Savory and Peppermint Essential Oils-Loaded Emulsions and Nanoemulsions Effects on Enterococcus faecium Isolated from Vacuum-Packed Cured Sausage

In this work, Enterococcus faecium, the specific spoilage organism responsible for bloating spoilage of sliced vacuum-packed cured emulsion-type sausage, was isolated and identified through molecular and biochemical techniques, and then the antibacterial activities of savory-loaded nanoemulsion (SNE), savory-loaded emulsion (SE), peppermint-loaded nanoemulsion (PNE), and peppermint-loaded emulsion (PE) were investigated against spoilage microorganisms. Nanoemulsions with average particle sizes in the range of 109.27 to 118.55 nm were developed by sonication and remained more stable than emulsion samples for 2 weeks. Regardless of emulsion type, the highest antimicrobial activity was detected for savory-loaded samples. Moreover, the significant enhancements in the antimicrobial activity of SNE compared to SE were confirmed by increasing the inhibition zone diameter (17.6%) and decreasing MIC (50%) and MBC (50%) due to the higher specific surface area of smaller droplets. The TEM and SEM micrographs confirmed the inhibitory effects of SNE due to the significant changes in the cell wall integrity of Enterococcus faecium.

Antibacterial and antibiofilm efficacy of colistin & meropenem conjugated silver nanoparticles against Escherichia coli and Klebsiella pneumoniae

The progressive increase in infections caused by multidrug-resistant (MDR) Gram-negative bacteria and the emergence of resistance to last-resort antimicrobial drugs in recent years necessitate the development of new therapeutic strategies. This study was conducted to obtain nanostructured antimicrobials by conjugating colistin (COL) and meropenem (MEM) antibiotics with biosynthesized silver nanoparticles (bio-AgNPs) via the green synthesis method using Rosa damascena extract, and to investigate the antibacterial and antibiofilm activity of these nanostructures against Escherichia coli and Klebsiella pneumoniae strains. Ultraviolet-visible spectrophotometry, high-resolution-transmission electron microscopy, atomic force microscopy, X-ray diffraction, and Fourier transform-infrared spectroscopy analyses were performed to determine the physical and chemical properties of synthesized bio-AgNPs, COL@bio-AgNPs, MEM@bio-AgNPs, and COL&MEM@bio-AgNPs. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration of nanoparticles were determined on standard and MDR clinical strains. The antibiofilm efficacy and cytotoxic effect of nanoparticles were evaluated by the crystal violet dye method and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide dye method, respectively. The characterization analyses demonstrated that the synthesized nanoparticles had crystal structure and spherical morphology (5.6-30.2 nm in size). Antibiotic conjugated nanoparticles exhibited better antimicrobial activity and lower MIC values (0.125-4 µg/mL) on the tested strains compared to free antibiotics, and MIC values were decreased up to 1024-fold (p < 0.05). Antibiotic conjugated nanoparticles were found to be more effective in biofilm eradication than free antibiotics and bio-AgNPs and had a less inhibitory effect on peripheral blood mononuclear cell viability. The findings revealed that antibiotic-conjugated nanoparticles have the potential to be used as an effective antimicrobial drug against MDR E. coli and K. pneumoniae strains.

Anti-adhesion and antibiofilm activities of Lavandula mairei humbert essential oil against Acinetobacter baumannii isolated from hospital intensive care units

This study aimed to assess, for the first time, the anti-adhesion and antibiofilm effects of Lavandula mairei Humbert essential oil against multidrug resistant Acinetobacter baumannii. Scanning electron microscope was used for visualizing its antibiofilm activity and the effect of this oil on surface physicochemical parameters was examined as a possible anti-adhesive target. Chemical analysis of Lavandulaa mairei essential oil showed a high content of carvacrol composition (79.12%). The oil tested exhibited antibacterial efficacy with inhibition diameters of 33 to 37.33 mm and minimum inhibitory and bactericidal concentrations of 1.56 µl ml^-1. The oil inhibited adhesion by 83.66%, detach 73.30% of adherent cells and eliminated 64.02% of the biofilm compared to the untreated control. Lavandula mairei essential oil has proven its possible application as a preventive strategy by intervening in the initial adhesion of Acinetobacter baumannii to polystyrene.

Convergence of Biofilm Formation and Antibiotic Resistance in Acinetobacter baumannii Infection

Acinetobacter baumannii (A. baumannii) is a leading cause of nosocomial infections as this pathogen has certain attributes that facilitate the subversion of natural defenses of the human body. A. baumannii acquires antibiotic resistance determinants easily and can thrive on both biotic and abiotic surfaces. Different resistance mechanisms or determinants, both transmissible and non-transmissible, have aided in this victory over antibiotics. In addition, the propensity to form biofilms (communities of organism attached to a surface) allows the organism to persist in hospitals on various medical surfaces (cardiac valves, artificial joints, catheters, endotracheal tubes, and ventilators) and also evade antibiotics simply by shielding the bacteria and increasing its ability to acquire foreign genetic material through lateral gene transfer. The biofilm formation rate in A. baumannii is higher than in other species. Recent research has shown how A. baumannii biofilm-forming capacity exerts its effect on resistance phenotypes, development of resistome, and dissemination of resistance genes within biofilms by conjugation or transformation, thereby making biofilm a hotspot for genetic exchange. Various genes control the formation of A. baumannii biofilms and a beneficial relationship between biofilm formation and "antimicrobial resistance" (AMR) exists in the organism. This review discusses these various attributes of the organism that act independently or synergistically to cause hospital infections. Evolution of AMR in A. baumannii, resistance mechanisms including both transmissible (hydrolyzing enzymes) and non-transmissible (efflux pumps and chromosomal mutations) are presented. Intrinsic factors [biofilm-associated protein, outer membrane protein A, chaperon-usher pilus, iron uptake mechanism, poly-β-(1, 6)-N-acetyl glucosamine, BfmS/BfmR two-component system, PER-1, quorum sensing] involved in biofilm production, extrinsic factors (surface property, growth temperature, growth medium) associated with the process, the impact of biofilms on high antimicrobial tolerance and regulation of the process, gene transfer within the biofilm, are elaborated. The infections associated with colonization of A. baumannii on medical devices are discussed. Each important device-related infection is dealt with and both adult and pediatric studies are separately mentioned. Furthermore, the strategies of preventing A. baumannii biofilms with antibiotic combinations, quorum sensing quenchers, natural products, efflux pump inhibitors, antimicrobial peptides, nanoparticles, and phage therapy are enumerated.

In Vitro and In Silico Approaches for the Evaluation of Antimicrobial Activity, Time-Kill Kinetics, and Anti-Biofilm Potential of Thymoquinone (2-Methyl-5-propan-2-ylcyclohexa-2,5-diene-1,4-dione) against Selected Human Pathogens

Thymoquinone (2-methyl-5-propan-2-ylcyclohexa-2,5-diene-1,4-dione; TQ), a principal bioactive phytoconstituent of Nigella sativa essential oil, has been reported to have high antimicrobial potential. Thus, the current study evaluated TQ’s antimicrobial potential against a range of selected human pathogens using in vitro assays, including time-kill kinetics and anti-biofilm activity. In silico molecular docking of TQ against several antimicrobial target proteins and a detailed intermolecular interaction analysis was performed, including binding energies and docking feasibility. Of the tested bacteria and fungi, S. epidermidis ATCC 12228 and Candida albicans ATCC 10231 were the most susceptible to TQ, with 50.3 ± 0.3 mm and 21.1 ± 0.1 mm zones of inhibition, respectively. Minimum inhibitory concentration (MIC) values of TQ are in the range of 12.5–50 µg/mL, while minimum biocidal concentration (MBC) values are in the range of 25–100 µg/mL against the tested organisms. Time-kill kinetics of TQ revealed that the killing time for the tested bacteria is in the range of 1–6 h with the MBC of TQ. Anti-biofilm activity results demonstrate that the minimum biofilm inhibitory concentration (MBIC) values of TQ are in the range of 25–50 µg/mL, while the minimum biofilm eradication concentration (MBEC) values are in the range of 25–100 µg/mL, for the tested bacteria. In silico molecular docking studies revealed four preferred antibacterial and antifungal target proteins for TQ: D-alanyl-D-alanine synthetase (Ddl) from Thermus thermophilus, transcriptional regulator qacR from Staphylococcus aureus, N-myristoyltransferase from Candida albicans, and NADPH-dependent D-xylose reductase from Candida tenuis. In contrast, the nitroreductase family protein from Bacillus cereus and spore coat polysaccharide biosynthesis protein from Bacillus subtilis and UDP-N-acetylglucosamine pyrophosphorylase from Aspergillus fumigatus are the least preferred antibacterial and antifungal target proteins for TQ, respectively. Molecular dynamics (MD) simulations revealed that TQ could bind to all four target proteins, with Ddl and NADPH-dependent D-xylose reductase being the most efficient. Our findings corroborate TQ’s high antimicrobial potential, suggesting it may be a promising drug candidate for multi-drug resistant (MDR) pathogens, notably Gram-positive bacteria and Candida albicans.

Multidrug Resistant Acinetobacter baumannii Biofilms: Evaluation of Phenotypic-Genotypic Association and Susceptibility to Cinnamic and Gallic Acids

Acinetobacter baumannii armed with multidrug resistance (MDR) and biofilm-forming ability is increasingly recognized as an alarming pathogen. A deeper comprehension of the correlation between these two armories is required in circumventing its infections. This study examined the biofilm-forming ability of the isolates by crystal violet staining and the antibiotic susceptibility by broth microdilution method. The genetic basis of the MDR and biofilm-forming phenotypes was screened by polymerase chain reaction. The antimicrobial activities of cinnamic and gallic acids against planktonic cells and biofilms of A. baumannii were investigated, and the findings were confirmed with scanning electron microscopy (SEM). Among 90 A. baumannii isolates, 69 (76.6%) were MDR, and all were biofilm formers; they were classified into weak (12.2%), moderate (53.3%), and strong (34.5%) biofilm formers. Our results underlined a significant association between MDR and enhanced biofilm formation. Genotypically, the presence of bla_VIM and bla_OXA–23 genes along with biofilm-related genes (ompA, bap, and csuE) was statistically associated with the biofilm-forming abilities. Impressively, both gallic and cinnamic acids could significantly reduce the MDR A. baumannii biofilms with variable degrees dependent on the phenotype–genotype characteristics of the tested isolates. The current findings may possess future therapeutic impact through augmenting antimicrobial arsenal against life-threatening infections with MDR A. baumannii biofilms.

Inhibition of Virulence Factors and Biofilm Formation of Acinetobacter Baumannii by Naturally-derived and Synthetic Drugs

Acinetobacter baumannii is a gram-negative, aerobic, non-motile, and pleomorphic bacillus. A. baumannii is also a highly-infectious pathogen causing high mortality and morbidity rates in intensive care units. The discovery of novel agents against A. baumannii infections is urgently needed due to the emergence of drug-resistant A. baumannii strains and the limited number of efficacious antibiotics available for treatment. In addition to the production of several virulence factors, A. baumannii forms biofilms on the host cell surface as well. Formation of biofilms occurs through initial surface attachment, microcolony formation, biofilm maturation, and detachment stages, and is one of the major drug resistance mechanisms employed by A. baumannii. Several studies have previously reported the efficacy of naturally-derived and synthetic compounds as anti- biofilm and anti-virulence agents against A. baumannii. Here, inhibition of biofilm formation and virulence factors of A. baumannii using naturally-derived and synthetic compounds are reviewed.

Effect of essential oils on oral halitosis treatment: a review

Halitosis is a very common condition which may affect up to 30% of the population. In about 90% of the cases, halitosis originates in the mouth due to inadequate plaque control, periodontal disease, dry mouth, faulty restorations, and in particular due to excessive bacterial growth. Oral malodor is mainly caused by a microbial degradation of amino acids into volatile, bad-smelling gases (volatile sulfur compounds - VSCs). Management of oral malodor is directed primarily at managing and reducing the VSC-producing bacteria count as well as masking the odor. Essential oils have been used for this purpose in traditional medicine for centuries. In the present review, data on the antimicrobial activity of essential oils against relevant oral VSC-producing bacteria are compiled and compared. Additionally, other positive aspects of essential oils with regard to oral odor are considered.

Antivirulence properties and related mechanisms of spice essential oils: A comprehensive review

In recent decades, reduced antimicrobial effectiveness, increased bacterial infection, and newly emerged microbial resistance have become global public issues, leading to an urgent need to find effective strategies to counteract these problems. Strategies targeting bacterial virulence factors rather than bacterial survival have attracted increasing interest, since the modulation of virulence factors may prevent the development of drug resistance in bacteria. Spices are promising natural sources of antivirulence compounds owing to their wide availability, diverse antivirulence phytochemical constituents, and generally favorable safety profiles. Essential oils are the predominant and most important antivirulence components of spices. This review addresses the recent efforts of using spice essential oils to inhibit main bacterial virulence traits, including the quorum sensing system, biofilm formation, motility, and toxin production, with an intensive discussion of related mechanisms. We hope that this review can provide a better understanding of the antivirulence properties of spice essential oils, which have the potential to be used as antibiotic alternatives by targeting bacterial virulence.

Combination of essential oil and ciprofloxacin to inhibit/eradicate biofilms in multidrug-resistant Klebsiella pneumoniae

AIM

This study aimed to test biofilm inhibition activities of each of essential oils (EOs), main compounds of EOs and enzymes against pathogenic Klebsiella pneumoniae.

METHODS AND RESULTS

The effect of seven EOs and three enzymes was tested on formation and eradication of K. pneumoniae biofilm. Peppermint oil showed a robust biofilm inhibitory effect, causing inhibition that ranged from 69·2 to 98·2% at 5 μl ml^-1 . Thyme oil was found to have the best biofilm eradication ability, causing eradication that ranged from 80·1 to 98·0% at 10 μl ml^-1 . The most effective EOs were analysed by GC/MS, to determine the major chemical constitutes of each oil. Pure menthol was found to cause 75·3-97·5% biofilm inhibition at 2·5 μg ml^-1 , whereas thymol caused 85·1-97·8% biofilm eradication at 5 μg ml^-1 . However, moderate inhibition activity was detected for α-amylase and bromelain, while poor activity was detected for β-amylase. Ciprofloxacin combination with thyme oil and thymol was found to enhance antibiotic activity, and affect biofilm cell viability. The observed inhibitory/eradication activity on K. pneumoniae biofilms was confirmed by scanning electron microscopy.

CONCLUSIONS

Thyme and peppermint EOs, and their active components are promising antibiofilm agents alone and/or in combination with ciprofloxacin to inhibit/eradicate biofilms of K. pneumoniae.

SIGNIFICANCE AND IMPACT OF THE STUDY

The presented results suggest the potential application of EOs against infections, caused by biofilm-producing K. pneumoniae, to prevent biofilm formation or decrease their resistance threshold. Moreover, the combination of EOs with ciprofloxacin minimizes the antibiotic concentration used and accordingly the potential accompanying toxic side effects.

Antibiofilm and Antihyphal Activities of Cedar Leaf Essential Oil, Camphor, and Fenchone Derivatives against Candida albicans

Candida albicans can form biofilms composed of yeast, hyphal, and pseudohyphal elements, and C. albicans cells in the hyphal stage could be a virulence factor. The present study describes the chemical composition, antibiofilm, and antihyphal activities of cedar leaf essential oil (CLEO), which was found to possess remarkable antibiofilm activity against C. albicans but not to affect its planktonic cell growth. Nineteen components were identified in CLEO by gas chromatography/mass spectrometry, and phenolics were the main constituents. Of these, camphor, fenchone, fenchyl alcohol, α-thujone, and borneol significantly reduced C. albicans biofilm formation. Notably, treatments with CLEO, camphor, or fenchyl alcohol at 0.01% clearly inhibited hyphal formation, and this inhibition appeared to be largely responsible for their antibiofilm effects. Transcriptomic analyses indicated that camphor and fenchyl alcohol downregulated some hypha-specific and biofilm related genes (ECE1, ECE2, RBT1, and EED1). Furthermore, camphor and fenchyl alcohol reduced C. albicans virulence in a Caenorhabditis elegans nematode model. These results demonstrate CLEO, camphor, and fenchyl alcohol might be useful for controlling C. albicans infections.

Methods for eradication of the biofilms formed by opportunistic pathogens using novel techniques – A review

The inconvenient environmental conditions force microorganisms to colonize either abiotic surfaces or animal and plant tissues and, therefore, form more resistant structures – biofilms. The phenomenon of microbial adherence, opportunistic pathogens in particular, is of a great concern. Colonization of medical devices and biofilm formation on their surface, may lead to severe infections mainly in humans with impaired immune system. Although, current research consider various methods for prevention of microbial biofilms formation, still, once a biofilm is formed, its elimination is almost impossible. This study focuses on the overview of novel methods applied for eradication of mature opportunistic pathogens' biofilms. Among various techniques the following: cold plasma, electric field, ultrasounds, ozonated water treatment, phagotherapy, matrix targeting enzymes, bacteriocins, synthetic chemicals and natural origin compounds used for biofilm matrix disruption were briefly described.