureus (MRSA) [2]. Anti MRSA potential of thermophilous fungi Acrophialophora levis this dramatic emergence of multi drug resistant (MDR) infections. Numerous medicinal plants have been explored worldwide to find novel drug molecules to fight the risk of ever increasing human diseases [3]. The present study was aimed to unveil the potential of a thermophilous Acrophialophora species IBSD-19 from the natural hot spring of Northeastern India for its antibacterial activity against S. aureus isolates. Scanning electron microscope (SEM) observations were carried out to probe the possible antibacterial mechanism against S. aureus and MRSA
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