Synergistic Anti-bacterial Effects of Phellinus baumii Ethyl Acetate Extracts and β-Lactam Antimicrobial Agents Against Methicillin-Resistant Staphylococcus aureus

The Dual Role of the Medicinal Mushroom Fomitopsis pinicola in Inhibiting Biofilm and Reducing Antibiotic Resistance of Methicillin-Resistant Staphylococcus aureus

This study investigates the antimicrobial, antibiofilm, and anti-quorum sensing activity of Fomitopsis pinicola against methicillin-resistant Staphylococcus aureus (MRSA) strains and its potential to improve the efficacy of conventional antibiotics and exert selective cytotoxic effects on cancer cells. Ethanolic extracts of F. pinicola were analyzed for antibacterial activity by MIC and time-kill assays. Synergistic interactions with antibiotics were quantified using checkerboard assays. Antibiofilm activity was analyzed on polystyrene and stainless-steel surfaces. Anti-quorum sensing activity was determined by the inhibition of violacein in Chromobacterium violaceum. Efflux pump inhibition was assessed by the accumulation of the ethidium bromide. The down-regulation of virulence genes (agrA, hla) was measured by qRT-PCR (quantitative real-time reverse-transcription PCR). FT-IR (Fourier transform infrared spectroscopy) spectroscopy characterized the bioactive compounds, and the cytotoxicity assays on HT-29 colon cancer and Vero cells evaluated selective toxicity. The extract showed strong antibacterial effects with a MIC of 312.5 μg/mL and concentration-dependent bactericidal activity. Synergistic interactions with antibiotics led to FIC indices ≤ 0.5. The extract significantly inhibited biofilm formation and eradicated already formed biofilms. Sub-MIC concentrations reduced quorum sensing by 85.01%, inhibited efflux pump activity, and down-regulated virulence-associated genes. FT-IR analysis confirmed the presence of triterpenoids and terpenoids. The extract displayed selective cytotoxicity on HT-29 cancer cells, showing strong inhibition, while normal Vero cells were spared. These results emphasize the potential of F. pinicola as a robust candidate for antimicrobial therapeutics, especially against biofilm-associated and multidrug-resistant pathogens, as well as a selective anticancer agent.

Synergism with Shikimic Acid Restores β-Lactam Antibiotic Activity against Methicillin-Resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) has evolved into a dangerous pathogen resistant to beta-lactam antibiotics (BLAs) and has become a worrisome superbug. In this study, a strategy in which shikimic acid (SA), which has anti-inflammatory and antibacterial activity, is combined with BLAs to restart BLA activity was proposed for MRSA treatment. The synergistic effects of oxacillin combined with SA against oxacillin resistance in vitro and in vivo were investigated. The excellent synergistic effect of the oxacillin and SA combination was confirmed by performing the checkerboard assay, time-killing assay, live/dead bacterial cell viability assay, and assessing protein leakage. SEM showed that the cells in the control group had a regular, smooth, and intact surface. In contrast, oxacillin and SA or the combination treatment group exhibited different degrees of surface collapse. q-PCR indicated that the combination treatment group significantly inhibited the expression of the mecA gene. In vivo, we showed that the combination treatment increased the survival rate and decreased the bacterial load in mice. These results suggest that the combination of oxacillin with SA is considered an effective treatment option for MRSA, and the combination of SA with oxacillin in the treatment of MRSA is a novel strategy.

Antifungal and Antibacterial Activities of Crude Extracts of Four Phellinus Species and Coltricia fragilissima (Agaricomycetes) from Cameroon and Democratic Republic of Congo

Antifungal and antibacterial activities of crude extracts of Phellinus extensus, Ph. gilvus, Ph. pachyphloeus, Ph. senex and Coltricia fragilissima were investigated on eleven species of bacteria and three fungal human pathogens. The minimum inhibitory concentration (MIC) was determined by the microdilution method. The results of this study reveal that for the eleven strains of bacteria tested, including Bacillus subtilis, Enterococcus faecalis, Staphylococcus aureus, S. epidermidis, Enterobacter cloacae, Klebsiella aerogenes, Mycobacterium smegmatis, Proteus vulgaris, Proteus mirabilis and Escherichia choli, the MIC of the crude extract of the four species of Phellinus as well as that of C. fragilissima ranged from 3.13 to 12.50 mg/mL. For the three strains of fungi tested including Candida albicans, Aspergillus ochraceus and A. fumigetus, the MIC of the crude extracts of the same four species of Phellinus as well as that of C. fragilissima ranged from 0.39 to 3.13 mg/mL. These data reveal that the antimicrobial activity of crude extracts of Phellinus and Coltricia species is stronger on pathogenic fungi than on bacteria. C. fragilissima being of the same family as Phellinus and having recorded the values of MIC eminently close to those of the latter may potentially be used for medicinal purposes like the investigated Phellinus species. Being highly represented in the sub-Saharan regions and owing to the above-mentioned results, these species could now be considered as part of the non-exhaustive list of medicinal mushrooms in these regions and may constitute a new source of natural molecules that may be more active than synthetic products against certain fungal and bacterial borne diseases.

Activity of aurisin A isolated from Neonothopanus nambi against methicillin-resistant Staphylococcus aureus strains

Mycopharmaceuticals from basidiomycetes represent a promising source of new antimicrobials to overcome the challenges of multidrug-resistant bacteria. Here we report for the first time the in vitro activity of aurisin A, a dimeric sesquiterpenoid isolated from wild bioluminescent basidiomycetes Neonothopanus nambi DSM 24013, against methicillin-resistant Staphylococcus aureus (MRSA). Aurisin A revealed strong anti-MRSA activity with minimum inhibitory concentration 7.81 μg/mL against ATCC 33591 and ATCC 43300 reference strains, and BD 16876 and BD 15358 clinical strains. Activity against the clinical strains is 10- to 40-fold higher than that of the antibiotic fusidic acid. Furthermore, aurisin A proved to be more potent (MIC 3.91 μg/mL) in inhibiting growth of vancomycin-intermediate S. aureus (VISA) ATCC 700699 and displayed a rapid time-dependent bactericidal activity against MRSA (complete killing within 1 h). Additionally, aurisin A and oxacillin combination displayed synergy with notable decrease in the MICs of both compounds against MRSA. Notable synergism was also observed in combinations with linezolid and fusidic acid. Our findings indicate that aurisin A is a promising candidate for developing therapeutic agents against multidrug-resistant S. aureus and warrants further investigation.

Strategies to combat antimicrobial resistance in Indian scenario

Antimicrobial resistance (AMR) is one of the major public health crisis recognised globally. Microbial infections cause significant productivity losses in animals and humans. In livestock, these microbial infections reduce the growth rates and fertility, diminish production of meat and milk, and occasionally lead to mortality, and are therefore, a major concern for animal welfare. In the dearth of alternative prophylactic measures, antibiotics remain the principal tool for their management. Once an antibiotic is used rampantly, resistance against it is inevidently seen in the microbe population and the hunt for a new drug grows. Discovery and development of a new antimicrobial drug is a time taking and expensive procedure with limited assurance of success. As a result, the past few decades have witnessed only a very few new classes of antibiotics. If the AMR can be restricted or reverted, the success rate of antimicrobial therapy can be boosted and many public health issues be avoided. All these ask for a comprehensive plan to prevent or reduce the antimicrobial resistance and economic losses to the animal husbandry sector. The present review provides an overview of AMR in India, mechanism of its occurrence and the possible roadmap to combat the emerging threat of AMR in Indian scenario.

The Antitumor Potential of Extract of the Oak Bracket Medicinal Mushroom Inonotus baumii in SMMC-7721 Tumor Cells

Inonotus baumii, a traditional medicinal mushroom, has been historically used in China and other countries of East Asia for the treatment of various diseases. The aim of this study is to investigate the antitumor activity of the extract of I. baumii (EIB) against hepatocellular carcinoma and the possible mechanism involved. The MTT assay was used to evaluate the proliferative activity of SMMC-7721 cells treated with EIB. Hoechst 33258 and JC-1 staining were used to determine nuclear morphological changes and mitochondrial membrane potential, respectively. Flow cytometry analysis indicated that EIB blocked the cell cycle at the S phase and induced significant apoptosis. EIB increased the protein expression of Bax, cytochrome c, cleaved caspase-3, and decreased Bcl-2 in SMMC-7721. Moreover, EIB induced autophagy, indicated by the increase of autophagy-related protein expression of LC3-II and decrease of p62, and the AMPK/mTOR/ULK1 pathway was involved in the autophagic cell death. In vivo, EIB was found to strongly inhibit the growth of tumors in BALB/c nude mice. Our results indicated that I. baumii might be a potential natural therapeutic agent for liver cancer, as it could induce apoptosis and autophagy in HCC cells.

Antimicrobial activity and synergism of ursolic acid 3-O-α-L-arabinopyranoside with oxacillin against methicillin-resistant Staphylococcus aureus

The objective of the present study was to investigate the antibacterial activity of a single constituent, ursolic acid 3-O-α-L-arabinopyranoside (URS), isolated from the leaves of Acanthopanax henryi (Oliv.) Harms, alone and in combination with oxacillin (OXA) against methicillin-resistant Staphylococcus aureus (MRSA). A broth microdilution assay was used to determine the minimal inhibitory concentration (MIC). The synergistic effects of URS and OXA were determined using a checkerboard dilution test and time-kill curve assay. The mechanism of action of URS against MRSA was analyzed using a viability assay in the presence of a detergent and an ATPase inhibitor. Morphological changes in the URS-treated MRSA strains were evaluated via transmission electron microscopy (TEM). In addition, the producing penicillin-binding protein 2a (PBP2a) protein level was analyzed using western blotting. The MIC value of URS against MRSA was found to be 6.25 µg/ml and there was a partial synergistic effect between OXA and URS. The time-kill growth curves were suppressed by OXA combined with URS at a sub-inhibitory level. Compared to the optical density at 600 nm (OD600) value of URS alone (0.09 µg/ml), the OD600 values of the suspension in the presence of 0.09 µg/ml URS and 0.00001% Triton X-100 or 250 µg/ml N,N'-dicyclohexylcarbodiimide reduced by 56.6 and 85.9%, respectively. The TEM images of MRSA indicated damage to the cell wall, broken cell membranes and cell lysis following treatment with URS and OXA. Finally, an inhibitory effect on the expression of PBP2a protein was observed when cells were treated with URS and OXA compared with untreated controls. The present study suggested that URS was significantly active against MRSA infections and revealed the potential of URS as an effective natural antibiotic.

Modulation of Drug Resistance in Staphylococcus aureus with Coumarin Derivatives

Semisynthetic and commercial coumarins were investigated for their antibacterial and adjuvant properties with antibiotic agents against norfloxacin, erythromycin, and tetracycline resistant Staphylococcus aureus as based on efflux mechanisms. The coumarins and certain commercial antibiotics had their Minimum Inhibitory Concentrations determined by broth microdilution assay against resistant S. aureus strains which overexpress efflux pump proteins. For evaluation of the modulatory activity, the antibiotics MICs were determined in the presence of the coumarin derivatives at subinhibitory concentration. Although the coumarins did not display relevant antibacterial activity (MIC ≥ 128 µg/mL), they did modulate the antibiotics activities. Various coumarins, especially the alkylated derivatives in combination with antibiotics at subinhibitory concentrations, modulated antibiotic activity, reducing the MIC for tetracycline and norfloxacin by 2 to 8 times. Polar Surface Area (PSA) studies were performed and the fact that the presence of apolar groups is an important factor for the modulatory activity of coumarins was corroborated. Docking on the Penicillin-Binding Protein from MRSA identified that 18 is a potential ligand presenting low E binding. The results indicate that coumarin derivatives modulated antibiotic resistance and may be used as potential antibiotic adjuvants, acting by bacterial efflux pump inhibition in S. aureus.