Confers Colonization Resistance Research Articles

Identification of a microbial sub-community from the feral chicken gut that reduces Salmonella colonization and improves gut health in a gnotobiotic chicken model.

A complex microbial community in the gut may prevent the colonization of enteric pathogens such as Salmonella. Some individual or a combination of species in the gut may confer colonization resistance against Salmonella. To gain a better understanding of the colonization resistance against Salmonella enterica, we isolated a library of 1,300 bacterial strains from feral chicken gut microbiota which represented a total of 51 species. Using a co-culture assay, we screened the representative species from this library and identified 30 species that inhibited Salmonella enterica subspecies enterica serovar Typhimurium in vitro. To improve the Salmonella inhibition capacity, from a pool of fast-growing species, we formulated 66 bacterial blends, each of which composed of 10 species. Bacterial blends were more efficient in inhibiting Salmonella as compared to individual species. The blend that showed maximum inhibition (Mix10) also inhibited other serotypes of Salmonella frequently found in poultry. The in vivo effect of Mix10 was examined in a gnotobiotic and conventional chicken model. The Mix10 consortium significantly reduced Salmonella load at day 2 post-infection in gnotobiotic chicken model and decreased intestinal tissue damage and inflammation in both models. Cell-free supernatant of Mix10 did not show Salmonella inhibition, indicating that Mix10 inhibits Salmonella through either nutritional competition, competitive exclusion, or through reinforcement of host immunity. Out of 10 species, 3 species in Mix10 did not colonize, while 3 species constituted more than 70% of the community. Two of these species were previously uncultured bacteria. Our approach could be used as a high-throughput screening system to identify additional bacterial sub-communities that confer colonization resistance against enteric pathogens and its effect on the host.IMPORTANCESalmonella colonization in chicken and human infections originating from Salmonella-contaminated poultry is a significant problem. Poultry has been identified as the most common food linked to enteric pathogen outbreaks in the United States. Since multi-drug-resistant Salmonella often colonize chicken and cause human infections, methods to control Salmonella colonization in poultry are needed. The method we describe here could form the basis of developing gut microbiota-derived bacterial blends as a microbial ecosystem therapeutic against Salmonella.

Short-chain fatty acids of various lengths differentially inhibit Klebsiella pneumoniae and Enterobacteriaceae species.

The gut microbiota is inextricably linked to human health and disease. It can confer colonization resistance against invading pathogens either through niche occupation and nutrient competition or via its secreted metabolites. Short-chain fatty acids (SCFA) are the primary metabolites in the gut as a result of dietary fiber fermentation by the gut microbiota. In this work, we demonstrate that the interaction of single-species gut commensals on solid media is insufficient for pathogen inhibition, but supernatants from monocultures of these commensal bacteria enriched in acetate confer inhibition against anaerobic growth of the enteric pathogen Klebsiella pneumoniae. The three primary SCFAs (acetate, propionate, and butyrate) strongly inhibit the intestinal commensal Escherichia coli Nissle as well as a panel of enteric pathogens besides K. pneumoniae at physiological pH of the cecum and ascending colon. This inhibition was significantly milder on anaerobic gut commensals Bacteroides thetaiotaomicron and Bifidobacterium adolescentis previously demonstrated to be associated with microbiota recovery after antibiotic-induced dysbiosis. We describe a general suppression of bacterial membrane potential by these SCFAs at physiological cecum and ascending colonic pH. Furthermore, the strength of bacterial inhibition increases with increasing alkyl chain length. Overall, the insights gained in this study shed light on the potential therapeutic use of SCFAs for conferring colonization resistance against invading pathogens in a dysbiotic gut.IMPORTANCERising antimicrobial resistance has made treatment of bacterial infections increasingly difficult. According to the World Health Organization, it has become a burgeoning threat to hospital and public health systems worldwide. This threat is largely attributed to the global rise of carbapenem-resistant Enterobacteriaceae in recent years, with common hospital-acquired pathogens growing increasingly resistant to last-line antibiotics. Antibiotics disrupt the homeostatic balance of the gut microbiota, resulting in the loss of colonization resistance against enteric pathogens. This work describes the ability of short-chain fatty acids (SCFAs) produced by gut microbiota to be effective against a wide panel of enteric pathogens without major impact on common gut commensal species. We also demonstrate a previously undescribed link between alkyl chain length and antibacterial effects of SCFAs. SCFAs, thus, hold promise as an alternative therapeutic option leveraging on the antimicrobial activity of these endogenously produced gut metabolites without disrupting gut microbiota homeostasis.

Fecal Microbiota Transplantation Reduces Campylobacter jejuni Colonization in Young Broiler Chickens Challenged by Oral Gavage but Not by Seeder Birds.

Campylobacter spp., particularly C. jejuni and C. coli, are major food safety concerns, transmitted to humans mainly via contaminated poultry meat. In a previous study, we found that some commercial broiler farms consistently produced Campylobacter-free flocks while others consistently reared Campylobacter-colonized flocks, and significant differences in the gut microbiota compositions between the two types of farm categories were revealed. Therefore, we hypothesized that gut microbiota influences Campylobacter colonization in poultry and that the microbiota from Campylobacter-free flocks may confer colonization resistance to Campylobacter in the chicken intestine. In this study, two fecal microbiota transplantation (FMT) trials were performed to test the hypothesis. Newly hatched chicks were given FMT via oral gavage of the cecal content of Campylobacter-free adult chickens (treatment groups) or PBS (control groups) before the feed consumption. Approximately two weeks after the FMT, the birds were challenged with C. jejuni either by oral gavage (trial 1) or by co-mingling with Campylobacter-colonized seeder birds (trial 2) to evaluate the potential protective effect of the FMT. Cecal contents were collected (3 times, 5 days apart) to determine the Campylobacter colonization levels via culture and microbiota compositions via 16S rRNA gene sequencing. FMT reduced cecal Campylobacter colonization significantly (log10 1.2-2.54 CFU/g) in trial 1 but not in trial 2, although FMT significantly impacted the diversity and compositions of the gut microbiota in both trials. Several genera, such as Butyricimonas, Parabacteroides, Parasutterella, Bilophila, Fournierella, Phascolarctobacterium, and Helicobacter, had increased abundance in the FMT-treated groups in both trials. Furthermore, Campylobacter abundance was found to be negatively correlated with the Escherichia and Ruminococcus_torques_group genera. These findings indicate that even though FMT with adult cecal microbiota can positively affect the subsequent development of the gut microbiota in young broilers, its inhibitory effect on Campylobacter colonization varies and appears to be influenced by the challenge models.

Host cells subdivide nutrient niches into discrete biogeographical microhabitats for gut microbes

Changes in the microbiota composition are associated with many human diseases, but factors that govern strain abundance remain poorly defined. We show that a commensal Escherichia coli strain and a pathogenic Salmonella enterica serovar Typhimurium isolate both utilize nitrate for intestinal growth, but each accesses this resource in a distinct biogeographical niche. Commensal E.coli utilizes epithelial-derived nitrate, whereas nitrate in the niche occupied by S. Typhimurium is derived from phagocytic infiltrates. Surprisingly, avirulent S. Typhimurium was shown to be unable to utilize epithelial-derived nitrate because its chemotaxis receptors McpB and McpC exclude the pathogen from the niche occupied by E.coli. In contrast, E.coli invades the niche constructed by S. Typhimurium virulence factors and confers colonization resistance by competing for nitrate. Thus, nutrient niches are not defined solely by critical resources, but they can be further subdivided biogeographically within the host into distinct microhabitats, thereby generating new niche opportunities for distinct bacterial species.

The Habitat Filters of Microbiota-Nourishing Immunity.

An imbalance in the microbiota may contribute to many human illnesses, which has prompted efforts to rebalance it by targeting the microbes themselves. However, by supplying the habitat, the host wields a prominent influence over microbial growth at body surfaces, raising the possibility that rebalancing the microbiota by targeting our immune system would be a viable alternative. Host control mechanisms that sculpt the microbial habitat form a functional unit with the microbiota, termed microbiota-nourishing immunity, that confers colonization resistance against pathogens. The host components of microbiota-nourishing immunity can be viewed as habitat filters that select for microbial traits licensing growth and survival in host habitat patches. Here we review current knowledge of how host-derived habitat filters shape the size, species composition, and spatial heterogeneity of the microbiota and discuss whether these host control mechanisms could be harnessed for developing approaches to rebalance microbial communities during dysbiosis.

Escherichia coli limits Salmonella Typhimurium infections after diet shifts and fat-mediated microbiota perturbation in mice

SummaryThe microbiota confers colonization resistance, which blocks Salmonella gut colonization 1. As diet affects microbiota composition, we studied whether food-composition shifts enhance susceptibility to infection. Shifting mice to diets with reduced fiber or elevated fat contents for 24h boosted S. Typhimurium or E. coli gut colonization and plasmid transfer. Here, we studied the effect of dietary fat. Colonization resistance was restored within 48h of return to maintenance diet. Salmonella gut colonization was also boosted by two oral doses of oleic acid, or bile salts. These pathogen blooms required Salmonella's AcrAB/TolC-dependent bile-resistance. Our data indicate that fat-elicited bile is promoting Salmonella gut colonization. Both, E. coli and Salmonella show much higher bile resistance than the microbiota. Correspondingly, competitive E. coli can be protective in the fat-challenged gut. Diet shifts and fat-elicited bile promote S. Typhimurium gut infections in mice lacking E. coli in their microbiota. This mouse model may be useful for studying pathogen-microbiota-host interactions, the protective effect of E. coli, for analyzing the spread of resistance plasmids and for assessing the impact of food components on the infection process.

The founder hypothesis: A basis for microbiota resistance, diversity in taxa carriage, and colonization resistance against pathogens.

Our skin and mucosal surfaces are colonized by diverse microbial communities, collectively known as the microbiota [1]. The microbiota provides benefits as microbial metabolites contribute to host nutrition and immune education, although the viability of germ-free animals conjectures that these two functions are not essential for life. However, environmental exposure makes germ-free animals prone to lethal infection, illustrating that the microbiota confers a third function that is often vital, namely, the ability to confer colonization resistance against pathogens [2]. Colonization resistance is an acquired trait, because the microbiota is assembled after birth by attaining maternal and environmental microbes [3]. To coexist, each species within the microbial community needs to be able to utilize a critical resource better than any other member of the microbiota, and the abundance of this growth-limiting resource determines the abundance of the species, a concept known as the nutrient-niche hypothesis [4]. The conceptual framework of the nutrient-niche hypothesis suggests that the neonate microbiota will mature until all discrete nutrient-niches have been filled with a suitable occupant, thereby reaching an equilibrium state [5]. Assuming the same anatomical location in different individuals exposes similar nutrient-niches, the nutrient-niche hypothesis further predicts that the metabolic pathways that enable each member within the microbial community to utilize its growth-limiting nutrient must be conserved between different individuals. Consistent with this prediction, metabolic pathways encoded by the microbiota are very similar between individuals [1]. However, carriage of microbial taxa varies greatly within a healthy population [1], an observation that is not explained by the nutrient-niche hypothesis and remains poorly understood. Priority effects generate variation in taxa carriage Host genetic variation explains only a small fraction of taxonomic microbiota variation between individuals, whereas environmental influences dominate this trait [6]. An important environmental influence in the gastrointestinal tract is the diet, which determines the availability of a subset of growth-limiting nutrients, thereby adding or subtracting nutrient-niches [7, 8]. For example, microbiota-accessible carbohydrates found in dietary fiber determine the abundance of fiber-consuming saccharolytic bacteria in the gut microbiota, and prolonged dietary fiber starvation can lead to an irreversible extinction of species specialized in devouring this critical resource by eliminating their nutrient-niche [8]. Although diet can generate statistically significant changes in the taxonomic composition of the gut microbiota, these changes are small compared to the variation observed between individuals. Furthermore, diet does not provide a plausible explanation for the taxonomic diversity observed in microbial communities outside the gastrointestinal tract [1]. Instead, a critical factor generating taxonomic microbiota diversity between individuals is the order of species arrival and timing by which host surfaces are colonized early in life [9]. The colonization order influences both the outcome of microbial community assembly and the ecological success of individual microbes [3, 9]. These priority effects are preserved in mice lacking adaptive immunity, suggesting that acquired host responses are not a major source of taxonomic diversity in the microbiota composition [9]. Priority effects are mediated through niche preemption or niche modification and can involve the genetic adaptation of microbes to a niche [9, 12], but the underlying mechanisms are incompletely understood. Mechanistic insights into this “first come, first serve” phenomenon suggest that the microbe that initially occupies a nutrient-niche in a neonate gains priority access to the growth-limiting nutrient that defines its nutrient-niche [10]. A growth-limiting resource that determines the abundance of facultative anaerobic Enterobacteriaceae (phylum Proteobacteria) within the microbiota of the large intestine is the availability of respiratory electron acceptors, such as oxygen [11]. Escherichia coli (family Enterobacteriaceae) has access to oxygen in the ceca of neonate chicks when it is inoculated one day prior to challenge with Salmonella enterica (family Enterobacteriaceae) but not when neonate chicks receive both species at the same time [10], suggesting that order and timing of gut colonization determine whether growth-limiting resources are accessible to a microbe. Henceforth we will refer to the concept that the founding occupant gains priority access to the growth-limiting resource that defines its nutrient-niche as the “founder hypothesis.” The founder hypothesis suggests that stochastic effects that govern the initial exposure of neonates to microbes that become founding occupants of each nutrient-niche are a prominent source of taxonomic variation in the microbiota composition between individuals (Fig 1) [3]. Open in a separate window Fig 1 The founder hypothesis. The principles of the founder hypothesis are shown schematically for a single nutrient-niche. Stochastic effects governing microbial exposure during infancy determine which microbial species (red or blue rods) establishes residency in the nutrient-niche, thereby generating diversity in taxa carriage between individuals. The founding occupant gains priority access to the growth-limiting resource that defines its nutrient-niche. These priority effects enable the occupant to confer colonization resistance against environmental exposure to microorganisms that are suitable contenders for the same nutrient-niche. The resulting resistance to stress imposed through environmental exposure to microorganisms produces microbiota resistance.

Commensal Enterobacteriaceae Protect against Salmonella Colonization through Oxygen Competition

Neonates are highly susceptible to infection with enteric pathogens, but the underlying mechanisms are not resolved. We show that neonatal chick colonization with Salmonella enterica serovar Enteritidisrequires a virulence-factor-dependent increase inepithelial oxygenation, which drives pathogen expansion by aerobic respiration. Co-infection experiments with an Escherichia coli strain carrying an oxygen-sensitive reporter suggest that S. Enteritidis competes with commensal Enterobacteriaceae for oxygen. A combination of Enterobacteriaceae and spore-forming bacteria, but not colonization with either community alone, confers colonization resistance against S.Enteritidis in neonatal chicks, phenocopying germ-free mice associated with adultchicken microbiota. Combining spore-forming bacteria with a probiotic E.coli isolate protects germ-free mice from pathogen colonization, but theprotection is lost when the ability to respire oxygen under micro-aerophilic conditions is genetically ablated in E.coli. These results suggest that commensal Enterobacteriaceae contribute to colonization resistance by competing with S. Enteritidis for oxygen, a resource critical for pathogen expansion.

Identifying predictive features of Clostridium difficile infection recurrence before, during, and after primary antibiotic treatment

BackgroundColonization by the pathogen Clostridium difficile often occurs in the background of a disrupted microbial community. Identifying specific organisms conferring resistance to invasion by C. difficile is desirable because diagnostic and therapeutic strategies based on the human microbiota have the potential to provide more precision to the management and treatment of Clostridium difficile infection (CDI) and its recurrence.MethodsWe conducted a longitudinal study of adult patients diagnosed with their first CDI. We investigated the dynamics of the gut microbiota during antibiotic treatment, and we used microbial or demographic features at the time of diagnosis, or after treatment, to predict CDI recurrence. To check the validity of the predictions, a meta-analysis using a previously published dataset was performed.ResultsWe observed that patients’ microbiota “before” antibiotic treatment was predictive of disease relapse, but surprisingly, post-antibiotic microbial community is indistinguishable between patients that recur or not. At the individual OTU level, we identified Veillonella dispar as a candidate organism for preventing CDI recurrence; however, we did not detect a corresponding signal in the conducted meta-analysis.ConclusionAlthough in our patient population, a candidate organism was identified for negatively predicting CDI recurrence, results suggest the need for larger cohort studies that include patients with diverse demographic characteristics to generalize species that robustly confer colonization resistance against C. difficile and accurately predict disease relapse.

Genome-guided design of a defined mouse microbiota that confers colonization resistance against Salmonella enterica serovar Typhimurium

Protection against enteric infections, also termed colonization resistance, results from mutualistic interactions of the host and its indigenous microbes. The gut microbiota of humans and mice is highly diverse and it is therefore challenging to assign specific properties to its individual members. Here, we have used a collection of murine bacterial strains and a modular design approach to create a minimal bacterial community that, once established in germ-free mice, provided colonization resistance against the human enteric pathogen Salmonella enterica serovar Typhimurium (S. Tm). Initially, a community of 12 strains, termed Oligo-Mouse-Microbiota (Oligo-MM12), representing members of the major bacterial phyla in the murine gut, was selected. This community was stable over consecutive mouse generations and provided colonization resistance against S. Tm infection, albeit not to the degree of a conventional complex microbiota. Comparative (meta)genome analyses identified functions represented in a conventional microbiome but absent from the Oligo-MM12. By genome-informed design, we created an improved version of the Oligo-MM community harbouring three facultative anaerobic bacteria from the mouse intestinal bacterial collection (miBC) that provided conventional-like colonization resistance. In conclusion, we have established a highly versatile experimental system that showed efficacy in an enteric infection model. Thus, in combination with exhaustive bacterial strain collections and systems-based approaches, genome-guided design can be used to generate insights into microbe-microbe and microbe-host interactions for the investigation of ecological and disease-relevant mechanisms in the intestine.

Purification and genetic characterization of gassericin E, a novel co-culture inducible bacteriocin from Lactobacillus gasseri EV1461 isolated from the vagina of a healthy woman.

BackgroundLactobacillus gasseri is one of the dominant Lactobacillus species in the vaginal ecosystem. Some strains of this species have a high potential for being used as probiotics in order to maintain vaginal homeostasis, since they may confer colonization resistance against pathogens in the vagina by direct inhibition through production of antimicrobial compounds, as bacteriocins. In this work we have studied bacteriocin production of gassericin E (GasE), a novel bacteriocin produced by L. gasseri EV1461, a strain isolated from the vagina of a healthy woman, and whose production was shown to be promoted by the presence of certain specific bacteria in co-culture. Biochemical and genetic characterization of this novel bacteriocin are addressed.ResultsWe found that the inhibitory spectrum of L. gasseri EV1461 was broad, being directed to species both related and non-related to the producing strain. Interestingly, L. gasseri EV1461 inhibited the grown of pathogens usually associated with bacterial vaginosis (BV). The antimicrobial activity was due to the production of a novel bacteriocin, gassericin E (GasE). Production of this bacteriocin in broth medium only was achieved at high cell densities. At low cell densities, bacteriocin production ceased and only was restored after the addition of a supernatant from a previous bacteriocin-producing EV1461 culture (autoinduction), or through co-cultivation with several other Gram-positive strains (inducing bacteria). DNA sequence of the GasE locus revealed the presence of two putative operons which could be involved in biosynthesis and immunity of this bacteriocin (gaeAXI), and in regulation, transport and processing (gaePKRTC). The gaePKR encodes a putative three-component regulatory system, involving an autoinducer peptide (GaeP), a histidine protein kinase (GaeK) and a response regulator (GaeR), while the gaeTC encodes for an ABC transporter (GaeT) and their accessory protein (GaeC), involved in transport and processing of the bacteriocin. The gaeAXI, encodes for the bacteriocin gassericin E (GasE), a putative peptide bacteriocin (GaeX), and their immunity protein (GaeI).ConclusionsThe origin of the strain (vagina of healthy woman) and its ability to produce bacteriocins with inhibitory activity against vaginal pathogens may be an advantage for using L. gasseri EV1461 as a probiotic strain to fight and/or prevent bacterial infections as bacterial vaginosis (BV), since it could be better adapted to live and compete into the vaginal environment.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-016-0663-1) contains supplementary material, which is available to authorized users.

Phytonutrient diet supplementation promotes beneficial Clostridia species and intestinal mucus secretion resulting in protection against enteric infection.

Plant extracts, or phytonutrients, are used in traditional medicine practices as supplements to enhance the immune system and gain resistance to various infectious diseases and are used in animal production as health promoting feed additives. To date, there are no studies that have assessed their mechanism of action and ability to alter mucosal immune responses in the intestine. We characterized the immunomodulatory function of six phytonutrients: anethol, carvacrol, cinnamaldehyde, eugenol, capsicum oleoresin and garlic extract. Mice were treated with each phytonutrient to assess changes to colonic gene expression and mucus production. All six phytonutrients showed variable changes in expression of innate immune genes in the colon. However only eugenol stimulated production of the inner mucus layer, a key mucosal barrier to microbes. The mechanism by which eugenol causes mucus layer thickening likely involves microbial stimulation as analysis of the intestinal microbiota composition showed eugenol treatment led to an increase in abundance of specific families within the Clostridiales order. Further, eugenol treatment confers colonization resistance to the enteric pathogen Citrobacter rodentium. These results suggest that eugenol acts to strengthen the mucosal barrier by increasing the thickness of the inner mucus layer, which protects against invading pathogens and disease.

Dysbiosis caused by vitamin D receptor deficiency confers colonization resistance to Citrobacter rodentium through modulation of innate lymphoid cells.

Vitamin D receptor (VDR) knockout (KO) mice had fewer Citrobacter rodentium in the feces than wild-type (WT) mice and the kinetics of clearance was faster in VDR KO than WT mice. VDR KO mice had more IL-22 producing innate lymphoid cells (ILC), and more anti-bacterial peptides than WT mice. The increased ILC in the VDR KO mice was a cell autonomous effect of VDR deficiency on ILC frequencies. BM transplantation from VDR KO mice into WT resulted in higher ILC and colonization resistance of the WT mice. Disruption of the gut microbiota using antibiotics in VDR KO mice reversed colonization resistance to C. rodentium infection. Confirming the role of the microbiota in the colonization resistance of VDR KO mice, transfer of the VDR KO microbiota to WT GF mice, resulted in colonization resistance. Once colonization resistance is overcome, VDR KO mice had increased susceptibility to C. rodentium. VDR expression is a regulator of ILC frequencies, IL-22, dysbiosis and C. rodentium susceptibility.

Colonization Resistance: Battle of the Bugs or Ménage à Trois with the Host?

The lower gastrointestinal tract is host to a dense microbial community, known as the gut microbiota, which is dominated by obligate anaerobic bacteria belonging to the phyla Bacteroidetes (class Bacteroidia) and Firmicutes (class Clostridia). This microbial community offers benefit by conferring niche protection against invading microbes, a property known as “colonization resistance” (reviewed in [1]). The concept of colonization resistance was initially derived from studies showing that an antibiotic-mediated disruption of gut-associated microbial communities greatly enhances the ability of facultative anaerobic Enterobacteriaceae, such as Escherichia coli or Salmonella enterica, to colonize the large bowel [2]–[4]. Conventional wisdom holds that resident Bacteroidia and Clostridia confer colonization resistance by “competitive exclusion” of Enterobacteriaceae (phylum Proteobacteria) through microbe-microbe interactions. However, recent studies draw a tantalizing new picture, which suggests that host interactions might play a central role in shaping the microbial community structure. Here we review these new hypotheses and their implications for human health.

The Microbiota Mediates Pathogen Clearance from the Gut Lumen after Non-Typhoidal Salmonella Diarrhea

Many enteropathogenic bacteria target the mammalian gut. The mechanisms protecting the host from infection are poorly understood. We have studied the protective functions of secretory antibodies (sIgA) and the microbiota, using a mouse model for S. typhimurium diarrhea. This pathogen is a common cause of diarrhea in humans world-wide. S. typhimurium (S. tm att, sseD) causes a self-limiting gut infection in streptomycin-treated mice. After 40 days, all animals had overcome the disease, developed a sIgA response, and most had cleared the pathogen from the gut lumen. sIgA limited pathogen access to the mucosal surface and protected from gut inflammation in challenge infections. This protection was O-antigen specific, as demonstrated with pathogens lacking the S. typhimurium O-antigen (wbaP, S. enteritidis) and sIgA-deficient mice (TCRβ−/−δ−/−, JH −/−, IgA−/−, pIgR−/−). Surprisingly, sIgA-deficiency did not affect the kinetics of pathogen clearance from the gut lumen. Instead, this was mediated by the microbiota. This was confirmed using ‘L-mice’ which harbor a low complexity gut flora, lack colonization resistance and develop a normal sIgA response, but fail to clear S. tm att from the gut lumen. In these mice, pathogen clearance was achieved by transferring a normal complex microbiota. Thus, besides colonization resistance ( = pathogen blockage by an intact microbiota), the microbiota mediates a second, novel protective function, i.e. pathogen clearance. Here, the normal microbiota re-grows from a state of depletion and disturbed composition and gradually clears even very high pathogen loads from the gut lumen, a site inaccessible to most “classical” immune effector mechanisms. In conclusion, sIgA and microbiota serve complementary protective functions. The microbiota confers colonization resistance and mediates pathogen clearance in primary infections, while sIgA protects from disease if the host re-encounters the same pathogen. This has implications for curing S. typhimurium diarrhea and for preventing transmission.

Immigration and emigration of Burkholderia cepacia and Pseudomonas aeruginosa between and within mixed biofilm communities.

To investigate the dynamics of binary culture biofilm formation through use of both the Sorbarod model of biofilm growth and the constant depth film fermenter (CDFF). Pseudo steady-state biofilm cultures of laboratory and clinical strains of Pseudomonas aeruginosa, selected on the basis of their ability to produce a Burkholderia cepacia growth-inhibitory substance, were established on Sorbarod filters and challenged with corresponding planktonic grown cultures of B. cepacia. Reverse challenges were also conducted. Both B. cepacia and P. aeruginosa were able to form steady-state monoculture biofilms after 48 h growth. When steady-state biofilms of B. cepacia NTCT 10661 were challenged with planktonically grown P. aeruginosa PAO1 known to produce a B. cepacia growth-inhibitory substance, the immigrant population was rapidly and almost completely bound to the biofilm, displacing B. cepacia. By contrast, established biofilms of P. aeruginosa PAO1 resisted immigration of B. cepacia 10661. Similar experiments conducted with a nongrowth inhibitory substance producing clinical pairing of P. aeruginosa 313113 and B. cepacia 313113 led to the formation of stable, mixed biofilm populations in both instances. Moreover, co-inoculation with these clinical isolates resulted in a stable, mixed steady-state biofilm. Similar observations were made for biofilms generated in CDFFs. In such instances following pan-swapping between two monoculture CDFFs, B. cepacia 313113 was able to integrate into an established P. aeruginosa 313113 biofilm to form a stable binary biofilm. Establishment of a mixed species community follows a specific sequence of inoculation that may either be due to some degree of match between co-colonizers or that P. aeruginosa predisposes uncolonized sections of the surface to permit B. cepacia colonization. Colonization of a surface with one bacterial species confers colonization resistance towards other species. Disinfection of a surface might well increase the probability of pathogen harbourage.

Biofilms: Their impact on health and their recalcitrance toward biocides

Am J Infect Control 2001;29:252-5