Hyperosmotic Agents and Antibiotics Affect Dissolved Oxygen and pH Concentration Gradients in Staphylococcus aureus Biofilms

Exploring the Potential of Bee-Derived Antioxidants for Maintaining Oral Hygiene and Dental Health: A Comprehensive Review

Honey bee products comprise various compounds, including honey, propolis, royal jelly, bee pollen, bee wax and bee venom, which have long been recognized for their pharmacological and health-promoting benefits. Scientists have discovered that periodontal disorders stem from dental biofilm, an inflammatory response to bacterial overgrowth produced by dysbiosis in the oral microbiome. The bee products have been investigated for their role in prevention of oral diseases, which are attributed to a myriad of biologically active compounds including flavonoids (pinocembrin, catechin, caffeic acid phenethyl ester (CAPE) and galangin), phenolic acids (hydroxybenzoic acid, hydroxycinnamic acid, p-coumaric, ellagic, caffeic and ferulic acids) and terpenoids. This review aims to update the current understanding of role of selected bee products, namely, honey, propolis and royal jelly, in preventing oral diseases as well as their potential biological activities and mechanism of action in relation to oral health have been discussed. Furthermore, the safety of incorporation of bee products is also critically discussed. To summarize, bee products could potentially serve as a therapy option for people suffering from a variety of oral disorders.

Do variations in nasal irrigation recipes and storage effect the risk of bacterial contamination?

OBJECTIVE

Make-at-home nasal irrigation solutions are often recommended for treating chronic rhinosinusitis. Many patients will store pre-made solution for convenient use. This study investigated the microbiological properties of differing recipes and storage temperatures.

METHOD

Three irrigation recipes (containing sodium chloride, sodium bicarbonate and sucrose) were stored at 5oC and 22oC. Further samples were inoculated with Staphylococcus aureus and Pseudomonas aeruginosa. Sampling and culturing were conducted at intervals from day 0-12 to examine for bacterial presence or persistence.

RESULTS

No significant bacterial growth was detected in any control solution stored at 5oC. Saline solutions remained relatively bacterial free, with poor survival of inoculated bacteria, which may be related to either lower pH or lower osmolality. Storing at room temperature increased the risk of contamination in control samples, particularly from pseudomonas.

CONCLUSION

If refrigerated, pre-made nasal irrigation solutions can be stored safely for up to 12 days without risking cross-contamination to irrigation equipment or patients.

Coexistence of Virulence Factors and Efflux Pump Genes in Clinical Isolates of Pseudomonas aeruginosa: Analysis of Biofilm-Forming Strains from Iran

Background

Biofilm formation and efflux pumps (EPs) correlation play a critical role in the pathogenicity and antibiotic resistance of Pseudomonas aeruginosa. In this study, biofilm formation and EP's collaborative role in clinical isolates of P. aeruginosa infection were investigated.

Methods

Eighty-six (86) P. aeruginosa isolates were collected from different clinical specimens and were confirmed using different biochemical tests. The formation of biofilm was investigated by using a crystal violet assay. Also, EP genes were identified by the PCR method.

Results

Based on the results, gentamicin-resistant (n = 50, 66.29%) and ciprofloxacin-resistant (n = 61, 69.66%) strains were the most frequent and colistin (n = 1, 1.12%) and ceftazidime (n = 12, 7.86%) resistant strains were the least prevalent. Furthermore, 22 isolates (31.42%) were MDR, and 11 isolates (12.35%) were XDR strains. Also, 19 isolates (22.47%) were classified as strong biofilm, 29 isolates (21.34%) as moderate biofilm, and 3 (11.23%) isolates as weak biofilm producers. The distribution of the EP genes was as follows: mexA (n = 44, 34.83%), mexB (n = 33, 32.58%), oprM (n = 59, 29.21%), oprD (n = 61, 30.33%), tetA (n = 22, 25.58%), tetR (n = 19, 22.09%), and emrE (n = 21, 24.41%). However, there was a strong significant association between biofilm formation and EPs in P. aeruginosa. Conclusions. In this study, we suggested that the presence of a multidrug resistance efflux pump, MexEF-OprN, significantly reduced P. aeruginosa pathogenicity. In contrast, the presence of the MexAB-OprM and MexCD-OprJ pumps did not affect virulence.

Development of a Solid Dispersion of Nystatin with Maltodextrin as a Carrier Agent: Improvements in Antifungal Efficacy against Candida spp. Biofilm Infections

The aim of this study was to improve the treatment of Candida albicans biofilms through the use of nystatin solid dispersions developed using maltodextrins as a hyperosmotic carrier. Characterization studies by differential scanning calorimetry, X-ray diffraction, dissolution studies, and particle size analysis were performed to evaluate changes in nystatin crystallinity. Antifungal activity and anti-biofilm efficacy were assessed by microbiological techniques. The results for nystatin solid dispersions showed that the enhancement of antifungal activity may be related to the high proportions of maltodextrins. Anti-biofilm assays showed a significant reduction (more than 80%) on biofilm formation with SD-N:MD [1:6] compared to the nystatin reference suspension. The elaboration process and physicochemical properties of SD-N:MD [1:6] could be a promising strategy for treatment of Candida biofilms.

Biofilms as Promoters of Bacterial Antibiotic Resistance and Tolerance

Multidrug resistant bacteria are a global threat for human and animal health. However, they are only part of the problem of antibiotic failure. Another bacterial strategy that contributes to their capacity to withstand antimicrobials is the formation of biofilms. Biofilms are associations of microorganisms embedded a self-produced extracellular matrix. They create particular environments that confer bacterial tolerance and resistance to antibiotics by different mechanisms that depend upon factors such as biofilm composition, architecture, the stage of biofilm development, and growth conditions. The biofilm structure hinders the penetration of antibiotics and may prevent the accumulation of bactericidal concentrations throughout the entire biofilm. In addition, gradients of dispersion of nutrients and oxygen within the biofilm generate different metabolic states of individual cells and favor the development of antibiotic tolerance and bacterial persistence. Furthermore, antimicrobial resistance may develop within biofilms through a variety of mechanisms. The expression of efflux pumps may be induced in various parts of the biofilm and the mutation frequency is induced, while the presence of extracellular DNA and the close contact between cells favor horizontal gene transfer. A deep understanding of the mechanisms by which biofilms cause tolerance/resistance to antibiotics helps to develop novel strategies to fight these infections.

Increased antibiotic efficacy and noninvasive monitoring of Staphylococcus epidermidis biofilms using per-cysteamine-substituted γ-cyclodextrin - A delivery effect validated by fluorescence microscopy

Limited and poor delivery of antibiotics is cited as one reason for the difficulty in treating antibiotic-resistant biofilms associated with chronic infections. We investigate the effectiveness of a positively charged, single isomer cyclodextrin derivative, octakis[6-(2-aminoethylthio)-6-deoxy]-γ-CD (γCys) to improve the delivery of antibiotics to biofilms. Using multiphoton laser scanning microscopy complemented with super-resolution fluorescence microscopy, we showed that γCys tagged with fluorescein (FITC) is uniformly distributed throughout live S. epidermidis biofilm cultures in vitro and results suggest it is localized extracellularly in the biofilm matrix. NMR spectroscopic data in aqueous solution confirm that γCys forms inclusion complexes with both the antibiotics oxacillin and rifampicin. Efficacy of γCys/antibiotic (oxacillin and rifampicin) was measured in the biofilms. While treatment with γCys/oxacillin had little improvement over oxacillin alone, γCys/rifampicin reduced the biofilm viability to background levels demonstrating a remarkable improvement over rifampicin alone. The strong synergistic effect for γCys/rifampicin is at this stage not clearly understood, but plausible explanations are related to increased solubility of rifampicin upon complexation and/or synergistic interference with components of the biofilm. The results demonstrate that designed cyclodextrin nanocarriers, like γCys, efficiently deliver suitable antibiotics to biofilms and that fluorescence microscopy offers a novel approach for mechanistic investigations.

Antimicrobial activity of honey in periodontal disease: a systematic review

BACKGROUND

Honey has shown positive antimicrobial and anti-inflammatory actions in several dermatological studies; however, it is unclear if it could be effective in the treatment of periodontal disease.

OBJECTIVES

To answer the question: Does honey have antimicrobial activity against periodontopathogens?

METHODS

Six electronic databases were screened from initiation to 31 January 2019 for randomized clinical trials (RCTs) and controlled in vitro studies exploring the antimicrobial effect of honey against periodontopathogens. Honey's botanical origin, periopathogens that showed microbial susceptibility to honey, MICs, microbial growth conditions, control product and clinical follow-up were the main investigated outcomes. The risk of bias (RoB) of included RCTs was assessed using the Cochrane Collaboration RoB tool. The RoB of in vitro studies was evaluated based on the Sarkis-Onofre judgement model adapted to the context of honey.

RESULTS

A total of 1448 publications were found as search results in the screened databases. Sixteen eligible papers were included based on predetermined inclusion criteria. Retained studies included 5 RCTs and 11 in vitro controlled trials. Manuka and multifloral honeys were the most studied varieties. The tested honeys showed a significant antimicrobial action, with different MICs, against eight periopathogens. Four of the five RCTs showed a high RoB, while 4 of the 11 retained in vitro studies showed a medium RoB.

CONCLUSIONS

Honey showed a significant antimicrobial activity against all targeted periopathogens. Additional experiments are required to explore the entire antimicrobial spectrum of honey towards all pathogens involved in periodontal disease.

Conceptual Model of Biofilm Antibiotic Tolerance That Integrates Phenomena of Diffusion, Metabolism, Gene Expression, and Physiology

Transcriptomic, metabolomic, physiological, and computational modeling approaches were integrated to gain insight into the mechanisms of antibiotic tolerance in an in vitro biofilm system. Pseudomonas aeruginosa biofilms were grown in drip flow reactors on a medium composed to mimic the exudate from a chronic wound. After 4 days, the biofilm was 114 μm thick with 9.45 log₁₀ CFU cm^-2 These biofilms exhibited tolerance, relative to exponential-phase planktonic cells, to subsequent treatment with ciprofloxacin. The specific growth rate of the biofilm was estimated via elemental balances to be approximately 0.37 h^-1 and with a reaction-diffusion model to be 0.32 h^-1, or one-third of the maximum specific growth rate for planktonic cells. Global analysis of gene expression indicated lower transcription of ribosomal genes and genes for other anabolic functions in biofilms than in exponential-phase planktonic cells and revealed the induction of multiple stress responses in biofilm cells, including those associated with growth arrest, zinc limitation, hypoxia, and acyl-homoserine lactone quorum sensing. Metabolic pathways for phenazine biosynthesis and denitrification were transcriptionally activated in biofilms. A customized reaction-diffusion model predicted that steep oxygen concentration gradients will form when these biofilms are thicker than about 40 μm. Mutant strains that were deficient in Psl polysaccharide synthesis, the stringent response, the stationary-phase response, and the membrane stress response exhibited increased ciprofloxacin susceptibility when cultured in biofilms. These results support a sequence of phenomena leading to biofilm antibiotic tolerance, involving oxygen limitation, electron acceptor starvation and growth arrest, induction of associated stress responses, and differentiation into protected cell states.IMPORTANCE Bacteria in biofilms are protected from killing by antibiotics, and this reduced susceptibility contributes to the persistence of infections such as those in the cystic fibrosis lung and chronic wounds. A generalized conceptual model of biofilm antimicrobial tolerance with the following mechanistic steps is proposed: (i) establishment of concentration gradients in metabolic substrates and products; (ii) active biological responses to these changes in the local chemical microenvironment; (iii) entry of biofilm cells into a spectrum of states involving alternative metabolisms, stress responses, slow growth, cessation of growth, or dormancy (all prior to antibiotic treatment); (iv) adaptive responses to antibiotic exposure; and (v) reduced susceptibility of microbial cells to antimicrobial challenges in some of the physiological states accessed through these changes.

Luminescent Nanosensors for Ratiometric Monitoring of Three-Dimensional Oxygen Gradients in Laboratory and Clinical Pseudomonas aeruginosa Biofilms

Bacterial biofilms can form persistent infections on wounds and implanted medical devices and are associated with many chronic diseases, such as cystic fibrosis. These infections are medically difficult to treat, as biofilms are more resistant to antibiotic attack than their planktonic counterparts. An understanding of the spatial and temporal variation in the metabolism of biofilms is a critical component toward improved biofilm treatments. To this end, we developed oxygen-sensitive luminescent nanosensors to measure three-dimensional (3D) oxygen gradients, an application of which is demonstrated here with Pseudomonas aeruginosa biofilms. The method was applied here and improves on traditional one-dimensional (1D) methods of measuring oxygen profiles by investigating the spatial and temporal variation of oxygen concentration when biofilms are challenged with antibiotic attack. We observed an increased oxygenation of biofilms that was consistent with cell death from comparisons with antibiotic kill curves for PAO1. Due to the spatial and temporal nature of our approach, we also identified spatial and temporal inhomogeneities in the biofilm metabolism that are consistent with previous observations. Clinical strains of P. aeruginosa subjected to similar interrogation showed variations in resistance to colistin and tobramycin, which are two antibiotics commonly used to treat P. aeruginosa infections in cystic fibrosis patients.IMPORTANCE Biofilm infections are more difficult to treat than planktonic infections for a variety of reasons, such as decreased antibiotic penetration. Their complex structure makes biofilms challenging to study without disruption. To address this limitation, we developed and demonstrated oxygen-sensitive luminescent nanosensors that can be incorporated into biofilms for studying oxygen penetration, distribution, and antibiotic efficacy-demonstrated here with our sensors monitoring antibiotic impacts on metabolism in biofilms formed from clinical isolates. The significance of our research is in demonstrating not only a nondisruptive method for imaging and measuring oxygen in biofilms but also that this nanoparticle-based sensing platform can be modified to measure many different ions and small molecule analytes.

Non-invasive imaging of oxygen concentration in a complex in vitro biofilm infection model using 19 F MRI: Persistence of an oxygen sink despite prolonged antibiotic therapy

PURPOSE

Oxygen availability is a critical determinant of microbial biofilm activity and antibiotic susceptibility. However, measuring oxygen gradients in these systems remains difficult, with the standard microelectrode approach being both invasive and limited to single-point measurement. The goal of the study was to develop a ¹⁹ F MRI approach for 2D oxygen mapping in biofilm systems and to visualize oxygen consumption behavior in real time during antibiotic therapy.

METHODS

Oxygen-sensing beads were created by encapsulating an emulsion of oxygen-sensing fluorocarbon into alginate gel. Escherichia coli biofilms were grown in and on the alginate matrix, which was contained inside a packed bed column subjected to nutrient flow, mimicking the complex porous structure of human wound tissue, and subjected to antibiotic challenge.

RESULTS

The linear relationship between ¹⁹ F spin-lattice relaxation rate R₁ and local oxygen concentration permitted noninvasive spatial mapping of oxygen distribution in real time over the course of biofilm growth and subsequent antibiotic challenge. This technique was used to visualize persistence of microbial oxygen respiration during continuous gentamicin administration, providing a time series of complete spatial maps detailing the continued bacterial utilization of oxygen during prolonged chemotherapy in an in vitro biofilm model with complex spatial structure.

CONCLUSIONS

Antibiotic exposure temporarily causes oxygen consumption to enter a pseudosteady state wherein oxygen distribution becomes fixed; oxygen sink expansion resumes quickly after antibiotic clearance. This technique may provide valuable information for future investigations of biofilms by permitting the study of complex geometries (typical of in vivo biofilms) and facilitating noninvasive oxygen measurement.

Biofilm-Leukocyte Cross-Talk: Impact on Immune Polarization and Immunometabolism

Biofilms are bacterial communities contained within an extracellular matrix, which can colonize both native tissues and artificial surfaces. In particular, indwelling medical devices and prosthetic implants are targets for biofilm formation because they facilitate bacterial attachment via host proteins that coat the foreign body. Biofilm infections are particularly challenging to treat, since they are not readily cleared by antibiotics, require invasive procedures to eradicate, and are prone to recurrence. It has been demonstrated that biofilm-derived products can actively suppress proinflammatory immune responses, as evident by the recruitment of myeloid-derived suppressor cells and macrophage (MФ) polarization towards an anti-inflammatory state. Recent studies have shown that alterations in leukocyte metabolism shape their inflammatory phenotype and function. For example, anti-inflammatory MФs are biased towards oxidative phosphorylation whereas proinflammatory MФs favor aerobic glycolysis. This review will compare the immune responses elicited by planktonic and biofilm bacterial infections, with a discussion on the metabolic properties of MФs and neutrophils in response to both bacterial growth conditions.