Variable characteristics of bacteriocin-producing Streptococcus salivarius strains isolated from Malaysian subjects

Potential and application of tandem mass spectrometry (MS/MS) in the analysis and identification of novel bacteriocins: a review

Bacteriocins are antimicrobial peptides synthesised ribosomally by Gram-positive or Gram-negative bacteria to gain a competitive advantage. The majority of bacteriocins are derived from Gram-positive bacteria, with lactic acid bacteria being the most common source. Because they are considered ‘natural’, there is currently significant development of bacteriocins for application as food preservative agents. As a preservative agent, bacteriocin activity is highly dependent on purity, down to the amino acid profile and sequence. Therefore, bacteriocin identification is important. Currently, MS is a cutting-edge tool in bacteriocin identification. This method has high selectivity, sensitivity and resolution. To the best of our knowledge, systematic reviews focusing on the application of MS for bacteriocin identification are currently limited. In light of this, the objective of this study is to provide a comprehensive review and summary of MS technologies in bacteriocin research, with a particular focus on the discovery and characterisation of novel sources of bacteriocin. Additionally, studies related to the discovery of bacteriocins from various sources, their role as antimicrobial agents, and their synthesis are emphasised. Thus, this study presents a comprehensive analysis of the advantages, limitations, and future perspectives of the methods employed.

Whole genome sequence analysis of Ligilactobacillus agilis C7 isolated from pig feces revealed three bacteriocin gene clusters

We here report the whole genome sequence of Ligilactobacillus agilis C7 with anti-listerial activity, which was isolated from pig feces. The genome size of L. agilis C7 (~ 3.0 Mb) is relatively larger compared with other L. agilis strains. L. agilis C7 carries three bacteriocin gene clusters encoding garvicin Q, salivaricin A, and Blp family class II bacteriocin. Garvicin Q and salivaricin A are reported to be active against Listeria monocytogenes and Micrococcus luteus, respectively, as well as against other Gram-positive bacteria. Meanwhile, the bacteriocin encoded in the blp cassette was shown to be active against pneumococci, mediating intraspecies competition. This report highlights the potential of L. agilis C7 for the production of bacteriocins inhibiting pathogenic bacteria.

Effect of a bacteriocin-producing Streptococcus salivarius on the pathogen Fusobacterium nucleatum in a model of the human distal colon

The gut microbiome is a vast reservoir of microbes, some of which produce antimicrobial peptides called bacteriocins that may inhibit specific bacteria associated with disease. Fusobacterium nucleatum is an emerging human bacterial pathogen associated with gastrointestinal diseases including colorectal cancer (CRC). In this study, fecal samples of healthy donors were screened for potential bacteriocin-producing probiotics with antimicrobial activity against F. nucleatum. A novel isolate, designated as Streptococcus salivarius DPC6993 demonstrated a narrow-spectrum of antimicrobial activity against F. nucleatum in vitro. In silico analysis of the S. salivarius DPC6993 genome revealed the presence of genes involved in the production of the bacteriocins salivaricin A5 and salivaricin B. After 6 h in a colon fermentation model, there was a significant drop in the number of F. nucleatum in samples that had been simultaneously inoculated with S. salivarius DPC6993 + F. nucleatum DSM15643 compared to those inoculated with F. nucleatum DSM15643 alone (mean ± SD: 9243.3 ± 3408.4 vs 29688.9 ± 4993.9 copies/μl). Furthermore, 16S rRNA amplicon analysis revealed a significant difference in the mean relative abundances of Fusobacterium between samples inoculated with both S. salivarius DPC6993 and F. nucleatum DSM15643 (0.05%) and F. nucleatum DSM15643 only (0.32%). Diversity analysis indicated minimal impact exerted by S. salivarius DPC6993 on the surrounding microbiota. Overall, this study highlights the ability of a natural gut bacterium to target a bacterial pathogen associated with CRC. The specific targeting of CRC-associated pathogens by biotherapeutics may ultimately reduce the risk of CRC development and positively impact CRC outcomes.

Listeriolysin S: A bacteriocin from Listeria monocytogenes that induces membrane permeabilization in a contact-dependent manner

Listeria monocytogenes (Lm) is a bacterial pathogen that causes listeriosis, a foodborne disease characterized by gastroenteritis, meningitis, bacteremia, and abortions in pregnant women. The most severe human listeriosis outbreaks are associated with a subset of Lm hypervirulent clones that encode the bacteriocin Listeriolysin S (LLS), which modifies the gut microbiota and allows efficient Lm gut colonization and invasion of deeper organs. Our present work identifies the killing mechanism displayed by LLS to outcompete gut commensal bacteria, demonstrating that it induces membrane permeabilization and membrane depolarization of target bacteria. Moreover, we show that LLS is a thiazole/oxazole–modified microcin that displays a contact-dependent inhibition mechanism.

Listeriolysin S (LLS) is a thiazole/oxazole–modified microcin (TOMM) produced by hypervirulent clones of Listeria monocytogenes. LLS targets specific gram-positive bacteria and modulates the host intestinal microbiota composition. To characterize the mechanism of LLS transfer to target bacteria and its bactericidal function, we first investigated its subcellular distribution in LLS-producer bacteria. Using subcellular fractionation assays, transmission electron microscopy, and single-molecule superresolution microscopy, we identified that LLS remains associated with the bacterial cell membrane and cytoplasm and is not secreted to the bacterial extracellular space. Only living LLS-producer bacteria (and not purified LLS-positive bacterial membranes) display bactericidal activity. Applying transwell coculture systems and microfluidic-coupled microscopy, we determined that LLS requires direct contact between LLS-producer and -target bacteria in order to display bactericidal activity, and thus behaves as a contact-dependent bacteriocin. Contact-dependent exposure to LLS leads to permeabilization/depolarization of the target bacterial cell membrane and adenosine triphosphate (ATP) release. Additionally, we show that lipoteichoic acids (LTAs) can interact with LLS and that LTA decorations influence bacterial susceptibility to LLS. Overall, our results suggest that LLS is a TOMM that displays a contact-dependent inhibition mechanism.

A New Approach to Harness Probiotics Against Common Bacterial Skin Pathogens: Towards Living Antimicrobials

In this study, the potential of certain lactic acid bacteria—classified as probiotics and known to be antimicrobially active against pathogens or food-poisoning microorganisms—was evaluated with respect to their activity against bacterial skin pathogens. The aim of the study was to develop a plaster/bandage for the application of inhibitory substances produced by these probiotics when applied to diseased skin. For this purpose, two Streptococcus salivarius strains and one Lactobacillus plantarum were tested for production of antimicrobials (bacteriocin-like substances) active against Gram-positive and Gram-negative pathogens using established methods. A newly designed membrane test ensured that the probiotics produce antimicrobials diffusible through membranes. Target organisms used were Cutibacterium acnes, Staphylococcus aureus, and Pseudomonas aeruginosa. Moreover, the L. plantarum 8P-A3 strain was tested against additional bacteria involved in skin disorders. The Lactobacillales used were active against all potential skin pathogens tested. These probiotics could be enclosed between polymer membranes—one tight, the other permeable for their products, preserved by vacuum drying, and reactivated after at least three months storage. Importantly, the reactivated pads containing the probiotics demonstrated antibacterial activity on agar plates against all pathogens tested. This suggests that the probiotic containing pads may be topically applied for the treatment of skin disorders without the need for a regular antibiotic treatment or as an adjunctive therapy.

Dysbiosis of the Salivary Microbiome is Associated with Hypertension and Correlated with Metabolic Syndrome Biomarkers

BACKGROUND

Hypertension (HT) is an idiopathic disease with severe complications and a high incidence of global mortality. Although the disease shares characteristic features with diabetes and obesity, the complex interplay of endogenous and environmental factors is not well characterized. The oral microbiome has recently been studied to better understand the role of commensal microorganisms in metabolic disorders, including HT, although its role in disease etiology is unclear.

METHODS

To bridge this gap, we compared the oral microbiome and clinical chemistry of adult subjects enrolled at Qatar Biobank. Clinical chemistry was performed using Roche Cobas-6000 analyzer. Saliva samples were subjected to 16S rRNA sequencing using Illumina MiSeq platform. Cross-gender comparisons were made between control (males/females) (C-M and C-F) and HT (HT-M and HT-F) groups.

RESULTS

The HT groups had higher (p ≤ 0.05) BMI, plasma glucose, insulin, C-peptide, and alkaline phosphatase (ALP) concentrations. Triglycerides, cholesterol, LDL-cholesterol, and sodium ions were similar among the groups. The microbiome was predominantly occupied by Firmicutes, Bacteroidetes, Proteobacteria, and Actinobacteria. Firmicutes were higher (p ≤ 0.05) in the HT groups, whereas Proteobacteria was only higher in the C-F group. Prevotella and Veillonella were significantly higher in the HT groups and exhibited a positive correlation with blood pressure and hyperglycemia. In contrast to other studies, the mathematical summation of priori-select microbes reveals that nitrate-reducing microbes were higher in the HT groups compared with the controls.

CONCLUSION

In conclusion, these observations suggest a strong association of HT with microbial dysbiosis, where microbial species other than nitrate-reducing microbes contribute to blood pressure regulation. The findings affirm plausible microbial signatures of hypertension and suggest manipulating these microbes as a novel treatment modality. Future experiments are warranted for the mechanistic investigation of hypertension metagenomics and microbial activity.

Cell-free supernatant of Streptococcus salivarius M18 impairs the pathogenic properties of Pseudomonas aeruginosa and Klebsiella pneumonia

M18 strain of Streptococcus salivarius is a bacterial replacement probiotic that has been suggested for use in the oral cavity. Here, we have shown that S. salivarius M18 cell-free supernatant reduced the growth of the two most common human pathogens Pseudomonas aeruginosa and Klebsiella pneumonia and sensitized the pathogenic bacteria to antibiotic. Besides, the supernatant inhibited biofilm formation of P. aeruginosa drastically. For pinpointing the biomolecular changes that occurred in P. aeruginosa incubated with the probiotic supernatant, attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy was used. Unsupervised learning algorithms, principal component analysis (PCA) and hierarchical cluster analysis (HCA), and intensity analyses of individual spectral bands exhibited comprehensive alterations in the polysaccharide and lipid contents and compositions of P. aeruginosa cultivated with S. salivarius M18 cell-free supernatant. These results indicate that S. salivarius M18 has the potential for the prevention or alleviation of different pathogen-induced infections along with the infections of oral pathogens.

Evolution of Lantibiotic Salivaricins: New Weapons to Fight Infectious Diseases

Lantibiotic salivaricins are polycyclic peptides containing lanthionine and/or β-methyllanthionine residues produced by certain strains of Streptococcus salivarius, which almost exclusively reside in the human oral cavity. The importance of these molecules stems from their antimicrobial activity towards relevant oral pathogens which has so far been applied through the development of salivaricin-producing probiotic strains. However, salivaricins may also prove to be of great value in the development of new and novel antibacterial therapies in this era of emerging antibiotic resistance. In this review, we describe the biosynthesis, antimicrobial activity, structure, and mode of action of the lantibiotic salivaricins characterized to date. Moreover, we also provide an expert opinion and suggestions for future development of this important field of microbiology.

Does Streptococcus Salivarius Strain M18 Assumption Make Black Stains Disappear in Children?

PURPOSE

This randomised controlled study evaluated the effectiveness of an oral probiotic, Streptococcus salivarius M18 (SsM18), in children with black stains (BSs) in order to counteract their reformation.

MATERIALS AND METHODS

Fifty-eight children (aged 4-10 years) presenting with BSs were enrolled. They were randomly divided into two groups: group A (n = 29) included children who were given the test product containing SsM18 once a day for 3 months; group B (n = 29) included children who did not receive any treatment. Before beginning the study, all the children underwent professional removal of BSs. The assessment of BSs was done after 3 months (T1) and after 6 months (T2).

RESULTS

Four patients (1 belonging to group A and 3 to group B) were excluded from the study because they started antibiotic therapy. After 3 months (T1), BSs were detected in 6 of the 28 children (21.2%) from group A and in 13 out of the 26 (50%) children from group B (p < 0.05). After 6 months (T2), BSs were detected in 9 out of the 28 (32.1%) children from group A and in 14 of the 26 (53.8%) children from group B (p > 0.05).

CONCLUSIONS

BSs formation in children could be prevented by administering S. salivarius M18.

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.

Effectiveness of the probiotic Streptococcus salivarius K12 for the treatment and/or prevention of sore throat: a systematic review

BACKGROUND

Sore throat resulting from pharyngotonsillitis is one of the commonest reasons for primary care consultation and inappropriate antibiotic prescription and finding effective alternative treatments is important.

OBJECTIVES

To review the evidence for using the probiotic Streptococcus salivarius K12 (SsK12) for the prevention or treatment of pharyngotonsillitis.

DATA SOURCES

PubMed, Embase, CINAHL and Cochrane Library.

STUDY ELIGIBILITY CRITERIA

Randomized controlled trials (RCTs).

PARTICIPANTS

Adults or children.

INTERVENTIONS

SsK12 as active treatment or prophylaxis, against pharyngotonsillitis.

METHODS

Literature search.

RESULTS

Four articles were identified (1846 participants). All were deemed to be of poor quality using the Cochrane risk-of-bias assessment. Two trials studied SsK12 prophylaxis for streptococcal pharyngitis (children without history of recurrence). One compared daily administration of SsK12 to no treatment over 6 months (n = 222, age 33-45 months), reporting significantly lower incidence in the SsK12 group (16.2% vs. 48.6%, p < 0.01), whereas another placebo-controlled RCT over four school terms (n = 1314, 5-14 years) found no significant difference (7.8% vs. 8.8%, p 0.34) with SsK12 (administered on school days). Another trial found daily SsK12 to significantly protect children (n = 250, 6-7 years) against chronic adenoiditis exacerbation over 3 months compared to no treatment (71.7% vs. 100%, p < 0.0001). The one placebo-controlled RCT in adults that studied the use of SsK12 for acute pharyngotonsillitis (concurrently with penicillin) showed no significant benefit. In all trials, SsK12 was safe and well tolerated.

CONCLUSIONS

SsK12 appears safe and well tolerated. However, further RCTs are required to establish its role as a prophylactic therapy, particularly among patients experiencing frequent exacerbations of pharyngitis. In the acute setting, SsK12 is unlikely to be effective if given concurrently with antibiotics; however, further RCTs should establish its role as an alternative to antibiotics in nonsevere cases or when prescribed after antibiotic therapy for the prevention of disease recurrence and/or secondary infection.

Characterization of a lytic vibriophage VP06 of Vibrio parahaemolyticus

Vibrio parahaemolyticus is a human enteropathogenic bacterium and is also pathogenic to shrimp and finfish. In a search for a biocontrol agent for V. parahaemolyticus and other pathogenic Vibrio species, a lytic phage VP06 was isolated from oyster using V. parahaemolyticus as the host. VP06 is a Siphoviridae phage with a polyhedral head and a long tail. The genome sequence of VP06 was 75,893 nucleotides in length and the G + C content was 49%; a total of 101 CDSs were identified in VP06, of which 39 exhibited functional domains/motifs. The genomic sequence of VP06 is similar to those of a lytic Vibrio vulnificus phage SSP002 and a temperate V. parahaemolyticus phage vB_VpaS_MAR10, although VP06 has distinct features in the CDS arrangement and 14 unique CDSs. Phylogenetic analysis revealed that VP06, SSP002 and vB_VpaS_MAR10 belong to a novel genus cluster of Siphoviridae phages. This phage lysed 28.1% of various Vibrio strains, and the efficiency of plating method revealed that VP06 was highly effective in lysing strains of Vibrio alginolyticus, Vibrio azureus, Vibrio harveyi and V. parahaemolyticus. The properties of VP06, including its broad range of hosts and resistance to environmental stresses, indicate that it may be a candidate biocontrol agent.

Pentocin MQ1: A Novel, Broad-Spectrum, Pore-Forming Bacteriocin From Lactobacillus pentosus CS2 With Quorum Sensing Regulatory Mechanism and Biopreservative Potential

Micrococcus luteus, Listeria monocytogenes, and Bacillus cereus are major food-borne pathogenic and spoilage bacteria. Emergence of antibiotic resistance and consumer demand for foods containing less of chemical preservatives led to a search for natural antimicrobials. A study aimed at characterizing, investigating the mechanism of action and regulation of biosynthesis and evaluating the biopreservative potential of pentocin from Lactobacillus pentosus CS2 was conducted. Pentocin MQ1 is a novel bacteriocin isolated from L. pentosus CS2 of coconut shake origin. The purification strategy involved adsorption-desorption of bacteriocin followed by RP-HPLC. It has a molecular weight of 2110.672 Da as determined by MALDI-TOF mass spectrometry and a molar extinction value of 298.82 M⁻¹ cm⁻¹. Pentocin MQ1 is not plasmid-borne and its biosynthesis is regulated by a quorum sensing mechanism. It has a broad spectrum of antibacterial activity, exhibited high chemical, thermal and pH stability but proved sensitive to proteolytic enzymes. It is potent against M. luteus, B. cereus, and L. monocytogenes at micromolar concentrations. It is quick-acting and exhibited a bactericidal mode of action against its targets. Target killing was mediated by pore formation. We report for the first time membrane permeabilization as a mechanism of action of the pentocin from the study against Gram-positive bacteria. Pentocin MQ1 is a cell wall-associated bacteriocin. Application of pentocin MQ1 improved the microbiological quality and extended the shelf life of fresh banana. This is the first report on the biopreservation of banana using bacteriocin. These findings place pentocin MQ1 as a potential biopreservative for further evaluation in food and medical applications.

Gut microbiome of mothers delivering prematurely shows reduced diversity and lower relative abundance of Bifidobacterium and Streptococcus

OBJECTIVE

Preterm birth is the main reason for neonatal deaths worldwide. We investigate whether maternal gut microbiota may play a previously overlooked role.

METHODS

The Norwegian Microbiota Study (NoMIC) is a case control study on preterm birth (<259 days of gestation, calculated primarily based on the last menstrual period), including two consecutively born term infants per infant born prematurely. Eligible mothers were fluent in Norwegian and recruited from the maternity ward at a county hospital in Eastern Norway in the period 2002-2005. Fecal samples were collected at day 4 postpartum, and analyzed using 16S ribosomal RNA gene sequencing. We used samples from 121 mothers giving birth vaginally. Measures of alpha diversity (Shannon, Phylogenetic Diversity and Observed Operational Taxonomic Units) and microbiome composition were combined with information from the Medical Birth Registry, pregnancy journals, and questionnaires.

RESULTS

The association between maternal gut diversity and preterm delivery was examined using logistic regression. One IQR increase in Shannon diversity was significantly associated with 38% lower odds of spontaneous preterm birth, (95% confident interval (CI): 1%, 61%), and the association was stronger when adjusting for maternal age, marital status, ethnicity, parity, BMI, education, antibiotic use, pets in the household, income and smoking (48% lower odds, 95% CI: 4.2%, 72%). Mothers delivering prematurely also had lower abundance of OTUs belonging to Bifidobacterium and Streptococcus, and of the Clostridiales order.

CONCLUSION

Analysis of maternal gut microbiota using next-generation sequencing shows that low gut diversity, with a distinct microbial composition, is associated with spontaneous preterm delivery.

Contact-dependent killing by Caulobacter crescentus via cell surface-associated, glycine zipper proteins

Most bacteria are in fierce competition with other species for limited nutrients. Some bacteria can kill nearby cells by secreting bacteriocins, a diverse group of proteinaceous antimicrobials. However, bacteriocins are typically freely diffusible, and so of little value to planktonic cells in aqueous environments. Here, we identify an atypical two-protein bacteriocin in the α-proteobacterium Caulobacter crescentus that is retained on the surface of producer cells where it mediates cell contact-dependent killing. The bacteriocin-like proteins CdzC and CdzD harbor glycine-zipper motifs, often found in amyloids, and CdzC forms large, insoluble aggregates on the surface of producer cells. These aggregates can drive contact-dependent killing of other organisms, or Caulobacter cells not producing the CdzI immunity protein. The Cdz system uses a type I secretion system and is unrelated to previously described contact-dependent inhibition systems. However, Cdz-like systems are found in many bacteria, suggesting that this form of contact-dependent inhibition is common.

Bacteriocins from lactic acid bacteria and their potential in the preservation of fruit products

Bacteriocins produced by lactic acid bacteria (LAB) are well-recognized for their potential as natural food preservatives. These antimicrobial peptides usually do not change the sensorial properties of food products and can be used in combination with traditional preservation methods to ensure microbial stability. In recent years, fruit products are increasingly being associated with food-borne pathogens and spoilage microorganisms, and bacteriocins are important candidates to preserve these products. Bacteriocins have been extensively studied to preserve foods of animal origin. However, little information is available for their use in vegetable products, especially in minimally processed ready-to-eat fruits. Although, many bacteriocins possess useful characteristics that can be used to preserve fruit products, to date, only nisin, enterocin AS-48, bovicin HC5, enterocin 416K1, pediocin and bificin C6165 have been tested for their activity against spoilage and pathogenic microorganisms in these products. Among these, only nisin and pediocin are approved to be commercially used as food additives, and their use in fruit products is still limited to certain countries. Considering the increasing demand for fresh-tasting fruit products and concern for public safety, the study of other bacteriocins with biochemical characteristics that make them candidates for the preservation of these products are of great interest. Efforts for their approval as food additives are also important. In this review, we discuss why the study of bacteriocins as an alternative method to preserve fruit products is important; we detail the biotechnological approaches for the use of bacteriocins in fruit products; and describe some bacteriocins that have been tested and have potential to be tested for the preservation of fruit products.

Injectable gentamicin-loaded thermo-responsive hyaluronic acid derivative prevents infection in a rabbit model

Despite the use of systemic antibiotic prophylaxis, the surgical fixation of open fractures with osteosynthesis implants is associated with high infection rates. Antibiotic-loaded biomaterials (ALBs) are increasingly used in implant surgeries across medical specialties to deliver high concentrations of antibiotics to the surgical site and reduce the risk of implant-associated infection. ALBs which are either less or not restricted in terms of spatial distribution and which may be applied throughout complex wounds could offer improved protection against infection in open fracture care. A thermo-responsive hyaluronic acid derivative (hyaluronic acid-poly(N-isopropylacrylamide) (HApN)) was prepared by a direct amidation reaction between the tetrabutyl ammonium (TBA) salt of hyaluronic acid and amine-terminated poly(N-isopropylacrylamide) (pN). The degree of grafting, and gelation properties of this gel were characterized, and the composition was loaded with gentamicin. The rheological- and release properties of this gentamicin-loaded HApN composition were tested in vitro and its efficacy in preventing infection was tested in a rabbit model of osteosynthesis contaminated with Staphylococcus aureus. The gentamicin-loaded HApN composition was able to prevent bacterial colonization of the implant site as shown by quantitative bacteriology. This finding was supported by histopathological evaluation of the humeri samples where no bacteria were found in the stained sections. In conclusion, this gentamicin-loaded HApN hydrogel effectively prevents infection in a complex wound, simulating a contaminated fracture treated with plating osteosynthesis.

STATEMENT OF SIGNIFICANCE

Fracture fixation after trauma is associated with high infection rates. Antibiotic loaded biomaterials (ALBs) can provide high local concentrations without systemic side effects. However, the currently available ALBs have limited accessibility to contaminated tissues in open fractures because of predetermined shape. Thus, a novel thermo-responsive hyaluronan based hydrogel with control over gelation temperature is reported. The efficacy of this gentamicin loaded hyaluronan derivative is demonstrated in an in vivo fracture model in the presence of fracture fixation hardware. The bacterial burden is cleared in all of the inoculated rabbits in the presence of the ALB. Thus, the proposed injectable thermo-responsive hyaluronan presents an effective ALB for the prevention of infection.

New insights into the mode of action of the lantibiotic salivaricin B

Salivaricin B is a 25 amino acid polycyclic peptide belonging to the type AII lantibiotics and first shown to be produced by Streptococcus salivarius. In this study we describe the bactericidal mode of action of salivaricin B against susceptible Gram-positive bacteria. The killing action of salivaricin B required micro-molar concentrations of lantibiotic whereas the prototype lantibiotic nisin A was shown to be potent at nano-molar levels. Unlike nisin A, salivaricin B did not induce pore formation or dissipate the membrane potential in susceptible cells. This was established by measuring the fluorescence of the tryptophan residue at position 17 when salivaricin B interacted with bacterial membrane vesicles. The absence of a fluorescence blue shift indicates a failure of salivaricin B to penetrate the membranes. On the other hand, salivaricin B interfered with cell wall biosynthesis, as shown by the accumulation of the final soluble cell wall precursor UDP-MurNAc-pentapeptide which is the backbone of the bacterial peptidoglycan. Transmission electron microscopy of salivaricin B-treated cells showed a reduction in cell wall thickness together with signs of aberrant septum formation in the absence of visible changes to cytoplasmic membrane integrity.

Integrate genome-based assessment of safety for probiotic strains: Bacillus coagulans GBI-30, 6086 as a case study

Probiotics are microorganisms that confer beneficial effects on the host; nevertheless, before being allowed for human consumption, their safety must be verified with accurate protocols. In the genomic era, such procedures should take into account the genomic-based approaches. This study aims at assessing the safety traits of Bacillus coagulans GBI-30, 6086 integrating the most updated genomics-based procedures and conventional phenotypic assays. Special attention was paid to putative virulence factors (VF), antibiotic resistance (AR) genes and genes encoding enzymes responsible for harmful metabolites (i.e. biogenic amines, BAs). This probiotic strain was phenotypically resistant to streptomycin and kanamycin, although the genome analysis suggested that the AR-related genes were not easily transferrable to other bacteria, and no other genes with potential safety risks, such as those related to VF or BA production, were retrieved. Furthermore, no unstable elements that could potentially lead to genomic rearrangements were detected. Moreover, a workflow is proposed to allow the proper taxonomic identification of a microbial strain and the accurate evaluation of risk-related gene traits, combining whole genome sequencing analysis with updated bioinformatics tools and standard phenotypic assays. The workflow presented can be generalized as a guideline for the safety investigation of novel probiotic strains to help stakeholders (from scientists to manufacturers and consumers) to meet regulatory requirements and avoid misleading information.