Inhibition of Bacterial Biofilm Formation by Phytotherapeutics with Focus on Overcoming Antimicrobial Resistance

Mechanistic Insights into the Antibiofilm Mode of Action of Ellagic Acid

Bacterial biofilm is a major contributor to the persistence of infection and the limited efficacy of antibiotics. Antibiofilm molecules that interfere with the biofilm lifestyle offer a valuable tool in fighting bacterial pathogens. Ellagic acid (EA) is a natural polyphenol that has shown attractive antibiofilm properties. However, its precise antibiofilm mode of action remains unknown. Experimental evidence links the NADH:quinone oxidoreductase enzyme WrbA to biofilm formation, stress response, and pathogen virulence. Moreover, WrbA has demonstrated interactions with antibiofilm molecules, suggesting its role in redox and biofilm modulation. This work aims to provide mechanistic insights into the antibiofilm mode of action of EA utilizing computational studies, biophysical measurements, enzyme inhibition studies on WrbA, and biofilm and reactive oxygen species assays exploiting a WrbA-deprived mutant strain of Escherichia coli. Our research efforts led us to propose that the antibiofilm mode of action of EA stems from its ability to perturb the bacterial redox homeostasis driven by WrbA. These findings shed new light on the antibiofilm properties of EA and could lead to the development of more effective treatments for biofilm-related infections.

Potential of Essential Oils in the Control of Listeria monocytogenes

Listeria monocytogenes is a foodborne pathogen, the causative agent of listeriosis. Infections typically occur through consumption of foods, such as meats, fisheries, milk, vegetables, and fruits. Today, chemical preservatives are used in foods; however, due to their effects on human health, attention is increasingly turning to natural decontamination practices. One option is the application of essential oils (EOs) with antibacterial features, since EOs are considered by many authorities as being safe. In this review, we aimed to summarize the results of recent research focusing on EOs with antilisterial activity. We review different methods via which the antilisterial effect and the antimicrobial mode of action of EOs or their compounds can be investigated. In the second part of the review, results of those studies from the last 10 years are summarized, in which EOs with antilisterial effects were applied in and on different food matrices. This section only included those studies in which EOs or their pure compounds were tested alone, without combining them with any additional physical or chemical procedure or additive. Tests were performed at different temperatures and, in certain cases, by applying different coating materials. Although certain coatings can enhance the antilisterial effect of an EO, the most effective way is to mix the EO into the food matrix. In conclusion, the application of EOs is justified in the food industry as food preservatives and could help to eliminate this zoonotic bacterium from the food chain.

Relapsing cellulitis associated with Campylobacter coli bacteremia in a Good’s syndrome patient: a case report

Background

Good’s syndrome (GS) is characterized by immunodeficiency, and patients diagnosed with GS are susceptible to infection or even bacteremia, which is the most evident complication. Campylobacter coli (C. coli) rarely causes bacteremia or extraintestinal infection. We report herein a case with GS in which right leg cellulitis associated with C. coli bacteremia occurred three times over one and a half years.

Case presentation

A 41-year-old Chinese male with GS was diagnosed with C. coli infection. He presented with swelling and redness of right lower leg and developed bacteremia due to C. coli repeatedly. Bacteremia was confirmed by bacteriological examination. Adding long-term oral antibiotic treatment with amoxicillin/clavulanate potassium and gentamicin following intravenous meropenem and amikacin was very effective. The blood cultures became negative and the patient has been free from any symptoms encountered for more than one year without relapse of bacteremia.

Conclusions

Patients with GS and their physicians should carefully consider the antibacterial treatment options against C. coli bacteremia. Combined anti-infective therapy involving aminoglycoside is preferred in the treatment of C. coli bacteremia in GS patients.

Evaluation of the antibacterial effects and mechanism of Plantaricin 149 from Lactobacillus plantarum NRIC 149 on the peri-implantitis pathogens

Peri-implantitis is a common reversible disease after tooth implantation, caused by a variety of pathogenic microorganisms. Based on non-surgical or surgical treatment principles, supplementation by local or systemic drugs might enhance treatment efficacy. Porphyromonas gingivalis (Pg) (ATCC 33,277) and Prevotella intermedius (Pi) (ATCC 25,611) were used as test strains. The effects of Pln 149 on the biofilm formation and growth of four periodontal pathogens were evaluated by RT-PCR, fluorescence microscopy, and scanning electron microscopy. The antibacterial mechanism was tested by the patch-clamp technique. The cytotoxicity of Pln 149 (125 µg/ml) to bone marrow stromal cell (BMSC) was assessed using an MTT assay. Pln 149 exhibited significant inhibitory effects on Pg and Pi (P < 0.05), with significant differences in the biofilm images of fluorescence microscope and scanning electron microscope (P < 0.05). Pln 149 could change the sodium channel currents and exerted no cytotoxicity on bone marrow stromal cell. Pln 149 could inhibit the biofilm formation and growth of periodontal pathogens. Considering the absence of antimicrobial resistance and cytotoxicity, we suggest that the Pln 149 from Lactobacillus plantarum 149 might be a promising option for managing peri-implantitis.

Effects of the Quinone Oxidoreductase WrbA on Escherichia coli Biofilm Formation and Oxidative Stress

The effects of natural compounds on biofilm formation have been extensively studied, with the goal of identifying biofilm formation antagonists at sub-lethal concentrations. Salicylic and cinnamic acids are some examples of these compounds that interact with the quinone oxidoreductase WrbA, a potential biofilm modulator and an antibiofilm compound biomarker. However, WrbA’s role in biofilm development is still poorly understood. To investigate the key roles of WrbA in biofilm maturation and oxidative stress, Escherichia coli wild-type and ∆wrbA mutant strains were used. Furthermore, we reported the functional validation of WrbA as a molecular target of salicylic and cinnamic acids. The lack of WrbA did not impair planktonic growth, but rather affected the biofilm formation through a mechanism that depends on reactive oxygen species (ROS). The loss of WrbA function resulted in an ROS-sensitive phenotype that showed reductions in biofilm-dwelling cells, biofilm thickness, matrix polysaccharide content, and H₂O₂ tolerance. Endogenous oxidative events in the mutant strain generated a stressful condition to which the bacterium responded by increasing the catalase activity to compensate for the lack of WrbA. Cinnamic and salicylic acids inhibited the quinone oxidoreductase activity of purified recombinant WrbA. The effects of these antibiofilm molecules on WrbA function was proven for the first time.

Sensitivity of Staphylococcal Biofilm to Selected Compounds of Plant Origin

Staphylococcus epidermidis is a bacterium that belongs to the human microbiota. It is most plentiful on the skin, in the respiratory system, and in the human digestive tract. Moreover, it is the most frequently isolated microorganism belonging to the group of Coagulase Negative Staphylococci (CoNS). In recent years, it has been recognized as an important etiological factor of mainly nosocomial infections and infections related to the cardiovascular system. On the other hand, Staphylococcus aureus, responsible for in-hospital and out-of-hospital infections, is posing an increasing problem for clinicians due to its growing resistance to antibiotics. Biofilm produced by both of these staphylococcal species in the course of infection significantly impedes therapy. The ability to produce biofilm hinders the activity of chemotherapeutic agents-the only currently available antimicrobial therapy. This also causes the observed significant increase in bacterial resistance. For this reason, we are constantly looking for new substances that can neutralize microbial cells. In the present review, 58 substances of plant origin with antimicrobial activity against staphylococcal biofilm were replaced. Variable antimicrobial efficacy of the substances was demonstrated, depending on the age of the biofilm. An increase in the activity of the compounds occurred in proportion to increasing their concentration. Appropriate use of the potential of plant-derived compounds as an alternative to antibiotics may represent an important direction of change in the support of antimicrobial therapy.

Advanced Killing Potential of Thymol against a Time and Temperature Optimized Attached Listeria monocytogenes Population in Lettuce Broth

Fresh vegetables and salads are increasingly implicated in outbreaks of foodborne infections, such as those caused by Listeria monocytogenes, a dangerous pathogen that can attach to the surfaces of the equipment creating robust biofilms withstanding the killing action of disinfectants. In this study, the antimicrobial efficiency of a natural plant terpenoid (thymol) was evaluated against a sessile population of a multi-strain L. monocytogenes cocktail developed on stainless steel surfaces incubated in lettuce broth, under optimized time and temperature conditions (54 h at 30.6 °C) as those were determined following response surface modeling, and in comparison, to that of an industrial disinfectant (benzalkonium chloride). Prior to disinfection, the minimum bactericidal concentrations (MBCs) of each compound were determined against the planktonic cells of each strain. The results revealed the advanced killing potential of thymol, with a concentration of 625 ppm (= 4 × MBC) leading to almost undetectable viable bacteria (more than 4 logs reduction following a 15-min exposure). For the same degree of killing, benzalkonium chloride needed to be used at a concentration of at least 20 times more than its MBC (70 ppm). Discriminative repetitive sequence-based polymerase chain reaction (rep-PCR) also highlighted the strain variability in both biofilm formation and resistance. In sum, thymol was found to present an effective anti-listeria action under environmental conditions mimicking those encountered in the salad industry and deserves to be further explored to improve the safety of fresh produce.