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

Understanding bacteriocin heterologous expression: A review

Bacteriocins are a diverse group of ribosomally synthesised antimicrobial peptides/proteins that play an important role in self-defence. They are widely used as bio-preservatives and effective substitutes for disease eradication. They can be used in conjunction with or as an alternative to antibiotics to minimize the risk of resistance development. There are remarkably few reports indicating resistance to bacteriocins. Although there are many research reports that emphasise heterologous expression of bacteriocin, there are no convincing reports on the significant role that intrinsic and extrinsic factors play in overexpression. A coordinated and cooperative expression system works in concert with multiple genetic elements encoding native proteins, immunoproteins, exporters, transporters and enzymes involved in the post-translational modification of bacteriocins. The simplest way could be to utilise the existing E. coli expression system, which is conventional, widely used for heterologous expression and has been further extended for bacteriocin expression. In this article, we will review the intrinsic and extrinsic factors, advantages, disadvantages and major problems associated with bacteriocin overexpression in E. coli. Finally, we recommend the most effective strategies as well as numerous bacteriocin expression systems from E. coli, Lactococcus, Kluveromyces lactis, Saccharomyces cerevisiae and Pichia pastoris for their suitability for successful overexpression.

Ribosomally synthesized bacteriocins of lactic acid bacteria: Simplicity yet having wide potentials - A review

Bacteriocins are ribosomally made bacterial peptides that have outstanding contributions in the field of food industry, as biopreservatives, and promising potentials in the medical field for improving human and animal health. Bacteriocins have many advantages over antibiotics such as being primary metabolites with relatively simpler biosynthetic mechanisms, which made their bioengineering for activity or specificity improving purposes much easier. Also, bacteriocins are degraded by proteolytic enzymes and do not stay in environment, which reduce chances of developing resistance. Bacteriocins can improve activity of some antibiotics, and some bacteriocins show potency against multidrug-resistant bacteria. Moreover, some potent bacteriocins have antiviral, antifungal, and antiprotozoal (antileishmanial) activities. On the other hand, bacteriocins have been introduced into the treatment of some ulcers and types of cancer. These potentials make bacteriocins attract extra attention as promising biotechnological tool. Hence, the history, characteristics, and classification of bacteriocins are described in this review. Furthermore, the main difference between bacteriocins and other antimicrobial peptides is clarified. Also, bacteriocins biosynthesis and identified modes of action are elucidated. Additionally, current and potential applications of bacteriocins in food and medical fields are highlighted. Finally, future perspectives concerning studying bacteriocins and their applications are discussed.

Utilisation of probiotics for disease management in giant freshwater prawn (Macrobrachium rosenbergii): Administration methods, antagonistic effects and immune response

The giant freshwater prawn (Macrobrachium rosenbergii) is a high-yielding prawn variety well-received worldwide due to its ability to adapt to freshwater culture systems. Macrobrachium rosenbergii is an alternative to shrimp typically obtained from marine and brackish aquaculture systems. However, the use of intensive culture systems can lead to disease outbreaks, particularly in larval and post-larval stages, caused by pathogenic agents such as viruses, bacteria, fungi, yeasts and protozoans. White tail disease (viral), white spot syndrome (viral) and bacterial necrosis are examples of economically significant diseases. Given the increasing antibiotic resistance of disease-causing microorganisms, probiotics have emerged as promising alternatives for disease control. Probiotics are live active microbes that are introduced into a target host in an adequate number or dose to promote its health. In the present paper, we first discuss the diseases that occur in M. rosenbergii production, followed by an in-depth discussion on probiotics. We elaborate on the common methods of probiotics administration and explain the beneficial health effects of probiotics as immunity enhancers. Moreover, we discuss the antagonistic effects of probiotics on pathogenic microorganisms. Altogether, this paper provides a comprehensive overview of disease control in M. rosenbergii aquaculture through the use of probiotics, which could enhance the sustainability of prawn culture.

Diversity of the bacteriocins, their classification and potential applications in combat of antibiotic resistant and clinically relevant pathogens

There is almost a century since discovery of penicillin by Alexander Fleming, a century of enthusiasm, abuse, facing development of antibiotic-resistance and clear conclusion that the modern medicine needs a new type of antimicrobials. Bacteriocins produced by Gram-positive and Gram-negative bacteria, Archaea and Eukaryotes were widely explored as potential antimicrobials with several applications in food industry. In last two decades bacteriocins showed their potential as promising alternative therapeutic for the treatment of antibiotic-resistant pathogens. Bacteriocins can be characterised as highly selective antimicrobials and therapeutics with low cytotoxicity. Most probably in order to solve the problems associated with the increasing number of antibiotic-resistant bacteria, the application of natural or bioengineered bacteriocins in addition to synergistically acting preparations of bacteriocins and conventional antibiotics, can be the next step in combat versus drug-resistant pathogens. In this overview we focussed on diversity of specific lactic acid bacteria and their bacteriocins. Moreover, some additional examples of bacteriocins from non-lactic acid, Gram-positive and Gram-negative bacteria, Archaea and eukaryotic organisms are presented and discussed. Therapeutic properties of bacteriocins, their bioengineering and combined applications, together with conventional antibiotics, were evaluated with the scope of application in human and veterinary medicine for combating (multi-)drug-resistant pathogens.

Enterocin LD3 from Enterococcus hirae LD3 Inhibits the Growth of Salmonella enterica subsp. enterica serovar Typhimurium ATCC 13311 in Fruit Juice

In order to prevent the growth of pathogens in food, bacteriocins produced by various probiotic lactic acid bacteria have been recognized as potential substitutes of chemical preservatives. In this study, enterocin LD3 was purified from the cell-free supernatant of a food isolate, Enterococcus hirae LD3 using multistep chromatography. In the fruit juice, lethal concentration (LC₅₀) of enterocin LD3 was found to be 260 µg/mL against Salmonella enterica subsp. enterica serovar Typhimurium ATCC 13311. The cells treated with enterocin LD3 were red colour indicating dead cells after propidium iodide staining, while untreated cells were found blue after staining with 4', 6-diamidino-2-phenylindole. The mechanism of cell killing was analyzed using infrared spectrum of cells treated with enterocin LD3 which was found altered in the range of 1,094.30 and 1,451.82 cm^-1 corresponding to nucleic acids and phospholipids, respectively. The morphology of target cells were severely ruptured and lysed as observed under electron microscopy. Thus, the present study suggested that enterocin LD3 showed bactericidal activity against Salm. enterica subsp. enterica serovar Typhimurium ATCC 13311 and may be applied as a bio-preservative for the safety of fruit juices.

Bacteriocins from lactic acid bacteria and their potential clinical applications

Bacteriocins are ribosomally synthesized antimicrobial peptides that have long been used in the food industry. Being a highly diverse and heterogeneous group of molecules the classification is ever-evolving. Their production is widespread among bacteria; nevertheless, their biosynthesis and mode of action remain fairly similar. With the advances in drug resistance mechanisms, it is important to look for alternatives to conventional approaches. Therefore, the advantages of bacteriocin over antibiotics need to be considered to provide a scientific basis for their use. Particularly in the last decade, intensive studies look at their potential as next-generation therapeutics against drug-resistant bacteria. Bacteriocins from lactic acid bacteria are being tested as controlling agents for bacterial and viral infections; they can inhibit biofilm synthesis and have potential as contraceptives. Bioengineered peptides have shown enhanced activity and thereby indicate the lack of knowledge we possess regarding these bacteriocins. In this review, we have listed various Gram-positive LAB bacteriocins with their synthesis and mechanism of action. Recent developments in screening and purification technologies have been analyzed with an emphasis on their potential clinical applications. Although extensive research has been done to identify multifunctional bacteriocins, it is important to focus on the mechanism of action of these peptides to get them from bench to bedside.

Microbiome therapeutics: exploring the present scenario and challenges

Human gut-microbiome explorations have enriched our understanding of microbial colonization, maturation, and dysbiosis in health-and-disease subsets. The enormous metabolic potential of gut microbes and their role in the maintenance of human health is emerging, with new avenues to use them as therapeutic agents to overcome human disorders. Microbiome therapeutics are aimed at engineering the gut microbiome using additive, subtractive, or modulatory therapy with an application of native or engineered microbes, antibiotics, bacteriophages, and bacteriocins. This approach could overcome the limitation of conventional therapeutics by providing personalized, harmonized, reliable, and sustainable treatment. Its huge economic potential has been shown in the global therapeutics market. Despite the therapeutic and economical potential, microbiome therapeutics is still in the developing stage and is facing various technical and administrative issues that require research attention. This review aims to address the current knowledge and landscape of microbiome therapeutics, provides an overview of existing health-and-disease applications, and discusses the potential future directions of microbiome modulations.

Polydiacetylene vesicles acting as colorimetric sensor for the detection of plantaricin LD1

The interaction of antimicrobial peptides with membrane lipids plays a major role in numerous physiological processes. In this study, polydiacetylene (PDA) vesicles were synthesized using 10, 12-tricosadiynoic acid (TRCDA) and 1, 2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC). These vesicles were applied as artificial membrane biosensor for the detection of plantaricin LD1 purified from Lactobacillus plantarum LD1. Plantaricin LD1 (200 μg/mL) was able to interact with PDA vesicles by changing the color from blue to red with colorimetric response 30.26 ± 0.59. Nisin (200 μg/mL), used as control, also changed the color of the vesicles with CR% 50.56 ± 0.98 validating the assay. The vesicles treated with nisin and plantaricin LD1 showed increased infrared absorbance at 1411.46 and 1000-1150 cm^-1 indicated the interaction of bacteriocins with phospholipids and fatty acids, respectively suggesting membrane-acting nature of these bacteriocins. Further, microscopic observation of bacteriocin-treated vesicles showed several damages indicating the interaction of bacteriocins. These findings suggest that the PDA vesicles may be used as bio-mimetic sensor for the detection of bacteriocins produced by several probiotics in food and therapeutic applications.

Thermophilin 110 inhibits growth and biofilm formation of Streptococcus mutans

•

S. thermophilus B59671 naturally produces thermophilin 110, a bacteriocin that inhibits the growth of the oral pathogen Streptococcus mutans

•

Thermophilin 110 was shown to prevent biofilm formation by S. mutans UA159

•

Co-culturing S. thermophilus B59671 with S. mutans UA159 prevented biofilm formation.

Dental caries continues to occur in both children and adults worldwide resulting in significant economic burden, and consumers have expressed interest in natural products that can prevent these recurrent infections. In this study, S. thermophilus B59671, which produces thermophilin 110, was shown to inhibit the growth of S. mutans UA159. A thermophilin concentration ≥ 80 AU ml⁻¹ prevented the growth of S. mutans UA159 in batch culture, while ≥ 160 AU ml⁻¹ was required to prevent biofilm growth. Co-culturing S. thermophilus B59671 and S. mutans UA159 also resulted in impaired biofilm growth. Thermophillin 110 was also shown inhibit additional S. mutans strains and commensal oral streptococci at higher concentrations (640-1280 AU ml⁻¹). These results suggest that thermophilin 110 could be used as a natural antimicrobial in oral care products and support the need for additional studies to assess the probiotic potential of S. thermophilus B59671.

Pre-formulation and delivery strategies for the development of bacteriocins as next generation antibiotics

Bacteriocins, a class of antimicrobial peptide produced by bacteria, may offer a potential alternative to traditional antibiotics, an important step towards mitigating the ever-increasing antimicrobial resistance crisis. They are active against a range of clinically relevant Gram-positive and Gram-negative bacteria. Bacteriocins have been discussed in the literature for over a century. Although they are used as preservatives in food, no medicine based on their antimicrobial activity exists on the market today. In order to formulate them into clinical antibiotics, pre-formulation studies on their biophysical and physicochemical properties that will influence their activity in vivo and their stability during manufacture must be elucidated. Thermal, pH and enzymatic stability of bacteriocins are commonly studied and regularly reported in the literature. Solubility, permeability and aggregation properties on the other hand are less frequently reported for many bacteriocins, which may contribute to their poor clinical progression. Promising cytotoxicity studies report that bacteriocins exhibit few cytotoxic effects on a variety of mammalian cell lines, at active concentrations. This review highlights the lack of quantitative data and in many cases even qualitative data, on bacteriocins' solubility, stability, aggregation, permeability and cytotoxicity. The formulation strategies that have been explored to date, proposed routes of administration, trends in in vitro/in vivo behaviour and efforts in clinical development are discussed. The future promise of bacteriocins as a new generation of antibiotics may require tailored local delivery strategies to fulfil their potential as a force to combat antimicrobial-resistant bacterial infections.

Current Applications of Bacteriocin

Bacteriocins are multifunctional, ribosomally produced, proteinaceous substances with pronounced antimicrobial activity at certain concentrations. They are produced by bacteria and certain members of archaea to inhibit the growth of similar or closely related bacterial strains. These molecules have antimicrobial activity against pathogenic and deteriorating bacteria, which justifies their biotechnological potential. They are classified into 3 major classes based on their structural and physicochemical properties: class I bacteriocin, class II bacteriocin, and class III bacteriocin. Bacteriocins inhibit the growth of target organisms by functioning primarily on the cell envelope and by affecting gene expression and protein production within cells. The use of bacteriocins has been reported for the following: food preservation, diverse therapeutic purposes such as treatment of peptic ulcer, spermicidal agent, and woman care, anticancerous agent, veterinary use, skincare, and oral care, and also for plant growth promotion in agriculture among others.

Inhibitory mechanism of BAC-IB17 against β-lactamase mediated resistance in methicillin-resistant Staphylococcus aureus and application as an oncolytic agent

Cancer remains a foremost cause of deaths worldwide, despite several advances in the medical science. The conventional chemotherapeutic methods are not only harmful for normal body cells but also become inactive due to the development of resistance by cancer cells. Therefore, the demand of safe anticancer agents is increasing and enforced the bottomless research on the bacteriocins. Several studies have reported the selective anticancer property of bacteriocins. Current research is the contribution to explore the exact mechanism of action and in vitro application of bacteriocin (BAC-IB17) as an oncolytic agent. In this study, β-lactamase mediated resistance of methicillin resistant Staphylococcus aureus (MRSA) was studied and inhibitory mechanism of MRSA by BAC-IB17 was investigated. Cytotoxic studies were conducted to analyze the anticancerous potential of BAC-IB17. Results revealed that BAC-IB17 inhibited the β-lactamase and produced profound effect on the membrane integrity of MRSA confirmed by scanning electron microscope (SEM). FTIR spectroscopic analysis revealed the changes in the functional groups of bacterial cells before and after treatment with BAC-IB17. BAC-IB17 also found anticancer in nature as it kills HeLa cell lines with the IC₅₀ value of 12.5 μg mL^-1 with no cytotoxic effect on normal cells at this concentration. This specific anticancer property of BAC-IB17 will make it a promising candidate for the treatment of cancer after further clinical trials. Moreover, BAC-IB17 may control MDR bacteria responsible for the secondary complications in cancer patients.

Synergistically-acting Enterocin LD3 and Plantaricin LD4 Against Gram-Positive and Gram-Negative Pathogenic Bacteria

The efficacy of antimicrobials is an important aspect during their applications in food and therapeutics. In this study, combination of two bacteriocins, enterocin LD3 and plantaricin LD4, was studied against two pathogenic bacteria, Staphylococcus aureus subsp. aureus ATCC25923 and Salmonella enterica subsp. enterica serovar Typhimurium ATCC13311 for increasing their potency and bactericidal activity. The minimal inhibitory concentrations (MICs) of enterocin LD3 and plantaricin LD4 against Staph. aureus subsp. aureus ATCC25923 were 180 and 220 μg/mL, whereas in combination, reduced to 115 μg/mL, respectively. The MICs of enterocin LD3 and plantaricin LD4 against Salm. enterica subsp. enterica serovar Typhimurium ATCC13311 were 240 and 320 μg/mL, respectively, whereas in combination, these were found to be 130 μg/mL, respectively. The fractional inhibitory concentration (FIC) indices calculated as 0.50 against Staph. aureus subsp. aureus ATCC25923 and 0.43 against Salm. enterica subsp. enterica serovar Typhimurium ATCC13311 were found to be ≤ 0.5 indicating the synergy. The isobologram showed MIC of combined bacteriocins falls below the plotted straight line further signifies synergy. The growth response of Staph. aureus subsp. aureus ATCC25923 and Salm. enterica subsp. enterica serovar Typhimurium ATCC13311 was significantly reduced in the presence of combined bacteriocins in comparison with their individual effects. The number of dead cells was higher as a result of combined effect as compared with their independent effect evidenced by fluorescent microscopy. Transmission electron microscopy (TEM) revealed the higher disruption of cell membrane in the combined bacteriocin-treated cells as compared with alone effects. The FTIR spectra of enterocin LD3-treated cells showed alteration at ~ 1,451.82 and ~ 1,094.30/cm corresponding to nucleic acids and phospholipids suggesting its interaction with cell membrane and nucleic acids. In contrast, plantaricin LD4-treated cells did not show such alterations suggesting plantaricin LD4 may kill target cells using other mechanism. Our data suggest that different mode of action of both bacteriocins results in division of labour and may be responsible for their synergistic activity against target cells. Similarly, the synergistic effect of bacteriocins was also observed against other pathogenic bacteria such as Proteus mirabilis ATCC43071, Pseudomonas aeruginosa ATCC27853 and Escherichia coli ATCC25922. These bacteriocins, therefore, act synergistically against target pathogens and may be applied in appropriate combinations for food safety and medical applications.

Bacteriocin encapsulation for food and pharmaceutical applications: advances in the past 20 years

The encapsulation of bacteriocins from lactic acid bacteria has involved several methods to protect them from unfavourable environmental conditions and incompatibilities. This review encompasses different methods for the encapsulation of bacteriocins and their applications in both food and pharmaceutical fields. Based on the bibliometric analysis of publications from well-reputed journals including different available patents during the period from 1996 to 2017, 135 articles and 60 patents were collected. Continent-wise contributions to the bacteriocins encapsulation research were carried out by America (52%), Asia (29%) and Europe (19%); with the United States of America, Brazil, Thailand and Italy the countries with major contributions. Till date, different methods proposed for encapsulation have been (i) Film coatings (50%), (ii) Liposomes (23%), (iii) Nanofibers (22%) and (iv) Nanoparticles (4%). Bacteriocins encapsulation methods frequently carried out in food protection (70%); while in the pharmaceutical field, 30% of the research was conducted on multi drug resistant therapy.

Streptococcus macedonicus strains isolated from traditional fermented milks: resistance to gastrointestinal environment and adhesion ability

In this study, Streptococcus macedonicus (S. macedonicus) strains were identified from Algerian traditional fermented milks (Lben and Rayeb). Important prerequisites of probiotic interest such as acidity, bile salts tolerance, and adhesion ability to epithelial cells were investigated. A combination of phenotypic (ability to grow on Bile Esculin Azide medium, BEA; on high salt content medium NaCl 6.5%; on alkaline medium pH 9.6) and genotypic approaches (16S rRNA, ITS genes sequencing and MLST technique) allowed to identify four genetically distinct strains of S. macedonicus. These four strains and two references, Streptococcus thermophilus LMD-9 and Lactobacillus rhamnosus GG (LGG), were tested for their capacity to survive at low pH values, and at different concentrations of an equimolar bile salts mixture (BSM). Two different cell lines, Caco-2 TC7 and HT29-MTX, were used for the adhesion study. The results show that S. macedonicus strains selected constitute a distinct genetic entity from the Greek strain S. macedonicus ACA-DC-198. They were able to survive up to pH 3 and could tolerate high concentrations of bile salts (10 mM), unlike LMD-9 and LGG strains. Our strains also display in vitro adhesion similar to the LGG strain on Caco-2 TC7 and higher adhesion than the LMD-9 strain to Caco-2 TC7 and HT29-MTX cell models. This first characterization allows considering S. macedonicus as a potential candidate for possible probiotic effects that need to be investigated.

Anti-staphylococcal activity of bacteriocins of food isolates Enterococcus hirae LD3 and Lactobacillus plantarum LD4 in pasteurized milk

Bacteriocins of Enterococcus hirae LD3 and Lactobacillus plantarum LD4 have been applied in milk for growth inhibition of Staphylococcus aureus. The enumeration of S. aureus cells in nutrient broth and milk was found log₁₀ 9.7 and 10.2 CFU/mL, respectively, whereas it was reduced with increasing concentration of bacteriocins suggesting loss of cell viability. The lethal concentration (LC₅₀) of enterocin LD3 and plantaricin LD4 against S. aureus was 160 and 220 µg/mL, respectively. Bacteriocin-treated cells were stained red with propidium iodide (PI) indicating dead cells further confirms bactericidal nature. The enterocin LD3-treated cells showed higher infrared absorbance at 1451.82 cm^- 1 corresponding to phospholipids suggesting membrane-acting nature of the bacteriocin. However, plantaricin LD4-treated cells did not show such alterations suggesting different mode of action. Both bacteriocins caused disruption and shrinkage of target cells, and leakage of intracellular contents as observed in transmission electron microscope (TEM). The present study suggests killing of S. aureus in milk, therefore, enterocin LD3 and plantaricin LD4 may be applied in biopreservation of milk and related food products.

Microbial production of bacteriocins: Latest research development and applications

Bacteriocins are low molecular weight peptides secreted by the predator bacterial cells to kill sensitive cells present in the same ecosystem competing for food and other nutrients. Exceptionally few bacteriocins along with their native antibacterial property also exhibit additional anti-viral and anti-fungal properties. Bacteriocins are generally produced by Gm+, Gm- and archaea bacteria. Bacteriocins from Gm + bacteria especially from lactic acid bacteria (LAB) have been thoroughly investigated considering their great biosafety and broad industrial applications. LAB expressing bacteriocins were isolated from fermented milk and milk products, rumen of animals and soil using deferred antagonism assay. Nisin is the only bacteriocin that has got FDA approval for application as a food preservative, which is produced by Lactococcus lactis subsp. Lactis. Its crystal structure explains that its antimicrobial properties are due to the binding of NH₂ terminal to lipid II molecule inhibiting the peptidoglycan synthesis and carboxy terminal forming pores in bacterial cell membrane leading to cell lysis. The hinge region connecting NH₂ and carboxy terminus has been mutated to generate mutant variants with higher antimicrobial activity. In a 50 ton fermentation of the mutant strain 3807 derived from L. lactis subsp. lactis ATCC 11454, 9,960 IU/mL of nisin was produced. Currently, high purity of nisin (>99%) is very expensive and hardly commercially available. Development of more advanced tools for cost-effective separation and purification of nisin would be commercially attractive. Chemical synthesis and heterologous expression of bacteriocins ended in low yields of pure proteins. At present, bacteriocins are almost solely applied in food industries, but they have a great potential to be used in other fields such as feeds, organic fertilizers, environmental protection and personal care products. The future of bacteriocins is largely dependent on getting FDA approval for use of other bacteriocins in addition to nisin to promote the research and applications.

Whole-Genome Sequences of Three Streptococcus macedonicus Strains Isolated from Italian Cheeses in the Veneto Region

We report here the genome sequences of three Streptococcus macedonicus strains isolated from different cheeses in the Veneto region of Italy. The presented data aim at increasing the scarce genomic information available for this species, which is frequently encountered in fermented foods and appears to be a promising technological microorganism.

Antibacterial effects of Lactobacillus and bacteriocin PLNC8 αβ on the periodontal pathogen Porphyromonas gingivalis

Background

The complications in healthcare systems associated with antibiotic-resistant microorganisms have resulted in an intense search for new effective antimicrobials. Attractive substances from which novel antibiotics may be developed are the bacteriocins. These naturally occurring peptides are generally considered to be safe and efficient at eliminating pathogenic bacteria. Among specific keystone pathogens in periodontitis, Porphyromonas gingivalis is considered to be the most important pathogen in the development and progression of chronic inflammatory disease. The aim of the present study was to investigate the antimicrobial effects of different Lactobacillus species and the two-peptide bacteriocin PLNC8 αβ on P. gingivalis.

Results

Growth inhibition of P. gingivalis was obtained by viable Lactobacillus and culture media from L. plantarum NC8 and 44048, but not L. brevis 30670. The two-peptide bacteriocin from L. plantarum NC8 (PLNC8 αβ) was found to be efficient against P. gingivalis through binding followed by permeabilization of the membranes, using Surface plasmon resonance analysis and DNA staining with Sytox Green. Liposomal systems were acquired to verify membrane permeabilization by PLNC8 αβ. The antimicrobial activity of PLNC8 αβ was found to be rapid (1 min) and visualized by TEM to cause cellular distortion through detachment of the outer membrane and bacterial lysis.

Conclusion

Soluble or immobilized PLNC8 αβ bacteriocins may be used to prevent P. gingivalis colonization and subsequent pathogenicity, and thus supplement the host immune system against invading pathogens associated with periodontitis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-016-0810-8) contains supplementary material, which is available to authorized users.

On bacteriocin delivery systems and potential applications

Bacteriocins are antimicrobial peptides produced by a variety of bacteria. These peptides can act as antibiotic synergists or alternatives to enhance the therapeutic effects of current infection treatments and decrease the prevalence of resistant strains. Two bacteriocins, namely nisin and pediocin PA-1, are currently being used by the food industry; however, the introduction of these and others into the biomedical industry, and further development of food applications, have been challenged by the slow development of reliable delivery systems. For bacteriocins, these systems rely on novel and pre-existing technologies. Many essential variables need to be accounted for to formulate successful delivery methods. In this review, documented and potential bacteriocin delivery systems are examined, with special attention paid to how those systems are being implemented in the food and medical industries.

FTIR spectroscopic evaluation of changes in the cellular biochemical composition of the phytopathogenic fungus Alternaria alternata induced by extracts of some Greek medicinal and aromatic plants

In this study, the biological activity of aquatic extracts of selected Greek medicinal and aromatic plants to the phytopathogenic fungus Alternaria alternata was investigated. Lamiaceae species (Hyssopus officinalis L., Melissa officinalis L., Origanum dictamnus L., Origanum vulgare L. and Salvia officinalis L.) were found to enhance significantly the mycelium growth whereas Crocus sativus appears to inhibit it slightly. M. officinalis and S. officinalis caused the highest stimulation in mycelium growth (+97%) and conidia production (+65%) respectively. In order to further investigate the bioactivity of plant extracts to A. alternata, we employed Fourier Transform Infrared Spectroscopy (FTIR). Differences of original spectra were assigned mainly to amides of proteins. The second derivative transformation of spectra revealed changes in spectral regions corresponding to absorptions of the major cellular constituents such as cell membrane and proteins. Principal component analysis of the second derivative transformed spectra confirmed that fatty acids of the cell membranes, amides of proteins and polysaccharides of the cell wall had the major contribution to data variation. FTIR band area ratios were found to correlate with fungal mycelium growth.

Probiotics in fish and shellfish culture: immunomodulatory and ecophysiological responses

Aquaculture is emerging as one of the most viable and promising enterprises for keeping pace with the surging need for animal protein, providing nutritional and food security to humans, particularly those residing in regions where livestock is relatively scarce. With every step toward intensification of aquaculture practices, there is an increase in the stress level in the animal as well as the environment. Hence, disease outbreak is being increasingly recognized as one of the most important constraints to aquaculture production in many countries, including India. Conventionally, the disease control in aquaculture has relied on the use of chemical compounds and antibiotics. The development of non-antibiotic and environmentally friendly agents is one of the key factors for health management in aquaculture. Consequently, with the emerging need for environmentally friendly aquaculture, the use of alternatives to antibiotic growth promoters in fish nutrition is now widely accepted. In recent years, probiotics have taken center stage and are being used as an unconventional approach that has numerous beneficial effects in fish and shellfish culture: improved activity of gastrointestinal microbiota and enhanced immune status, disease resistance, survival, feed utilization and growth performance. As natural products, probiotics have much potential to increase the efficiency and sustainability of aquaculture production. Therefore, comprehensive research to fully characterize the intestinal microbiota of prominent fish species, mechanisms of action of probiotics and their effects on the intestinal ecosystem, immunity, fish health and performance is reasonable. This review highlights the classifications and applications of probiotics in aquaculture. The review also summarizes the advancement and research highlights of the probiotic status and mode of action, which are of great significance from an ecofriendly, sustainable, intensive aquaculture point of view.

Effect of exogenous factors on bacteriocin production from Lactobacillus paracasei J23 by using a resting cell system

A resting cell system was developed for bacteriocin Lac-B23 production from Lactobacillus paracasei J23. The resting cell medium contained (g/L): Glucose 20, Sodium acetate 5.0, MnSO₄ 0.25 MgSO₄ 0.5, Ammoniumhydrogencitrate 1.0, KH₂PO₄ 1.0. The resting cell incubation time and temperature were 20 h and 37 °C and the effects of exogenous factors, including amino acids, glycerol, pyruvic acid, and α-ketoglutaric acid were investigated. Cys and Gly could stimulate the production of bacteriocin, while no stimulus effect was observed for Glu, Tyr and Ala. Glycerol and pyruvic acid increased bacteriocin production and the optimum concentrations were 1% and 30 g/L, respectively. Bacteriocin could act as an inducer of its own biosynthesis. These findings are of importance for the further study of bacteriocin biosynthesis regulation and for the improvement of bacteriocin production yields.