Biofilm dispersion in Pseudomonas aeruginosa

Physico-chemical characterization of caesium and strontium using fluorescent intensity of bacteria in a microfluidic platform

Recently, the impact of radioactive caesium (Cs) and strontium (Sr) on human health and the ecosystem has been a major concern due to the use of nuclear energy. However, this study observed changes in green-fluorescent (GFP)-tagged Pseudomonas aeruginosa PAO1 biofilms by injecting non-radioactive caesium chloride (CsCl) and strontium chloride (SrCl₂) into microstructures embedded in polydimethylsiloxane microfluidic devices, which were used due to their strong toxicity limitations. Four types of microstructures with two different diameters were used in the study. The change of biofilm thickness from fluid velocity and wall shear stress was estimated using computational fluid dynamics and observed throughout the experiment. The effect of pore space became a significant physical factor when the fluid was flowing through the microfluidic devices. As the pore space increased, the biofilm growth increased; therefore, triangular microstructures with the largest pore space showed the best growth of biofilm. Caesium chloride (CsCl) and strontium chloride (SrCl₂), less toxic than radioactive caesium (Cs) and strontium (Sr), completely eradicated the P. aeruginosa PAO1 biofilm with low concentrations. The combined effect of toxicity, fluid velocity, wall shear stress and microstructures increased the efficiency of biofilm eradication. These findings on microfluidic chips can help to indirectly predict the impact on human public health and ecosystems without using radioactive chemicals.

Perspectives towards antibiotic resistance: from molecules to population

For a long time, antibiotics have been 'magical weapons' to combat pathogenic microbes. The success of antibiotics is now greatly threatened by resistance to antibiotics and many scientists have already talked about the coming of the postantibiotic era. This special issue is prepared to understand recent research findings and new concepts about antibiotic resistance. Above all, this special issue explores mechanisms for the generation, selection, and spread of antibiotic resistance, and gives insight into what to target to prevent the development of antibiotic resistance. Just as antibiotics came from the concept of "magic bullet", a breakthrough will come from a new concept based on a profound understanding of antibiotic resistance.

Sensitizing bacterial cells to antibiotics by shape recovery triggered biofilm dispersion

Microbial biofilms are a leading cause of chronic infections in humans and persistent biofouling in industries due to extremely high-level tolerance of biofilm cells to antimicrobial agents. Eradicating mature biofilms is especially challenging because of the protection of the extracellular matrix and slow growth of biofilm cells. Recently, we reported that established biofilms can be effectively removed (e.g. 99.9% dispersion of 48 h Pseudomonas aeruginosa PAO1 biofilms) by shape memory polymer-based dynamic changes in surface topography. Here, we demonstrate that such biofilm dispersion also sensitizes biofilm cells to conventional antibiotics. For example, shape recovery in the presence of 50 µg/mL tobramycin reduced biofilm cell counts by more than 3 logs (2,479-fold) compared to the static flat control. The observed effects were attributed to the disruption of biofilm structure and increase in cellular activities as evidenced by an 11.8-fold increase in intracellular level of adenosine triphosphate (ATP), and 4.1-fold increase in expression of the rrnB gene in detached cells. These results can help guide the design of new control methods to better combat biofilm associated antibiotic-resistant infections. STATEMENT OF SIGNIFICANCE: Microbial infections are challenging due to high-level antibiotic resistance of biofilm cells. The protection of an extracellular matrix and slow growth of biofilm cells render conventional antibiotics ineffective. Thus, it is important to develop new technologies that can remove mature biofilms and sensitize biofilm cells to antibiotics. Recently, we demonstrated that dynamic change in surface topography can remove 48 h Pseudomonas aeruginosa PAO1 biofilms by 99.9%. In this study, we investigated how shape recovery triggered dispersion affect the physiology of biofilm cells and associated antibiotic susceptibility. These results are helpful for understanding biofilm dispersion and developing more effective control methods.

Circular pellicles formed by Pseudomonas alkylphenolica KL28 are a sophisticated architecture principally designed by matrix substance

The colonization of liquid surfaces as floating biofilms or pellicles is a bacterial adaptation to optimally occupy the airliquid (A-L) niche. In aerobic heterotrophs, pellicle formation is beneficial for the utilization of O₂ and nonpolar organic compounds. Pseudomonas alkylphenolica KL28, an alkylphenol degrader, forms flat circular pellicles that are 0.3-0.5 mm in diameter. In this study, we first monitored the pellicle developmental patterns of multicellular organization from the initial settlement stage. The pellicles developed by clonal growth and mutants for flagella and pilus formation established normal pellicles. In contrast, the mutants of an epm gene cluster for biosynthesis of alginate-like polymer were incompetent in cell alignment for initial two-dimensional (2D) pellicle growth, suggesting the role of the Epm polymer as a structural scaffold for pellicle biofilms. Microscopic observation revealed that the initial 2D growth transited to multilayers by an accumulated self-produced extracellular polymeric substance that may exert a constraint force. Electron microscopy and confocal laser scanning microscopy revealed that the fully matured pellicle structures were densly packed with matrix-encased cells displaying distinct arrangements. The cells on the surface of the pellicle were relatively flat, and those inside were longitudinally cross-packed. The extracellular polysaccharide stained by Congo red was denser on the pellicle rim and a thin film was observed in the open spaces, indicative of its role in pellicle flotation. Our results demonstrate that P. alkylphenolica KL28 coordinately dictates the cell arrangements of pellicle biofilms by the controlled growth of constituent cells that accumulate extracellular polymeric substances.

Antibiofilm effect of biofilm-dispersing agents on clinical isolates of Pseudomonas aeruginosa with various biofilm structures

Pseudomonas aeruginosa, an opportunistic human pathogen, causes many biofilm-mediated chronic infections. In this study, biofilm structures of various clinical strains of P. aeruginosa isolated from hospitalized patients were examined and their influence on the biofilm-dispersing effects of chemicals was investigated. The clinical isolates formed structurally distinct biofilms that could be classified into three different groups: 1) mushroom-like, 2) thin flat, and 3) thick flat structures. A dispersion of these differently structured biofilms was induced using two biofilm-dispersing agents, anthranilate and sodium nitroprusside (SNP). Although both SNP and anthranilate could disperse all types of biofilms, the thick flat biofilms were dispersed less efficiently than the biofilms of other structures. This suggests that biofilm-dispersing agents have higher potency on the biofilms of porous structures than on densely packed biofilms.

Molecules and Mechanisms Underlying the Antimicrobial Activity of Escapin, an l-Amino Acid Oxidase from the Ink of Sea Hares

Many marine animals use chemicals to defend themselves and their eggs from predators. Beyond their ecologically relevant functions, these chemicals may also have properties that make them beneficial for humans, including biomedical and industrial applications. For example, some chemical defenses are also powerful antimicrobial or antitumor agents with relevance to human health and disease. One such chemical defense, escapin, an l-amino acid oxidase in the defensive ink of the sea hare Aplysia californica, and related proteins have been investigated for their biomedical properties. This review details our current understanding of escapin's antimicrobial activity, including the array of molecules generated by escapin's oxidation of its major substrates, l-lysine and l-arginine, and mechanisms underlying these molecules' bactericidal and bacteriostatic effects on planktonic cells and the prevention of formation and removal of bacterial biofilms. Models of escapin's effects are presented, and future directions are proposed.

Effect of bacterial components of mixed culture supernatants of planktonic and biofilm Pseudomonas aeruginosa with commensal Escherichia coli on the neutrophil response in vitro

Pseudomonas aeruginosa (PA) responsible for acute and chronic infections often forms a well-organized bacterial population with different microbial species including commensal strains of Escherichia coli. Bacterial extracellular components of mixed culture can modulate the influence of bacteria on the neutrophil functions. The objective of this study was to compare the effect of pyocyanin, pyoverdine, LPS, exopolysaccharide of single species and mixed culture supernatants of PA strains and E. coli K12 on microbicidal, secretory activity of human neutrophils in vitro. Bacterial components of E. coli K12 in mixed supernatants with 'biofilm' PA strains (PA ATCC, PA BALG) enhanced short-term microbicidal mechanisms and inhibited neutrophil secretion delayed in time. The influence of 'planktonic' PA (PA 9-3) exometabolites in mixed culture is almost mimicked by E. coli K12 effect on functional neutrophil changes. This investigation may help to understand some of the mechanisms of neutrophil response to mixed infections of different PA with other bacteria species.

Interdependence between iron acquisition and biofilm formation in Pseudomonas aeruginosa

Bacterial biofilms remain a persistent threat to human healthcare due to their role in the development of antimicrobial resistance. To combat multi-drug resistant pathogens, it is crucial to enhance our understanding of not only the regulation of biofilm formation, but also its contribution to bacterial virulence. Iron acquisition lies at the crux of these two subjects. In this review, we discuss the role of iron acquisition in biofilm formation and how hosts impede this mechanism to defend against pathogens. We also discuss recent findings that suggest that biofilm formation can also have the reciprocal effect, influencing siderophore production and iron sequestration.

Recent perspectives on the molecular basis of biofilm formation by Pseudomonas aeruginosa and approaches for treatment and biofilm dispersal

Pseudomonas aeruginosa, a Gram-negative, rod-shaped bacterium causes widespread diseases in humans. This bacterium is frequently related to nosocomial infections such as pneumonia, urinary tract infections (UTIs) and bacteriaemia especially in immunocompromised patients. The current review focuses on the recent perspectives on biofilms formation by these bacteria. Biofilms are communities of microorganisms in which cells stick to each other and often adhere to a surface. These adherent cells are usually embedded within a self-produced matrix of extracellular polymeric substance (EPS). Pel, psl and alg operons present in P. aeruginosa are responsible for the biosynthesis of extracellular polysaccharide which plays an important role in cell surface interactions during biofilm formation. Recent studies suggested that cAMP signalling pathway, quorum-sensing pathway, Gac/Rsm pathway and c-di-GMP signalling pathway are the main mechanism that leads to the biofilm formation. Understanding the bacterial virulence depends on a number of cell-associated and extracellular factors and is very essential for the development of potential drug targets. Thus, the review focuses on the major genes involved in the biofilm formation, the state of art update on the biofilm treatment and the dispersal approaches such as targeting adhesion and maturation, targeting virulence factors and other strategies such as small molecule-based inhibitors, phytochemicals, bacteriophage therapy, photodynamic therapy, antimicrobial peptides and natural therapies and vaccines to curtail the biofilm formation by P. aeruginosa.

Use of Whole-Cell Bioassays for Screening Quorum Signaling, Quorum Interference, and Biofilm Dispersion

In most bacteria, a global level of regulation, termed quorum sensing (QS), exists involving intercellular communication via the production and response to cell density-dependent signal molecules. QS has been associated with a number of important features in bacteria including virulence regulation and biofilm formation. Consequently, there is considerable interest in understanding, detecting, and inhibiting QS. N-acylated homoserine lactones (AHLs) are used as extracellular QS signals by a variety of Gram-negative bacteria. Chromobacterium violaceum, commonly found in soil and water, produces the characteristic purple pigment violacein, regulated by AHL-mediated QS. Based on this readily observed pigmentation phenotype, C. violaceum strains can be used to detect various aspects of AHL-mediated QS activity. In another commonly used bioassay organism, Agrobacterium tumefaciens, QS can be detected by the use of a reporter gene such as lacZ. Here, we describe several commonly used approaches incorporating C. violaceum and A. tumefaciens that can be used to detect AHL and QS inhibitors. Due to the inherent low susceptibility of biofilm bacteria to antimicrobial agents, biofilm dispersion, whereby bacteria reenter the planktonic community, is another increasingly important area of research. At least one signal, distinct from traditional QS, has been identified and there are a variety of other environmental factors that also trigger dispersion. We describe a microtiter-based experimental strategy whereby potential biofilm dispersion compounds can be screened.

Antibiofilm agents: A new perspective for antimicrobial strategy

Biofilms are complex microbial architectures that attach to surfaces and encase microorganisms in a matrix composed of self-produced hydrated extracellular polymeric substances (EPSs). In biofilms, microorganisms become much more resistant to antimicrobial treatments, harsh environmental conditions, and host immunity. Biofilm formation by microbial pathogens greatly enhances survival in hosts and causes chronic infections that result in persistent inflammation and tissue damages. Currently, it is believed over 80% of chronic infectious diseases are mediated by biofilms, and it is known that conventional antibiotic medications are inadequate at eradicating these biofilm-mediated infections. This situation demands new strategies for biofilm-associated infections, and currently, researchers focus on the development of antibiofilm agents that are specific to biofilms, but are nontoxic, because it is believed that this prevents the development of drug resistance. Here, we review the most promising antibiofilm agents undergoing intensive research and development.

Mutation of the cyclic di-GMP phosphodiesterase gene in Burkholderia lata SK875 attenuates virulence and enhances biofilm formation

Burkholderia sp. is a gram-negative bacterium that commonly exists in the environment, and can cause diseases in plants, animals, and humans. Here, a transposon mutant library of a Burkholderia lata isolate from a pig with swine respiratory disease in Korea was screened for strains showing attenuated virulence in Caenorhabditis elegans. One such mutant was obtained, and the Tn5 insertion junction was mapped to rpfR, a gene encoding a cyclic di-GMP phosphodiesterase that functions as a receptor. Mutation of rpfR caused a reduction in growth on CPG agar and swimming motility as well as a rough colony morphology on Congo red agar. TLC analysis showed reduced AHL secretion, which was in agreement with the results from plate-based and bioluminescence assays. The mutant strain produced significantly more biofilm detected by crystal violet staining than the parent strain. SEM of the mutant strain clearly showed that the overproduced biofilm contained a filamentous structure. These results suggest that the cyclic di-GMP phosphodiesterase RpfR plays an important role in quorum sensing modulation of the bacterial virulence and biofilm formation.

Anti-biofilm effects of anthranilate on a broad range of bacteria

Anthranilate, one of tryptophan degradation products has been reported to interfere with biofilm formation by Pseudomonas aeruginosa. Here, we investigated the effects of anthranilate on biofilm formation by various bacteria and the mechanisms responsible. Anthranilate commonly inhibited biofilm formation by P. aeruginosa, Vibrio vulnificus, Bacillus subtilis, Salmonella enterica serovar Typhimurium, and Staphylococcus aureus, and disrupted biofilms preformed by these bacteria. Because anthranilate reduced intracellular c-di-GMP and enhanced swimming and swarming motilities in P. aeruginosa, V. vulnificus, B. subtilis, and S. enterica, it is likely that anthranilate disrupts biofilms by inducing the dispersion of these bacteria. On the other hand, in S. aureus, a non-flagellate bacterium that has no c-di-GMP signaling, anthranilate probably inhibits biofilm formation by reducing slime production. These results suggest that anthranilate has multiple ways for biofilm inhibition. Furthermore, because of its good biofilm inhibitory effects and lack of cytotoxicity to human cells even at high concentration, anthranilate appears to be a promising agent for inhibiting biofilm formation by a broad range of bacteria.

Mechanisms and Regulation of Extracellular DNA Release and Its Biological Roles in Microbial Communities

The capacity to release genetic material into the extracellular medium has been reported in cultures of numerous species of bacteria, archaea, and fungi, and also in the context of multicellular microbial communities such as biofilms. Moreover, extracellular DNA (eDNA) of microbial origin is widespread in natural aquatic and terrestrial environments. Different specific mechanisms are involved in eDNA release, such as autolysis and active secretion, as well as through its association with membrane vesicles. It is noteworthy that in microorganisms, in which DNA release has been studied in detail, the production of eDNA is coordinated by the population when it reaches a certain cell density, and is induced in a subpopulation in response to the accumulation of quorum sensing signals. Interestingly, in several bacteria there is also a relationship between eDNA release and the development of natural competence (the ability to take up DNA from the environment), which is also controlled by quorum sensing. Then, what is the biological function of eDNA? A common biological role has not been proposed, since different functions have been reported depending on the microorganism. However, it seems to be important in biofilm formation, can be used as a nutrient source, and could be involved in DNA damage repair and gene transfer. This review covers several aspects of eDNA research: (i) its occurrence and distribution in natural environments, (ii) the mechanisms and regulation of its release in cultured microorganisms, and (iii) its biological roles. In addition, we propose that eDNA release could be considered a social behavior, based on its quorum sensing-dependent regulation and on the described functions of eDNA in the context of microbial communities.

Synthetic biology engineering of biofilms as nanomaterials factories

Bottom-up fabrication of nanoscale materials has been a significant focus in materials science for expanding our technological frontiers. This assembly concept, however, is old news to biology — all living organisms fabricate themselves using bottom-up principles through a vast self-organizing system of incredibly complex biomolecules, a marvelous dynamic that we are still attempting to unravel. Can we use what we have gleaned from biology thus far to illuminate alternative strategies for designer nanomaterial manufacturing? In the present review article, new synthetic biology efforts toward using bacterial biofilms as platforms for the synthesis and secretion of programmable nanomaterials are described. Particular focus is given to self-assembling functional amyloids found in bacterial biofilms as re-engineerable modular nanomolecular components. Potential applications and existing challenges for this technology are also explored. This novel approach for repurposing biofilm systems will enable future technologies for using engineered living systems to grow artificial nanomaterials.

Relative susceptibility of airway organisms to antimicrobial effects of nitric oxide

BACKGROUND

Nitric oxide (NO) is released in the airway as a critical component of innate immune defense against invading pathogenic organisms. It is well documented that bacteriostatic and bactericidal effects of NO are concentration-dependent. However, few data exist comparing relative susceptibility of common pathogens to NO at physiologic concentrations. In this study we evaluated the effects of NO on 4 common airway bacteria and 1 fungus, and examined the potential implications of discrepancies in sensitivity.

METHODS

Staphylococcus epidermis, Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Candida albicans cultures were adjusted to a uniform optical density (OD) and grown in log phase at 37°C with varying concentrations of NO formed by DETA NONOate. Both OD readings and colony forming units (CFUs) were measured at varying time-points to evaluate for inhibitory effects of NO.

RESULTS

P aeruginosa and C albicans were significantly more sensitive to NO at physiologic concentrations typical of the human airway. S aureus was attenuated by NO to a lesser degree, and K pneumoniae and S epidermis were more resistant to NO at all concentrations tested. Air surface liquid from cultured human sinonasal epithelial cells had an additive effect in bacterial killing of P aeruginosa, but not in S aureus.

CONCLUSION

Common airway pathogens have varying levels of susceptibility to NO at physiologic concentrations of innate immune defense. Relative sensitivity of P aeruginosa and relative resistance of S epidermis may help explain the composition of the healthy microbiome, as well as opportunistic infection in the absence of induced NO release.

Phage "delay" towards enhancing bacterial escape from biofilms: a more comprehensive way of viewing resistance to bacteriophages

In exploring bacterial resistance to bacteriophages, emphasis typically is placed on those mechanisms which completely prevent phage replication. Such resistance can be detected as extensive reductions in phage ability to form plaques, that is, reduced efficiency of plating. Mechanisms include restriction-modification systems, CRISPR/Cas systems, and abortive infection systems. Alternatively, phages may be reduced in their “vigor” when infecting certain bacterial hosts, that is, with phages displaying smaller burst sizes or extended latent periods rather than being outright inactivated. It is well known, as well, that most phages poorly infect bacteria that are less metabolically active. Extracellular polymers such as biofilm matrix material also may at least slow phage penetration to bacterial surfaces. Here I suggest that such “less-robust” mechanisms of resistance to bacteriophages could serve bacteria by slowing phage propagation within bacterial biofilms, that is, delaying phage impact on multiple bacteria rather than necessarily outright preventing such impact. Related bacteria, ones that are relatively near to infected bacteria, e.g., roughly 10+ µm away, consequently may be able to escape from biofilms with greater likelihood via standard dissemination-initiating mechanisms including erosion from biofilm surfaces or seeding dispersal/central hollowing. That is, given localized areas of phage infection, so long as phage spread can be reduced in rate from initial points of contact with susceptible bacteria, then bacterial survival may be enhanced due to bacteria metaphorically “running away” to more phage-free locations. Delay mechanisms—to the extent that they are less specific in terms of what phages are targeted—collectively could represent broader bacterial strategies of phage resistance versus outright phage killing, the latter especially as require specific, evolved molecular recognition of phage presence. The potential for phage delay should be taken into account when developing protocols of phage-mediated biocontrol of biofilm bacteria, e.g., as during phage therapy of chronic bacterial infections.

The Social Life of Aeromonas through Biofilm and Quorum Sensing Systems

Bacteria of the genus Aeromonas display multicellular behaviors herein referred to as “social life”. Since the 1990s, interest has grown in cell-to-cell communication through quorum sensing signals and biofilm formation. As they are interconnected, these two self-organizing systems deserve to be considered together for a fresh perspective on the natural history and lifestyles of aeromonads. In this review, we focus on the multicellular behaviors of Aeromonas, i.e., its social life. First, we review and discuss the available knowledge at the molecular and cellular levels for biofilm and quorum sensing. We then discuss the complex, subtle, and nested interconnections between the two systems. Finally, we focus on the aeromonad multicellular coordinated behaviors involved in heterotrophy and virulence that represent technological opportunities and applied research challenges.

Rhamnolipids Mediate an Interspecies Biofilm Dispersal Signaling Pathway

Bacterial biofilms are problematic in natural and anthropogenic environments, and they confer protective properties on their constituent cells, making them difficult to treat with conventional antibiotics. Antibiofilm strategies, therefore, represent a promising direction of research for treating biofilm infections. Natural autodispersal and interspecies dispersal signaling pathways provide insight into cell-cell communication mechanisms, species dynamics in mixed communities, and potential targets for infection therapies. Here, we describe a novel interspecies dispersal signaling pathway between Pseudomonas aeruginosa and Escherichia coli. E. coli biofilms disperse in response to compounds in P. aeruginosa culture supernatant. Two components of the P. aeruginosa Las and Rhl quorum sensing systems, N-(3-oxo-dodecanoyl) homoserine lactone (3oxoC12HSL) and rhamnolipids, are found to act cooperatively to disperse E. coli biofilms. Our results indicate that rhamnolipids do not affect growth, biofilm development, or dispersal in E. coli but instead complement 3oxoC12HSL signaling by inducing selective permeability of the E. coli membrane. The increased target cell permeability is consistent with rhamnolipid-mediated removal of lipopolysaccharide from E. coli membranes and appears to selectively increase the permeability of lipophilic acyl homoserine lactones. This work suggests that rhamnolipids play a critical role in P. aeruginosa-E. coli interspecies signaling. Rhamnolipids and other biosurfactants may have similar effects in other intra- and interspecies chemical signaling pathways.

N-acetylcysteine eradicates Pseudomonas aeruginosa biofilms in bone cement

Biofilm is an example of bacterial group behavior. We investigated the effect of N-acetylcysteine (NAC) alone and in combination with ciprofloxacin on Pseudomonas aeruginosa biofilm formation. Four groups (each contains six molds) of standardized bone cement molds were infected. NAC, ciprofloxacin each alone, and NAC/ciprofloxacin combination were evaluated in point of inhibiting and eradicating biofilm capacity using microbiological and electron microscopical evaluation techniques. Microbial counts and electron microscopical observations showed that the effect of NAC and ciprofloxacin combination on biofilm formation in bone cement is valuable. NAC enhances the beneficial effect of ciprofloxacin when used in combination with it in bone cement. SCANNING 38:766-770, 2016. © 2016 Wiley Periodicals, Inc.

Plasticity of Candida albicans Biofilms

Candida albicans, the most pervasive fungal pathogen that colonizes humans, forms biofilms that are architecturally complex. They consist of a basal yeast cell polylayer and an upper region of hyphae encapsulated in extracellular matrix. However, biofilms formed in vitro vary as a result of the different conditions employed in models, the methods used to assess biofilm formation, strain differences, and, in a most dramatic fashion, the configuration of the mating type locus (MTL). Therefore, integrating data from different studies can lead to problems of interpretation if such variability is not taken into account. Here we review the conditions and factors that cause biofilm variation, with the goal of engendering awareness that more attention must be paid to the strains employed, the methods used to assess biofilm development, every aspect of the model employed, and the configuration of the MTL locus. We end by posing a set of questions that may be asked in comparing the results of different studies and developing protocols for new ones. This review should engender the notion that not all biofilms are created equal.

Human upper airway epithelium produces nitric oxide in response to Staphylococcus epidermidis

BACKGROUND

Nitric oxide (NO) is produced by sinonasal epithelial cells as part of the innate immune response against bacteria. We previously described bitter-taste-receptor-dependent and -independent NO responses to product(s) secreted by Pseudomonas aeruginosa and Staphylococcus aureus, respectively. We hypothesized that sinonasal epithelium would be able to detect the gram-positive, coagulase-negative bacteria Staphylococcus epidermidis and mount a similar NO response.

METHODS

Sinonasal air-liquid interface cultures were treated with conditioned medium (CM) from lab strains and clinical isolates of coagulase-negative staphylococci and S aureus. NO production was quantified by fluorescence imaging. Bitter taste receptor signaling inhibitors were utilized to characterize the pathway responsible for NO production in response to S epidermidis CM.

RESULTS

S epidermidis CM contains a low-molecular-weight, heat, and protease-stabile product that induces an NO synthase (NOS)-mediated NO production that is less robust than the response triggered by S aureus CM. The S epidermidis CM-stimulated NO response is not inhibited by antagonists of phospholipase C isoform β-2 nor the transient receptor potential melastatin isoform 5 ion channel, both critical to bitter taste signaling.

CONCLUSION

This study identifies an NO-mediated innate defense response in sinonasal epithelium elicited by S epidermidis product(s). The active bacterial product is likely a small, nonpeptide molecule that stimulates a pathway independent of bitter taste receptors. Although the NO response to S epidermidis is less vigorous compared with S aureus, the product(s) share similar characteristics. Together, the responses to staphylococci species may help explain the pathophysiology of upper respiratory infections.