Synergistic inhibition of Streptococcal biofilm by ribose and xylitol

A fungal metabolic regulator underlies infectious synergism during Candida albicans-Staphylococcus aureus intra-abdominal co-infection

Candida albicans and Staphylococcus aureus are two commonly associated pathogens that cause nosocomial infections with high morbidity and mortality. Our prior and current work using a murine model of polymicrobial intra-abdominal infection (IAI) demonstrates that synergistic lethality is driven by Candida-induced upregulation of functional S. aureus α-toxin leading to polymicrobial sepsis and organ damage. In order to determine the candidal effector(s) mediating enhanced virulence, an unbiased screen of C. albicans transcription factor mutants was undertaken revealing that zcf13Δ/Δ fails to drive augmented α-toxin or lethal synergism during co-infection. A combination of transcriptional and phenotypic profiling approaches shows that ZCF13 regulates genes involved in pentose metabolism, including RBK1 and HGT7 that contribute to fungal ribose catabolism and uptake, respectively. Subsequent experiments reveal that ribose inhibits the staphylococcal agr quorum sensing system and concomitantly represses toxicity. Unlike wild-type C. albicans, zcf13Δ/Δ did not effectively utilize ribose during co-culture or co-infection leading to exogenous ribose accumulation and agr repression. Forced expression of RBK1 and HGT7 in the zcf13Δ/Δ mutant fully restores pathogenicity during co-infection. Collectively, our results detail the interwoven complexities of cross-kingdom interactions and highlight how intermicrobial metabolism impacts polymicrobial disease pathogenesis with devastating consequences for the host.

Alteration of oral microbial biofilms by sweeteners

There is a growing interest in using sweeteners for taste improvement in the food and drink industry. Sweeteners were found to regulate the formation or dispersal of structural components of microbial biofilms. Dietary sugars may enhance biofilm formation and facilitate the development of antimicrobial resistance, which has become a major health issue worldwide. In contrast, bulk and non-nutritive sweeteners are also beneficial for managing microbial infections. This review discusses the clinical significance of oral biofilms formed upon the administration of nutritive and non-nutritive sweeteners. The underlying mechanism of action of sweeteners in the regulation of mono- or poly-microbial biofilm formation and destruction is comprehensively discussed. Bulk and non-nutritive sweeteners have also been used in conjunction with antimicrobial substances to reduce microbial biofilm formation. Formulations with bulk and non-nutritive sweeteners have been demonstrated to be particularly efficient in this regard. Finally, future perspectives with respect to advancing our understanding of mechanisms underlying biofilm regulation activities of sweeteners are presented as well. Several alternative strategies for the application of bulk sweeteners and non-nutritive sweeteners have been employed to control the biofilm-forming microbial pathogens. Gaining insight into the underlying mechanisms responsible for enhancing or inhibiting biofilm formation and virulence properties by both mono- and poly-microbial species in the presence of the sweetener is crucial for developing a therapeutic agent to manage microbial infections.

A fungal metabolic regulator underlies infectious synergism during Candida albicans - Staphylococcus aureus intra-abdominal co-infection

Candida albicans and Staphylococcus aureus are two commonly associated pathogens that cause nosocomial infections with high morbidity and mortality. Our prior and current work using a murine model of polymicrobial intra-abdominal infection (IAI) uncovered synergistic lethality that was driven by Candida -induced upregulation of functional S. aureus ⍺-toxin leading to polymicrobial sepsis and organ damage. In order to determine the candidal effector(s) mediating enhanced virulence, an unbiased screen of C. albicans transcription factor mutants was undertaken and revealed that zcf13 Δ/Δ failed to drive augmented ⍺-toxin or lethal synergism during co-infection. Using a combination of transcriptional and phenotypic profiling approaches, ZCF13 was shown to regulate genes involved in pentose metabolism, including RBK1 and HGT7 that contribute to fungal ribose catabolism and uptake, respectively. Subsequent experiments revealed that ribose inhibited the staphylococcal agr quorum sensing system and concomitantly repressed toxicity. Unlike wild-type C. albicans , zcf13 Δ/Δ was unable to effectively utilize ribose during co-culture or co-infection leading to exogenous ribose accumulation and agr repression. Forced expression of RBK1 and HGT7 in the zcf13 Δ/Δ mutant fully restored pathogenicity during co-infection. Collectively, our results detail the interwoven complexities of cross-kingdom interactions and highlight how intermicrobial metabolism impacts polymicrobial disease pathogenesis with devastating consequences for the host.

Biochemical and microbiological characterization of a thermotolerant bacterial consortium involved in the corrosion of Aluminum Alloy 7075

Microorganisms can play a significant role in material corrosion, with bacterial biofilms as major participants in microbially influenced corrosion (MIC). The exact mechanisms by which this takes place are poorly understood, resulting in a scarcity of information regarding MIC detection and prevention. In this work, a consortium of moderately thermophilic bacteria isolated from a biofilm growing over aluminum alloy 7075 was characterized. Its effect over the alloy was evaluated on a 40-day period using Electron Microscopy, demonstrating acceleration of corrosion in comparison to the abiotic control. The bacterial consortium was biochemically and microbiologically characterized as an attempt to elucidate factors contributing to corrosion. Molecular analysis revealed that the consortium consisted mainly of members of the Bacillus genus, with lower abundance of other genera such as Thermoanaerobacterium, Anoxybacillus and Paenibacillus. The EPS polysaccharide presented mainly mannose, galactose, rhamnose and ribose. Our observations suggest that the acidification of the culture media resulting from bacterial metabolism acted as the main contributor to corrosion, hinting at an unspecific mechanism. The consortium was not sulfate-reducing, but it was found to produce hydrogen, which could also be a compounding factor for corrosion.

Structural variations on Salmonella biofilm by exposition to river water

Biofilm formation, as adapting strategies, is the result of stressful conditions that Salmonella faces in hostile environments like surface water. We evaluated river water effect on Salmonella biofilm formation ability in terms of physical, morphological characteristics and chemical composition. A new morphotype SPAM (soft, pink and mucoid) was detected in Oranienburg strains S-76 and S-347 (environmental and clinical isolate). Oranienburg serotypes showed very marked behavior in adherence, pellicle liquid-air and resistance, being Oranienburg S-76 the strongest biofilm producer. All strains when exposed to river water presented an overlapping mucoid layer in the morphotype and increased their motility except Oranienburg S-347. The most motile was Typhimurium (control) and the least Infantis S-304 (clinical isolate). Mannose, glucose, galactose and ribose were the main biofilm sugar components; type and concentration of sugar suggest a morphotype/serotype dependent pattern. Strong morphotypes expressed in this study may be an effective protective strategy for Salmonella in hostile environments.

Strategies to Combat Caries by Maintaining the Integrity of Biofilm and Homeostasis during the Rapid Phase of Supragingival Plaque Formation

Bacteria in the oral cavity, including commensals and opportunistic pathogens, are organized into highly specialized sessile communities, coexisting in homeostasis with the host under healthy conditions. A dysbiotic environment during biofilm evolution, however, allows opportunistic pathogens to become the dominant species at caries-affected sites at the expense of health-associated taxa. Combining tooth brushing with dentifrices or rinses combat the onset of caries by partially removes plaque, but resulting in the biofilm remaining in an immature state with undesirables’ consequences on homeostasis and oral ecosystem. This leads to the need for therapeutic pathways that focus on preserving balance in the oral microbiota and applying strategies to combat caries by maintaining biofilm integrity and homeostasis during the rapid phase of supragingival plaque formation. Adhesion, nutrition, and communication are fundamental in this phase in which the bacteria that have survived these adverse conditions rebuild and reorganize the biofilm, and are considered targets for designing preventive strategies to guide the biofilm towards a composition compatible with health. The present review summarizes the most important advances and future prospects for therapies based on the maintenance of biofilm integrity and homeostasis as a preventive measure of dysbiosis focused on these three key factors during the rapid phase of plaque formation.

Xylitol enhances synthesis of propionate in the colon via cross-feeding of gut microbiota

BACKGROUND

Xylitol, a white or transparent polyol or sugar alcohol, is digestible by colonic microorganisms and promotes the proliferation of beneficial bacteria and the production of short-chain fatty acids (SCFAs), but the mechanism underlying these effects remains unknown. We studied mice fed with 0%, 2% (2.17 g/kg/day), or 5% (5.42 g/kg/day) (weight/weight) xylitol in their chow for 3 months. In addition to the in vivo digestion experiments in mice, 3% (weight/volume) (0.27 g/kg/day for a human being) xylitol was added to a colon simulation system (CDMN) for 7 days. We performed 16S rRNA sequencing, beneficial metabolism biomarker quantification, metabolome, and metatranscriptome analyses to investigate the prebiotic mechanism of xylitol. The representative bacteria related to xylitol digestion were selected for single cultivation and co-culture of two and three bacteria to explore the microbial digestion and utilization of xylitol in media with glucose, xylitol, mixed carbon sources, or no-carbon sources. Besides, the mechanisms underlying the shift in the microbial composition and SCFAs were explored in molecular contexts.

RESULTS

In both in vivo and in vitro experiments, we found that xylitol did not significantly influence the structure of the gut microbiome. However, it increased all SCFAs, especially propionate in the lumen and butyrate in the mucosa, with a shift in its corresponding bacteria in vitro. Cross-feeding, a relationship in which one organism consumes metabolites excreted by the other, was observed among Lactobacillus reuteri, Bacteroides fragilis, and Escherichia coli in the utilization of xylitol. At the molecular level, we revealed that xylitol dehydrogenase (EC 1.1.1.14), xylulokinase (EC 2.7.1.17), and xylulose phosphate isomerase (EC 5.1.3.1) were key enzymes in xylitol metabolism and were present in Bacteroides and Lachnospiraceae. Therefore, they are considered keystone bacteria in xylitol digestion. Also, xylitol affected the metabolic pathway of propionate, significantly promoting the transcription of phosphate acetyltransferase (EC 2.3.1.8) in Bifidobacterium and increasing the production of propionate.

CONCLUSIONS

Our results revealed that those key enzymes for xylitol digestion from different bacteria can together support the growth of micro-ecology, but they also enhanced the concentration of propionate, which lowered pH to restrict relative amounts of Escherichia and Staphylococcus. Based on the cross-feeding and competition among those bacteria, xylitol can dynamically balance proportions of the gut microbiome to promote enzymes related to xylitol metabolism and SCFAs. Video Abstract.

Quorum sensing systems as a new target to prevent biofilm-related oral diseases

OBJECTIVE

The present study summarizes the current knowledge on the role of bacterial extracellular signaling systems, known as quorum sensing (QS), in oral biofilm formation, and on the possibility of blocking these microbial communication systems as a potential approach to prevent and treat oral infectious diseases.

METHODS

A detailed literature review of the current knowledge of QS in the oral cavity was performed, using the databases MEDLINE (through PubMed) and Web of Science.

RESULTS

Accumulating direct and indirect evidence indicates an important role of QS molecules in the oral microbial ecosystem.

CONCLUSIONS

The mechanisms regulating gene expression through bacterial communication systems constitute a promising target to control oral biofilm formation. Although cell-to-cell communication is pivotal for biofilm formation of many pathogenic bacteria, knowledge concerning microbial interactions and signaling processes within multispecies biofilms in the oral cavity is still limited.

Optical nanosensors for biofilm detection in the food industry: principles, applications and challenges

Biofilms are the universal lifestyle of bacteria enclosed in extracellular polymeric substances (EPS) on the contact surfaces of food processing facilities. The EPS-encapsulated foodborne bacterial pathogens are the main food contaminant sources, posing a serious threat to human health. The microcrystalline, sophisticated and dynamic biofilms necessitate the development of conventional microscopic imaging and spectral technology. Nanosensors, which can transfer the biochemical information into optical signals, have recently emerged for biofilm optical detection with high sensitivity and high spatial resolution at nanoscale scopes. Therefore, the aim of this review is to clarify the main detection scope in biofilms and the detection principles of optical nanosensors arousing Raman enhancement, fluoresce conversion and color change. The difficulties and challenges of biofilm characterization including the secretion and variation of main biochemical components are first discussed, the details about the principles and application examples of bioassays targeting foodborne pathogens based on optical nanosensors are then summarized. Finally, the challenges and future trends in developing optical nanosensors are also highlighted. The current review indicates that optical nanosensors have taken the challenges of detecting biofilm in complex food samples, including the characterization of biofilm formation mechanism, identification of microbial metabolic activities, diagnosis of potential food pathogens and sanitation monitoring of food processing equipment. Numerous in-depth explorations and various trials have proven that the bioassays based on multifunctional optical nanosensors are promising to ensure and promote food safety and quality. However, there still remains a daunting challenge to structure reproducible, biocompatible and applicable nano-sensors for biofilm characterization, identification, and imaging.

Exploration of singular and synergistic effect of xylitol and erythritol on causative agents of dental caries

Non-cariogenic sweet substances, like sugar alcohols, are used to decrease the risk of caries by reducing the growth of dental plaque. The aim of our study was to reveal the impact of xylitol and erythritol on the growth and biofilm formation of cariogenic bacteria including as a novelty, set of clinical mutans streptococci and Scardovia wiggsiae and to assess the possible synergistic influence of these polyols. We found both xylitol and erythritol to express high growth inhibition effect on cariogenic bacteria. In synergistic effect experiments, 10% polyol combination with excess of erythritol was found to be more effective against growth of Streptococcus mutans and the combination with excess of xylitol more effective against growth of Streptococcus sobrinus and S. wiggsiae. In biofilm inhibition experiments, solutions of 10% polyols in different combinations and 15% single polyols were equally effective against mutans streptococci. At the same time, higher biofilm formation of S. wiggsiae compared to experiments without polyols was detected in different polyol concentrations for up to 34%. In conclusion, both erythritol and xylitol as well as their combinations inhibit the growth of different cariogenic bacteria. Biofilm formation of mutans streptococci is also strongly inhibited. When applying polyols in caries prophylaxis, it is relevant to consider that the profile of pathogens in a particular patient may influence the effect of polyols used.

Integrated Univariate, Multivariate, and Correlation-Based Network Analyses Reveal Metabolite-Specific Effects on Bacterial Growth and Biofilm Formation in Necrotizing Soft Tissue Infections

Necrotizing soft-tissue infections (NSTIs) have multiple causes, risk factors, anatomical locations, and pathogenic mechanisms. In patients with NSTI, circulating metabolites may serve as a substrate having impact on bacterial adaptation at the site of infection. Metabolic signatures associated with NSTI may reveal the potential to be useful as diagnostic and prognostic markers and novel targets for therapy. This study used untargeted metabolomics analyses of plasma from NSTI patients (n = 34) and healthy (noninfected) controls (n = 24) to identify the metabolic signatures and connectivity patterns among metabolites associated with NSTI. Metabolite-metabolite association networks were employed to compare the metabolic profiles of NSTI patients and noninfected surgical controls. Out of 97 metabolites detected, the abundance of 33 was significantly altered in NSTI patients. Analysis of metabolite-metabolite association networks showed a more densely connected network: specifically, 20 metabolites differentially connected between NSTI and controls. A selected set of significantly altered metabolites was tested in vitro to investigate potential influence on NSTI group A streptococcal strain growth and biofilm formation. Using chemically defined media supplemented with the selected metabolites, ornithine, ribose, urea, and glucuronic acid, revealed metabolite-specific effects on both bacterial growth and biofilm formation. This study identifies for the first time an NSTI-specific metabolic signature with implications for optimized diagnostics and therapies.

Enhanced synergistic effects of xylitol and isothiazolones for inhibition of initial biofilm formation by Pseudomonas aeruginosa ATCC 9027 and Staphylococcus aureus ATCC 6538

Bacterial biofilms, formed on biotic or abiotic surfaces, can lead to serious environmental or medical problems. Therefore, it is necessary to find novel antimicrobial agents to combat biofilms, or more effective combinations of existing biocides. In this study, initial biofilms of Pseudomonas aeruginosa ATCC 9027 and Staphylococcus aureus ATCC 6538 in the presence of xylitol or xylitol and isothiazolones were determined using crystal violet staining in 96-well microplates and confocal laser scanning microscopy. Xylitol and isothiazolones exhibited enhanced synergistic inhibition of initial biofilm formation, and also the structure and production of extracellular polymeric substances by P. aeruginosa ATCC 9027 and S. aureus ATCC 6538 in a dose-dependent manner. In addition, xylitol and isothiazolones inhibited and restored the swimming motility of P. aeruginosa ATCC 9027, respectively. These findings show that a combination of xylitol and isothiazolones exerts pronounced antimicrobial activity against P. aeruginosa and S. aureus biofilms and may be applicable for preventing or reducing bacterial biofilms in vitro.

Inhibition of Streptococcus mutans and S. sobrinus biofilms by liamocins from Aureobasidium pullulans

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Liamocins are polyol lipids that specifically inhibit Streptococcus spp..

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Liamocins inhibited biofilms of S. mutans and S. sobrinus in MTP assays.

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MTP results were verified in biofilm flow cell assays.

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Liamocins are potential new inhibitors of oral streptococcal biofilms.

The aim of this study was to determine if the novel anti-streptococcal inhibitors, liamocins, also inhibit biofilm formation by S. mutans and S. sobrinus. S. mutans strain ATCC 25175 and S. sobrinus strain ATCC 33478 were tested for biofilm formation in a rapid microtiter plate (MTP) assay and the effects of added liamocins were determined. This assay measures relative biofilm growth on pin lids. Results were verified in a biofilm flow cell assay, using hydroxyapatite-coated coupons to simulate dental material. Planktonic cultures of S. mutans and S. sobrinus were inhibited by 0.1 mg liamocins/ml. When liamocins were added after the adhesion phase in a rapid microtiter plate assay, S. mutans was inhibited 53% by 5 mg liamocins/ml, while S. sobrinus was more sensitive, showing 100% inhibition at 0.5 mg liamocins/ml. When liamocins were added during the adhesion phase, biofilms of S. mutans showed 78% inhibition at 3.0 mg liamocins/ml. In a biofilm flow cell assay, liamocins added after the adhesion phase at 0.5 mg liamocins/ml inhibited biofilms of S. sobrinus, and appeared to remove biofilms over time. Liamocins were shown for the first time to inhibit biofilm formation by S. mutans and S. sobrinus. Since liamocins are specific for Streptococcus spp., they are potential new inhibitors of oral streptococcal biofilms that should not affect normal oral microflora.

D-Ribose Interferes with Quorum Sensing to Inhibit Biofilm Formation of Lactobacillus paraplantarum L-ZS9

Biofilms help bacteria survive under adverse conditions, and the quorum sensing (QS) system plays an important role in regulating their activities. Quorum sensing inhibitors (QSIs) have great potential to inhibit pathogenic biofilm formation and are considered possible replacements for antibiotics; however, further investigation is required to understand the mechanisms of action of QSIs and to avoid inhibitory effects on beneficial bacteria. Lactobacillus paraplantarum L-ZS9, isolated from fermented sausage, is a bacteriocin-producing bacteria that shows potential to be a probiotic starter. Since exogenous autoinducer-2 (AI-2) promoted biofilm formation of the strain, expression of genes involved in AI-2 production was determined in L. paraplantarum L-ZS9, especially the key gene luxS. D-Ribose was used to inhibit biofilm formation because of its AI-2 inhibitory activity. Twenty-seven differentially expressed proteins were identified by comparative proteomic analysis following D-ribose treatment and were functionally classified into six groups. Real-time quantitative PCR showed that AI-2 had a counteractive effect on transcription of the genes tuf, fba, gap, pgm, nfo, rib, and rpoN. Over-expression of the tuf, fba, gap, pgm, and rpoN genes promoted biofilm formation of L. paraplantarum L-ZS9, while over-expression of the nfo and rib genes inhibited biofilm formation. In conclusion, D-ribose inhibited biofilm formation of L. paraplantarum L-ZS9 by regulating multiple genes involved in the glycolytic pathway, extracellular DNA degradation and transcription, and translation. This research provides a new mechanism of QSI regulation of biofilm formation of Lactobacillus and offers a valuable reference for QSI application in the future.

Survival of the House Fly (Diptera: Muscidae) on Truvia and Other Sweeteners

The house fly, Musca domestica L. (Diptera: Muscidae), is a disease vector of mechanically transmitted pathogens including bacteria, viruses, and protozoans. Opportunities for pathogen transmission can increase as fly longevity increases. Dietary preferences play an important role in insect longevity; therefore, we investigated house fly preferences, sucrose availability, and caloric constraints on house fly longevity. Experimental goals were: 1) to test the effects of calorie restriction on survival of house flies by manipulating concentrations of erythritol (low caloric content) and sucrose (high caloric content), and comparing commercial sweeteners of differing calorie content, 2) to identify house fly preferences for either erythritol or sucrose, and 3) to evaluate the insecticidal activity or toxicity of erythritol on house flies. Our data show that house flies may prefer high calorie options when given a choice and that house fly longevity likely increases as calorie content increases. Additionally, no significant differences in longevity were observed between the water only control (zero calories) and erythritol treatments. This suggests that decreased survival rates and death could be the result of starvation rather than insecticidal activity. This research furthers our understanding of house fly survival and sugar-feeding behavior.

Insights on Klebsiella pneumoniae Biofilms Assembled on Different Surfaces Using Phenotypic and Genotypic Approaches

Klebsiella pneumoniae is a prominent etiological agent of healthcare associated infections (HAIs). In this context, multidrug-resistant and biofilm-producing bacteria are of special public health concern due to the difficulties associated with treatment of human infections and eradication from hospital environments. Here, in order to study the impact of medical devices-associated materials on the biofilm dynamics, we performed biofilm phenotypic analyses through a classic and a new scanning electron microscopy (SEM) technique for three multidrug-resistant K. pneumoniae isolates growing on polystyrene and silicone. We also applied whole-genome sequencing (WGS) to search for genetic clues underlying biofilm phenotypic differences. We found major differences in the extracellular polymeric substances (EPS) content among the three strains, which were further corroborated by in-depth EPS composition analysis. WGS analysis revealed a high nucleotide similarity within the core-genome, but relevant differences in the accessory genome that may account for the detected biofilm phenotypic dissimilarities, such as genes already associated with biofilm formation in other pathogenic bacteria (e.g., genes coding haemogglutinins and haemolysins). These data reinforce that the research efforts to defeat bacterial biofilms should take into account that their dynamics may be contingent on the medical devices-associated materials.

Optimization of culture conditions for Gardnerella vaginalis biofilm formation

Bacterial vaginosis is the leading vaginal disorder in women in reproductive age. Although bacterial vaginosis is related with presence of a biofilm composed predominantly by Gardnerella vaginalis, there has not been a detailed information addressing the environmental conditions that influence the biofilm formation of this bacterial species. Here, we evaluated the influence of some common culture conditions on G. vaginalis biofilm formation, namely inoculum concentration, incubation period, feeding conditions and culture medium composition. Our results showed that culture conditions strongly influenced G. vaginalis biofilm formation and that biofilm formation was enhanced when starting the culture with a higher inoculum, using a fed-batch system and supplementing the growth medium with maltose.