Quorum sensing modulation and inhibition in biofilm forming foot ulcer pathogens by selected medicinal plants

Synthetic non-toxic anti-biofilm agents as a strategy in combating bacterial resistance

The tremendous increase in the bacterial resistance to the available antibiotics is a serious problem for the treatment of various infections. Biofilm formation in bacteria significantly contributes to the bacterial survival in host cells, and is considered as an crucial factor, responsible for bacterial resistance. The response of the bacterial cells in the biofilm to antibiotics is completely different from that of the free floating planktonic cells of the same strain. The anti-biofilm agents that could inhibit the biofilm production without affecting the bacterial growth, apply less selective pressure over the bacterial strains than the traditional antibiotics; thus the development of bacterial resistance would be of low incidence. Many attempts have been performed to discover novel agents capable of interfering with the bacterial biofilm life cycle, and several compounds have shown promising activities in suppressing the biofilm production or in dispersing mature existing biofilms. This review describes the different chemical classes that have anti-biofilm effects against different Gram-positive and Gram-negative bacteria without affecting the bacterial growth.

Phytochemical Composition, Antioxidant, Antimicrobial, Antibiofilm, and Antiquorum Sensing Potential of Methanol Extract and Essential Oil from Acanthus polystachyus Delile (Acanthaceae)

The evolution of microbes in response to conventional antimicrobials leads to antimicrobial resistance (AMR) and multidrug resistance (MDR), and it is a global threat to public health. Natural products are possible solutions to this massive challenge. In this study, the potential of Acanthus polystachyus extracts was investigated for phytochemical composition and biological properties as antimicrobials. Gas chromatography-mass spectra (GC-MS) analysis of methanol extract (ME) and essential oil (EO) detected 79 and 20 compounds, respectively. The major compounds identified in ME and their abundance were β-sitosterol acetate (16.06%), cholest-5-en-3-yl (9Z)-9-octadecenoate (9.54%), 1-dodecanol (7.57%), (S)-(E)-(-)-4-acetoxy-1-phenyl-2-dodecen-1-one (6.03%), neophytadiene (5.7%), (E)-2-nonadecene (3.9%), hexanol-4-D2 (2.92%), and decane (2.4%). Most compounds have known bioactive functions. In EO, the major compounds were stearyl alcohol (25.38%); cis-9-tetradecenoic acid, isobutyl ester (22.95%); butyl 9-tetradecenoate (10.62%); 11,13-dimethyl-12-tetradecen-1-ol acetate (10.14%); ginsenol (3.48%); and diisooctyl phthalate (2.54%). All compounds are known to be bioactive. The antioxidant activity of ME and EO ranged from 48.3 to 84.2% radical scavenging activity (RSA) and 45.6 to 82% RSA, respectively, with dose dependency. The disc diffusion assay for the antimicrobial activity of ME revealed high inhibition against Acenetobacter baumannii (130.2%), Pseudomonas aeruginosa (100.3%), and Staphylococcus aureus (87.7%). The MIC, MBC/MFC, and MBIC values for ME were 0.5-1.0, 2-4, and 0.5-1.0 mg/mL and for EO were 0.31-0.62, 1.25-2.5, and 0.31-0.62 μL/mL, respectively, indicating inhibition potential as well as inhibition of biofilm formation. The tolerance test values indicated bactericidal activity against most strains and bacteriostatic/fungistatic activity against A. baumannii, E. faecalis, and C. albicans. The antiquorum sensing activity of ME achieved by pyocyanin inhibition assay on P. aeruginosa showed a 51.6% inhibition at 500 μg/mL. These results suggest that ME and EO derived from A. polystachyus leaves are potent, valuable, cost-effective antioxidants and antimicrobials. Both extracts may effectively combat pathogenic and resistant microbes.

Extracts of Selected South African Medicinal Plants Mitigate Virulence Factors in Multidrug-Resistant Strains of Klebsiella pneumoniae

The emergence of multidrug-resistant (MDR) Klebsiella pneumoniae remains a global health threat due to its alarming rates of becoming resistant to antibiotics. Therefore, identifying plant-based treatment options to target this pathogen's virulence factors is a priority. This study examined the antivirulence activities of twelve plant extracts obtained from three South African medicinal plants (Lippia javanica, Carpobrotus dimidiatus, and Helichrysum populifolium) against carbapenem-resistant (CBR) and extended-spectrum beta-lactamase (ESBL) positive K. pneumoniae strains. The plant extracts (ethyl acetate, dichloromethane, methanol, and water) were validated for their inhibitory activities against bacterial growth and virulence factors such as biofilm formation, exopolysaccharide (EPS) production, curli expression, and hypermucoviscosity. The potent extract on K. pneumoniae biofilm was observed with a scanning electron microscope (SEM), while exopolysaccharide topography and surface parameters were observed using atomic force microscopy (AFM). Chemical profiling of the potent extract in vitro was analysed using liquid chromatography-mass spectrometry (LC-MS). Results revealed a noteworthy minimum inhibitory concentration (MIC) value for the C. dimidiatus dichloromethane extract at 0.78 mg/mL on CBR- K. pneumoniae. L. javanica (ethyl acetate) showed the highest cell attachment inhibition (67.25%) for CBR- K. pneumoniae. SEM correlated the in-vitro findings, evidenced by a significant alteration of the biofilm architecture. The highest EPS reduction of 34.18% was also noted for L. javanica (ethyl acetate) and correlated by noticeable changes observed using AFM. L. javanica (ethyl acetate) further reduced hypermucoviscosity to the least length mucoid string (1 mm-2 mm) at 1.00 mg/mL on both strains. C. dimidiatus (aqueous) showed biofilm inhibition of 45.91% for the ESBL-positive K. pneumoniae and inhibited curli expression at 0.50 mg/mL in both K. pneumoniae strains as observed for H. populifolium (aqueous) extract. Chemical profiling of L. javanica (ethyl acetate), C. dimidiatus (aqueous), and H. populifolium (aqueous) identified diterpene (10.29%), hydroxy-dimethoxyflavone (10.24%), and 4,5-dicaffeoylquinic acid (13.41%), respectively, as dominant compounds. Overall, the ethyl acetate extract of L. javanica revealed potent antivirulence properties against the studied MDR K. pneumoniae strains. Hence, it is a promising medicinal plant that can be investigated further to develop alternative therapy for managing K. pneumoniae-associated infections.

Chemical constituents of Aspergillus udagawae isolated from the soil of the Xingren coal areas and their antibacterial activities

A new helvolic acid derivative (1), together with nine known compounds (2-10) were isolated from the metabolites of Aspergillus udagawae MST1-10 with the bioassay-guided fractionation method. Their structures were identified on the basis of spectroscopic analysis. The absolute configuration of compound 1 was elucidated through NOESY and ECD spectra. Compound 2 displayed significant antibacterial activities against Stenotrophomonas maltophilia with MIC value of 2 μg/mL (Trimethoprim, MIC = 64 μg/mL), and with biofilm inhibition rates of 96.41%, 87.77%, and 41.70% at 4MIC, 2MIC, and MIC, respectively.

Overview of Antimicrobial Biodegradable Polyester-Based Formulations

As the clinical complications induced by microbial infections are known to have life-threatening side effects, conventional anti-infective therapy is necessary, but not sufficient to overcome these issues. Some of their limitations are connected to drug-related inefficiency or resistance and pathogen-related adaptive modifications. Therefore, there is an urgent need for advanced antimicrobials and antimicrobial devices. A challenging, yet successful route has been the development of new biostatic or biocide agents and biomaterials by considering the indisputable advantages of biopolymers. Polymers are attractive materials due to their physical and chemical properties, such as compositional and structural versatility, tunable reactivity, solubility and degradability, and mechanical and chemical tunability, together with their intrinsic biocompatibility and bioactivity, thus enabling the fabrication of effective pharmacologically active antimicrobial formulations. Besides representing protective or potentiating carriers for conventional drugs, biopolymers possess an impressive ability for conjugation or functionalization. These aspects are key for avoiding malicious side effects or providing targeted and triggered drug delivery (specific and selective cellular targeting), and generally to define their pharmacological efficacy. Moreover, biopolymers can be processed in different forms (particles, fibers, films, membranes, or scaffolds), which prove excellent candidates for modern anti-infective applications. This review contains an overview of antimicrobial polyester-based formulations, centered around the effect of the dimensionality over the properties of the material and the effect of the production route or post-processing actions.