Streptococcal bacteriocins and the case for Streptococcus salivarius as model oral probiotics

Novel Probiotic Mechanisms of the Oral Bacterium Streptococcus sp. A12 as Explored with Functional Genomics

Health-associated biofilms in the oral cavity are composed of a diverse group of microbial species that can foster an environment that is less favorable for the outgrowth of dental caries pathogens, like Streptococcus mutans A novel oral bacterium, designated Streptococcus A12, was previously isolated from supragingival dental plaque of a caries-free individual and was shown to interfere potently with the growth and virulence properties of S. mutans In this study, we applied functional genomics to begin to identify molecular mechanisms used by A12 to antagonize, and to resist the antagonistic factors of, S. mutans Using bioinformatics, genes that could encode factors that enhance the ability of A12 to compete with S. mutans were identified. Selected genes, designated potential competitive factors (pcf), were deleted. Certain mutant derivatives showed a reduced capacity to compete with S. mutans compared to that of the parental strain. The A12 pcfO mutant lost the ability to inhibit comX -inducing peptide (XIP) signaling by S. mutans, while mutants with changes in the pcfFEG locus were impaired in sensing of, and were more sensitive to, the lantibiotic nisin. Loss of PcfV, annotated as a colicin V biosynthetic protein, resulted in diminished antagonism of S. mutans Collectively, the data provide new insights into the complexities and variety of factors that affect biofilm ecology and virulence. Continued exploration of the genomic and physiological factors that distinguish commensals from truly beneficial members of the oral microbiota will lead to a better understanding of the microbiome and new approaches to promote oral health.IMPORTANCE Advances in defining the composition of health-associated biofilms have highlighted the important role of beneficial species in maintaining health. Comparatively little, however, has been done to address the genomic and physiological bases underlying the probiotic mechanisms of beneficial commensals. In this study, we explored the ability of a novel oral bacterial isolate, Streptococcus A12, to compete with the dental pathogen Streptococcus mutans using various gene products with diverse functions. A12 displayed enhanced competitiveness by (i) disrupting intercellular communication pathways of S. mutans, (ii) sensing and resisting antimicrobial peptides, and (iii) producing factors involved in the production of a putative antimicrobial compound. Research on the probiotic mechanisms employed by Streptococcus A12 is providing essential insights into how beneficial bacteria may help maintain oral health, which will aid in the development of biomarkers and therapeutics that can improve the practice of clinical dentistry.

Effects of Streptococcus salivarius K12 with nystatin on oral candidiasis-RCT

OBJECTIVE

To evaluate the efficacy and safety of Streptococcus salivarius K12 as an adjuvant in treating oral candidiasis.

METHODS

A total of 56 patients were participated in the randomized, double-blinded, placebo-controlled clinical trial. The S. salivarius K12 or placebo lozenges plus nystatin tablets were given for up to 4 weeks at 1-week interval and then followed up for 1 week thereafter. We collected and analyzed the mycological and clinical data, treatment course, and safety data.

RESULTS

At the end of the treatment, significant differences were found in the mycological cure rates between K12 group and control group (90.48% and 55.56%, respectively, p = 0.008). Survival analysis demonstrated no statistical difference in overall cure rates comprehensively considering mycological cure, clinical improvement, and recurrence (p = 0.078), while statistical difference was found in mycological cure (p = 0.013) between the two groups. The median treatment courses of K12 group and control group were 3 weeks and 4 weeks, respectively. No severe events were reported during the study.

CONCLUSION

Streptococcus salivarius K12 exhibited potential efficacy and safety as an adjuvant in treating oral candidiasis by enhancing mycological cure and shortening the treatment course of conventional antifungal therapy in this randomized, double-blinded, placebo-controlled clinical trial. Further large-scale clinical studies are desired to accumulate more evidence for its clinical applications.

Commensal Bacteria: An Emerging Player in Defense Against Respiratory Pathogens

A diverse community of trillions of commensal bacteria inhabits mucosal and epidermal surfaces in humans and plays an important role in defense against pathogens, including respiratory pathogens. Commensal bacteria act on the host's immune system to induce protective responses that prevent colonization and invasion by pathogens. On the other hand, these bacteria can directly inhibit the growth of respiratory pathogens by producing antimicrobial products/signals and competing for nutrients and adhesion sites. Such mechanisms preserve the niche for commensal bacteria and support the host in containing respiratory infections. Herein, we discuss current evidence on the role of commensal bacteria in conferring protection against respiratory pathogens and the underlying mechanisms by which these bacteria do so. A deeper knowledge of how commensal bacteria interact with the host and pathogens might provide new insights that are poised to aid in the development of vaccines and therapeutics that target infectious diseases.

Oral probiotics reduce halitosis in patients wearing orthodontic braces: a randomized, triple-blind, placebo-controlled trial

Orthodontic braces can impede oral hygiene and promote halitosis. The aim of the study was to investigate the effect of the oral probiotic Streptococcus salivarius M18 on oral hygiene indices and halitosis in patients wearing orthodontic braces. The study was a prospective, randomized, triple-blind, placebo-controlled trial. Patients undergoing fixed orthodontic treatment were randomly allocated to a probiotic group (n = 32) and a placebo group (n = 32). Patients consumed 2 lozenges d^-1 for one month. Assessments were taken at baseline, at the end of the intervention, and at a 3 month follow-up. The outcome measures were plaque index (PI), gingival index (GI) and halitosis-causing volatile sulfur compound (VSC) levels. The dental biofilms before and after the intervention were analyzed utilizing next-generation sequencing of bacterial 16S rRNA genes. PI and GI scores were not significantly influenced by the probiotic intervention (intervention × time: p > 0.05). The level of VSCs decreased significantly in both the probiotic group (VSC reduction = -8.5%, 95%CI = -7.4% to -9.1%, p = 0.015) and the placebo group (-6.5%, 95%CI = -6.0% to -7.4%, p = 0.039) after 1 month intervention. However, at the 3 month follow-up, the VSC levels in the placebo group returned to baseline levels whereas those in the probiotic group decreased further (-10.8%, 95%CI = -10.5% to -12.9%, p = 0.005). Time, but not treatment, was associated with the decrease in microbial community alpha diversity and a modest effect on beta diversity. Oral probiotic S. salivarius M18 reduced the level of halitosis in patients with orthodontic braces, but had minimal effects on PI, GI and dental biofilm microflora.

Atlas of group A streptococcal vaccine candidates compiled using large-scale comparative genomics

Group A Streptococcus (GAS; Streptococcus pyogenes) is a bacterial pathogen for which a commercial vaccine for humans is not available. Employing the advantages of high-throughput DNA sequencing technology to vaccine design, we have analyzed 2,083 globally sampled GAS genomes. The global GAS population structure reveals extensive genomic heterogeneity driven by homologous recombination and overlaid with high levels of accessory gene plasticity. We identified the existence of more than 290 clinically associated genomic phylogroups across 22 countries, highlighting challenges in designing vaccines of global utility. To determine vaccine candidate coverage, we investigated all of the previously described GAS candidate antigens for gene carriage and gene sequence heterogeneity. Only 15 of 28 vaccine antigen candidates were found to have both low naturally occurring sequence variation and high (>99%) coverage across this diverse GAS population. This technological platform for vaccine coverage determination is equally applicable to prospective GAS vaccine antigens identified in future studies.

Mobilization of Microbiota Commensals and Their Bacteriocins for Therapeutics

With the specter of resurgence of pathogens due to the propagation of antibiotic-resistance genes, innovative antimicrobial strategies are needed. In this review, we summarize the beneficial aspects of bacteriocins, a set of miscellaneous peptide-based bacterium killers, compared with classical antibiotics, and emphasize their use in cocktails to curb the emergence of new resistance. We highlight that their prey spectrum, their molecular malleability, and their multiple modes of production might lead to specific and personalized treatments to prevent systemic disorders. Complementarily, we discuss how we might exploit prevailing bacterial commensals, such as Streptococcus salivarius, and deliberately mobilize their bacteriocin arsenal 'on site' to cure multiresistant infections or finely reshape the endogenous microbiota for prophylaxis purposes.

Bacteriotherapy with Streptococcus salivarius 24SMB and Streptococcus oralis 89a oral spray for children with recurrent streptococcal pharyngotonsillitis: a randomized placebo-controlled clinical study

PURPOSE

Group A beta-hemolytic Streptococcus (GABHS) causes a recurrent acute pharyngotonsillitis (RAPT) in children. Moreover, the repeated use of antibiotics contributes to its resistance. However, S. Salivarius 24SMB and S. oralis 89a were effective probiotics in other infections. Thus, we decided to evaluate this combination efficacy compared to placebo in RAPT.

METHODS

Patients with microbiologically confirmed GABHS were enrolled in this randomized, placebo-controlled trial. They received the aforementioned combination or placebo as an oral spray. We investigated episodes of frequency and duration, need for antibiotics, school days lost, the treatment impact on life quality, treatment compliance and side effects during a 90-day treatment and a 6-month follow-up.

RESULTS

We included 41 patients in each group. The mean number of GABHS infection was significantly lower during both study periods for the two groups. However, our treatment group showed a lower rate. Moreover, the probiotic group had a lower mean number and a shorter median duration of GABHS episodes during both study periods than controls. Furthermore, the mean duration of antibiotic treatment was lower in the probiotic group during the 90-day and 6-month follow-up periods. Similarly, patients in the probiotic group showed a significantly lower mean number of absence days from school but higher EQ-VAS score. Indeed, all patients included were compliant to treatment.

CONCLUSIONS

We identified potential probiotics, possessing desirable features against GABHS pharyngotonsillitis. Our findings represent the first evidence which throws the light on using these probiotics that can reduce antibiotics use which did not have efficient results regarding recurrence.

Probiotics study with Streptococcus salivarius and its ability to produce bacteriocins and adherence to KB cells

Abstract Introduction Streptococcus salivarius is a dominant oral species and the best suitable candidate for probiotic of the oral cavity. Since Streptococcus salivarius is able to produce bacteriocins against Streptococcus pyogenes interest has been focused on the use of it as a probiotic to avoid sore throats by Streptococcus pyogenes. Objective This study is for selecting Streptococcus salivarius strains for potential use as probiotics for the oral mucosa, that is, production of bacteriocin against Streptococcus pyogenes and the ability to bind to KB cells. Material and method Tongue material from 45 students was collected and seeded on Mitis Salivarius Agar plaques. The strains were tested by the production of bacteriocin-like substances (BLIS) against S. pyogenes, biochemically and PCR for identification of S. salivarius. The best strains were tested for adherence to KB cells. Briefly, S. salivarius strains were cultured in broth, washed and suspended at 108cells/ml. KB cells were inoculated into plaques, washed and incubated with the bacteria, for adhesion. These were washed for lysis of the KB cells and release bacteria for determination of CFU. Result The bacteriocin test showed that 133 strains presented inhibition of S. pyogenes. The samples tested for adhesion to KB cells, presented different profiles and only three strains presenting high adhesion capacity. Conclusion The selection of strains of Streptococcus salivarius with high inhibitory activity against Streptococcus pyogenes, as well as adherence to KB cells leads us to the next future step, that is, to use the best strains for in vivo colonization tests

Draft Genome Sequence of the Lantibiotic-Producing Strain Streptococcus salivarius HS0302

Streptococcus salivarius is a prevalent commensal species of human oral mucosal surfaces. S. salivarius strain HS0302 produces the type AII lantibiotic salivaricin A2. Here, we report its draft genome sequence, revealing its potential to produce a variety of bacteriocins.

Probiotics Streptococcus salivarius 24SMB and Streptococcus oralis 89a interfere with biofilm formation of pathogens of the upper respiratory tract

Background

Infections of the ears, paranasal sinuses, nose and throat are very common and represent a serious issue for the healthcare system. Bacterial biofilms have been linked to upper respiratory tract infections and antibiotic resistance, raising serious concerns regarding the therapeutic management of such infections. In this context, novel strategies able to fight biofilms may be therapeutically beneficial and offer a valid alternative to conventional antimicrobials. Biofilms consist of mixed microbial communities, which interact with other species in the surroundings and communicate through signaling molecules. These interactions may result in antagonistic effects, which can be exploited in the fight against infections in a sort of “bacteria therapy”. Streptococcus salivarius and Streptococcus oralis are α-hemolytic streptococci isolated from the human pharynx of healthy individuals. Several studies on otitis-prone children demonstrated that their intranasal administration is safe and well tolerated and is able to reduce the risk of acute otitis media. The aim of this research is to assess S. salivarius 24SMB and S. oralis 89a for the ability to interfere with biofilm of typical upper respiratory tract pathogens.

Methods

To investigate if soluble substances secreted by the two streptococci could inhibit biofilm development of the selected pathogenic strains, co-cultures were performed with the use of transwell inserts. Mixed-species biofilms were also produced, in order to evaluate if the inhibition of biofilm formation might require direct contact. Biofilm production was investigated by means of a spectrophotometric assay and by confocal laser scanning microscopy.

Results

We observed that S. salivarius 24SMB and S. oralis 89a are able to inhibit the biofilm formation capacity of selected pathogens and even to disperse their pre-formed biofilms. Diffusible molecules secreted by the two streptococci and lowered pH of the medium revealed to be implied in the mechanisms of anti-biofilm activity.

Conclusions

S. salivarius 24SMB and S. oralis 89a possess desirable characteristics as probiotic for the treatment and prevention of infections of the upper airways. However, the nature of the inhibition appear to be multifactorial and additional studies are required to get further insights.

Electronic supplementary material

The online version of this article (10.1186/s12879-018-3576-9) contains supplementary material, which is available to authorized users.

Nanocarriers with conjugated antimicrobials to eradicate pathogenic biofilms evaluated in murine in vivo and human ex vivo infection models

Conventional antimicrobials are becoming increasingly ineffective for treating bacterial infection due to the emergence of multi-drug resistant (MDR) pathogens. In addition, the biofilm-mode-of-growth of infecting bacteria impedes antimicrobial penetration in biofilms. Here, we report on poly(ethylene)glycol-poly(β-amino esters) (PEG-PAE) micelles with conjugated antimicrobials, that can uniquely penetrate biofilms, target themselves to bacterial cell surfaces once inside the low-pH environment of a biofilm and release conjugated antimicrobials through degradation of their ester-linkage with PAE by bacterial lipases. In vitro, PEG-PAE micelles with conjugated Triclosan (PEG-PAE-Triclosan) yielded no inadvertent leakage of their antimicrobial cargo and better killing of MDR Staphylococcus aureus, Escherichia coli and oral streptococcal biofilms than Triclosan in solution. In mice, PEG-PAE-Triclosan micelles with conjugated Triclosan yielded better eradication efficacy towards a MDR S. aureus-infection compared with Triclosan in solution and Triclosan-loaded micelles at equal Triclosan-equivalent concentrations. Ex vivo exposure of multi-species oral biofilms collected from orthodontic patients to PEG-PAE-Triclosan micelles, demonstrated effective bacterial killing at 30-40 fold lower Triclosan-equivalent concentrations than achieved by Triclosan in solution. Importantly, Streptococcus mutans, the main causative organism of dental caries, was preferentially killed by PEG-PAE-Triclosan micelles. Thus PEG-PAE-Triclosan micelles present a promising addendum to the decreasing armamentarium available to combat infection in diverse sites of the body. STATEMENT OF SIGNIFICANCE: pH-adaptive polymeric micelles with conjugated antimicrobials can efficiently eradicate infectious biofilms from diverse body sites in mice and men. An antimicrobial was conjugated through an ester-linkage to a poly(ethylene glycol) (PEG)/poly(β-amino ester) block copolymer to create micellar nanocarriers. Stable micelle structures were formed by the hydrophobic poly(β-amino ester) inner core and a hydrophilic PEG outer shell. Thus formed PEG-PAE-Triclosan micelles do not lose their antimicrobial cargo underway to an infection site through the blood circulation, but penetrate and accumulate in biofilms to release antimicrobials once inside a biofilm through degradation of its ester-linkage by bacterial lipases, to kill biofilm-embedded bacteria at lower antimicrobial concentrations than when applied in solution. PEG-PAE-Triclosan micelles effectively eradicate biofilms of multi-drug-resistant pathogens and oral bacteria, most notably highly cariogenic Streptococcus mutans, in mice and men respectively, and possess excellent clinical translation possibilities.

The short-term impact of probiotic consumption on the oral cavity microbiome

The dysbiosis of the oral microbiome is associated with both localized and systemic diseases. Modulating the resident microbial communities by the dietary consumption of probiotics has become an appealing means to promote host health by either restoring host-microbe balance or preventing dysbiosis. Most probiotics strategies target the intestinal microbiome, but little is known about their impact on the oral microbiome. We analyzed here the saliva microbiome from 21 volunteers, longitudinally collected before, during, and after consumption of a commercial probiotic and a standard yoghurt using 16S amplicon sequencing. The alpha diversity of the saliva microbiome had a statistically significant increase (P-value = 0.0011) in one of the groups that consumed the probiotic. The overall structure of the microbiome was however not significantly impacted by the probiotic, although oligotyping analysis revealed that both Streptococci and Lactobacilli present in the probiotic product persisted in the saliva microbiome. In contrast, non-probiotic yoghurt consumption had a lesser impact on the overall diversity and Lactobacillus and Streptococcus persistence. Our results suggest that consumption of commercial probiotics in healthy subjects increase the overall diversity of the oral cavity microbiome in the short term, but such dietary interventions are not able to substantially modify the structure of the microbiome.

Effect of Oral Probiotic Streptococcus salivarius K12 on Group A Streptococcus Pharyngitis: A Pragmatic Trial in Schools

BACKGROUND

The aim of this study was to examine effectiveness of oral probiotic Streptococcus salivarius K12 in preventing group A streptococcus pharyngitis in 5- to 14-year-old children at high risk of acute rheumatic fever. New Zealand has high rates of acute rheumatic fever among Māori and Pacific children. Children were already enrolled in a school-based Ministry of Health throat swabbing and treatment program. Children self-identified and reported sore throats daily and were swabbed twice weekly.

METHODS

A total of 1314 children were quasirandomized (based on odd or even birthdates) to receive either K12 (2.5 × 10(9) cfu per lozenge) or placebo lozenges and continued observed daily treatment (in the school week, during school time) for one school year.

RESULTS

A total of 801 children (61.0%) reported a sore throat on one or more occasions resulting in 2927 pharyngeal swabs. Of these swabs, 1525 (52.1%) were taken from 411 children receiving K12 and 119 (7.8%) of these were positive for group A streptococcus on routine culture. In addition, 1402 (47.8%) swabs were taken from 390 children receiving placebo and 124 (8.8%) were positive. Overall there was a nonsignificant 11.2% relative reduction in positive swabs among children receiving K12. This relative reduction was greater for older children, 7-9 years of age, 15.6%, and for children 10 years and older, 30.2%.

CONCLUSIONS

S. salivarius K12 had modest nonsignificant effects on culture-positive sore throats when given at school, during the school day. Based on our pragmatic trial, the routine use of this probiotic in the prevention of pharyngitis associated with GAS detection is not supported.

The Role of Skin and Orogenital Microbiota in Protective Immunity and Chronic Immune-Mediated Inflammatory Disease

The skin and orogenital mucosae, which constitute complex protective barriers against infection and injuries, are not only the first to come into contact with pathogens but are also colonized by a set of microorganisms that are essential to maintain a healthy physiological environment. Using 16S ribosomal RNA metagenomic sequencing, scientists recognized that the microorganism colonization has greater diversity and variability than previously assumed. These microorganisms, such as commensal bacteria, affect the host’s immune response against pathogens and modulate chronic inflammatory responses. Previously, a single pathogen was thought to cause a single disease, but current evidence suggests that dysbiosis of the tissue microbiota may underlie the disease status. Dysbiosis results in aberrant immune responses at the surface and furthermore, affects the systemic immune response. Hence, understanding the initial interaction between the barrier surface immune system and local microorganisms is important for understanding the overall systemic effects of the immune response. In this review, we describe current evidence for the basis of the interactions between pathogens, microbiota, and immune cells on surface barriers and offer explanations for how these interactions may lead to chronic inflammatory disorders.

Exploring the microbiome in health and disease

The analysis of human microbiome is an exciting and rapidly expanding field of research. In the past decade, the biological relevance of the microbiome for human health has become evident. Microbiome comprises a complex collection of microorganisms, with their genes and metabolites, colonizing different body niches. It is now well known that the microbiome interacts with its host, assisting in the bioconversion of nutrients and detoxification, supporting immunity, protecting against pathogenic microbes, and maintaining health. Remarkable new findings showed that our microbiome not only primarily affects the health and function of the gastrointestinal tract but also has a strong influence on general body health through its close interaction with the nervous system and the lung. Therefore, a perfect and sensitive balanced interaction of microbes with the host is required for a healthy body. In fact, growing evidence suggests that the dynamics and function of the indigenous microbiota can be influenced by many factors, including genetics, diet, age, and toxicological agents like cigarette smoke, environmental contaminants, and drugs. The disruption of this balance, that is called dysbiosis, is associated with a plethora of diseases, including metabolic diseases, inflammatory bowel disease, chronic obstructive pulmonary disease, periodontitis, skin diseases, and neurological disorders. The importance of the host microbiome for the human health has also led to the emergence of novel therapeutic approaches focused on the intentional manipulation of the microbiota, either by restoring missing functions or eliminating harmful roles. In the present review, we outline recent studies devoted to elucidate not only the role of microbiome in health conditions and the possible link with various types of diseases but also the influence of various toxicological factors on the microbial composition and function.

The effect of immune modulation of Streptococcus constellatus SC10 strain upon Acinetobactor baumannii infection

Acinetobacter baumannii is a tiny, plump and rod-shaped Gram-negative coccobacillus, notorious as an opportunistic pathogen, which is now being considered by CDC as a serious public health threat. Preventing colonization may be a better therapeutic choice using microbiota to protect against A. baumannii transmission. Human microbiota not only regulates immune homeostasis as well provides essential health benefits therefore discovering the interface due microbiota in host immune system will allow to recognise novel immuno- or microbe-based therapies. Streptococcus constellatus frequently isolated from oral cavity was selected for this study to check if its guards against A. baumannii by improving the immune response and the immune signalling pathway. In a mouse model we explored various parameters which include mouse body weight, internal organ weight, level of sIgA and different cytokine changes to evaluate its prophylactic effect against A. baumannii. Administration of S. constellatus SC10 was able to control the weight lose induced by A. bumannii infection in both the protected and treated groups. Particularly resistant against infection was more in treated group where the different cytokine following administration of SC10 strain remarkably controlled the infection and induced more sIgA production. The level of different interleukins IL-4, IL-10, IL-12 and IFN-γ was suppressed in treatment and protected group after exposure of S. constellatus. The excretion of sIgA following infection was many folds high in both group treated and protected groups Study suggests that SC10 L16 have potential immunomodulating effect which is able to regulate cytokines and sIgA response at the early phase of infection and modulate the further progress of clinical symptoms during infection.

Complete Genome Sequence of the Gamma-Aminobutyric Acid-Producing Strain Streptococcus thermophilus APC151

Here is presented the whole-genome sequence of Streptococcus thermophilus APC151, isolated from a marine fish. This bacterium produces gamma-aminobutyric acid (GABA) in high yields and is biotechnologically suitable to produce naturally GABA-enriched biofunctional yogurt. Its complete genome comprises 2,097 genes and 1,839,134 nucleotides, with an average G+C content of 39.1%.

A probiotic combination attenuates experimental colitis through inhibition of innate cytokine production

Inflammatory bowel disease (IBD) is a severe immune cell-mediated syndrome characterised by extensive inflammatory and effector mucosal responses leading to tissue destruction in the colon and small intestine. The leading hypothesis is that dysbiosis of the gut flora causes an excessive immune response and inflammation in the gastrointestinal track. Lactic acid bacteria (LAB) can correct dysbiosis of the normal microbiota. In the current study, the therapeutic potential of seven LAB strains in combination to treat IBD was evaluated using experimental colitis model. This LAB cocktail, designated GI7, includes four strains of Lactobacillus acidophilus, Lactobacillus plantarum, Lactobacillus rhamnosus, Lactococcus lactis, two strains of Bifidobacterium bifidum, Bifidobacterium breve, and one strain of Streptococcus thermophilus. We confirmed that GI7 suppressed pro-inflammatory cytokines in Raw264.7 macrophages. When dextran sulphate sodium-induced colitic mice were treated with GI7, their symptoms of colitis, as assessed by body weight, colon length, myeloperoxidase activity, intestinal bleeding, and histological damage, were reduced compared to untreated mice. In addition, GI7 treatment significantly inhibited the production of innate pro-inflammatory cytokines during colitic progression. Therefore, we suggest that GI7, a combination of seven LAB, has a potential role in the treatment of IBD.

Microbiome of the paranasal sinuses: Update and literature review

BACKGROUND

Our understanding of the resident microbiome of the paranasal sinuses has changed considerably in recent years. Once presumed to be sterile, healthy sinus cavities are now known to harbor a diverse assemblage of microorganisms, and, it is hypothesized that alterations in the kinds and quantities of these microbes may play a role in the pathogenesis of chronic rhinosinusitis (CRS).

OBJECTIVES

To review the current literature regarding the sinus microbiome and collate research findings from relevant studies published to date.

METHODS

A systematic literature review was performed on all molecular studies that investigated the microbial communities of the paranasal sinuses. Methods of detection, microbiome composition, and comparative profiling between patients with and without CRS were explored.

RESULTS

A complex consortium of microorganisms has been demonstrated in the sinuses of both patients with and without CRS. However, the latter generally have been characterized by reduced biodiversity compared with controls, with selective enrichment of particular microbes (e.g., Staphylococcus aureus). Such disruptions in the resident microbiome may contribute to disease pathogenesis by enhancing the virulence of potential pathogens and adversely modulating immune responses.

CONCLUSION

The advent of culture-independent molecular approaches has led to a greater appreciation of the intricate microbial ecology of the paranasal sinuses. Microbiota composition, distribution, and abundance impact mucosal health and influence pathogen growth and function. A deeper understanding of the host-microbiome relationship and its constituents may encourage development of new treatment paradigms for CRS, which target restoration of microbiome homeostasis and cultivation of optimal microbial communities.

A Rare Case of Peritonitis: Streptococcus Salivarius

Streptococcus salivarius is a Gram-positive bacteria that may cause infections like endocarditis and meningitis. However, it has not been reported as a causative agent of peritonitis in peritoneal dialysis patients. In this paper we present a rare case of peritonitis with Streptococcus salivarius admitted to our Clinic with abdominal pain, who had been on peritoneal dialysis treatment for 19 months. Streptococus salivarius was cultured from the effluent, sensitive to ampicillin and penicillin G. Patient was discharged completely cured. Peritonitis is the most important clinical issue that occurs in patients treated with peritoneal dialysis, and every effort should be invested to determine the causative agent while even rare bacteria as Streptococcus salivarius may be found.

A microfluidic platform with pH imaging for chemical and hydrodynamic stimulation of intact oral biofilms

A microfluidic platform with a fluorescent nanoparticle-based sensor is demonstrated for real-time, ratiometric pH imaging of biofilms. Sensing is accomplished by a thin patterned layer of covalently bonded Ag@SiO2+FiTC nanoparticles on an embedded planar glass substrate. The system is designed to be sensitive, responsive and give sufficient spatial resolution to enable new micro-scale studies of the dynamic response of oral biofilms to well-controlled chemical and hydrodynamic stimulation. Performance under challenging operational conditions is demonstrated, which include long-duration exposure to sheer stresses, photoexcitation and pH sensor biofouling. After comprehensive validation, the device was used to monitor pH changes at the attachment surface of a biofilm of the oral bacteria, Streptococcus salivarius. By controlling flow and chemical concentration conditions in the microchannel, biochemical and mass transport contributions to the Stephan curve could be probed individually. This opens the way for the analysis of separate contributions to dental caries due to localized acidification directly at the biofilm tooth interface.

Complete Genome Sequence of Streptococcus salivarius HSISS4, a Human Commensal Bacterium Highly Prevalent in the Digestive Tract

The human commensal bacterium Streptococcus salivarius plays a major role in the equilibrium of microbial communities of the digestive tract. Here, we report the first complete genome sequence of a Streptococcus salivarius strain isolated from the small intestine, namely, HSISS4. Its circular chromosome comprises 1,903 coding sequences and 2,100,988 nucleotides.

What are We Learning and What Can We Learn from the Human Oral Microbiome Project?

Extraordinary technological advances have greatly accelerated our ability to identify bacteria, at the species level, present in clinical samples taken from the human mouth. In addition, technologies are evolving such that the oral samples can be analyzed for their protein and metabolic products. As a result, pictures are the advent of personalized dental medicine is becoming closer to reality.

Extended Safety Data for the Oral Cavity Probiotic Streptococcus salivarius K12

Previous studies of the bacteriocin-producing Streptococcus salivarius K12 monitored a variety of intrinsic strain characteristics of potential relevance to its application as an oral probiotic in humans. These included the content of antibiotic resistance and virulence determinants, the production of deleterious metabolic by-products and its genetic stability. In the present study, we examined additional safety factors including the responses of rats to either short- or long-term oral dosing with strain K12 preparations. In addition, the potential genotoxicity of strain K12 was tested using a bacterial reverse mutation assay. To determine the occurrence and concentrations in human saliva of S. salivarius having the same bacteriocin phenotype as strain K12, saliva samples from 780 children were evaluated. The level of dosing with strain K12 required to achieve oral cavity colonization levels similar to those occurring naturally for this type of bacteriocin-producing S. salivarius was established using 100 human subjects. Following the oral instillation of lyophilized S. salivarius K12 cells in these subjects, its persistence was not at levels higher than those found naturally for this type of bacterium. The various sets of data obtained in this study showed no evidence of genotoxicity and no acute or subacute toxicity effects associated with strain K12. Based on the previously published data, the long history of use by humans and the information presented here, it is concluded that S. salivarius K12 is safe for human consumption.

Bioengineering Lantibiotics for Therapeutic Success

Several examples of highly modified antimicrobial peptides have been described. While many such peptides are non-ribosomally synthesized, ribosomally synthesized equivalents are being discovered with increased frequency. Of the latter group, the lantibiotics continue to attract most attention. In the present review, we discuss the implementation of in vivo and in vitro engineering systems to alter, and even enhance, the antimicrobial activity, antibacterial spectrum and physico-chemical properties, including heat stability, solubility, diffusion and protease resistance, of these compounds. Additionally, we discuss the potential applications of these lantibiotics for use as therapeutics.

Molecular epidemiology and genomics of group A Streptococcus

Streptococcus pyogenes (group A Streptococcus; GAS) is a strict human pathogen with a very high prevalence worldwide. This review highlights the genetic organization of the species and the important ecological considerations that impact its evolution. Recent advances are presented on the topics of molecular epidemiology, population biology, molecular basis for genetic change, genome structure and genetic flux, phylogenomics and closely related streptococcal species, and the long- and short-term evolution of GAS. The application of whole genome sequence data to addressing key biological questions is discussed.

Anti-inflammatory effects of Lactococcus lactis NCDO 2118 during the remission period of chemically induced colitis

Background

Many probiotic bacteria have been described as promising tools for the treatment and prevention of inflammatory bowel diseases (IBDs). Most of these bacteria are lactic acid bacteria, which are part of the healthy human microbiota. However, little is known about the effects of transient bacteria present in normal diets, including Lactococcus lactis.

Methods

In the present study, we analysed the immunomodulatory effects of three L. lactis strains in vitro using intestinal epithelial cells. L. lactis NCDO 2118 was administered for 4 days to C57BL/6 mice during the remission period of colitis induced by dextran sodium sulphate (DSS).

Results

Only one strain, L. lactis NCDO 2118, was able to reduce IL-1β-induced IL-8 secretion in Caco-2 cells, suggesting a potential anti-inflammatory effect. Oral treatment using L. lactis NCDO 2118 resulted in a milder form of recurrent colitis than that observed in control diseased mice. This protective effect was not attributable to changes in secretory IgA (sIgA); however, NCDO 2118 administration was associated with an early increase in IL-6 production and sustained IL-10 production in colonic tissue. Mice fed L. lactis NCDO 2118 had an increased number of regulatory CD4⁺ T cells (Tregs) bearing surface TGF-β in its latent form (Latency-associated peptide-LAP) in the mesenteric lymph nodes and spleen.

Conclusions

Here, we identified a new probiotic strain with a potential role in the treatment of IBD, and we elucidated some of the mechanisms underlying its anti-inflammatory effect.

Investigating the effects of probiotics on pneumococcal colonization using an in vitro adherence assay

Adherence of Streptococcus pneumoniae (the pneumococcus) to the epithelial lining of the nasopharynx can result in colonization and is considered a prerequisite for pneumococcal infections such as pneumonia and otitis media. In vitro adherence assays can be used to study the attachment of pneumococci to epithelial cell monolayers and to investigate potential interventions, such as the use of probiotics, to inhibit pneumococcal colonization. The protocol described here is used to investigate the effects of the probiotic Streptococcus salivarius on the adherence of pneumococci to the human epithelial cell line CCL-23 (sometimes referred to as HEp-2 cells). The assay involves three main steps: 1) preparation of epithelial and bacterial cells, 2) addition of bacteria to epithelial cell monolayers, and 3) detection of adherent pneumococci by viable counts (serial dilution and plating) or quantitative real-time PCR (qPCR). This technique is relatively straightforward and does not require specialized equipment other than a tissue culture setup. The assay can be used to test other probiotic species and/or potential inhibitors of pneumococcal colonization and can be easily modified to address other scientific questions regarding pneumococcal adherence and invasion.

Enhanced microbial diversity in the saliva microbiome induced by short-term probiotic intake revealed by 16S rRNA sequencing on the IonTorrent PGM platform

Microbial communities populating several human body habitats are important determinants of human health. Cultivation-free community-wide approaches like bacterial 16S rRNA sequencing recently revolutionized the study of such human-associated microbial diversity, and the continuously decreasing cost/throughput ratio of current sequencing platforms is further enhancing the availability and effectiveness of microbiome research. The IonTorrent PGM platform is among the latest available commercial high-throughput sequencing tools, but it is just starting to be used for 16S rRNA surveys with only episodic assessments of its performance. We present here the first IonTorrent profiling of the human saliva microbiome collected from 12 healthy individuals. In this cohort, a subset of the volunteers was asked to assume a probiotic product, in order to investigate its impact on the composition and the structure of the saliva microbiome. Analysis of the generated dataset suggests the suitability of the IonTorrent platform for 16S rRNA surveys, even though some platform-specific choices are required to optimize the consistency of the obtained bacterial profiles. Interestingly, we found a marked and statistically significant increase of the overall bacterial diversity in the saliva of individuals who received the probiotic product compared to the control group, suggesting a short-term effect of probiotic product administration on oral microbiome composition.

Composition of microbial oral biofilms during maturation in young healthy adults

In the present study we aimed to analyze the bacterial community structure of oral biofilms at different maturation stages in young healthy adults. Oral biofilms established on membrane filters were collected from 32 human subjects after 5 different maturation intervals (1, 3, 5, 9 and 14 days) and the respective phylogenetic diversity was analyzed by 16S rDNA amplicon sequencing. Our analyses revealed highly diverse entire colonization profiles, spread into 8 phyla/candidate divisions and in 15 different bacterial classes. A large inter-individual difference in the subjects' microbiota was observed, comprising 35% of the total variance, but lacking conspicuous general temporal trends in both alpha and beta diversity. We further obtained strong evidence that subjects can be categorized into three clusters based on three differently occurring and mutually exclusive species clusters.

The impact of dairy consumption on salivary inoculum

Quantitative levels of harmful oral microbes present following complex surgical excisions of head and neck cancer are important since wounds are often contaminated through direct connection to the oral cavity and its flora. This possibility is especially important in irradiated patients who have decreased protective salivary function. In addition, high oral microbial levels increase and intensify oral mucositis leading to significant morbidity in patients treated with radiation therapy. One previously untested surgical teaching to decrease the bacterial inoculum present in the oral cavity is to counsel patients against consuming otherwise nutritious dairy products, as they are thought to coat the oral cavity with rate-limiting nutrients vital for bacterial growth. This risk may extend to individuals with chronic laryngeal penetration or aspiration, since salivary bacterial load might represent a lethal threat in the presence of marginal pulmonary reserve. A crossover study using six healthy adult volunteers and six patients who had previously undergone radiation therapy to an oropharyngeal primary site was performed. Saliva samples were quantitatively cultured in both groups with and without the consumption of dairy products at 1-h and 5-h intervals. Analysis of quantitative cultures demonstrated that the consumption of dairy products had no influence on bacterial levels present in previously radiated subjects and nonirradiated controls. Additionally, the consumption of dairy did not affect the composition of microbes present. Due to the lack of changes in both quantity and composition of oral bacteria seen in this study, patients would not benefit from the avoidance of dairy products.

Community interactions of oral streptococci

It is now clear that the most common oral diseases, dental caries and periodontitis, are caused by mixed-species communities rather than by individual pathogens working in isolation. Oral streptococci are central to these disease processes since they are frequently the first microorganisms to colonize oral surfaces and they are numerically the dominant microorganisms in the human mouth. Numerous interactions between oral streptococci and other bacteria have been documented. These are thought to be critical for the development of mixed-species oral microbial communities and for the transition from oral health to disease. Recent metagenomic studies are beginning to shed light on the co-occurrence patterns of streptococci with other oral bacteria. Refinements in microscopy techniques and biofilm models are providing detailed insights into the spatial distribution of streptococci in oral biofilms. Targeted genetic manipulation is increasingly being applied for the analysis of specific genes and networks that modulate interspecies interactions. From this work, it is clear that streptococci produce a range of extracellular factors that promote their integration into mixed-species communities and enable them to form social networks with neighboring taxa. These "community integration factors" include coaggregation-mediating adhesins and receptors, small signaling molecules such as peptides or autoinducer-2, bacteriocins, by-products of metabolism including hydrogen peroxide and lactic acid, and a range of extracellular enzymes. Here, we provide an overview of various types of community interactions between oral streptococci and other microorganisms, and we consider the possibilities for the development of new technologies to interfere with these interactions to help control oral biofilms.

Transcriptional analysis of the Streptococcus pyogenes salivaricin locus

The sal lantibiotic locus plays an important role in the virulence of Streptococcus pyogenes. Our transcriptional analysis of the sal locus provides new information on the complex regulation of this operon. Transcription of the operon is regulated by a promoter upstream of the operon and by a second internal promoter upstream of the salKRZ genes. Here we identify the location of the internal promoter and provide information on how this promoter is autoregulated by proteins within the locus. We determined by primer extension that the salKR promoter is located within the salY gene and identified several regulatory regions important for expression. The higher activity of the promoter in a salKR deletion strain indicates a role in repression by the SalR response regulator. Further, this promoter had higher activity in a salA deletion strain, implicating corepression or a signaling role for the SalA peptide. Finally, we demonstrate that this promoter can be controlled by host factors. Analysis of transcriptional regulation of this locus provides a better understanding of the function of the sal locus in S. pyogenes pathogenesis.

Bacterial behaviors associated with the quorum-sensing peptide pheromone ('alarmone') in streptococci

Streptococci are among the predominant bacterial species living in the human body. They are normally harmless bacteria, but have the ability to cause diverse infections, ranging from mild (e.g., tooth decay and sore throat) to life-threatening (e.g., endocarditis and meningitis). Streptococci have evolved various means of coping with the deleterious effects of environmental stressors and avoiding the host immune system. Recently, several studies have shown that streptococci colonizing the mouth and upper respiratory tract are able to mount complex stress responses in order to persist and successfully survive competition in their ecological niche. Using a small quorum-sensing peptide pheromone acting as a stress-inducible 'alarmone', oral streptococci synchronize the gene expression of a specific group of cells to coordinate important biological activities.

Persistence of the oral probiotic Streptococcus salivarius M18 is dose dependent and megaplasmid transfer can augment their bacteriocin production and adhesion characteristics

Bacteriocin-producing probiotic Streptococcus salivarius M18 offers beneficial modulatory capabilities within the oral microbiome, apparently through potent inhibitory activity against potentially deleterious bacteria, such as Streptococcus pyogenes. The oral cavity persistence of S. salivarius M18 was investigated in 75 subjects receiving four different doses for 28 days. Sixty per cent of the subjects already had some inhibitor-producing S. salivarius in their saliva prior to probiotic intervention. Strain M18's persistence was dependent upon the dose, but not the period of administration. Culture analysis indicated that in some individuals the introduced strain had almost entirely replaced the indigenous S. salivarius, though the total numbers of the species did not increase. Selected subjects showing either high or low probiotic persistence had their salivary populations profiled using Illumina sequencing of the V6 region of the 16S rRNA gene. Analysis indicated that while certain bacterial phenotypes were markedly modulated, the overall composition of the oral microbiome was not modified by the probiotic treatment. Megaplasmids encoding bacteriocins and adhesion factors were transferred in vitro to generate a transconjugant S. salivarius exhibiting enhanced antimicrobial production and binding capabilities to HEp-2 cells. Since no widespread perturbation of the existing indigenous microbiota was associated with oral instillation and given its antimicrobial activity against potentially pathogenic streptococci, it appears that application of probiotic strain M18 offers potential low impact alternative to classical antibiotic prophylaxis. For candidate probiotic strains having relatively poor antimicrobial or adhesive properties, unique derivatives displaying improved probiotic performance may be engineered in vitro by megaplasmid transfer.

Influence of the probiotic Streptococcus salivarius strain M18 on indices of dental health in children: a randomized double-blind, placebo-controlled trial

The prevalence of dental caries continues to increase, and novel strategies to reverse this trend appear necessary. The probiotic Streptococcus salivarius strain M18 offers the potential to confer oral health benefits as it produces bacteriocins targeting the important cariogenic species Streptococcus mutans, as well as the enzymes dextranase and urease, which could help reduce dental plaque accumulation and acidification, respectively. In a randomized double-blind, placebo-controlled study of 100 dental caries-active children, treatment with M18 was administered for 3 months and the participants were assessed for changes to their plaque score and gingival and soft-tissue health and to their salivary levels of S. salivarius, S. mutans, lactobacilli, β-haemolytic streptococci and Candida species. At treatment end, the plaque scores were significantly (P = 0.05) lower for children in the M18-treated group, especially in subjects having high initial plaque scores. The absence of any significant adverse events supported the safety of the probiotic treatment. Cell-culture analyses of sequential saliva samples showed no differences between the probiotic and placebo groups in counts of the specifically enumerated oral micro-organisms, with the exception of the subgroup of the M18-treated children who appeared to have been colonized most effectively with M18. This subgroup exhibited reduced S. mutans counts, indicating that the anti-caries activity of M18 probiotic treatments may be enhanced if the efficiency of colonization is increased. It was concluded that S. salivarius M18 can provide oral health benefits when taken regularly.

Developing oral probiotics from Streptococcus salivarius

Considerable human illness can be linked to the development of oral microbiota disequilibria. The predominant oral cavity commensal, Streptococcus salivarius has emerged as an important source of safe and efficacious probiotics, capable of fostering more balanced, health-associated oral microbiota. Strain K12, the prototype S. salivarius probiotic, originally introduced to counter Streptococcus pyogenes infections, now has an expanded repertoire of health-promoting applications. K12 and several more recently proposed S. salivarius probiotics are now being applied to control diverse bacterial consortia infections including otitis media, halitosis and dental caries. Other potential applications include upregulation of immunological defenses against respiratory viral infections and treatment of oral candidosis. An overview of the key steps required for probiotic development is also presented.

Beneficial microbes for the oral cavity: time to harness the oral streptococci?

Indigenous microbes are known to influence human health outcomes and various approaches are now being made to positively modulate these microbe-induced outcomes via the administration of probiotics. The application of probiotics that are specific to the oral cavity is a relatively undeveloped field, and their emergence has largely occurred as a reasoned follow-up to initial studies in which probiotics that had already been developed and obtained regulatory approval for intestinal applications were then also evaluated for their putative influence on oral microbiota functionality. These attempts to extend the application of existing probiotics were probably at least in part motivated by recognition of the substantial safety and regulatory hurdles that must be overcome prior to the introduction of a novel probiotic agent. Nevertheless, from an efficacy perspective it appears more logical to develop microbes of oral origin as the specific providers of probiotic solutions for oral diseases, rather than attempting to adapt intestinally-derived strains for this role. Oral bacteria and their bioactive molecules have evolved to operate optimally in this environment and in some cases are known to persist only in oral sites. Amongst the bacteria of more than 700 species now identified within the human oral microbiota, it is the streptococci that are numerically predominant. Although this review highlights the development of the oral cavity bacterium Streptococcus salivarius as an oral probiotic, a number of other streptococcal species have also been shown to have considerable potential as probiotic candidates.

Inhibition of Streptococcus pneumoniae adherence to human epithelial cells in vitro by the probiotic Lactobacillus rhamnosus GG

Background

Colonization of the nasopharynx by Streptococcus pneumoniae is considered a prerequisite for pneumococcal infections such as pneumonia and otitis media. Probiotic bacteria can influence disease outcomes through various mechanisms, including inhibition of pathogen colonization. Here, we examine the effect of the probiotic Lactobacillus rhamnosus GG (LGG) on S. pneumoniae colonization of human epithelial cells using an in vitro model. We investigated the effects of LGG administered before, at the same time as, or after the addition of S. pneumoniae on the adherence of four pneumococcal isolates.

Results

LGG significantly inhibited the adherence of all the pneumococcal isolates tested. The magnitude of inhibition varied with LGG dose, time of administration, and the pneumococcal isolate used. Inhibition was most effective when a higher dose of LGG was administered prior to establishment of pneumococcal colonization. Mechanistic studies showed that LGG binds to epithelial cells but does not affect pneumococcal growth or viability. Administration of LGG did not lead to any significant changes in host cytokine responses.

Conclusions

These findings demonstrate that LGG can inhibit pneumococcal colonization of human epithelial cells in vitro and suggest that probiotics could be used clinically to prevent the establishment of pneumococcal carriage.

Otitis media among high-risk populations: can probiotics inhibit Streptococcus pneumoniae colonisation and the risk of disease?

Otitis media is the second most common infection in children and the leading cause for seeking medical advice. Indigenous populations such as the Inuits, indigenous Australians and American Indians have a very high prevalence of otitis media and are considered to be high-risk populations. Streptococcus pneumoniae, one of the three main bacterial causes of otitis media, colonises the nasopharynx prior to disease development. In high-risk populations, early acquisition of high bacterial loads increases the prevalence of otitis media. In these settings, current treatment strategies are insufficient. Vaccination is effective against invasive pneumococcal infection but has a limited impact on otitis media. Decreasing the bacterial loads of otitis media pathogens and/or colonising the nasopharynx with beneficial bacteria may reduce the prevalence of otitis media. Probiotics are live microorganisms that offer health benefits by modulating the microbial community and enhancing host immunity. The available data suggest that probiotics may be beneficial in otitis media. This review discusses the potential use of probiotics to reduce pathogen colonisation and decrease the prevalence of otitis media, providing justification for further investigation.

Incidence of Bacteriocins Produced by Food-Related Lactic Acid Bacteria Active towards Oral Pathogens

In the present study we investigated the incidence of bacteriocins produced by 236 lactic acid bacteria (LAB) food isolates against pathogenic or opportunistic pathogenic oral bacteria. This set of LAB contained several strains (≥17%) producing bacteriocins active against food-related bacteria. Interestingly only Streptococcus macedonicus ACA-DC 198 was able to inhibit the growth of Streptococcus oralis, Streptococcus sanguinis and Streptococcus gordonii, while Lactobacillus fermentum ACA-DC 179 and Lactobacillus plantarun ACA-DC 269 produced bacteriocins solely against Streptococcus oralis. Thus, the percentage of strains that were found to produce bacteriocins against oral bacteria was ~1.3%. The rarity of bacteriocins active against oral LAB pathogens produced by food-related LAB was unexpected given their close phylogenetic relationship. Nevertheless, when tested in inhibition assays, the potency of the bacteriocin(s) of S. macedonicus ACA-DC 198 against the three oral streptococci was high. Fourier-transform infrared spectroscopy combined with principal component analysis revealed that exposure of the target cells to the antimicrobial compounds caused major alterations of key cellular constituents. Our findings indicate that bacteriocins produced by food-related LAB against oral LAB may be rare, but deserve further investigation since, when discovered, they can be effective antimicrobials.

The oral microbiome in health and disease

The human mouth harbours one of the most diverse microbiomes in the human body, including viruses, fungi, protozoa, archaea and bacteria. The bacteria are responsible for the two commonest bacterial diseases of man: dental caries (tooth decay) and the periodontal (gum) diseases. Archaea are restricted to a small number of species of methanogens while around 1000 bacterial species have been found, with representatives from the phyla Actinobacteria, Bacteroidetes, Firmicutes, Proteobacteria, Spirochaetes, Synergistetes and Tenericutes and the uncultured divisions GN02, SR1 and TM7. Around half of oral bacteria are as yet uncultured and culture-independent methods have been successfully used to comprehensively describe the oral bacterial community. The human oral microbiome database (HOMD, www.homd.org) provides a comprehensive resource consisting of descriptions of oral bacterial taxa, a 16S rRNA identification tool and a repository of oral bacterial genome sequences. Individuals' oral microbiomes are highly specific at the species level, although overall the human oral microbiome shows few geographical differences. Although caries and periodontitis are clearly bacterial diseases, they are not infectious diseases in the classical sense because they result from a complex interaction between the commensal microbiota, host susceptibility and environmental factors such as diet and smoking. Periodontitis, in particular, appears to result from an inappropriate inflammatory reaction to the normal microbiota, exacerbated by the presence of some disease-associated bacterial species. In functional terms, there appears to considerable redundancy among the oral microbiota and a focus on functional rather than phylogenetic diversity may be required in order to fully understand host-microbiome interactions.

Complete genome sequence of Streptococcus salivarius PS4, a strain isolated from human milk

Streptococcus salivarius is a commensal species commonly found in the human oropharyngeal tract. Some strains of this species have been developed for use as oral probiotics, while others have been associated with a variety of opportunistic human infections. Here, we report the complete sequence of strain PS4, which was isolated from breast milk of a healthy woman.