Bacteriocins: Properties and potential use as antimicrobials

A variety of bacteriocins originate from lactic acid bacteria, which have recently been modified by scientists. Many strains of lactic acid bacteria related to food groups could produce bacteriocins or antibacterial proteins highly effective against foodborne pathogens such as Staphylococcus aureus, Pseudomonas fluorescens, P. aeruginosa, Salmonella typhi, Shigella flexneri, Listeria monocytogenes, Escherichia coli O157:H7, and Clostridium botulinum. A wide range of bacteria belonging primarily to the genera Bifidobacterium and Lactobacillus have been characterized with different health‐promoting attributes. Extensive studies and in‐depth understanding of these antimicrobials mechanisms of action could enable scientists to determine their production in specific probiotic lactic acid bacteria, as they are potentially crucial for the final preservation of functional foods or for medicinal applications. In this review study, the structure, classification, mode of operation, safety, and antibacterial properties of bacteriocins as well as their effect on foodborne pathogens and antibiotic‐resistant bacteria were extensively studied.

Development of a new antimicrobial concept for boar semen preservation based on bacteriocins

The conventional storage temperature of 16-18 °C provides optimal conditions for the preservation of boar sperm quality, which are extremely cold sensitive cells. On the other hand, however, it requires the addition of antibiotics to inhibit bacterial growth. Rising numbers of antibiotic resistant bacteria call for alternatives to this conventional storing method. As potential alternative, three different bacteriocin candidates with known bacteriolytic activity against E. coli were examined on possible negative effects concerning the sperm quality and on their impact on bacterial growth of E. coli ILSH 02692 in BTS-extended semen w/o antibiotics. Although the lower concentrations (0.01 and 0.25%) of all bacteriocins did not show any impact on the quality of the semen, the higher concentrations (0.5 and 1.0%) of two bacteriocins led to a significant (P < 0.05) reduction in several sperm quality characteristics. The bacteriocin 860/1c after AMS/dialysis did not affect the sperm quality in any of the tested concentrations and in all tested extenders (BTS, MIII, Androstar Premium and Androhep all w/o antibiotics) at 16 °C as well as at 6 °C. This bacteriocin reduced growth of E. coli ILSH 02692 in BTS-extended semen by 50% compared to the control w/o bacteriocin. Furthermore, a preliminary insemination trial indicated no impact of the selected bacteriocin on fertility. These promising results show that the application of bacteriocins in liquid-preserved semen is a feasible possibility in the future.

Molecular insights into probiotic mechanisms of action employed against intestinal pathogenic bacteria

Gastrointestinal (GI) diseases, and in particular those caused by bacterial infections, are a major cause of morbidity and mortality worldwide. Treatment is becoming increasingly difficult due to the increase in number of species that have developed resistance to antibiotics. Probiotic lactic acid bacteria (LAB) have considerable potential as alternatives to antibiotics, both in prophylactic and therapeutic applications. Several studies have documented a reduction, or prevention, of GI diseases by probiotic bacteria. Since the activities of probiotic bacteria are closely linked with conditions in the host's GI-tract (GIT) and changes in the population of enteric microorganisms, a deeper understanding of gut-microbial interactions is required in the selection of the most suitable probiotic. This necessitates a deeper understanding of the molecular capabilities of probiotic bacteria. In this review, we explore how probiotic microorganisms interact with enteric pathogens in the GIT. The significance of probiotic colonization and persistence in the GIT is also addressed.

Genetic Analysis of Mutacin B-Ny266, a Lantibiotic Active against Caries Pathogens

Bacteriocins are ribosomally synthesized proteinaceous antibacterial peptides. They selectively interfere with the growth of other bacteria. The production and secretion of bacteriocins confer a distinct ecological advantage to the producer in competing against other bacteria that are present in the same ecological niche. Streptococcus mutans, a significant contributor to the development of dental caries, is one of the most prolific producers of bacteriocins, known as mutacins in S. mutans In this study, we characterized the locus encoding mutacin B-Ny266, a lantibiotic with a broad spectrum of activity. The chromosomal locus is composed of six predicted operon structures encoding proteins involved in regulation, antimicrobial activity, biosynthesis, modification, transport, and immunity. Mutacin B-Ny266 was purified from semisolid cultures, and two inhibitory peptides, LanA and LanA', were detected. Both peptides were highly modified. Such modifications include dehydration of serine and threonine and the formation of a C-terminal aminovinyl-cysteine (AviCys) ring. While LanA peptide alone is absolutely required for antimicrobial activity, the presence of LanA' enhanced the activity of LanA, suggesting that B-Ny266 may function as a two-peptide lantibiotic. The activation of lanAA' expression is most likely controlled by the conserved two-component system NsrRS, which is activated by LanA peptide but not by LanA'. The chromosomal locus encoding mutacin B-Ny266 was not universally conserved in all sequenced S. mutans genomes. Intriguingly, the genes encoding LanAA' peptides were restricted to the most invasive serotypes of S. mutans IMPORTANCE Although dental caries is largely preventable, it remains the most common and costly infectious disease worldwide. Caries is initiated by the presence of dental plaque biofilm that contains Streptococcus mutans, a species extensively characterized by its role in caries development and formation. S. mutans deploys an arsenal of strategies to establish itself within the oral cavity. One of them is the production of bacteriocins that confer a competitive advantage by targeting and killing closely related competitors. In this work, we found that mutacin B-Ny266 is a potent lantibiotic that is effective at killing a wide array of oral streptococci, including nearly all S. mutans strains tested. Lantibiotics produced by oral bacteria could represent a promising strategy to target caries pathogens embedded in dental plaque biofilm.

Anti-infective activities of lactobacillus strains in the human intestinal microbiota: from probiotics to gastrointestinal anti-infectious biotherapeutic agents

A vast and diverse array of microbial species displaying great phylogenic, genomic, and metabolic diversity have colonized the gastrointestinal tract. Resident microbes play a beneficial role by regulating the intestinal immune system, stimulating the maturation of host tissues, and playing a variety of roles in nutrition and in host resistance to gastric and enteric bacterial pathogens. The mechanisms by which the resident microbial species combat gastrointestinal pathogens are complex and include competitive metabolic interactions and the production of antimicrobial molecules. The human intestinal microbiota is a source from which Lactobacillus probiotic strains have often been isolated. Only six probiotic Lactobacillus strains isolated from human intestinal microbiota, i.e., L. rhamnosus GG, L. casei Shirota YIT9029, L. casei DN-114 001, L. johnsonii NCC 533, L. acidophilus LB, and L. reuteri DSM 17938, have been well characterized with regard to their potential antimicrobial effects against the major gastric and enteric bacterial pathogens and rotavirus. In this review, we describe the current knowledge concerning the experimental antibacterial activities, including antibiotic-like and cell-regulating activities, and therapeutic effects demonstrated in well-conducted, placebo-controlled, randomized clinical trials of these probiotic Lactobacillus strains. What is known about the antimicrobial activities supported by the molecules secreted by such probiotic Lactobacillus strains suggests that they constitute a promising new source for the development of innovative anti-infectious agents that act luminally and intracellularly in the gastrointestinal tract.

Antibacterial Peptides: Opportunities for the Prevention and Treatment of Dental Caries

Dental caries is a multifactorial disease that is a growing and costly global health concern. The onset of disease is a consequence of an ecological imbalance within the dental plaque biofilm that favors specific acidogenic and aciduric caries pathogens, namely Streptococcus mutans and Streptococcus sobrinus. It is now recognized by the scientific and medical community that it is neither possible nor desirable to totally eliminate dental plaque. Conversely, the chemical biocides most commonly used for caries prevention and treatment indiscriminately attack all plaque microorganisms. These treatments also suffer from other drawbacks such as bad taste, irritability, and staining. Furthermore, the public demand for safe and natural personal hygiene products continues to rise. Therefore, there are opportunities that exist to develop new strategies for the treatment of this disease. As an alternative to conventional antibiotics, antibacterial peptides have been explored greatly over the last three decades for many different therapeutic uses. There are currently tens of hundreds of antibacterial peptides characterized across the evolutionary spectrum, and among these, many demonstrate physical and/or biological properties that may be suitable for a more targeted approach to the selective control or elimination of putative caries pathogens. Additionally, many peptides, such as nisin, are odorless, colorless, and tasteless and do not cause irritation or staining. This review focuses on antibacterial peptides for their potential role in the treatment and prevention of dental caries and suggests candidates that need to be explored further. Practical considerations for the development of antibacterial peptides as oral treatments are also discussed.

Characterization of bacterial antimicrobial peptides active against Campylobacter jejuni

Campylobacter jejuni is one of the major causes of food poisoning, often resulting from the consumption of improperly cooked poultry products. The emergence of C. jejuni strains resistant to conventional antibiotics necessitates the evaluation of other possible treatments or preventative measures to minimize the impact and prevalence of infections. Antimicrobial peptides produced by bacteria have begun to emerge as a potential means of decreasing the levels of C. jejuni in poultry, thereby limiting Campylobacter contamination in associated food products. A number of bacteriocins produced by Gram-positive bacteria have unexpectedly been described as having antimicrobial activity against the Gram-negative C. jejuni. Additionally, some nonribosomal lipopeptides produced by Bacillus and Paenibacillus spp. show efficacy against this pathogen. This review will describe the bacterial antimicrobial peptides reported to be active against C. jejuni, with an emphasis on the characterization of their primary structures. However, for many of these peptides, little is known about their amino acid sequences and structures. Furthermore, there are unusual inconsistencies associated with the reported amino acid sequences for several of the more well-studied bacteriocins. Clarifying the chemical nature of these promising antimicrobial peptides is necessary before their potential utility for livestock protection from C. jejuni can be fully explored. Once these peptides are better characterized, they may prove to be strong candidates for minimizing the impact of Campylobacter on human health.

Bacteriocins and other bioactive substances of probiotic lactobacilli as biological weapons against Neisseria gonorrhoeae

In the search of new antimicrobial agents against Neisseria gonorrhoeae, the bacteriocins-producing probiotic lactobacilli deserve special attention. The inhibitory effects of biosubstances such as organic acids, hydrogen peroxide and each bacteriocin-like inhibitory substance (BLIS) L23 and L60 on the growth of different gonococcal strains were investigated. Different non-treated and treated cell-free supernatants of two probiotic lactobacilli containing these metabolites were used. The aims of this work were (i) to evaluate the antimicrobial activity of the biosubstances produced by two probiotic lactobacilli, estimating the proportion in which each of them is responsible for the inhibitory effect, (ii) to define their minimum inhibitory concentrations (MICs) and, (iii) to determine the potential interactions between these biosubstances against N. gonorrhoeae. The main antimicrobial metabolites were the BLIS-es L23 and L60 in comparison with other biosubstances. Proportionally, their contributions to the inhibition on the gonococcal growth were 87.28% and 80.66%, respectively. The MIC values of bacteriocins were promising since these substances, when diluted, showed considerable inhibitory activity for all gonococci. In the interaction between bacteriocins, 100% of synergism was found on the gonococcal growth. In summary, this study indicates that both L23 and L60 could potentially serve to design new bioproducts against N. gonorrhoeae.

Conformation of dehydropentapeptides containing four achiral amino acid residues - controlling the role of L-valine

Structural studies of pentapeptides containing an achiral block, built from two dehydroamino acid residues (Δ^ZPhe and ΔAla) and two glycines, as well as one chiral L-Val residue were performed using NMR spectroscopy. The key role of the L-Val residue in the generation of the secondary structure of peptides is discussed. The obtained results suggest that the strongest influence on the conformation of peptides arises from a valine residue inserted at the C-terminal position. The most ordered conformation was found for peptide Boc-Gly-ΔAla-Gly-Δ^ZPhe-Val-OMe (3), which adopts a right-handed helical conformation.

'Bac' to the future: bioengineering lantibiotics for designer purposes

Bacteriocins are bacterially produced peptides or proteins that inhibit the growth of other bacterial strains. They can have a broad (effective against multiple genera) or narrow (effective against specific species) spectrum of activity. The diversity of bacteriocins found in Nature, in terms of both spectrum of activity and physiochemical properties, offers the possibility of multiple applications in the food and pharmaceutical industries. However, traditional screening strategies may not provide a sufficient range of natural molecules with specifically desired properties. Research suggests that bioengineering of existing inhibitors has the potential to address this issue, extending the application of natural bacteriocins for use in novel settings and against different targets. In the present paper, we discuss the successful implementation of bioengineering strategies to alter and even improve the functional characteristics of a bacteriocin, using the prototypical lantibiotic nisin as an example. Additionally, we describe the recent use of the nisin-modification machinery in vivo to enhance the properties of medically significant peptides.

Bacteriocins - a viable alternative to antibiotics?

Solutions are urgently required for the growing number of infections caused by antibiotic-resistant bacteria. Bacteriocins, which are antimicrobial peptides produced by certain bacteria, might warrant serious consideration as alternatives to traditional antibiotics. These molecules exhibit significant potency against other bacteria (including antibiotic-resistant strains), are stable and can have narrow or broad activity spectra. Bacteriocins can even be produced in situ in the gut by probiotic bacteria to combat intestinal infections. Although the application of specific bacteriocins might be curtailed by the development of resistance, an understanding of the mechanisms by which such resistance could emerge will enable researchers to develop strategies to minimize this potential problem.

Biology and genome sequence of Streptococcus mutans phage M102AD

M102AD is the new designation for a Streptococcus mutans phage described in 1993 as phage M102. This change was necessitated by the genome analysis of another S. mutans phage named M102, which revealed differences from the genome sequence reported here. Additional host range analyses confirmed that S. mutans phage M102AD infects only a few serotype c strains. Phage M102AD adsorbed very slowly to its host, and it cannot adsorb to serotype e and f strains of S. mutans. M102AD adsorption was blocked by c-specific antiserum. Phage M102AD also adsorbed equally well to heat-treated and trypsin-treated cells, suggesting carbohydrate receptors. Saliva and polysaccharide production did not inhibit plaque formation. The genome of this siphophage consisted of a linear, double-stranded, 30,664-bp DNA molecule, with a GC content of 39.6%. Analysis of the genome extremities indicated the presence of a 3'-overhang cos site that was 11 nucleotides long. Bioinformatic analyses identified 40 open reading frames, all in the same orientation. No lysogeny-related genes were found, indicating that phage M102AD is strictly virulent. No obvious virulence factor gene candidates were found. Twelve proteins were identified in the virion structure by mass spectrometry. Comparative genomic analysis revealed a close relationship between S. mutans phages M102AD and M102 as well as with Streptococcus thermophilus phages. This study also highlights the importance of conducting research with biological materials obtained from recognized microbial collections.

Leukocytic responses and intestinal mucin dynamics of broilers protected with Enterococcus faecium EF55 and challenged with Salmonella Enteritidis

The protective effect of Enterococcus faecium EF55 in chickens challenged with Salmonella enterica serovar Enteritidis phage type 4 (SE PT4) was assessed. The antibacterial effect on the bacterial microflora in the small intestine in relation to white blood cell count, phenotyping of peripheral blood and intestinal lymphocytes, functional activity of lymphocytes and phagocytes and mucin quantitation were investigated. Day-old chicks (85) were randomly divided into four groups. The probiotic group (EF) and Salmonella+probiotic group (EFSE) received E. faecium EF55 (10(9) CFU - 3 g/group/day) for 21 days. The Salmonella group (SE) and EFSE group were infected with Salmonella Enteritidis (10(8) CFU in 0.2 ml PBS) in a single dose per os on day four of the experiment. The control group chicks (C) were fed a commercial diet without added bacteria. Supplementation of EF55 in the diet of the chickens in the EFSE group, challenged with S. Enteritidis, caused the density of the intestinal mucin layer to increase significantly in non-specific regions (duodenum and jejunum), but decrease significantly in target regions (caeca) for S. Enteritidis. Probiotic treatment also appeared to result in a significantly higher number of lymphocytes in peripheral blood and a tendency to increase CD3, CD4, CD8, and IgM positive cells 3 days post-infection with S. Enteritidis. The results demonstrated an antibacterial effect and suggested that EF55 had a moderating effect on intestinal mucin production and leukocytic response in the early phase of S. Enteritidis infection.

Discovery and development of lantibiotics; antimicrobial agents that have significant potential for medical application

INTRODUCTION

Antimicrobial drug resistance is driving the need for novel therapeutics. Amongst the most promising antibacterial agents that are being investigated as replacements for current therapeutic antibiotics are antibacterial peptides, such as the lanthionine-containing peptide antibiotics (lantibiotics).

AREAS COVERED

This review focuses on the current methods used for discovery of potentially exploitable lantibiotics for medical applications and discusses relevant recent innovations that will have a positive impact on the discovery of useful lantibiotics.

EXPERT OPINION

Recent technological advances in a number of fields mean that increased research into the identification and characterisation of new lantibiotics is feasible. We need to increase our understanding of the various mechanisms of antibacterial action exhibited by lantibiotics and apply this knowledge to peptide engineering or novel practical applications. The advent of next-generation sequencing approaches now negate the need for extensive reverse genetics and employment of bioinformatics approaches is greatly assisting the identification of potentially useful inhibitors in the genomes of a range of clinically significant bacteria. These advances in genetic analysis and engineering will facilitate increased exploitation of lantibiotics in medical therapy.

Bioengineering of a Nisin A-producing Lactococcus lactis to create isogenic strains producing the natural variants Nisin F, Q and Z

Nisin is the prototypical example of the lantibiotic family of antimicrobial peptides and has been employed as a food preservative for over half a century. It has also attracted attention due to its potency against a number of multidrug‐resistant clinical pathogens. Nisin A is the originally isolated form of Nisin and a further five natural variants have been described which differ by up to 10 amino acids (of 34 in total in Nisin A). Nisins A, Z, F and Q are produced by Lactococcus lactis, while Nisins U and U2 are produced by Streptococcus sp. In this study we bioengineered the nisA gene of a Nisin A producer to generate genes encoding Nisins Z, F, Q, U and U2. We determined that while active Nisin Z, F and Q can be produced against this genetic background, active forms of Nisin U and U2 are not generated. Minimum inhibitory concentration studies with Nisin A, Z, F and Q variants against a series of different clinically significant pathogens establish differences in specific activities against selected targets. Nisin F was most impressive, being the most active, or one of the most active, against the MRSA strain ST 525, EC 676, EC 725, VISA 22900, VISA 22781, hVISA 35197, Staphylococcus aureus 8325‐4 and L. lactis HP. Nisin Z was most active against ST 299, hVISA 32683 and, together with Nisin F, HP but had contrastingly poor activity against ST 525, EC 676 and 8325‐4. Nisin F, Q and A exhibited similar potency against VISA 22900. This was the only target against which Nisin Q and Nisin A were among the most active variants.

Pseudomonads from rabbits and their sensitivity to antibiotics and natural antimicrobials

The sensitivity/resistance of Pseudomonas spp. isolated from rabbits gastrointestinal tract and faeces to antibiotics, enterocins and herbal extracts was tested in this study. The counts of Pseudomonas-like bacteria were higher in faeces (3.23-6.16 log(10) CFU/mL/g) than in caecum (1.36-4.08 log(10) CFU/mL/g). Nineteen isolates (16 faecal, 3 caecal) were oxidase positive. The strains were allotted by phenotypization to Pseudomonas spp., Brevundimonas diminuta and Brevundimonasvesicularis. High percentage of resistant strains was observed to all antibiotics. The tested strains were more susceptible to natural substances, mainly to plant extracts oregano (95%) and sage extracts (58%). Comparing the antibacterial effect of antibiotics and enterocins against rabbits pseudomonads, enterocins were more effective; the strongest inhibitory activity was determined in the case of partially purified enterocins PPBs EF2019, EK13 and EF55.

The dual role of bacteriocins as anti- and probiotics

Bacteria employed in probiotic applications help to maintain or restore a host's natural microbial floral. The ability of probiotic bacteria to successfully outcompete undesired species is often due to, or enhanced by, the production of potent antimicrobial toxins. The most commonly encountered of these are bacteriocins, a large and functionally diverse family of antimicrobials found in all major lineages of Bacteria. Recent studies reveal that these proteinaceous toxins play a critical role in mediating competitive dynamics between bacterial strains and closely related species. The potential use of bacteriocin-producing strains as probiotic and bioprotective agents has recently received increased attention. This review will report on recent efforts involving the use of such strains, with a particular focus on emerging probiotic therapies for humans, livestock, and aquaculture.

Capacity of human nisin- and pediocin-producing lactic Acid bacteria to reduce intestinal colonization by vancomycin-resistant enterococci

This study demonstrated the capacity of bacteriocin-producing lactic acid bacteria (LAB) to reduce intestinal colonization by vancomycin-resistant enterococci (VRE) in a mouse model. Lactococcus lactis MM19 and Pediococcus acidilactici MM33 are bacteriocin producers isolated from human feces. The bacteriocin secreted by P. acidilactici is identical to pediocin PA-1/AcH, while PCR analysis demonstrated that L. lactis harbors the nisin Z gene. LAB were acid and bile tolerant when assayed under simulated gastrointestinal conditions. A well diffusion assay using supernatants from LAB demonstrated strong activity against a clinical isolate of VRE. A first in vivo study was done using C57BL/6 mice that received daily intragastric doses of L. lactis MM19, P. acidilactici MM33, P. acidilactici MM33A (a pediocin mutant that had lost its ability to produce pediocin), or phosphate-buffered saline (PBS) for 18 days. This study showed that L. lactis and P. acidilactici MM33A increased the concentrations of total LAB and anaerobes while P. acidilactici MM33 decreased the Enterobacteriaceae populations. A second in vivo study was done using VRE-colonized mice that received the same inocula as those in the previous study for 16 days. In L. lactis-fed mice, fecal VRE levels 1.73 and 2.50 log(10) CFU/g lower than those in the PBS group were observed at 1 and 3 days postinfection. In the P. acidilactici MM33-fed mice, no reduction was observed at 1 day postinfection but a reduction of 1.85 log(10) CFU/g was measured at 3 days postinfection. Levels of VRE in both groups of mice treated with bacteriocin-producing LAB were undetectable at 6 days postinfection. No significant difference in mice fed the pediocin-negative strain compared to the control group was observed. This is the first demonstration that human L. lactis and P. acidilactici nisin- and pediocin-producing strains can reduce VRE intestinal colonization.

Alternative mechanisms of action of cationic antimicrobial peptides on bacteria

Cationic antimicrobial peptides are a novel type of antibiotic offering much potential in the treatment of microbial-related diseases. They offer many advantages for commercial development, including a broad spectrum of action and modest size. However, despite the identification or synthetic production of thousands of such peptides, the mode of action remains elusive, except for a few examples. While the dogma for the mechanism of action of antimicrobial peptides against bacteria is believed to be through pore formation or membrane barrier disruption, some peptides clearly act differently and other intracellular target sites have been identified. This article presents an updated review of how cationic antimicrobial peptides are able to affect bacterial killing, with a focus on internal targets.

Bacteriocins reduce Campylobacter colonization and alter gut morphology in turkey poults

Campylobacter is a leading cause of food-borne illness in the United States. Recent evidence has demonstrated that bacteriocins produced by Bacillus circulans and Paenibacillus polymyxa reduce cecal Campylobacter colonization in broiler chickens infected with Campylobacter jejuni. As Campylobacter coli is the most prevalent Campylobacter isolate recovered in turkeys, the objectives of the present study were to evaluate the efficacy of these bacteriocins against C. coli colonization and their influence on the gastrointestinal architecture of young turkeys. In 3 separate trials, a total of 135 day-of-hatch poults (n = 45/trial) were orally challenged on d 3 with approximately 10(6) cfu of a mixture of 3 C. coli isolates. Immediately before bacteriocin treatment (d 10), cecal Campylobacter concentrations averaged 1.1 x 10(7) cfu/ g of cecal contents (n = 15/trial). On d 10 to 12 posthatch, 2 bacteriocin treatment groups were given free access to feed supplemented with purified, microencapsulated bacteriocins, whereas the positive control treatment group had access to untreated feed (n = 10/treatment group per trial). At the end of the 3-d dosing period, ceca and duodenal loops were collected for analysis. In each of the 3 separate trials, treatment with bacteriocin eliminated detectable ceca Campylobacter concentrations (detection limit, 1 x 10(2) cfu/g of cecal contents) vs. controls (1.0 x 106 cfu of Campylobacter/g of cecal contents). Duodenum crypt depth and goblet cell numbers were also reduced in turkeys treated with either bacteriocin vs. controls (P < 0.05). The dynamic reduction in crypt depth and goblet cell density in turkeys dosed with bacteriocin may provide clues to how bacteriocins inhibit enteric Campylobacter.

An alternative bactericidal mechanism of action for lantibiotic peptides that target lipid II

Lantibiotics are polycyclic peptides containing unusual amino acids, which have binding specificity for bacterial cells, targeting the bacterial cell wall component lipid II to form pores and thereby lyse the cells. Yet several members of these lipid II-targeted lantibiotics are too short to be able to span the lipid bilayer and cannot form pores, but somehow they maintain their antibacterial efficacy. We describe an alternative mechanism by which members of the lantibiotic family kill Gram-positive bacteria by removing lipid II from the cell division site (or septum) and thus block cell wall synthesis.

Mutacin H-29B is identical to mutacin II (J-T8)

BACKGROUND

Streptococcus mutans produces bacteriocins named mutacins. Studies of mutacins have always been hampered by the difficulties in obtaining active liquid preparations of these substances. Some of them were found to be lantibiotics, defined as bacterial ribosomally synthesised lanthionine-containing peptides with antimicrobial activity. The goal of this study was to produce and characterize a new mutacin from S. mutans strain 29B, as it shows a promising activity spectrum against current human pathogens.

RESULTS

Mutacin H-29B, produced by S. mutans strain 29B, was purified by successive hydrophobic chromatography from a liquid preparation consisting of cheese whey permeate (6% w/v) supplemented with yeast extract (2%) and CaCO3 (1%). Edman degradation revealed 24 amino acids identical to those of mutacin II (also known as J-T8). The molecular mass of the purified peptide was evaluated at 3246.08 +/- 0.1 Da by MALDI-TOF MS.

CONCLUSION

A simple procedure for production and purification of mutacins along with its characterization is presented. Our results show that the amino acid sequence of mutacin H-29B is identical to the already known mutacin II (J-T8) over the first 24 residues. S. mutans strains of widely different origins may thus produce very similar bacteriocins.

In vivo activity of mutacin B-Ny266

OBJECTIVES

The objective of this study was to assess the in vivo activity of mutacin B-Ny266 (a bacteriocin produced by Streptococcus mutans) in order to eventually use it as an antibiotic.

METHODS

Intraperitoneal infection was induced with a methicillin-susceptible Staphylococcus aureus strain in mice. Some of the mice were simultaneously injected intraperitoneally with mutacin B-Ny266, some with the vehicle only and some with vancomycin.

RESULTS

While there was 70 and 100% mortality in the control groups of mice, no mortality was observed in the mice injected with vancomycin or mutacin B-Ny266.

CONCLUSIONS

The results presented here show, for the first time, the in vivo efficacy of a mutacin (B-Ny266) against an experimental intraperitoneal infection by S. aureus in a mouse model.

Improved methods for mutacin detection and production

Studies of mutacins have always been hampered by the difficulties in obtaining active liquid preparations of these substances. In order to be commercially produced, good mutacin yields have to be obtained, preferably in inexpensive media. The results presented here indicate that mutacins can be produced in supplemented cheese whey permeate. The influence of carbon and nitrogen supplements on mutacin production varied according to the producer strain. The use of CaCO3 as a buffer in batch cultures resulted in improved yields of mutacin in the supernatants. Antimicrobial activity assays were improve by acidification of the diluent (pH 2) and were less variable in peptone water (0.5%). The culture medium consisting of cheese whey permeate (6% w/v), yeast extract (2% w/v) and CaCO3 (1% w/v) was found to be an inexpensive medium for the efficient production of mutacins.

Antagonism of Helicobacter pylori by bacteriocins of lactic acid bacteria

Antimicrobial activity of seven bacteriocins produced by lactic acid bacteria against Helicobacter pylori strains (ATCC 43504, Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH [DSM] 4867, DSM 9691, and DSM 10242) was investigated in vitro using a broth microdilution assay. The bacteriocins chosen for the study were nisin A; lacticins A164, BH5, JW3, and NK24; pediocin PO2; and leucocin K. Antimicrobial activity of the bacteriocins varied among the H. pylori strains tested, of which strain ATCC 43504 was the most tolerant. Among the bacteriocins tested, lacticins A164 and BH5 produced by Lactococcus lactis subsp. lactis A164 and L. lactis BH5, respectively, showed the strongest antibacterial activity against H. pylori strains. MICs of the lacticins against H. pylori strains, when assessed by the critical dilution micromethod, ranged from 0.097 to 0.390 mg/liter (DSM strains) or from 12.5 to 25 mg/liter (ATCC 43504), supporting the strain-dependent sensitivity of the pathogen. Pediocin PO2 was less active than the lacticins against four strains of H. pylori, and leucocin K was the least active peptide, with no inhibition toward H. pylori ATCC 43504. Anti-Helicobacter activity of lacticin A164 was dependent on initial inoculum size as well as concentration of the bacteriocin added.

Macedocin, a food-grade lantibiotic produced by Streptococcus macedonicus ACA-DC 198

Streptococcus macedonicus ACA-DC 198, a strain isolated from Greek Kasseri cheese, produces a food-grade lantibiotic named macedocin. Macedocin has a molecular mass of 2,794.76 +/- 0.42 Da, as determined by electrospray mass spectrometry. Partial N-terminal sequence analysis revealed 22 amino acid residues that correspond with the amino acid sequence of the lantibiotics SA-FF22 and SA-M49, both of which were isolated from the pathogen Streptococcus pyogenes. Macedocin inhibits a broad spectrum of lactic acid bacteria, as well as several food spoilage and pathogenic bacteria, including Clostridium tyrobutyricum. It displays a bactericidal effect towards the most sensitive indicator strain, Lactobacillus sakei subsp. sakei LMG 13558(T), while the producer strain itself displays autoinhibition when it is grown under conditions that do not favor bacteriocin production. Macedocin is active at pHs between 4.0 and 9.0, and it retains activity even after incubation for 20 min at 121 degrees C with 1 atm of overpressure. Inhibition of macedocin by proteolytic enzymes is variable.

Diversity of Streptococcus mutans bacteriocins as confirmed by DNA analysis using specific molecular probes

Mutacin-producing strains have been classified into 24 groups (designated by letters A to X) by similarity in activity spectra and cross-immunity. Similarity in primary structure among these groups can be revealed using DNA hybridization. The amino acid sequences of four mutacins (B-Ny266, 1140/mutacin III and mutacin II) were used to design two DNA probes in order to detect similar genes among groups of Streptococcus mutans strains demonstrating inhibitory activity. In addition to the appropriate parent strain, each probe hybridized with the total DNA from only two out of the 24 mutacin group type strains. Thus, the remaining 18 groups of strains produce mutacins that differ from the mutacins sequenced to date. In order to explore the similarity between genes coding for mutacins B-Ny266 and JH1140, the group B specific probe was utilized to detect a DNA fragment of 1.9 kb in the genome of S. mutans strain Ny266. The sequence of the cloned fragment codes for three open reading frames (lanA, lanA' and lanB) similar to those of strains JH1140 and UA787. The gene lanA' is strongly similar to the structural gene lanA (67%), but only one RNA transcript of about 300 bases was detected by Northern hybridization using the lanA-lanA' probe. Transcription of lanA alone was verified by RT-PCR.