Lactobacillus rhamnosus GG inhibits the toxic effects of Staphylococcus aureus on epidermal keratinocytes

A survey of multiple candidate probiotic bacteria reveals specificity in the ability to modify the effects of key wound pathogens

We have evaluated the inhibitory effects of supernatants and lysates derived from several candidate probiotics, on the growth and biofilm formation of wound pathogens, and their ability to protect human primary epidermal keratinocytes from the toxic effects of pathogens. Supernatants (neutralized and non-neutralized) and lysates (via sonication) from Lactiplantibacillus plantarum, Limosilactobacillus reuteri, Bifidobacterium longum, Lacticaseibacillus rhamnosus GG, and Escherichia coli Nissle 1917 were tested for their inhibitory effects against Staphylococcus aureus, Streptococcus pyogenes, Escherichia coli, Pseudomonas aeruginosa, and Acinetobacter baumanni. The supernatants of L. plantarum, L. rhamnosus, B. longum, and L. rhamnosus GG reduced the growth of S. aureus, E. coli, and A. baumanni. B. longum additionally inhibited P. aeruginosa growth. However, neutralized Lactobacillus supernatants did not inhibit growth and in some cases were stimulatory. Lysates of L. plantarum and L. reuteri inhibited S. pyogenes while B. longum lysates inhibited E. coli and S. aureus growth. E. coli Nissle 1917 lysates enhanced the growth of S. pyogenes and P. aeruginosa. Biofilm formation by E. coli was reduced by lysates of L. reuteri and neutralized supernatants of all candidate probiotics. P. aeruginosa biofilm formation was reduced by E. coli Nissle supernatant but increased by L. plantarum, L. reuteri, and Bifidobacterium longum lysates. L. reuteri decreased the toxic effects of S. aureus on keratinocytes while E. coli Nissle 1917 lysates protected keratinocytes from S. pyogenes toxicity. In conclusion, lactobacilli and E. coli Nissle lysates confer inhibitory effects on pathogenic growth independently of acidification and may beneficially alter the outcome of interactions between host cell-pathogen in a species-specific manner.IMPORTANCEOne of the attributes of probiotics is their ability to inhibit pathogens. For this reason, many lactobacilli have been investigated for their effects as potential topical therapeutics against skin pathogens. However, this field is in its infancy. Even though probiotics are known to be safe when taken orally, the potential safety concerns when applied to potentially compromised skin are unknown. For this reason, we believe that extracts of probiotics will offer advantages over the use of live bacteria. In this study, we have surveyed five candidate probiotics, when used as extracts, in terms of their effects against common wound pathogens. Our data demonstrate that some probiotic extracts promote the growth of pathogens and highlight the need for careful selection of species and strains when probiotics are to be used topically.

Mechanisms of medicinal, pharmaceutical, and immunomodulatory action of probiotics bacteria and their secondary metabolites against disease management: an overview

Probiotics or bacteriotherapy is today's hot issue for public entities (Food and Agriculture Organization, and World Health Organization) as well as health and food industries since Metchnikoff and his colleagues hypothesized the correlation between probiotic consumption and human's health. They contribute to the newest and highly efficient arena of promising biotherapeutics. These are usually attractive in biomedical applications such as gut-related diseases like irritable bowel disease, diarrhea, gastrointestinal disorders, fungal infections, various allergies, parasitic and bacterial infections, viral diseases, and intestinal inflammation, and are also worth immunomodulation. The useful impact of probiotics is not limited to gut-related diseases alone. Still, these have proven benefits in various acute and chronic infectious diseases, like cancer, human immunodeficiency virus (HIV) diseases, and high serum cholesterol. Recently, different researchers have paid special attention to investigating biomedical applications of probiotics, but consolidated data regarding bacteriotherapy with a detailed mechanistically applied approach is scarce and controversial. The present article reviews the bio-interface of probiotic strains, mainly (i) why the demand for probiotics?, (ii) the current status of probiotics, (iii) an alternative to antibiotics, (iv) the potential applications towards disease management, (v) probiotics and industrialization, and (vi) futuristic approach.

Probiotics in Wound Healing

Wound infections caused by opportunistic bacteria promote persistent infection and represent the main cause of delayed healing. Probiotics are acknowledged for their beneficial effects on the human body and could be utilized in the management of various diseases. They also possess the capacity to accelerate wound healing, due to their remarkable anti-pathogenic, antibiofilm, and immunomodulatory effects. Oral and topical probiotic formulations have shown promising openings in the field of dermatology, and there are various in vitro and in vivo models focusing on their healing mechanisms. Wound dressings embedded with prebiotics and probiotics are now prime candidates for designing wound healing therapeutic approaches to combat infections and to promote the healing process. The aim of this review is to conduct an extensive scientific literature review regarding the efficacy of oral and topical probiotics in wound management, as well as the potential of wound dressing embedding pre- and probiotics in stimulating the wound healing process.

Strong Activity and No Resistance Induction Exerted by Cell-Free Supernatants from Lacticaseibacillus rhamnosus against Mono-Species and Dual-Species Biofilms of Wound Pathogens in In Vivo-like Conditions

It is widely agreed that microbial biofilms play a major role in promoting infection and delaying healing of chronic wounds. In the era of microbial resistance, probiotic strains or their metabolic products are emerging as an innovative approach for the treatment of hard-to-heal (chronic) wounds due to their antimicrobial, healing, and host immune-modulatory effects. In this study, we aimed to investigate the potential of cell-free supernatants (CFS) from Lacticaseibacillus rhamnosus GG against mono- and dual-species biofilms of wound pathogens in a 3D in vitro infection model. Mature biofilms of Pseudomonas aeruginosa and Staphylococcus aureus were obtained on collagen scaffolds in the presence of a simulant wound fluid (SWF) and treated with CFS at different doses and time intervals. At 1:4 dilution in SWF, CFS caused a marked reduction in the colony forming-unit (CFU) numbers of bacteria embedded in mono-species biofilms as well as bacteria released by the biofilms in the supernatant. CFU count and electron microscopy imaging also demonstrated a marked antibiofilm effect against dual-species biofilms starting from 8 h of incubation. Furthermore, CFS exhibited acceptable levels of cytotoxicity at 24 h of incubation against HaCaT cells and, differently from ciprofloxacin, failed to induce resistance after 15 passages at sub-inhibitory concentrations. Overall, the results obtained point to L. rhamnosus GG postbiotics as a promising strategy for the treatment of wound biofilms.

Protective Effect of Probiotics against Pseudomonas aeruginosa Infection of Human Corneal Epithelial Cells

Probiotic therapy needs consideration as an alternative strategy to prevent and possibly treat corneal infection. This study aimed to assess the preventive effect of Lactobacillus reuteri and Bifidobacterium longum subsp. infantis on reducing the infection of human corneal epithelial (HCE) cells caused by Pseudomonas aeruginosa. The probiotics' preventive effect against infection was evaluated in cell monolayers pretreated with each probiotic 1 h and 24 h prior to P. aeruginosa challenge followed by 1 h and 24 h of growth in combination. Cell adhesion, cytotoxicity, anti-inflammatory, and antinitrosative activities were evaluated. L. reuteri and B. longum adhered to HCE cells, preserved occludin tight junctions' integrity, and increased mucin production on a SkinEthicTM HCE model. Pretreatment with L. reuteri or B. longum significantly protected HCE cells from infection at 24 h, increasing cell viability at 110% (110.51 ± 5.15; p ≤ 0.05) and 137% (137.55 ± 11.97; p ≤ 0.05), respectively. Each probiotic showed anti-inflammatory and antinitrosative activities, reducing TNF-α level (p ≤ 0.001) and NOx amount (p ≤ 0.001) and reestablishing IL-10 level (p ≤ 0.001). In conclusion, this study demonstrated that L. reuteri and B. longum exert protective effects in the context of corneal infection caused by P. aeruginosa by restoring cell viability and modulating inflammatory cytokine release.

Pharmacotechnical aspects of a stable probiotic formulation toward multidrug-resistance antibacterial activity: design and quality control

As a well-known group of the probiotic family, the Lactobacillus has increasingly contributed to hindering the growth of pathogens, particularly resistant species, in the last decades. Since antibiotic resistance has become a severe problem in global healthcare systems and considerably increased the mortality and morbidity rate in infectious diseases, we aimed to obtain a new stable formulation of Lactobacillus to overcome resistant infections. For this purpose, we designed various gel formulations containing Lactobacillus rhamnosus (L. rhamnosus) as an active pharmaceutical ingredient (API) in a water base and oil base gel, evaluated the probiotic stability in formulation to obtain an optimum formulation, and finally, investigated the antibacterial activities of that against two common hospital-associated multidrug-resistant pathogens, methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE). Furthermore, the pharmaceutical aspects of the optimum formulation, including stability, homogeneity, spreadability, pH value, conductivity, and rheological behavior, were assessed.The results indicated that the optimum formulation based on glycerol exhibited desirable pharmaceutical properties, including long-term stability, a perfect level of homogeneity, an acceptable range of spreadability with pseudo-plastic thixotropic behavior, and a promising antibacterial potential against MRSA and VRE. Our findings indicate that this novel probiotic formulation could be an excellent candidate to cope with antibiotic-resistant species, representing a hopeful treatment potential for topical applications, particularly in incurable infections. However, further in vivo studies seem warranted to evaluate their bactericidal activity against multi-drug resistant microorganisms.

A prebiotic diet modulates the oral microbiome composition and results in the attenuation of oropharyngeal candidiasis in mice

Oral bacteria can influence the ability of Candida albicans to cause oropharyngeal candidiasis (OPC). We recently reported that a Lactobacillus johnsonii-enriched oral microbiota reduced C. albicans virulence in an immunosuppressed OPC mouse model. As a follow-up, in this work, we aimed to enrich the resident oral Lactobacillus communities with a prebiotic diet to further assess their effect on the severity of OPC. We tested the effect of a prebiotic xylo-oligosaccharides (XOS)-enriched diet in the oral global bacterial composition and severity of OPC. We assessed changes in the oral microbiome composition via 16S-rRNA gene high-throughput sequencing, validated by qPCR. The impact of the prebiotic diet on Candida infection was assessed by quantifying changes in oral fungal and bacterial biomass and scoring tongue lesions. Contrary to expectations, oral Lactobacillus communities were not enriched by the XOS-supplemented diet. Yet, XOS modulated the oral microbiome composition, increasing Bifidobacterium abundance and reducing enterococci and staphylococci. In the OPC model, the XOS diet attenuated Candida virulence and bacterial dysbiosis, increasing lactobacilli and reducing enterococci on the oral mucosa. We conclude that XOS attenuates Candida virulence by promoting a bacterial microbiome structure more resilient to Candida infection. IMPORTANCE This is the first study on the effects of a prebiotic diet on the oral mucosal bacterial microbiome and an oropharyngeal candidiasis (OPC) mouse model. We found that xylo-oligosaccharides change the oral bacterial community composition and attenuate OPC. Our results contribute to the understanding of the impact of the oral bacterial communities on Candida virulence.

Biodiversity of Skin Microbiota as an Important Biomarker for Wound Healing

Cutaneous wound healing is a natural and complex repair process that is implicated within four stages. However, microorganisms (e.g., bacteria) can easily penetrate through the skin tissue from the wound bed, which may lead to disbalance in the skin microbiota. Although commensal and pathogenic bacteria are in equilibrium in normal skin, their imbalance in the wound area can cause the delay or impairment of cutaneous wounds. Moreover, skin microbiota is in constant crosstalk with the immune system and epithelial cells, which has significance for the healing of a wound. Therefore, understanding the major bacteria species in the cutaneous wound as well as their communication with the immune system has gained prominence in a way that allows for the emergence of a new perspective for wound healing. In this review, the major bacteria isolated from skin wounds, the role of the crosstalk between the cutaneous microbiome and immune system to heal wounds, the identification techniques of these bacteria populations, and the applied therapies to manipulate the skin microbiota are investigated.

Looking for the Ideal Probiotic Healing Regime

Wound healing is a multi-factorial response to tissue injury, aiming to restore tissue continuity. Numerous recent experimental and clinical studies clearly indicate that probiotics are applied topically to promote the wound-healing process. However, the precise mechanism by which they contribute to healing is not yet clear. Each strain appears to exert a distinctive, even multi-factorial action on different phases of the healing process. Given that a multi-probiotic formula exerts better results than a single strain, the pharmaceutical industry has embarked on a race for the production of a formulation containing a combination of probiotics capable of playing a role in all the phases of the healing process. Hence, the object of this review is to describe what is known to date of the distinctive mechanisms of each of the most studied probiotic strains in order to further facilitate research toward the development of combinations of strains and doses, covering the whole spectrum of healing. Eleven probiotic species have been analyzed, the only criterion of inclusion being a minimum of two published research articles.

The Antimicrobial Effect of Various Single-Strain and Multi-Strain Probiotics, Dietary Supplements or Other Beneficial Microbes against Common Clinical Wound Pathogens

The skin is the largest organ in the human body and is colonized by a diverse microbiota that works in harmony to protect the skin. However, when skin damage occurs, the skin microbiota is also disrupted, and pathogens can invade the wound and cause infection. Probiotics or other beneficial microbes and their metabolites are one possible alternative treatment for combating skin pathogens via their antimicrobial effectiveness. The objective of our study was to evaluate the antimicrobial effect of seven multi-strain dietary supplements and eleven single-strain microbes that contain probiotics against 15 clinical wound pathogens using the agar spot assay, co-culturing assay, and agar well diffusion assay. We also conducted genera-specific and species-specific molecular methods to detect the DNA in the dietary supplements and single-strain beneficial microbes. We found that the multi-strain dietary supplements exhibited a statistically significant higher antagonistic effect against the challenge wound pathogens than the single-strain microbes and that lactobacilli-containing dietary supplements and single-strain microbes were significantly more efficient than the selected propionibacteria and bacilli. Differences in results between methods were also observed, possibly due to different mechanisms of action. Individual pathogens were susceptible to different dietary supplements or single-strain microbes. Perhaps an individual approach such as a 'probiogram' could be a possibility in the future as a method to find the most efficient targeted probiotic strains, cell-free supernatants, or neutralized cell-free supernatants that have the highest antagonistic effect against individual clinical wound pathogens.

In Vitro and In Vivo Evaluation of Lacticaseibacillus rhamnosus GG and Bifidobacterium lactis Bb12 Against Avian Pathogenic Escherichia coli and Identification of Novel Probiotic-Derived Bioactive Peptides

Avian pathogenic E. coli (APEC), an extra-intestinal pathogenic E. coli (ExPEC), causes colibacillosis in poultry and is also a potential foodborne zoonotic pathogen. Currently, APEC infections in poultry are controlled by antibiotic medication; however, the emergence of multi-drug-resistant APEC strains and increased restrictions on the use of antibiotics in food-producing animals necessitate the development of new antibiotic alternative therapies. Here, we tested the anti-APEC activity of multiple commensal and probiotic bacteria in an agar-well diffusion assay and identified Lacticaseibacillus rhamnosus GG and Bifidobacterium lactis Bb12 producing strong zone of inhibition against APEC. In co-culture assay, L. rhamnosus GG and B. lactis Bb12 completely inhibited the APEC growth by 24 h. Further investigation revealed that antibacterial product(s) in the culture supernatants of L. rhamnosus GG and B. lactis Bb12 were responsible for the anti-APEC activity. The analysis of culture supernatants using LC-MS/MS identified multiple novel bioactive peptides (VQAAQAGDTKPIEV, AFDNTDTSLDSTFKSA, VTDTSGKAGTTKISNV, and AESSDTNLVNAKAA) in addition to the production of lactic acid. The oral administration (10⁸ CFU/chicken) of L. rhamnosus GG significantly (P < 0.001) reduced the colonization (~ 1.6 logs) of APEC in the cecum of chickens. Cecal microbiota analysis revealed that L. rhamnosus GG moderated the APEC-induced alterations of the microbial community in the cecum of chickens. Further, L. rhamnosus GG decreased (P < 0.05) the abundance of phylum Proteobacteria, particularly those belonging to Enterobacteriaceae (Escherichia-Shigella) family. These studies indicate that L. rhamnosus GG is a promising probiotic to control APEC infections in chickens. Further studies are needed to optimize the delivery of L. rhamnosus GG in feed or water and in conditions simulating the field to facilitate its development for commercial applications.

Analysis of Chemical Structure and Antibiofilm Properties of Exopolysaccharides from Lactiplantibacillus plantarum EIR/IF-1 Postbiotics

Previous studies have indicated that the exopolysaccharides of lactic acid bacteria exhibit antibiofilm activity against non-oral bacteria by preventing their initial adhesion to surfaces and by downregulating the expression of genes responsible for their biofilm formation. The aims of this study were to (1) characterize the exopolysaccharides (EPSs) of Lactobacillus plantarum EIR/IF-1 postbiotics, (2) test their antibiofilm effect on dual biofilms, and (3) evaluate their bacterial auto-aggregation, co-aggregation, and hydrocarbon-binding inhibitory activity. The EPSs were characterized by FTIR, HPLC, and thermogravimetric analysis. Bacterial auto- and co-aggregation were tested by Kolenbrander’s method and hydrocarbon binding was tested by Rosenberg’s method. Dual biofilms were formed by culturing Fusobacterium nucleatum ATCC 25586 with one of the following bacteria: Prevotella denticola ATCC 33185, P. denticola AHN 33266, Porphyromonas gingivalis ATCC 33277, P. gingivalis AHN 24155, and Filifactor alocis ATCC 35896. The EPSs contained fractions with different molecular weights (51 and 841 kDa) and monosaccharides of glucose, galactose, and fructose. The EPSs showed antibiofilm activity in all the biofilm models tested. The EPSs may have inhibited bacterial aggregation and binding to hydrocarbons by reducing bacterial hydrophobicity. In conclusion, the EPSs of L. plantarum EIR/IF-1, which consists of two major fractions, exhibited antibiofilm activity against oral bacteria, which can be explained by the inhibitory effect of EPSs on the auto-aggregation and co-aggregation of bacteria and their binding to hydrocarbons.

Probiotic Adhesion to Skin Keratinocytes and Underlying Mechanisms

Simple Summary

The use of probiotics to ameliorate skin conditions has been suggested. This is based in the fact that they compete with pathogenic bacteria for adhesion sites, thereby displacing unwanted microorganisms. Lacticaseibacillus rhamnosus was able to adhere effectively to keratinocytes decreasing the number of adherent pathogenic bacteria. In the presence of pathogens all tested probiotics decreased invasion by S. aureus, one of the most relevant skin pathogens. Ex vivo models also showed wound healing capacity of L. rhamnosus with a concomitant decrease in the viable numbers of S. aureus, suggesting it is a good candidate as a co-adjuvant in the treatment of skin infections by this pathogen.

Abstract

The effects of probiotics on the skin are not yet well understood. Their topical application and benefits derived thereafter have recently been investigated. Improvements in different skin disorders such as atopic dermatitis, acne, eczema, and psoriasis after their use have, however, been reported. One of the mechanisms through which such benefits are documented is by inhibiting colonization by skin pathogens. Bacterial adhesion is the first step for colonization to occur; therefore, to avoid pathogenic colonization, inhibiting adhesion is crucial. In this study, invasion and adhesion studies have been carried out using keratinocytes. These showed that Escherichia coli is not able to invade skin keratinocytes, but adhered to them. Lacticaseibacillus rhamnosus and Propioniferax innocua decreased the viable counts of the three pathogens under study. L. rhamnosus significantly inhibited S. aureus adhesion. P. innocua did not inhibit pathogenic bacteria adhesion, but when added simultaneously with S. aureus (competition assay) a significant adhesion reduction (1.12 ± 0.14 log₁₀CFU/mL) was observed. Probiotic bacteria seem to use carbohydrates to adhere to the keratinocytes, while S. aureus uses proteins. Lacticaseibacillus rhamnosus showed promising results in pathogen inhibition in both in vitro and ex vivo experiments and can potentially be used as a reinforcement of conventional therapies for skin dysbiosis.

Multiple Proteins of Lacticaseibacillus rhamnosus GG Are Involved in the Protection of Keratinocytes From the Toxic Effects of Staphylococcus aureus

We have previously shown that lysates of Lacticaseibacillus rhamnosus GG confer protection to human keratinocytes against Staphylococcus aureus. L. rhamnosus GG inhibits the growth of S. aureus as well as competitively excludes and displaces the pathogen from keratinocytes. In this study, we have specifically investigated the anti-adhesive action. We have tested the hypothesis that this activity is due to quenching of S. aureus binding sites on keratinocytes by molecules within the Lacticaseibacillus lysate. Trypsinisation or heat treatment removed the protective effect of the lysate suggesting the involvement of proteins as effector molecules. Column separation of the lysate and analysis of discrete fractions in adhesion assays identified a fraction of moderate hydrophobicity that possessed all anti-adhesive functions. Immunoblotting demonstrated that this fraction contained the pilus protein, SpaC. Recombinant SpaC inhibited staphylococcal adhesion to keratinocytes in a dose-dependent manner and improved keratinocyte viability following challenge with viable S. aureus. However, SpaC did not confer the full anti-adhesive effects of the LGG lysate and excluded but did not displace S. aureus from keratinocytes. Further purification produced four protein-containing peaks (F1–F4). Of these, F4, which had the greatest column retention time, was the most efficacious in anti-staphylococcal adhesion and keratinocyte viability assays. Identification of proteins by mass spectrometry showed F4 to contain several known “moonlighting proteins”—i.e., with additional activities to the canonical function, including enolase, Triosephosphate isomerase (TPI), Glyceraldehyde 3 phosphate dehydrogenase (G3P) and Elongation factor TU (EF-Tu). Of these, only enolase and TPI inhibited S. aureus adhesion and protected keratinocytes viability in a dose-dependent manner. These data suggest that inhibition of staphylococcal binding by the L. rhamnosus GG lysate is mediated by SpaC and specific moonlight proteins.

Lacticaseibacillus rhamnosus: A Suitable Candidate for the Construction of Novel Bioengineered Probiotic Strains for Targeted Pathogen Control

Probiotics, with their associated beneficial effects, have gained popularity for the control of foodborne pathogens. Various sources are explored with the intent to isolate novel robust probiotic strains with a broad range of health benefits due to, among other mechanisms, the production of an array of antimicrobial compounds. One of the shortcomings of these wild-type probiotics is their non-specificity. A pursuit to circumvent this limitation led to the advent of the field of pathobiotechnology. In this discipline, specific pathogen gene(s) are cloned and expressed into a given probiotic to yield a novel pathogen-specific strain. The resultant recombinant probiotic strain will exhibit enhanced species-specific inhibition of the pathogen and its associated infection. Such probiotics are also used as vehicles to deliver therapeutic agents. As fascinating as this approach is, coupled with the availability of numerous probiotics, it brings a challenge with regard to deciding which of the probiotics to use. Nonetheless, it is indisputable that an ideal candidate must fulfil the probiotic selection criteria. This review aims to show how Lacticaseibacillus rhamnosus, a clinically best-studied probiotic, presents as such a candidate. The objective is to spark researchers’ interest to conduct further probiotic-engineering studies using L. rhamnosus, with prospects for the successful development of novel probiotic strains with enhanced beneficial attributes.

Selective targeting of skin pathobionts and inflammation with topically applied lactobacilli

Tailored skin microbiome modulation approaches with probiotics are highly challenging. Here, we show that lactobacilli are underestimated members of the skin microbiota. We select specific strains of nomadic lactobacilli for their functional applicability on the skin and capacity to inhibit growth and inflammation by skin pathobionts. The strains are formulated as microcapsules for topical formulations and tested in patients with mild-to-moderate acne. The selected lactobacilli are able to reduce inflammatory lesions in a pilot and placebo-controlled study. Daily application for 8 weeks is associated with an in vivo temporary modulation of the microbiome, including a reduction in relative abundance of staphylococci and Cutibacterium acnes, and an increase in lactobacilli. The reduction in inflammatory lesions is still apparent 4 weeks after the topical application of the lactobacilli ended, indicating a possible additional immunomodulatory effect. This study shows that carefully selected and formulated lactobacilli are a viable therapeutic option for common acne lesions.

The role of microbiota-derived postbiotic mediators on biofilm formation and quorum sensing-mediated virulence of Streptococcus mutans: A perspective on preventing dental caries

Dental caries is not only one of the most prevalent diseases worldwide, but also a public health problem, undoubtedly. Among the various types of cariogenic bacteria, Streptococcus mutans is considered to be the major etiological pathogen of dental caries. The present study aimed to assess the influence of microbiota-derived postbiotic mediators (PMs) on the pathogenesis of dental caries. Within this aim, the antibacterial (agar diffusion method) and antibiofilm (crystal violet assay) characteristics of PMs derived from Lactiplantibacillus plantarum EIR/IF-1, Lactiplantibacillus curvatus EIR/DG-1, and Lactiplantibacillus curvatus EIR/BG-2 against S. mutans (ATCC 25175) were analyzed. According to the results, PM of the strain EIR/IF-1, isolated from infant feces showed the highest inhibitory effect (pH-dependent). Besides, sub-MIC doses of all PMs eliminated the biofilm formation following the co-incubation and pre-treatment assays. The reduction of cell viability and notable changes in biofilm formation was also confirmed both on glass coverslips and ex vivo human tooth surfaces by confocal laser scanning microscopy and scanning electron microscopy. Moreover, sub-MIC values of PMs down-regulated the expression of gtfC, comA, and comX, without any significant growth inhibition. Organic acids, fatty acids, and vitamins in PMs were also reported. Overall, these findings indicated the possible preventive roles of microbiota-derived PMs for the pathogenesis of dental caries.

Topical Delivery of Lactobacillus Culture Supernatant Increases Survival and Wound Resolution in Traumatic Acinetobacter baumannii Infections

Species of Lactobacillus have been proposed as potential candidates for treating wound infections due to their ability to lower pH, decrease inflammation, and release antimicrobial compounds. This study investigated the impact of lactobacilli (Lactobacillus acidophilus ATCC 4356, Lactobacillus casei ATCC 393, Lactobacillus reuteri ATCC 23272) secreted products on wound pathogens in vitro and in a murine wound infection model. Evaluation of 1-5 day lactobacilli conditioned media (CM) revealed maximal inhibition against wound pathogens using the 5-day CM. The minimum inhibitory concentration (MIC) of 5-day Lactobacillus CMs was tested by diluting CM in Mueller-Hinton (MH) broth from 0 to 25% and was found to be 12.5% for A. baumannii. Concentrating the CM to 10× with a 3 kDa centrifuge filter decreased the CM MIC to 6.25-12.5% for A. baumannii planktonic cells. Minimal impact of 5-day CMs was observed against bacterial biofilms. No toxicity was observed when these Lactobacillus CMs were injected into Galleria melonella waxworms. For the murine A. baumannii wound infection studies, improved survival was observed following topical treatment with L. acidophilus ATCC 4356 or L. reuteri ATCC 23272, while L. reuteri ATCC 23272 treatment alone improved wound resolution. Overall, this study suggests that the topical application of certain Lactobacillus species byproducts could be effective against gram-negative multi-drug resistant (MDR) wound pathogens, such as A. baumannii.

The role of the skin microbiota in the modulation of cutaneous inflammation-Lessons from the gut

Inflammation is a vital defense mechanism used to protect the body from invading pathogens, but dysregulation can lead to chronic inflammatory disorders such as psoriasis and atopic dermatitis. Differences in microbiota composition have been observed in patients with inflammatory skin conditions compared with healthy individuals, particularly within lesions. There is also increasing evidence accumulating to support the notion that the microbiome contributes to the onset or modulates the severity of inflammatory diseases. Despite the known protective effects of orally administered lactic acid bacteria against inflammation, few studies have investigated the potential protective effects of topical application of bacteria on skin health and even fewer have looked at the potential anti-inflammatory effects of skin commensals. If lack of diversity and reduction in the abundance of specific commensal strains is observed in inflammatory skin lesions, and it is known that commensal bacteria can produce anti-inflammatory compounds, we suggest that certain members of the skin microbiota have anti-inflammatory properties that can be harnessed for use as topical therapeutics in inflammatory skin disorders.

Antibiotic Resistance Crisis: An Update on Antagonistic Interactions between Probiotics and Methicillin-Resistant Staphylococcus aureus (MRSA)

Antimicrobial resistance (AMR) havoc is a global multifaceted crisis endowing a significant challenge for the successful eradication of devastating pathogens. Methicillin-Resistant Staphylococcus aureus (MRSA) is an enduring superbug involved in causing devastating infections. Although MRSA is a frequent colonizer of human skin, wound, and anterior nares, the intestinal colonization of MRSA has greatly increased the risk of inducing MRSA-associated colitis besides creating a conducive environment for horizontal transfer of resistant genes to commensal microbes. On the other hand, staphylococcal resistance to last-resort antibiotics has urged the development of novel antimicrobial agents for the effective decolonization of MRSA. In response, probiotics and their metabolites (postbiotics) have been proposed as the adjunct therapeutic avenues. Probiotics exhibit a multitude of anti-MRSA actions (anti-bacterial, anti-biofilm, anti-virulence, anti-drug resistance, co-aggregation, and anti-quorum sensing) through the production of numerous antagonistic compounds such as organic acids, hydrogen peroxide, low molecular weight compounds, biosurfactants, bacteriocins, and bacteriocins like inhibitory substances. Besides, probiotics stabilize the epithelial barrier function and positively modulate the host immune system via regulating various signal transduction mechanisms. Preclinical and human intervention studies have suggested that probiotics outcompete with MRSA by exhibiting anti-colonization mechanisms via protective, competitive, and displacement mode. In this review, we aim to highlight the dynamics of MRSA associated virulence and drug resistance properties, and how probiotics antagonize MRSA through various mechanism of action.

The role of lactobacilli in inhibiting skin pathogens

The human skin microbiota forms a key barrier against skin pathogens and is important in modulating immune responses. Recent studies identify lactobacilli as endogenous inhabitants of healthy skin, while inflammatory skin conditions are often associated with a disturbed skin microbiome. Consequently, lactobacilli-based probiotics are explored as a novel treatment of inflammatory skin conditions through their topical skin application. This review focuses on the potential beneficial role of lactobacilli (family Lactobacillaceae) in the skin habitat, where they can exert multifactorial local mechanisms of action against pathogens and inflammation. On one hand, lactobacilli have been shown to directly compete with skin pathogens through adhesion inhibition, production of antimicrobial metabolites, and by influencing pathogen metabolism. The competitive anti-pathogenic action of lactobacilli has already been described mechanistically for common different skin pathogens, such as Staphylococcus aureus, Cutibacterium acnes, and Candida albicans. On the other hand, lactobacilli also have an immunomodulatory capacity associated with a reduction in excessive skin inflammation. Their influence on the immune system is mediated by bacterial metabolites and cell wall-associated or excreted microbe-associated molecular patterns (MAMPs). In addition, lactobacilli can also enhance the skin barrier function, which is often disrupted as a result of infection or in inflammatory skin diseases. Some clinical trials have already translated these mechanistic insights into beneficial clinical outcomes, showing that topically applied lactobacilli can temporarily colonize the skin and promote skin health, but more and larger clinical trials are required to generate in vivo mechanistic insights and in-depth skin microbiome analysis.

Antimicrobial and anti-biofilm effects of probiotic Lactobacillus plantarum KU200656 isolated from kimchi

The probiotic properties and anti-pathogenic effects of Lactobacillus plantarum KU200656 (KU200656) isolated from Korean fermented kimchi against Staphylococcus aureus, Listeria monocytogenes, Escherichia coli, and Salmonella Typhimurium were investigated. KU200656 showed high tolerance to artificial gastric acid (99.48%) and bile salts (102.40%) and this strain was safe according to antibiotic sensitivity test; it could not produce harmful enzymes, including β-glucuronidase. KU200656 exhibited high adhesion (4.45%) to intestinal cells, HT-29 cells, with high cell surface hydrophobicity (87.31% for xylene and 81.11% for toluene). Moreover, KU200656 co-aggregated with pathogenic bacteria and exhibited antibacterial activity and anti-adhesion properties against pathogens. The cell-free supernatant (CFS) of KU200656 inhibited biofilm formation by pathogenic bacteria. In addition, half of the minimum inhibitory concentration of the KU200656 CFS downregulated the expression of biofilm-related genes, as determined by quantitative real-time PCR. Therefore, KU200656 was demonstrated to possess anti-pathogenic effects and have potential for use as probiotics in the food industry.

Cell-Free Lactobacillus sp Supernatants Modulate Staphylococcus aureus Growth, Adhesion and Invasion to Human Osteoblast (HOB) Cells

The increase of antibiotic resistance has become a problem. Probiotic bacteria play an important role in preventive/supportive medicine. Therefore, we examined the inhibitory effects of four different Lactobacillus species' (L. acidophilus-La, L. plantarum-Lp, L. fermentum-Lf and L. rhamnosus-Lr) cell-free supernatants (CFSs) on growth, adhesion, invasion, and biofilm formation of Staphylococcus aureus and effects of S. aureus, CFSs, and S. aureus-CFSs co-existence on human osteoblast (HOB) cell viability. Growth alterations were measured spectrophotometrically. Adhesive/invasive bacterial counts were detected by colony counting. Biofilm was evaluated using microtiter plate assay. The MTT assay was used for detection of HOB cell viability. The growth of MSSA significantly (P < 0.01) decreased in the presence of two CFSs (Lf and Lr) (P < 0.01); the growth of MRSA significantly (P < 0.05) reduced in the presence of La CFSs. All tested CFSs were found to reduce adhesion and invasion of MSSA (P < 0.0001). The adhesion of MRSA was enhanced (P < 0.0001) in the presence of all CFSs except La and the invasion of MRSA was decreased (P < 0.01) in the presence of Lr and Lf CFSs. All tested CFSs were shown to inhibit biofilm formation significantly (P < 0.0001). The reduction of S. aureus infected HOB cell viability and exposed to all CFSs except Lr that was found to be significant (P < 0.0001). The viability of HOB cell during co-incubation with MSSA and CFSs was shown to be decreased significantly. However co-existence of MRSA and CFSs did not alter HOB cell viability. These results suggested that lactobacilli as probiotics have low protective effects on MRSA-infected host cells.

Characterization and in vitro Analysis of Probiotic-Derived Peptides Against Multi Drug Resistance Bacterial Infections

An inexorable switch from antibiotics has become a major desideratum to overcome antibiotic resistance. Bacteriocin from Lactobacillus casei, a cardinal probiotic was used to design novel antibacterial peptides named as Probiotic Bacteriocin Derived and Modified (PBDM) peptides (PBDM1: YKWFAHLIKGLC and PBDM2: YKWFRHLIKKLC). The loop-shaped 3D structure of peptides was characterized in silico via molecular dynamics simulation as well as biophysically via spectroscopic methods. Thereafter, in vitro results against multidrug resistant bacterial strains and hospital samples demonstrated the strong antimicrobial activity of PBDM peptides. Further, in vivo studies with PBDM peptides showed downright recovery of balb/c mice from Vancomycin Resistant Staphylococcus aureus (VRSA) infection to its healthy condition. Thereafter, in vitro study with human epithelial cells showed no significant cytotoxic effects with high biocompatibility and good hemocompatibility. In conclusion, PBDM peptides displayed significant antibacterial activity against certain drug resistant bacteria which cause infections in human beings. Future analysis are required to unveil its mechanism of action in order to execute it as an alternative to antibiotics.

Exploring the wound healing, anti-inflammatory, anti-pathogenic and proteomic effects of lactic acid bacteria on keratinocytes

The topical application of lactic acid bacteria (LAB) is recognized as a useful approach to improve skin health. This work aims to characterize by a multidisciplinary approach, the wound healing, anti-inflammatory, anti-pathogens and proteomic effects of six LAB lysates, belonging to the genus Lactobacillus. Our results demonstrated that the lysates of tested LAB stimulated the proliferation of keratinocytes, and that L. plantarum SGL 07 and L. salivarius SGL 19 accelerated the re-epithelization by inducing keratinocyte migration. The bacterial lysates also reduced the secretion of specific pro-inflammatory mediators from keratinocytes. Furthermore, viable L. salivarius SGL 19 and L. fermentum SGL 10 had anti-pathogenic effects against S. aureus and S. pyogenes, while L. brevis SGL 12 and L. paracasei SGL 04 inhibited S. aureus and S. pyogenes, respectively. The tested lactobacilli lysates also induced specific proteome modulation of the exposed keratinocytes, involving dysregulation of proteins (such as interleukin enhancer-binding factor 2 and ATP-dependent RNA helicase) and pathways (such as cytokine, NF-kB, Hedgehog, and RUNX signaling) associated with their specific wound healing and anti-inflammatory effects. This study indicates the different potential of selected lactobacilli, suggesting that they may be successfully used in the future together with conventional therapies to bring relief from skin disorders.

Lactobacillus reuteri DSM 17938 as a Novel Topical Cosmetic Ingredient: A Proof of Concept Clinical Study in Adults with Atopic Dermatitis

Atopic Dermatitis (AD) is a chronically relapsing skin condition characterized by dry, itchy, and inflamed skin where sufferers can frequently be subject to infections. Probiotics are known to be potent immune-modulators, and live Lactobacillus reuteri DSM 17938 has shown to be anti-inflammatory but also to possess antimicrobial and barrier function properties. This study aimed to investigate and compare two investigational ointment products (topical probiotic and control) for cutaneous acceptability, safety, and efficacy under normal conditions of use, in adult subjects with atopic dermatitis. The products were applied twice daily for 8 weeks, and cutaneous acceptability, SCORAD index, local SCORAD, and adverse events were evaluated after 4 and 8 weeks of treatment. At the end of the observations, it was demonstrated that both the probiotic-containing and probiotic-free ointments were both cutaneously acceptable and safe. It importantly showed a statistically and clinically significant improvement of the SCORAD index and local SCORAD in adult subjects with AD after 4 and 8 weeks of continuous use. In conclusion, we show evidence that the probiotic product, containing live L. reuteri DSM 17938 as an extra ingredient, is safe and promising as a novel topical cosmetic ointment and with further testing could be a standard topical product for the management of atopic dermatitis or other disorders associated with the skin.

Extrinsic Factors Shaping the Skin Microbiome

Human skin, our most environmentally exposed organ, is colonized by a vast array of microorganisms constituting its microbiome. These bacterial communities are crucial for the fulfillment of human physiological functions such as immune system modulation and epidermal development and differentiation. The structure of the human skin microbiome is established during the early life stages, starting even before birth, and continues to be modulated throughout the entire life cycle, by multiple host-related and environmental factors. This review focuses on extrinsic factors, ranging from cosmetics to the environment and antibacterial agents, as forces that impact the human skin microbiome and well-being. Assessing the impact of these factors on the skin microbiome will help elucidate the forces that shape the microbial populations we coexist with. Furthermore, we will gain additional insight into their tendency to stimulate a healthy environment or to increase the propensity for skin disorder development.

Therapeutic effect of Lactobacillus rhamnosus SHA113 on intestinal infection by multi-drug-resistant Staphylococcus aureus and its underlying mechanisms

Staphylococcus aureus, especially multi-drug-resistant (MDR) pathogenic S. aureus, poses a severe threat to food safety and human health. Probiotics offer promising potential for the control of MDR pathogens because of their safe and biofunctional properties. This study shows that Lactobacillus rhamnosus SHA113, a strain isolated from the milk of healthy women, could efficiently inhibit MDR S. aureus both in vitro and in vivo. In vitro, L. rhamnosus efficiently inhibited and even killed drug resistant and drug sensitive S. aureus strains. In vivo experiments showed that SHA113 could efficiently decrease the number of S. aureus cells, inhibit the expression of inflammatory factors TNF-α and IL-6, and restore the level of white cells and neutrophils in the blood. SHA113 could also efficiently repair damage of the intestinal barrier and other functions impaired by S. aureus infection. This was indicated by a change of intestinal villi length and structure, and an up-regulated expression of tight junction proteins ZO-1 and occludin. SHA113 also restored the structural damage of immune organs, such as the enlargement of the spleen and the increased level of inflammatory cytokines caused by S. aureus infection. More importantly, L. rhamnosus SHA113 showed more effective inhibitory and therapeutic effects on MDR S. aureus strain ZBQ006 than on drug sensitive S. aureus strain 29213. These results illustrated that L. rhamnosus SHA113 has great potential for the treatment of MDR S. aureus contamination as food control and for therapeutic treatment.

Lysates of Lactobacillus acidophilus combined with CTLA-4-blocking antibodies enhance antitumor immunity in a mouse colon cancer model

Previous reports have suggested that many gut microbiomes were associated with the development of colorectal cancer (CRC), and could modulate response to numerous forms of cancer therapy, including checkpoint blockade immunotherapy. Here we evaluated the protective efficacy of Lactobacillus acidophilus (L. acidophilus) cell lysates combined with an anti-CTL antigen-4 blocking antibody (CTLA-4 mAb) in syngeneic BALB/c mice CRC models induce by a single intraperitoneal injection of 10 mg/kg azoxymethane (AOM), followed by three cycles of 2% dextran sulfate sodium (DSS) in drinking water. In contrast to CTLA-4 mAb monotherapy, L. acidophilus lysates could attenuate the loss of body weight and the combined administration significantly protected mice against CRC development, which suggested that the lysates enhanced antitumor activity of CTLA-4 mAb in model mice. The enhanced efficacy was associated with the increased CD8 + T cell, increased effector memory T cells (CD44 + CD8 + CD62L+), decreased Treg (CD4 + CD25 + Foxp3+) and M2 macrophages (F4/80 + CD206+) in the tumor microenvironment. In addition, our results revealed that L. acidophilus lysates had an immunomodulatory effect through inhibition the M2 polarization and the IL-10 expressed levels of LPS-activated Raw264.7 macrophages. Finally, the 16S rRNA gene sequencing of fecal microbiota demonstrated that the combined administration significantly inhibited the abnormal increase in the relative abundance of proteobacteria and partly counterbalance CRC-induced dysbiosis in model mice. Overall, these data support promising clinical possibilities of L. acidophilus lysates with CTLA-4 mAb in cancer patients and the hypothesis that probiotics help shape the anticancer immune response.

Efficacy of Using Probiotics with Antagonistic Activity against Pathogens of Wound Infections: An Integrative Review of Literature

The skin and its microbiota serve as physical barriers to prevent invasion of pathogens. Skin damage can be a consequence of illness, surgery, and burns. The most effective wound management strategy is to prevent infections, promote healing, and prevent excess scarring. It is well established that probiotics can aid in skin healing by stimulating the production of immune cells, and they also exhibit antagonistic effects against pathogens via competitive exclusion of pathogens. Our aim was to conduct a review of recent literature on the efficacy of using probiotics against pathogens that cause wound infections. In this integrative review, we searched through the literature published in the international following databases: PubMed, ScienceDirect, Web of Science, and Scopus using the search terms “probiotic” AND “wound infection.” During a comprehensive review and critique of the selected research, fourteen in vitro studies, 8 animal studies, and 19 clinical studies were found. Two of these in vitro studies also included animal studies, yielding a total of 39 articles for inclusion in the review. The most commonly used probiotics for all studies were well-known strains of the species Lactobacillus plantarum, Lactobacillus casei, Lactobacillus acidophilus, and Lactobacillus rhamnosus. All in vitro studies showed successful inhibition of chosen skin or wound pathogens by the selected probiotics. Within the animal studies on mice, rats, and rabbits, probiotics showed strong opportunities for counteracting wound infections. Most clinical studies showed slight or statistically significant lower incidence of surgical site infections, foot ulcer infection, or burn infections for patients using probiotics. Several of these studies also indicated a statistically significant wound healing effect for the probiotic groups. This review indicates that exogenous and oral application of probiotics has shown reduction in wound infections, especially when used as an adjuvant to antibiotic therapy, and therefore the potential use of probiotics in this field remains worthy of further studies, perhaps focused more on typical skin inhabitants as next-generation probiotics with high potential.

Soluble Fraction from Lysates of Selected Probiotic Strains Differently Influences Re-Epithelialization of HaCaT Scratched Monolayer through a Mechanism Involving Nitric Oxide Synthase 2

A growing body of evidence supports the use of probiotics in the treatment of several skin conditions, including wounds. Even if in vitro and in vivo studies have highlighted the pro-healing effects of some probiotic bacteria, the underlying mechanisms are still not fully defined. The current investigation aimed to determine the re-epithelialization potential of the soluble fraction from lysate of seven different probiotic strains belonging to different genera (i.e., Streptococcus, Lactobacillus, and Bifidobacterium) on in vitro physically wounded HaCaT monolayer model. The results suggested that the soluble fraction of S. thermophilus, L. plantarum, and L. acidophilus promoted the re-epithelialization of scratched HaCaT monolayers, whereas those from B. longum, B. infantis, and B. breve significantly inhibited the process. On the other hand, L. bulgaricus showed no significant effect on in vitro wound repair. The mechanisms underlying the pro- or anti-healing properties of selected bacterial strains strictly and positively correlated with their ability to modulate nitric oxide synthase 2 (NOS2) expression and activity. Accordingly, the pre-treatment with aminoguanidine (AG), a specific inhibitor of NOS2 activity, abrogated the pro-healing effects of S. thermophilus, L. plantarum, and L. acidophilus.

Probiotics in Extraintestinal Diseases: Current Trends and New Directions

Probiotics are defined as live microorganisms that when administered in adequate amounts confer a health benefit to the host. Their positive supplementation outcomes on several gastrointestinal disorders are well defined. Nevertheless, their actions are not limited to the gut, but may also impart their beneficial effects at distant sites and organs. In this regard, in this review article we: (i) comprehensively describe the main mechanisms of action of probiotics at distant sites, including bones, skin, and brain; (ii) critically present their therapeutic potential against bone, skin, and neuronal diseases (e.g., osteoporosis, non-healing wounds and autoimmune skin illnesses, mood, behavior, memory, and cognitive impairments); (iii) address the current gaps in the preclinical and clinical research; and (iv) indicate new research directions and suggest future investigations.

Human Microbiome: Composition and Role in Inflammatory Skin Diseases

This review focuses on recent evidences about human microbiome composition and functions, exploring the potential implication of its impairment in some diffuse and invalidating inflammatory skin diseases, such as atopic dermatitis, psoriasis, hidradenitis suppurativa and acne. We analysed current scientific literature, focusing on the current evidences about gut and skin microbiome composition and the complex dialogue between microbes and the host. Finally, we examined the consequences of this dialogue for health and skin diseases. This review highlights how human microbes interact with different anatomic niches modifying the state of immune activation, skin barrier status, microbe-host and microbe-microbe interactions. It also shows as most of the factors affecting gut and skin microorganisms' activity have demonstrated to be effective also in modulating chronic inflammatory skin diseases. More and more evidences demonstrate that human microbiome plays a key role in human health and diseases. It is to be expected that these new insights will translate into diagnostic, therapeutic and preventive measures in the context of personalized/precision medicine.

In vitro evaluation of antagonism, modulation of cytokines and extracellular matrix proteins by Bifidobacterium strains

A healthy skin provides a protective barrier against pathogenic micro-organisms. Recent studies have shown that probiotics, as those of Bifidobacterium genus, could act beneficially in dermatology, both when ingested and by topical use. In the present study, we evaluated by in vitro antagonism assays and using two skin cell lines the potential of four strains of Bifidobacterium spp. Among the four bifidobacteria, Bifidobacterium longum 5^1A was the only one able to inhibit the growth of the eight pathogenic indicators tested. Production of some cytokines and extracellular matrix proteins was determined when ccc or inactivated cells of the bifidobacteria were incubated with keratinocyte and/or fibroblast cell cultures. Significant results were observed only for IL-6, IL-8 and IL-18 production, and inactivated Bifidobacterium pseudolongum 119^1A was the only one which significantly stimulated collagen production, whereas lumican was stimulated by treatments with live Bifidobacterium bifidum 162^2A , B. longum 5^1A and B. pseudolongum 119^1A . Highest adhesion and internalization capabilities were observed with B. bifidum 162^2A and Bifidobacterium breve 110^1A . Concluding, B. longum 5^1A was highlighted for its antagonistic capacity and B. bifidum 162^2A and B. pseudolongum 119^1A for stimulating the production of cytokines and proteins of the extracellular matrix.

SIGNIFICANCE AND IMPACT OF THE STUDY

The skin is the first line of defence against invasive micro-organisms, and its local microbiota provides additional protective functions based on antagonism against pathogenic micro-organisms and immunomodulation. Based on in vitro assays using Bifidobacterium spp. we demonstrated the antagonistic potential, as well as capacity in stimulating the production of cytokines and proteins of the extracellular matrix that these bacteria may exert on skin cells. This positive influence suggests the use of a consortium of these bifidobacteria in a topical product for dermatological treatments.

Infectious Complications in Atopic Dermatitis

Atopic dermatitis is characterized by the interplay of skin barrier defects with the immune system and skin microbiome that causes patients to be at risk for infectious complications. This article reviews the pathogenesis of atopic dermatitis and the mechanisms through which patients are at risk for infection from bacterial, viral, and fungal pathogens. Although these complications may be managed acutely, prevention of secondary infections depends on a multipronged approach in the maintenance of skin integrity, control of flares, and microbial pathogens.

Probiotics or pro-healers: the role of beneficial bacteria in tissue repair

Probiotics are beneficial microorganisms, known to exert numerous positive effects on human health, primarily in the battle against pathogens. Probiotics have been associated with improved healing of intestinal ulcers, and healing of infected cutaneous wounds. This article reviews the latest findings on probiotics related to their pro-healing properties on gut epithelium and skin. Proven mechanisms by which probiotic bacteria exert their beneficial effects include direct killing of pathogens, competitive displacement of pathogenic bacteria, reinforcement of epithelial barrier, induction of fibroblasts, and epithelial cells' migration and function. Beneficial immunomodulatory effects of probiotics relate to modulation and activation of intraepithelial lymphocytes, natural killer cells, and macrophages through induced production of cytokines. Systemic effects of beneficial bacteria and link between gut microbiota, immune system, and cutaneous health through gut-brain-skin axes are discussed as well. In light of growing antibiotic resistance of pathogens, antibiotic use is becoming less effective in treating cutaneous and systemic infections. This review points to a new perspective and therapeutic potential of beneficial probiotic species as a safe alternative approach for treatment of patients affected by wound healing disorders and cutaneous infections.

Cutaneous Nod2 Expression Regulates the Skin Microbiome and Wound Healing in a Murine Model

The skin microbiome exists in dynamic equilibrium with the host, but when the skin is compromised, bacteria can colonize the wound and impair wound healing. Thus, the interplay between normal skin microbial interactions versus pathogenic microbial interactions in wound repair is important. Bacteria are recognized by innate host pattern recognition receptors, and we previously showed an important role for the pattern recognition receptor NOD2 in skin wound repair. NOD2 is implicated in changes in the composition of the intestinal microbiota in Crohn’s disease, but its role on skin microbiota is unknown. Nod2-deficient (Nod2^–/–) mice had an inherently altered skin microbiome compared with wild-type controls. Furthermore, we found that Nod2^–/– skin microbiome dominated and caused impaired healing, shown in cross-fostering experiments of wild-type pups with Nod2^–/– pups, which then acquired altered cutaneous bacteria and delayed healing. High-throughput sequencing and quantitative real-time PCR showed a significant compositional shift, specifically in the genus Pseudomonas in Nod2^–/– mice. To confirm whether Pseudomonas species directly impair wound healing, wild-type mice were infected with Pseudomonas aeruginosa biofilms and, akin to Nod2^–/– mice, were found to exhibit a significant delay in wound repair. Collectively, these studies show the importance of the microbial communities in skin wound healing outcome.

Host Responses to Biofilm

From birth to death the human host immune system interacts with bacterial cells. Biofilms are communities of microbes embedded in matrices composed of extracellular polymeric substance (EPS), and have been implicated in both the healthy microbiome and disease states. The immune system recognizes many different bacterial patterns, molecules, and antigens, but these components can be camouflaged in the biofilm mode of growth. Instead, immune cells come into contact with components of the EPS matrix, a diverse, hydrated mixture of extracellular DNA (bacterial and host), proteins, polysaccharides, and lipids. As bacterial cells transition from planktonic to biofilm-associated they produce small molecules, which can increase inflammation, induce cell death, and even cause necrosis. To survive, invading bacteria must overcome the epithelial barrier, host microbiome, complement, and a variety of leukocytes. If bacteria can evade these initial cell populations they have an increased chance at surviving and causing ongoing disease in the host. Planktonic cells are readily cleared, but biofilms reduce the effectiveness of both polymorphonuclear neutrophils and macrophages. In addition, in the presence of these cells, biofilm formation is actively enhanced, and components of host immune cells are assimilated into the EPS matrix. While pathogenic biofilms contribute to states of chronic inflammation, probiotic Lactobacillus biofilms cause a negligible immune response and, in states of inflammation, exhibit robust antiinflammatory properties. These probiotic biofilms colonize and protect the gut and vagina, and have been implicated in improved healing of damaged skin. Overall, biofilms stimulate a unique immune response that we are only beginning to understand.

Live and Heat-Killed Lactobacillus rhamnosus ATCC 7469 May Induce Modulatory Cytokines Profiles on Macrophages RAW 264.7

This study aimed to evaluate the capacity of Lactobacillus rhamnosus and/or its products to induce the synthesis of cytokines (TNF-α, IL-1β, IL-4, IL-6, IL-10, and IL-12) by mouse macrophages (RAW 264.7). Three microorganism preparations were used: live L. rhamnosus (LLR) suspension, heat-killed L. rhamnosus (HKLR) suspension, and the supernatant of a heat-killed L. rhamnosus (SHKLR) suspension, which were cultured with macrophages (37°C, 5% CO₂) for 2 h and 30 min. After that, cells were cultured for 16 h. The supernatants were used for the quantitation of cytokines, by ELISA. The results were compared with the synthesis induced by lipopolysaccharide (LPS) and analysed, using ANOVA and Tukey test, 5%. LLR and HKLR groups were able to significantly increase the production of TNF-α, IL-6, and IL-10 (P < 0.05). SHKLR also significantly increased the production of TNF-α and IL-10 (P < 0.05) but not IL-6 (P > 0.05). All the L. rhamnosus suspensions were not able to produce detectable levels of IL-1β or significant levels of IL-4 and IL-12 (P > 0.05). In conclusion, live and heat-killed L. rhamnosus suspensions were able to induce the synthesis of different cytokines with proinflammatory (TNF-α and IL-6) or regulatory (IL-10) functions, suggesting the role of strain L. rhamnosus ATCC 7469 in the modulation or in the stimulation of immune responses.

Lactobacillus rhamnosus GG Lysate Increases Re-Epithelialization of Keratinocyte Scratch Assays by Promoting Migration

A limited number of studies have investigated the potential of probiotics to promote wound healing in the digestive tract. The aim of the current investigation was to determine whether probiotic bacteria or their extracts could be beneficial in cutaneous wound healing. A keratinocyte monolayer scratch assay was used to assess re-epithelialization; which comprises keratinocyte proliferation and migration. Primary human keratinocyte monolayers were scratched then exposed to lysates of Lactobacillus (L) rhamnosus GG, L. reuteri, L. plantarum or L. fermentum. Re-epithelialization of treated monolayers was compared to that of untreated controls. Lysates of L. rhamnosus GG and L. reuteri significantly increased the rate of re-epithelialization, with L. rhamnosus GG being the most efficacious. L. reuteri increased keratinocyte proliferation while L. rhamnosus GG lysate significantly increased proliferation and migration. Microarray analysis of L. rhamnosus GG treated scratches showed increased expression of multiple genes including the chemokine CXCL2 and its receptor CXCR2. These are involved in normal wound healing where they stimulate keratinocyte proliferation and/or migration. Increased protein expression of both CXCL2 and CXCR2 were confirmed by ELISA and immunoblotting. These data demonstrate that L. rhamnosus GG lysate accelerates re-epithelialization of keratinocyte scratch assays, potentially via chemokine receptor pairs that induce keratinocyte migration.

Microbiome and pediatric atopic dermatitis

Atopic dermatitis is a chronic inflammatory skin condition with drastic impacts on pediatric health. The pathogenesis of this common disease is not well understood, and the complex role of the skin microbiome in the pathogenesis and progression of atopic dermatitis is being elucidated. Skin commensal organisms promote normal immune system functions and prevent the colonization of pathogens. Alterations in the skin microbiome may lead to increased Staphylococcus aureus colonization and atopic dermatitis progression. Despite the evidence for their important role, probiotics have not been deemed efficacious for the treatment of atopic dermatitis, although studies suggest that probiotics may be effective at preventing the development of atopic dermatitis when given to young infants. This review will cover the most recent published work on the microbiome and pediatric atopic dermatitis.