Biofilms of vaginal Lactobacillus reuteri CRL 1324 and Lactobacillus rhamnosus CRL 1332: kinetics of formation and matrix characterization

How to study biofilms: technological advancements in clinical biofilm research

Biofilm formation is an important survival strategy commonly used by bacteria and fungi, which are embedded in a protective extracellular matrix of organic polymers. They are ubiquitous in nature, including humans and other animals, and they can be surface- and non-surface-associated, making them capable of growing in and on many different parts of the body. Biofilms are also complex, forming polymicrobial communities that are difficult to eradicate due to their unique growth dynamics, and clinical infections associated with biofilms are a huge burden in the healthcare setting, as they are often difficult to diagnose and to treat. Our understanding of biofilm formation and development is a fast-paced and important research focus. This review aims to describe the advancements in clinical biofilm research, including both in vitro and in vivo biofilm models, imaging techniques and techniques to analyse the biological functions of the biofilm.

Fabric Fiber as a Biofilm Carrier for Halomonas sp. H09 Mixed with Lactobacillus rhamnosus GG

Biofilm bacteria have stronger resistance to the adverse external environment compared to planktonic bacteria, and biofilms of non-pathogenic bacteria have strong potential for applications in food. In this experiment, Halomonas sp. H09 and Lactobacillus rhamnosus GG, which have film-forming ability in monoculture and better film-forming ability in mixed culture than the two strains alone, were selected as the target strains for mixed culture. According to SEM observation and bacterial dry weight measurement, the target strain formed a dense biofilm on a 0.1 g/L chitosan-modified cellulose III carrier. Furthermore, the presence of extracellular polymeric substances in biofilms was verified by EDS and FTIR. The results showed that 0.1 g/L chitosan-modified cellulose III was an ideal carrier material for immobilization of Halomonas sp. H09 with Lactobacillus rhamnosus GG biofilm. This research provided a basis for the selection of non-pathogenic mixed-bacteria biofilm carriers.

Probiotic profiling of bifidobacteria indigenous to the human intestinal mucosa shows alleviation of dysbiosis-associated pathogen biofilms

The present study was undertaken to isolate bifidobacterial probiotics and characterize the biodiversity of mucosal bacteria in the human distal gut through 16S rRNA amplicon sequencing. Bifidobacterial strains obtained by selective culturing were investigated for biofilms and probiotic characteristics. Both culture-dependent and culture-independent approaches revealed substantial microbial diversity. Bifidobacterium strains yielded robust biofilms with predominantly exopolysaccharides and eDNA matrix. Microscopy revealed species-dependent spatial arrangement of microcolonies. Following probiotic profiling and safety assessment, the inter- and intra-specific interactions in in dual strain bifidobacterial biofilms were studied. As a species, only strains of B. bifidum exhibited exclusively inductive type of interactions whereas in other species, the interactions were more varied. On the other hand, in dual species biofilms, a preponderance of inductive interactions was evident between B. adolescentis, B. thermophilum, B. bifidum, and B. longum. The strong biofilm-formers also diminished pathogenic biofilm viability, and some were proficient in cholesterol removal in vitro. None of the strains exhibited harmful enzymatic activities associated with disease pathology. Interaction between biofilm-forming bifidobacterial strains provides an understanding of their functionality and persistence in the human host, and food or medicine. Their anti-pathogenic activity represents a therapeutic strategy against drug-resistant pathogenic biofilms.

Multi-dimensional experimental and computational exploration of metabolism pinpoints complex probiotic interactions

Multi-strain probiotics are widely regarded as effective products for improving gut microbiota stability and host health, providing advantages over single-strain probiotics. However, in general, it is unclear to what extent different strains would cooperate or compete for resources, and how the establishment of a common biofilm microenvironment could influence their interactions. In this work, we develop an integrative experimental and computational approach to comprehensively assess the metabolic functionality and interactions of probiotics across growth conditions. Our approach combines co-culture assays with genome-scale modelling of metabolism and multivariate data analysis, thus exploiting complementary data- and knowledge-driven systems biology techniques. To show the advantages of the proposed approach, we apply it to the study of the interactions between two widely used probiotic strains of Lactobacillus reuteri and Saccharomyces boulardii, characterising their production potential for compounds that can be beneficial to human health. Our results show that these strains can establish a mixed cooperative-antagonistic interaction best explained by competition for shared resources, with an increased individual exchange but an often decreased net production of amino acids and short-chain fatty acids. Overall, our work provides a strategy that can be used to explore microbial metabolic fingerprints of biotechnological interest, capable of capturing multifaceted equilibria even in simple microbial consortia.

Brain effects of gestating germ-free persist in mouse neonates despite acquisition of a microbiota at birth

At birth, mammals experience a massive colonization by microorganisms. We previously reported that newborn mice gestated and born germ-free (GF) have increased microglial labeling and alterations in developmental neuronal cell death in the hippocampus and hypothalamus, as well as greater forebrain volume and body weight when compared to conventionally colonized (CC) mice. To test whether these effects are solely due to differences in postnatal microbial exposure, or instead may be programmed in utero, we cross-fostered GF newborns immediately after birth to CC dams (GF→CC) and compared them to offspring fostered within the same microbiota status (CC→CC, GF→GF). Because key developmental events (including microglial colonization and neuronal cell death) shape the brain during the first postnatal week, we collected brains on postnatal day (P) 7. To track gut bacterial colonization, colonic content was also collected and subjected to 16S rRNA qPCR and Illumina sequencing. In the brains of GF→GF mice, we replicated most of the effects seen previously in GF mice. Interestingly, the GF brain phenotype persisted in GF→CC offspring for almost all measures. In contrast, total bacterial load did not differ between the CC→CC and GF→CC groups on P7, and bacterial community composition was also very similar, with a few exceptions. Thus, GF→CC offspring had altered brain development during at least the first 7 days after birth despite a largely normal microbiota. This suggests that prenatal influences of gestating in an altered microbial environment programs neonatal brain development.

Lacticaseibacillus rhamnosus CA15 (DSM 33960) as a Candidate Probiotic Strain for Human Health

Lactobacilli with probiotic properties have emerged as promising tools for both the prevention and treatment of vaginal dysbiosis. The present study aimed to study the in vitro probiotic potential of the Lacticaseibacillus rhamnosus CA15 (DSM 33960) strain isolated from a healthy vaginal ecosystem. The strain was evaluated for both functional (antagonistic activity against pathogens; H₂O₂, organic acid, and lactic acid production; antioxidant and anti-inflammatory activities; ability to adhere to intestinal mucus and to both CaCo-2 and VK7/E6E7 cell lines; exopolysaccharide production; surface properties; and ability to survive during gastrointestinal transit) and safety (hemolytic, DNase, and gelatinase activities; mucin degradation ability; production of biogenic amines; and resistance to antimicrobials) characteristics. Data revealed that the tested strain was able to antagonize a broad spectrum of vaginal pathogens. In addition, the adhesion capacity to both vaginal and intestinal cell lines, as well as anti-inflammatory and antioxidant activities, was detected. The ability of the Lacticaseibacillus rhamnosus CA15 (DSM 33960) strain to survive under harsh environmental conditions occurring during the gastrointestinal passage suggests its possible oral delivery. Thus, in vitro data highlighted interesting probiotic properties of the CA15 (DSM 33960) strain, which could represent a valuable candidate for in vivo vaginal infections treatment.

Advances and future perspectives in epithelial drug delivery

Epithelial surfaces protect exposed tissues in the body against intrusion of foreign materials, including xenobiotics, pollen and microbiota. The relative permeability of the various epithelia reflects their extent of exposure to the external environment and is in the ranking: intestinal≈ nasal ≥ bronchial ≥ tracheal > vaginal ≥ rectal > blood-perilymph barrier (otic), corneal > buccal > skin. Each epithelium also varies in their morphology, biochemistry, physiology, immunology and external fluid in line with their function. Each epithelium is also used as drug delivery sites to treat local conditions and, in some cases, for systemic delivery. The associated delivery systems have had to evolve to enable the delivery of larger drugs and biologicals, such as peptides, proteins, antibodies and biologicals and now include a range of physical, chemical, electrical, light, sound and other enhancement technologies. In addition, the quality-by-design approach to product regulation and the growth of generic products have also fostered advancement in epithelial drug delivery systems.

Bacterioboat-A novel tool to increase the half-life period of the orally administered drug

The short half-life in the GI tract necessitates an excess of drugs causing side effects of oral formulations. Here, we report the development and deployment of Bacterioboat, which consists of surface-encapsulated mesoporous nanoparticles on metabolically active Lactobacillus reuteri as a drug carrier suitable for oral administration. Bacterioboat showed up to 16% drug loading of its dry weight, intestinal anchorage around alveoli regions, sustained release, and stability in physiological conditions up to 24 hours. In vivo studies showed that oral delivery of 5-fluorouracil leads to increased potency, resulting in improved shrinkage of solid tumors, enhanced life expectancy, and reduced side effects. This novel design and development make this system ideal for orally administrable drugs with low solubility or permeability or both and even making them effective at a lower dose.

The Vaginal Microbiota, Bacterial Biofilms and Polymeric Drug-Releasing Vaginal Rings

The diversity and dynamics of the microbial species populating the human vagina are increasingly understood to play a pivotal role in vaginal health. However, our knowledge about the potential interactions between the vaginal microbiota and vaginally administered drug delivery systems is still rather limited. Several drug-releasing vaginal ring products are currently marketed for hormonal contraception and estrogen replacement therapy, and many others are in preclinical and clinical development for these and other clinical indications. As with all implantable polymeric devices, drug-releasing vaginal rings are subject to surface bacterial adherence and biofilm formation, mostly associated with endogenous microorganisms present in the vagina. Despite more than 50 years since the vaginal ring concept was first described, there has been only limited study and reporting around bacterial adherence and biofilm formation on rings. With increasing interest in the vaginal microbiome and vaginal ring technology, this timely review article provides an overview of: (i) the vaginal microbiota, (ii) biofilm formation in the human vagina and its potential role in vaginal dysbiosis, (iii) mechanistic aspects of biofilm formation on polymeric surfaces, (iv) polymeric materials used in the manufacture of vaginal rings, (v) surface morphology characteristics of rings, (vi) biomass accumulation and biofilm formation on vaginal rings, and (vii) regulatory considerations.

Antimicrobial properties of Lactobacillus cell-free supernatants against multidrug-resistant urogenital pathogens

The healthy vaginal microbiota is dominated by Lactobacillus spp., which provide an important critical line of defense against pathogens, as well as giving beneficial effects to the host. We characterized L. gasseri 1A‐TV, L. fermentum 18A‐TV, and L. crispatus 35A‐TV, from the vaginal microbiota of healthy premenopausal women, for their potential probiotic activities. The antimicrobial effects of the 3 strains and their combination against clinical urogenital bacteria were evaluated together with the activities of their metabolites produced by cell‐free supernatants (CFSs). Their beneficial properties in terms of ability to interfere with vaginal pathogens (co‐aggregation, adhesion to HeLa cells, biofilm formation) and antimicrobial activity mediated by CFSs were assessed against multidrug urogenital pathogens (S. agalactiae, E. coli, KPC‐producing K. pneumoniae, S. aureus, E. faecium VRE, E. faecalis, P. aeruginosa, P. mirabilis, P. vulgaris, C. albicans, C. glabrata). The Lactobacilli tested exhibited an extraordinary ability to interfere and co‐aggregate with urogenital pathogens, except for Candida spp., as well as to adhere to HeLa cells and to produce biofilm in the Lactobacillus combination. Lactobacillus CFSs and their combination revealed a strong bactericidal effect on the multidrug resistant indicator strains tested, except for E. faecium and E. faecalis. The antimicrobial activity was maintained after heat treatment but decreased after enzymatic treatment. All Lactobacilli showed lactic dehydrogenase activity and production of D‐ and L‐lactic acid isomers on Lactobacillus CFSs, while only 1A‐TV and 35A‐TV released hydrogen peroxide and carried helveticin J and acidocin A bacteriocins. These results suggest that they can be employed as a new vaginal probiotic formulation and bio‐therapeutic preparation against urogenital infections. Further, in vivo studies are needed to evaluate human health benefits in clinical situations.

Screening of autochthonous vaginal beneficial lactobacilli strains by their growth at high temperatures for technological applications

The pharmaceutical industry shows an emerging interest in formulas that contain live and beneficial microorganisms, also known as probiotics or pharmabiotics, which in many cases, are host-specific. The resistance to higher temperature is an essential feature of these microorganisms when working on the design of products for vaginal formula. In order to obtain a high number of viable cells and a prolonged shelf life in the designed product, it is required to apply technological procedures using high temperatures or abrupt changes of them, which result in conditions that are different from the optimal growth temperature and can affect the metabolic capabilities of the bacteria when administered to the host in order to reestablish the ecological mucosa. The aim of this work was to evaluate the behavior of 30 different species and strains of autochthonous beneficial vaginal lactobacilli (BVL) when exposed to high temperatures, determine their survival capabilities and analyze their pre-adaptation to those temperatures, in order that they still maintain their viability after technological processes and further conservation. BVL were exhibited to temperatures higher than optimal, with the purpose of evaluating their growth kinetics and parameters. Later, they were exposed to higher temperatures, and then, returned to their optimal, to determine if they were able to grow again. The strains that showed higher resistance were selected, and their viability and beneficial properties studied further. The growth kinetics of strains exposed to higher temperatures showed different patterns, which provided evidence that the thermal adaptation is strain-dependent and is not related to any particular species and/or metabolic group in which the strains were taxonomically classified. The pre-adaptive step allowed the growth of some of the strains, preserving their viability and probiotic properties after the high temperatures were applied. The results shows that BVL can be exposed to high temperatures used in different technological processes that are applied for pharmabiotic formulations, such as spray dried or vacuum rotary evaporation, and/or during the conservation period. The results obtained indicate that some specific BVL strains resist high temperatures and grow afterwards at optimal conditions.

Chemical Functionalization of the Zinc Selenide Surface and Its Impact on Lactobacillus rhamnosus GG Biofilms

Bacteria grow on surfaces and form communities called biofilms. Bacterial adhesion and properties of the derived biofilms depend on, among others, the nature of the supporting substrate. Here, we report how the surface properties of the substrate affect the biofilm growth of probiotic Lactobacillus rhamnosus GG (LGG). Hydrophilic (OH), hydrophobic (CH₃), and positively charged (NH₃⁺) surfaces were obtained by the functionalization of a ZnSe crystal with alkanethiol self-assembled monolayers (SAM). The self-assembly of alkanethiols onto ZnSe was studied in situ using infrared spectroscopy in attenuated total reflection mode (ATR-FTIR). The organization of grafted SAMs was analyzed based on the results of ATR-FTIR, high-energy elastic backscattering spectrometry, and contact angle measurements. The kinetics and adhesion strength of LGG initial attachment as well as its physiological state on surfaces terminated by the different functional groups were assessed by the combination of ATR-FTIR, force measurements based on atomic force microscopy, and fluorescent staining of bacteria. The strength of interactions between LGG and the surface was strongly affected by the terminal group of the alkanethiol chain. The -NH₃⁺ groups displayed the highest affinity with LGG at the first stage of interaction. The surface properties also played an important role when LGG biofilms were further grown in a nutritive medium for 24 h under flow conditions. Notably, the analysis of the infrared spectra recorded during the biofilm cultivation revealed differences in the kinetics of growth and in the polysaccharide features of the biofilm depending on the substrate functionality. LGG biofilm was stable only on the positively charged surface upon rinsing. Findings of this work clearly show that the adhesion features and the growth of LGG biofilms are substrate-dependent.

Detection and Quantification of eDNA-Associated Bacterial Membrane Vesicles by Flow Cytometry

Bacteria generate membrane vesicles, which are structures known as extracellular vesicles (EVs), reported to be involved in different pathogenic mechanisms, as it has been demonstrated that EVs participate in biofilm formation, cell-to-cell communication, bacteria–host interactions, and nutrients supply. EVs deliver nucleic acids, proteins, and polysaccharides. It has been reported that Helicobacter pylori (H. pylori) and Lactobacillus reuteri (L. reuteri), of both planktonic and biofilm phenotypes, produce EVs carrying extracellular DNA (eDNA). Here, we used polychromatic flow cytometry (PFC) to identify, enumerate, and characterize EVs as well as the eDNA-delivering EV compartment in the biofilm and planktonic phenotypes of H.pylori ATCC 43629 and L. reuteri DSM 17938. Biofilm formation was demonstrated and analyzed by fluorescence microscopy, using a classical live/dead staining protocol. The enumeration of EVs and the detection of eDNA-associated EVs were performed by PFC, analyzing both whole samples (cells plus vesicles) and EVs isolated by ultracentrifugation confirm EVs isolated by ultracentrifugation. PFC analysis was performed relying on a known-size beaded system and a mix of three different fluorescent tracers. In detail, the whole EV compartment was stained by a lipophilic cationic dye (LCD), which was combined to PKH26 and PicoGreen that selectively stain lipids and DNA, respectively. Fluorescence microscopy results displayed that both H. pylori and L. reuteri produced well-structured biofilms. PFC data highlighted that, in both detected bacterial species, biofilms produced higher EVs counts when paralleled to the related planktonic phenotypes. Furthermore, the staining with PicoGreen showed that most of the generated vesicles were associated with eDNA. These data suggest that the use of PFC, set according to the parameters here described, allows for the study of the production of eDNA-associated EVs in different microbial species in the same or several phases of growth, thus opening new perspectives in the study of microbial derived EVs in clinical samples.

Characterization of the immunomodulatory and anti-Helicobacter pylori properties of the human gastric isolate Lactobacillus rhamnosus UCO-25A

The ability to form biofilms and the potential immunomodulatory properties of the human gastric isolate Lactobacillus rhamnosus UCO-25A were characterized in vitro. It was demonstrated that L. rhamnosus UCO-25A is able to form biofilms on abiotic and cell surfaces, and to modulate the inflammatory response triggered by Helicobacter pylori infection in gastric epithelial cells and THP-1 macrophages. L. rhamnosus UCO-25A exhibited a substantial anti-inflammatory effect in both cell lines and improved IL-10 levels produced by challenged macrophages. Additionally, UCO-25A protected AGS cells against H. pylori infection with a higher pathogen inhibition when a biofilm was formed. Given the importance of inflammation in H. pylori-mediated diseases, the differential modulation of the inflammatory response in the gastric mucosa by an autochthonous strain is an attractive alternative for improving H. pylori eradication and reducing the severity of the diseases that arise from the resulting chronic inflammation.

The Use of Probiotic Therapy to Modulate the Gut Microbiota and Dendritic Cell Responses in Inflammatory Bowel Diseases

Recent investigations have shown that different conditions such as diet, the overuse of antibiotics or the colonization of pathogenic microorganisms can alter the population status of the intestinal microbiota. This modification can produce a change from homeostasis to a condition known as imbalance or dysbiosis; however, the role-played by dysbiosis and the development of inflammatory bowel diseases (IBD) has been poorly understood. It was actually not until a few years ago that studies started to develop regarding the role that dendritic cells (DC) of intestinal mucosa play in the sensing of the gut microbiota population. The latest studies have focused on describing the DC modulation, specifically on tolerance response involving T regulatory cells or on the inflammatory response involving reactive oxygen species and tissue damage. Furthermore, the latest studies have also focused on the protective and restorative effect of the population of the gut microbiota given by probiotic therapy, targeting IBD and other intestinal pathologies. In the present work, the authors propose and summarize a recently studied complex axis of interaction between the population of the gut microbiota, the sensing of the DC and its modulation towards tolerance and inflammation, the development of IBD and the protective and restorative effect of probiotics on other intestinal pathologies.

α-Chymotrypsin Immobilized on a Low-Density Polyethylene Surface Successfully Weakens Escherichia coli Biofilm Formation

The protease α-chymotrypsin (α-CT) was covalently immobilized on a low-density polyethylene (LDPE) surface, providing a new non-leaching material (LDPE-α-CT) able to preserve surfaces from biofilm growth over a long working timescale. The immobilized enzyme showed a transesterification activity of 1.24 nmol/h, confirming that the immobilization protocol did not negatively affect α-CT activity. Plate count viability assays, as well as confocal laser scanner microscopy (CLSM) analysis, showed that LDPE-α-CT significantly impacts Escherichia coli biofilm formation by (i) reducing the number of adhered cells (-70.7 ± 5.0%); (ii) significantly affecting biofilm thickness (-81.8 ± 16.7%), roughness (-13.8 ± 2.8%), substratum coverage (-63.1 ± 1.8%), and surface to bio-volume ratio (+7.1 ± 0.2-fold); and (iii) decreasing the matrix polysaccharide bio-volume (80.2 ± 23.2%). Additionally, CLSM images showed a destabilized biofilm with many cells dispersing from it. Notably, biofilm stained for live and dead cells confirmed that the reduction in the biomass was achieved by a mechanism that did not affect bacterial viability, reducing the chances for the evolution of resistant strains.

Structural Characterization of the Lactobacillus Plantarum FlmC Protein Involved in Biofilm Formation

Lactobacillus plantarum is one of the most predominant species in the human gut microbiota of healthy individuals. We have previously characterized some probiotic features of L. plantarum LM3, as the high resistance to different stress, the binding ability toward some extracellular matrix proteins and plasminogen and the immunomodulatory role of the surface expressed adhesin EnoA1. We have also identified the flmA, flmB and flmC genes, coding for putative proteins named FlmA, FlmB and FlmC, whose null mutations partially impaired biofilm development; the L. plantarum LM3–6 strain, carrying a deletion in flmC, showed a high rate of autolysis, supporting the hypothesis that FlmC might be involved in cell wall integrity. Here, we report the in-silico characterization of ΔTM-FlmC, a portion of the FlmC protein. The protein has been also expressed, purified and characterized by means of CD spectroscopy, ICP-mass and UHPLC-HRMS. The obtained experimental data validated the predicted model unveiling also the presence of a bound lipid molecule and of a Mg(II) ion. Overall, we provide strong evidences that ΔTM-FlmC belongs to the LytR-CpsA-Psr (LCP) family of domains and is involved in cell envelope biogenesis.

Inhibitory effect of biofilm-forming Lactobacillus kunkeei strains against virulent Pseudomonas aeruginosa in vitro and in honeycomb moth (Galleria mellonella) infection model

Biofilms correspond to complex communities of microorganisms embedded in an extracellular polymeric matrix. Biofilm lifestyle predominates in Pseudomonas aeruginosa, an opportunistic Gram negative pathogen responsible for a wide spectrum of infections in humans, plants and animals. In this context, anti-biofilm can be considered a key strategy to control P. aeruginosa infections, thereby more research in the field is required. On the other hand, Lactobacillus species have been described as beneficial due to their anti-biofilm properties and their consequent effect against a wide spectrum of pathogens. In fact, biofilm-forming Lactobacilli seem to be more efficient than their planktonic counterpart to antagonise pathogenic bacteria. In this work, we demonstrated that Lactobacillus kunkeei, a novel Lactobacillus species isolated from honeybee guts, can form biofilms in vitro. In addition, the L. kunkeei biofilm can, in turn, inhibit the formation of P. aeruginosa biofilms. Finally, we found that L. kunkeei strains attenuate infection of P. aeruginosa in the Galleria mellonella model, presumably by affecting P. aeruginosa biofilm formation and/or their stability. Since L. kunkeei presents characteristics of a probiotic, this work provides evidence arguing that the use of this Lactobacillus species in both animals (including insects) and humans could contribute to impair P. aeruginosa biofilm formation.

Biofilm Forming Lactobacillus: New Challenges for the Development of Probiotics

Probiotics are live bacteria, generally administered in food, conferring beneficial effects to the host because they help to prevent or treat diseases, the majority of which are gastrointestinal. Numerous investigations have verified the beneficial effect of probiotic strains in biofilm form, including increased resistance to temperature, gastric pH and mechanical forces to that of their planktonic counterparts. In addition, the development of new encapsulation technologies, which have exploited the properties of biofilms in the creation of double coated capsules, has given origin to fourth generation probiotics. Up to now, reviews have focused on the detrimental effects of biofilms associated with pathogenic bacteria. Therefore, this work aims to amalgamate information describing the biofilms of Lactobacillus strains which are used as probiotics, particularly L. rhamnosus, L. plantarum, L. reuteri, and L. fermentum. Additionally, we have reviewed the development of probiotics using technology inspired by biofilms.