Purification and characterization of plantaricin LR14: a novel bacteriocin produced by Lactobacillus plantarum LR/14

Structural and biosynthetic diversity of plantaricins from Lactiplantibacillus

Lactiplantibacillus plantarum (L. plantarum) produces an antimicrobial peptide known as plantaricin. Plantaricin-producing L. plantarum is of interest for its gut-friendly nature, wide range of sugar utilization, palatability, and probiotic attributes, making it a better candidate for the food industry. Numerous strains of plantaricin-producing L. plantarum have been isolated from different ecological niches and found to follow different mechanisms for plantaricin production. The mechanism of plantaricin production is sensitive to environmental factors; therefore, any alteration in the optimum conditions can inhibit/halt bacteriocin production. To regain the lost or hidden plantaricin-producing character of the L. plantarum strains under ideal laboratory conditions, it is essential to understand the mechanism of plantaricin production. Previously, discrete information on various mechanisms of plantaricin production has been elaborated. However, based on the literature analysis, we observed that a systematic classification of plantaricins produced by L. plantarum is not explored. Hence, we aim to collect information about rapidly emerging plantaricins and distribute them among the different classes of bacteriocin, followed by classifying them based on different mechanisms of plantaricin production. This may help scaleup the bacteriocin production at industrial levels, which is otherwise challenging to achieve. This will also help the reader understand plantaricins and their mechanism of plantaricin production to a deeper extent and to characterize/reproduce the peptide where plantaricin production is a hidden character. KEY POINTS: • L. plantarum produces the antimicrobial compound plantaricin. • L. plantarum has different regulatory operons which control plantaricin production. • Based on the regulatory operon, the mechanism of plantaricin production is different.

Isolation, Characterization, and Effect on Biofilm Formation of Bacteriocin Produced by Lactococcus lactis F01 Isolated from Cyprinus carpio and Application for Biopreservation of Fish Sausage

The aim of this work was the screening of bacteriocin-producing LABs isolated from fish, the selection of promising/prominent strain(s), the characterization of the bacteriocin produced, and the evaluation of its potential to be used as biopreservative(s). Amplification and sequencing of the 16S rRNA gene of the bacteriocin-producing strain was performed. Then a partial purification of the produced bacteriocin, using a combination of ammonium sulfate and chloroform-methanol precipitation, was done. Its molecular weight was determined by SDS-PAGE. In addition, the action spectrum, the hemolysis test, and its ability to inhibit biofilm formation were analyzed. A total of 88 isolates of lactic acid bacteria (LAB) including one bacteriocin producer, which was identified as Lactococcus lactis F01, were collected. The bacteriocin was partially purified with an estimated yield of 40%. Regarding the SDS-PAGE profile, the secreted bacteriocin has molecular weight of about 3.5 kDa and was identified as class I bacteriocin. The antimicrobial test showed that the bacteriocin inhibits pathogenic and/or spoilage bacteria, 10 Gram-positive and 16 Gram-negative bacterial species. Moreover, it can inhibit biofilm formation from 1.3% (Escherichia coli) to 63.92% (Pseudomonas aeruginosa ATCC15692) depending on the strain. The hemolytic activity of novel bacteriocin was observed at the concentration of 10 μg/ml of bacteriocin crude extract, which was $0.7\pm 0.0029\%$ . In addition, it exhibited good thermal and pH stability with retained antibacterial activity of 85.25% after treatment at 121°C for 20 min, as well as at a pH range between 2.0 and 10.0. Moreover, this bacteriocin showed the ability to inhibit the growth of bacterial culture load in fish sausage stored at 8°C for 28 days. Considering the results obtained, bacteriocin could be potentially exploited as an alternative to chemical preservatives or as a substitute for antibiotics.

Bacteriocin from Lacticaseibacillus rhamnosus sp. A5: Isolation, Purification, Characterization, and Antibacterial Evaluation for Sustainable Food Processing

A new Lacticaseibacillus rhamnosus strain A5 was isolated from pickle soup and characterized for its probiotic suitability. Strain A5 was Gram-positive, catalase-negative, acid-producing, and exhibited potential antibacterial activity against Escherichia coli (inhibition zone 17.3 mm), Bacillus subtilis (inhibition zone 14.5 mm), Salmonella enterica (zone of inhibition 16.1 mm) and Staphylococcus aureus (zone of inhibition 14.2 mm) by performing investigations on the disc diffusion. The cell-free supernatant of newly isolated strain A5 retained its inhibition ability of the growth of test bacteria at pH 2.0 to 5.0, temperature 121 °C for 30 min and UV irradiation for 8 h. However, the inhibitory effects of cell-free supernatant disappeared when subjected to papain, trypsin, and pepsin enzymatic treatments. By eliminating the interferences of organic acid and hydrogen peroxide, the cell-free supernatant possessed antibacterial activity against two indicator bacteria (E. coli and B. subtilis) and showed high thermal tolerance. These results indicated that the antibacterial substances produced by strain A5 were proteinaceous in nature, namely bacteriocin. The antibacterial bacteriocins in the supernatant of the strain A5 culture were further purified by ammonium sulfate fractionation and gel filtration chromatography. The purified bacteriocins also showed a pronounced inhibitory effect against E. coli and B. subtilis. The approximated molecular weight of bacteriocins was less than 14 kDa after determining by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In conclusion, the newly isolated strain A5 and its bacteriocins could be potentially applied in food preservation to prevent the risk of foodborne illness.

Purification, amino acid sequence, and characterization of bacteriocin GA15, a novel class IIa bacteriocin secreted by Lactiplantibacillus plantarum GCNRC_GA15

The bacteriocins produced by lactic acid bacteria (LAB) are attracting attention due to their promising applications in food and pharmaceuticals fields. Hence, a LAB strain, GCNRC_GA15, was isolated from Egyptian goat cheese, and molecularly identified as Lactiplantibacillus plantarum. This strain showed a wide antimicrobial spectrum, which was found to be of proteineous nature, suggesting that L. plantarum GCNRC_GA15 is a bacteriocin-producer. This bacteriocin (bacteriocin GA15) was partially purified using cation exchange, and hydrophobic interaction chromatography. Tricine SDS-PAGE analysis for the fraction showing bacteriocin activity has estimated the molecular mass to be 4369 Da. Furthermore, amino acid sequencing of this peptide has detected 34 amino acids, and comparing its amino acid sequence with those of some pediocin-like bacteriocins revealed that bacteriocin GA15 has the conserved sequence (YYGNGV/L) in its N-terminal region which identified bacteriocin GA15 as a pediocin-like bacteriocin. Bacteriocin GA15 showed good heat and pH stabilities, and its activity was enhanced after treatment with Tween 80 or Triton X-100. Bacteriocin production medium was statistically optimized using the Plackett-Burman and Central Composite designs. As a result, bacteriocin production increased from 800 to 12,800 AU/ml using the optimized medium in comparison with result recorded for the un-optimized medium.

Bacteriocins from lactic acid bacteria: purification strategies and applications in food and medical industries: a review

Background

Bacteriocins are generally defined as ribosomally synthesized peptides, which are produced by lactic acid bacteria (LAB) that affect the growth of related or unrelated microorganisms. Conventionally, the extracted bacteriocins are purified by precipitation, where ammonium sulphate is added to precipitate out the protein from the solution.

Main text

To achieve the high purity of bacteriocins, a combination with chromatography is used where the hydrophobicity and cationic properties of bacteriocins are employed. The complexity column inside the chromatography can afford to resolve the loss of bacteriocins during the ammonium sulphate precipitation. Recently, an aqueous two-phase system (ATPS) has been widely used in bacteriocins purification due to the several advantages of its operational simplicity, mild process conditions and versatility. It reduces the operation steps and processing time yet provides high recovery products which provide alternative ways to conventional methods in downstream processing. Bacteriocins are widely approached in the food and medical industry. In food application, nisin, which is produced by Lactococcus lactis subsp. has been introduced as food preservative due to its natural, toxicology safe and effective against the gram-positive bacteria. Besides, bacteriocins provide a board range in medical industries where they are used as antibiotics and probiotics.

Short conclusion

In summary, this review focuses on the downstream separation of bacteriocins from various sources using both conventional and recent ATPS techniques. Finally, recommendations for future interesting areas of research that need to be pursued are highlighted.

Enterocins: Classification, Synthesis, Antibacterial Mechanisms and Food Applications

Enterococci, a type of lactic acid bacteria, are widely distributed in various environments and are part of the normal flora in the intestinal tract of humans and animals. Although enterococci have gradually evolved pathogenic strains causing nosocomial infections in recent years, the non-pathogenic strains have still been widely used as probiotics and feed additives. Enterococcus can produce enterocin, which are bacteriocins considered as ribosomal peptides that kill or inhibit the growth of other microorganisms. This paper reviews the classification, synthesis, antibacterial mechanisms and applications of enterocins, and discusses the prospects for future research.

Recent developments in antifungal lactic acid bacteria: Application, screening methods, separation, purification of antifungal compounds and antifungal mechanisms

Fungal contamination of food, which causes large economic losses and public health problems, is a global concern. Chemical methods are typically used in the food industry to inhibit the growth of spoilage fungus, but there are several drawbacks of chemical methods. Thus, the development of consumer-friendly and ecologically sustainable biological preservation technology has become a hot spot in food research. As a natural biological control agent, lactic acid bacteria (LAB) is a good choice in food preservation due to its antifungal properties. In order to screen and identify new antifungal LAB and antifungal compounds, this review compares three screening methods (overlay method, agar diffusion method, and microplate inhibition method) of antifungal LAB and summarizes the separation and purification techniques of antifungal compounds. A discussion of the effects of LAB, media, temperature, pH, and incubation period on the antifungal activity of LAB to highlight the antifungal properties of LAB for future studies then follows. Additionally, the antifungal mechanism of LAB is elucidated from three aspects: 1) LAB cells, 2) antifungal compounds, and 3) co-cultivation. Finally, research regarding antifungal LAB in food preservation (fruits, vegetables, grain cereals, bakery products, and dairy products) is summarized, which demonstrates the potential application value of LAB in food.

Purification, molecular characterization of Lactocin 63 produced by Lactobacillus coryniformis FZU63 and its antimicrobial mode of action against Shewanella putrefaciens

Bacteriocins derived from lactic acid bacteria (LAB) are well recognized as promising food preservative due to high safety and potent antibacterial activity against foodborne pathogens and spoilage bacteria. In this study, an antimicrobial agent-producing strain FZU63 from Chinese sauerkraut was identified as Lactobacillus coryniformis based on physio-biochemical characterization and 16S rDNA sequence analysis. In addition, a bacteriocin was purified from the culture supernatant of L. coryniformis FZU63, and its molecular mass was determined as 1493.709 Da. Moreover, the amino acid sequence of the bacteriocin was predicted to be RQQPMTLDYRW-NH₂ using nanoliter/microliter liquid chromatography combined with triple quadrupole-linear ion trap tandem mass spectrometry and was named as Lactocin 63. Furthermore, Lactocin 63 displays potent antimicrobial activity against the tested Gram-positive and negative bacteria based on the results of determining MICs. Subsequently, the action mode of Lactocin 63 against Shewanella putrefaciens was investigated. The results demonstrated that Lactocin 63 targets and is adsorbed onto the bacterial cell wall and membrane and then disrupts cytoplasmic membrane, which is leading to leakage of cytoplasm according to the results of flow cytometry analysis and the observation of cellular ultra-structure using confocal laser microscopy and atomic force microscopy. Collectively, these results are helpful and providing the theoretical base for developing and applying LAB-derived bacteriocins as promising bio-preservatives to combat foodborne pathogens and spoilage bacteria in seafood industries.Key points• A bacteriocin-producing strain Lactobacillus coryniformis was isolated.• A novel bacteriocin produced by Lactobacillus coryniformis FZU63 was characterized.• Action mechanism of the bacteriocin against S. putrefaciens was elucidated in vitro.

Bacteriocins, A Natural Weapon Against Bacterial Contamination for Greater Safety and Preservation of Food: A Review

Nowadays, consumers have become increasingly attentive to human health and the use of more natural products. Consequently, the demand for natural preservatives in the food industry is more frequent. This has led to intense research to discover new antimicrobial compounds of natural origin that could effectively fight foodborne pathogens. This research aims to safeguard the health of consumers and, above all, to avoid potentially harmful chemical compounds. Lactobacillus is a bacterial genus belonging to the Lactic Acid Bacteria and many strains are defined GRAS, generally recognized as safe. These strains are able to produce substances with antibacterial activity against food spoilage bacteria and contaminating pathogens: the bacteriocins. The aim of this review was to focus on this genus and its capability to produce antibacterial peptides. The review collected all the information from the last few years about bacteriocins produced by Lactobacillus strains, isolated from clinical or food samples, with remarkable antimicrobial activities useful for being exploited in the food field. In addition, the advantages and disadvantages of their use and the possible ways of improvement for industrial applications were described.

Acetate and auto-inducing peptide are independent triggers of quorum sensing in Lactobacillus plantarum

The synthesis of plantaricin in Lactobacillus plantarum is regulated by quorum sensing. However, the nature of the extra-cytoplasmic (EC) sensing domain of the histidine kinase (PlnB1) and the ability to recognize the auto-inducing peptide PlnA1 is not known. We demonstrate the key motif Ile-Ser-Met-Leu of auto-inducing peptide PlnA1 binds to the hydrophobic region Phe-Ala-Ser-Gln-Phe of EC loop 2 of PlnB1 via hydrophobic interactions and hydrogen bonding. Moreover, we identify a new inducer, acetate, that regulates the synthesis of plantaricin by binding to a positively charged region (Arg-Arg-Tyr-Ser-His-Lys) in loop 4 of PlnB1 via electrostatic interaction. The side chain of Phe143 on loop 4 determined the specificity and affinity of PlnB1 to recognize acetate. PlnA1 activates quorum sensing in log phase growth and acetate in stationary phase to maintain the synthesis of plantaricin under conditions of reduced growth. Acetate activation of PlnB was also evident in four types of PlnB present in different Lb. plantarum strains. Finally, we proposed a model to explain the developmental regulation of plantaricin synthesis by PlnA and acetate. These results have potential applications in improving food fermentation and bacteriocin production.

Purification and characterization of bacteriocins-like inhibitory substances from food isolated Enterococcus faecalis OS13 with activity against nosocomial enterococci

Nosocomial infections caused by enterococci are an ongoing global threat. Thus, finding therapeutic agents for the treatment of such infections are crucial. Some Enterococcus faecalis strains are able to produce antimicrobial peptides called bacteriocins. We analyzed 65 E. faecalis isolates from 43 food samples and 22 clinical samples in Egypt for 17 common bacteriocin-encoding genes of Enterococcus spp. These genes were absent in 11 isolates that showed antimicrobial activity putatively due to bacteriocins (three from food, including isolate OS13, and eight from clinical isolates). The food-isolated E. faecalis OS13 produced bacteriocin-like inhibitory substances (BLIS) named enterocin OS13, which comprised two peptides (enterocin OS13α OS13β) that inhibited the growth of antibiotic-resistant nosocomial E. faecalis and E. faecium isolates. The molecular weights of enterocin OS13α and OS13β were determined as 8079 Da and 7859 Da, respectively, and both were heat-labile. Enterocin OS13α was sensitive to proteinase K, while enterocin OS13β was resistant. Characterization of E. faecalis OS13 isolate revealed that it belonged to sequence type 116. It was non-hemolytic, bile salt hydrolase-negative, gelatinase-positive, and sensitive to ampicillin, penicillin, vancomycin, erythromycin, kanamycin, and gentamicin. In conclusion, BLIS as enterocin OS13α and OS13β represent antimicrobial agents with activities against antibiotic-resistant enterococcal isolates.

Expression of Hybrid Peptide EF-1 in Pichia pastoris, Its Purification, and Antimicrobial Characterization

EF-1 is a novel peptide derived from two bacteriocins, plantaricin E and plantaricin F. It has a strong antibacterial activity against Escherichia coli and with negligible hemolytic effect on red blood cells. However, the chemical synthesis of EF-1 is limited by its high cost. In this study, we established a heterologous expression of EF-1 in Pichia pastoris. The transgenic strain successfully expressed hybrid EF-1 peptide, which had a molecular weight of ~5 kDa as expected. The recombinant EF-1 was purified by Ni²⁺ affinity chromatography and reversed-phase high performance liquid chromatography (RP-HPLC), which achieved a yield of 32.65 mg/L with a purity of 94.9%. The purified EF-1 exhibited strong antimicrobial and bactericidal activities against both Gram-positive and -negative bacteria. Furthermore, propidium iodide staining and scanning electron microscopy revealed that EF-1 can directly induce cell membrane permeabilization of E. coli. Therefore, the hybrid EF-1 not only preserves the individual properties of the parent peptides, but also acquires the ability to disrupt Gram-negative bacterial membrane. Meanwhile, such an expression system can reduce both the time and cost for large-scale peptide production, which ensures its potential application at the industrial level.

Lactobacillus Plantarum 108 Inhibits Streptococcus mutans and Candida albicans Mixed-Species Biofilm Formation

Streptococcus mutans is the principal biofilm forming oral pathogen associated with dental caries. Studies have shown that Candida albicans, a commensal oral fungus is capable of forming pathogenic mixed-species biofilms with S. mutans. The treatment of bacterial and fungal infections using conventional antimicrobial agents has become challenging due to the antimicrobial resistance of the biofilm mode of growth. The present study aimed to evaluate the efficacy of secretory components of Lactobacillus plantarum 108, a potentially promising probiotic strain, against S. mutans and C. albicans single and mixed-species biofilms. L. plantarum 108 supernatant inhibited S. mutans and C. albicans single-species biofilms as shown by XTT reduction assay, crystal violet assay, and colony forming units counting. The probiotic supernatant significantly inhibited the S. mutans and C. albicans mixed-species biofilm formation. The pre-formed mixed-species biofilms were also successfully reduced. Confocal microscopy showed poorly developed biofilm architecture in the probiotic supernatant treated biofilms. Moreover, the expression of S. mutans genes associated with glucosyltransferase activity and C. albicans hyphal specific genes (HWP1, ALS1 and ALS3) were down-regulated in the presence of the probiotic supernatant. Altogether, the data demonstrated the capacity of L. plantarum 108 supernatant to inhibit the S. mutans and C. albicans mixed-species biofilms. Herein, we provide a new insight on the potential of probiotic-based strategies to prevent bacterial-fungal mixed-species biofilms associated with dental caries.

Genome Analysis of Lactobacillus plantarum Isolated From Some Indian Fermented Foods for Bacteriocin Production and Probiotic Marker Genes

In this study, Lactobacillus plantarum strain DHCU70 isolated from dahi, a fermented milk product and L. plantarum strain DKP1 isolated from kinema, a fermented soybean food of India, respectively were evaluated for their bacteriocin production and probiotic properties. Both strains of L. plantarum (DHCU70 and DKP1) were found to have potent antimicrobial activity against Kocuria rhizophila ATCC 9341. Bacteriocin produced by L. plantarum strains DHCU70 and DKP1 did not exhibit inhibition of cell wall, DNA and fatty acids biosynthesis mechanisms as evaluated by whole cell reporter assays. We characterized the bacteriocin encoding genes in L. plantarum strains DHCU70 and DKP1 by whole genome sequence which consisted of a single and circular chromosome with genome size of 3.38 Mb (GC content of 44.3%) and 3.39 Mb, respectively and a GC content of 44.3%. L. plantarum DHCU70 has 3252 number of protein encoding genes comprising 89 number of RNA genes (69tRNA, 16rRNA, 4nc RNA) whereas L. plantarum DKP1 has total of 3277 number of protein encoding genes with 89 number. of RNA genes (69tRNA, 16S rRNA, 4nc RNA). Analysis revealed the presence of 20.5 kb long and 23 numbers of plantaricin encoding locus (pln locus) for production of antimicrobial compound. BAGEL analysis has shown that the pln locus of both the strains of L. plantarum showed maximum sequence similarity with plantaricin NC8 of L. plantarum NC8, originally isolated from grass silage. Annotated whole genome sequence of both strains DHCU70 and DKP1 was analyzed for the presence of probiotic marker genes. The probiotic properties of these strains of were also evaluated in vitro. Due to the presence of genes responsible for antimicrobial activity and probiotic properties, both strains of L. plantarum may be considered as a suitable probiotic candidate in food industry.

Characterization of a broad spectrum bacteriocin produced by Lactobacillus plantarum MXG-68 from Inner Mongolia traditional fermented koumiss

An agar well diffusion assay (AWDA) was used to isolate a high bacteriocin-producing strain with a broad spectrum of antibacterial activity, strain MXG-68, from Inner Mongolia traditional fermented koumiss. Lactobacillus plantarum MXG-68 was identified by morphological, biochemical, and physiological characteristics and 16S rDNA analysis. The production of antibacterial substance followed a growth-interrelated model, starting at the late lag phase of 4 h and arriving at a maximum value in the middle of the stationary phase at 24 h. Antibacterial activity was abolished or decreased in the presence of pepsin, chymotrypsin, trypsin, proteinase, and papain K. The results showed that antibacterial substances produced by L. plantarum MXG-68 were proteinaceous and could thus be classified as the bacteriocin, named plantaricin MXG-68. The molar mass of plantaricin MXG-68 was estimated to be 6.5 kDa, and the amino acid sequence of its N-terminal was determined to be VYGPAGIFNT. The mode of plantaricin MXG-68 action was determined to be bactericidal. Bacteriocin in cell-free supernatant (CFS) at pH 7 was stable at different temperatures (60 °C, 80 °C, 100 °C, 121 °C for 30 min; 4 °C and - 20 °C for 30 days), as well as at pH 2.0-10.0. Antibacterial activity maintained stable after treatment with organic solvents, surfactants, and detergents but increased in response to EDTA. Response surface methodology (RSM) revealed the optimum conditions of bacteriocin production in L. plantarum MXG-68, and the bacteriocin production in medium optimized by RSM was 26.10% higher than that in the basal MRS medium.

Isolation, Identification of Lactobacillus mucosae AN1 and its Antilisterial Peptide Purification and Characterization

Lactobacillus mucosae strain AN1 isolated from sheep milk and characterized for its probiotic suitability. In vitro evaluation of critical gut endurance properties of this strain were assessed by different screening methods such as bile salt, gastric acid, lysozyme tolerance assays, hemolytic, cholesterol reduction properties, and HT-29 cell line adhesion assay. Antibacterial peptide from this strain was purified using ammonium sulphate precipitation, gel filtration chromatography and reverse-phase HPLC. The molecular mass of peptides was determined by Tricine-SDS-PAGE and confirmed by matrix-assisted laser desorption ionization-time of flight mass spectroscopy (MALDI-TOF-MS). Purified peptide was named as AN1 having a molecular mass of 10.66 kDa. Helical structures of peptide were determined using circular dichroism spectroscopy. Stability of peptide AN1 towards different parameters such as pH, temperature, organic solvents, proteolytic, and glycolytic enzymes was also analyzed.

Membrane-acting bacteriocin purified from a soil isolate Pediococcus pentosaceus LB44 shows broad host-range

Bacteriocin LB44 was purified from cell-free supernatant (CFS) of Pediococcus pentosaceus LB44 using activity-guided chromatography techniques. It was stable up to 121 °C, pH 2.0-6.0, sensitive to proteinase K, papain and trypsin, and retained complete activity in the presence of organic solvents tested. The molecular weight of bacteriocin was ∼6 kDa and initial ten amino acid residues (GECGMCXECG) suggested a new compound. The loss in viable cell count and K⁺ ion efflux of target cells of Micrococcus luteus suggested bactericidal activity. The cell membrane of bacteriocin-treated cells was found to be ruptured which was further confirmed by Fourier Transform Infrared (FTIR) analysis suggesting interaction of bacteriocin with phospholipids in cell membrane. It showed broad host-range and inhibited the growth of Lactobacillus delbrueckii NRRL B-4525, L. plantarum NRRL B-4496, L. acidophilus NRRL B-4495, Enterococcus hirae LD3, Weissella confusa LM85, Staphylococcus aureus, Salmonella typhi ATCC 13311, Serratia marcescens ATCC 27137, Pseudomonas aeruginosa ATCC 27853, Proteus vulgaris ATCC 29905, Haloferax larsenii HA1, HA3, HA8, HA9 and HA10. These properties suggested a new bacteriocin from soil isolate P. pentosaceus LB44 which may offers possible applications in food-safety and therapeutics.

Purification and antibacterial mechanism of fish-borne bacteriocin and its application in shrimp (Penaeus vannamei) for inhibiting Vibrio parahaemolyticus

Vibrio parahaemolyticus: is recognized as the main cause of gastroenteritis associated with consumption of seafood. Bacteriocin-producing Lactobacillus plantarum FGC-12 isolated from golden carp intestine had strong antibacterial activity toward V. parahaemolyticus. The fish-borne bacteriocin was purified by a three-step procedure consisting of ethyl acetate extraction, gel filtration chromatography and high performance liquid chromatography. Its molecular weight was estimated at 4.1 kDa using SDS-PAGE. The fish-borne bacteriocin reached the maximum production at stationary phase after 20 h. It was heat-stable (30 min at 121 °C) and remained active at pH range from 3.0 to 5.5, but was sensitive to nutrasin, papain and pepsin. Its minimum inhibitory concentration for V. parahaemolyticus was 6.0 mg/ml. Scanning electron microscopy analysis showed that the fish-borne bacteriocin disrupted cell wall of V. parahaemolyticus. The antibacterial mechanism of the fish-borne bacteriocin against V. parahaemolyticus might be described as action on membrane integrity in terms of the leakage of electrolytes, the losses of Na⁺K⁺-ATPase, AKP and proteins. The addition of the fish-borne bacteriocin to shrimps leaded V. parahaemolyticus to reduce 1.3 log units at 4 °C storage for 6 day. Moreover, a marked decline in total volatile base nitrogen and total viable counts was observed in bacteriocin treated samples than the control. It is clear that this fish-borne bacteriocin has promising potential as biopreservation for the control of V. parahaemolyticus in aquatic products.

Functional Analysis of Plantaricin E and Its Mutant by Heterologous Expression in Escherichia coli

Plantaricins are a group of ribosomally synthesized antimicrobial peptides in Lactobacillus plantarum that exert antimicrobial activities against some foodborne pathogens. In this study, we observed that plantaricin E in L. plantarum 163 was missing 19 amino acids (plnE mutant amino acid sequence: FNRGGYNFGKSVRH, plnE amino acid sequence: FNRGGYNFGKSVRHVVDAIGSVAGIRGILKSIR). In order to study the effects of mutant plnE, plnE mutant genes with and without the signal peptide were cloned from the L. plantarum 163 genome, linked to the pET32a vector, and expressed via a fusion protein (thioredoxin) in Escherichia coli BL21 (DE3). All target proteins were purified using Ni-NTA, SP FF columns, and RP-HPLC. The purified proteins were stable in an acidic environment and at temperatures below 80 °C, but they were easily degraded under alkaline conditions and by protease treatment. They showed antimicrobial activity against gram-positive bacteria such as Micrococcus luteus, Staphylococcus epidermidis, Lactococcus lactis, Lactobacillus paracasei, and Listeria innocua. In addition, SP-plnE and PlnE exerted stronger activity than nisin. The signal peptide had a positive effect on the activities of PlnE and PlnEm. Thus, these purified proteins may have potential applications in the food industry to control foodborne pathogens.

Scaling Up the Production of Recombinant Antimicrobial Plantaricin E from a Heterologous Host, Escherichia coli

Enhanced production of heterologously expressed plantaricin (plnE) from Escherichia coli BL21 (DE3) was achieved from a small- to large-scale batch culture. Starting from a 15-ml shake-flask culture grown in Luria-Bertani (LB) broth, the protein expression could be scaled up using 50 ml, 100 ml, 1 l, and 2 l batch culture. Using similar condition, plantaricin E (PlnE) was successfully expressed in a 30-l stirred fermenter. The protein was expressed as TRX-(His)6-fusion protein and separated by Ni(2+) affinity chromatography. Growth in two complex media, LB and Terrific broth (TB), was optimized and compared for the production of PlnE, which was higher in LB in comparison with that of TB. In the fermenter, 140 and 180 mg of PlnE could be produced from 12 l of culture volume at 30 and 25 °C, respectively. The yield of heterologously purified PlnE was found to be 1.2-1.5%, which was much higher in comparison with the plantaricins produced from the native strain of Lactobacillus plantarum (0.3-0.7%). Overproduction of PlnE with the help of heterologous expression can overcome the constraint of the low yield from producer strain and provides an easy and low-cost strategy for large-scale production.

In vivo Toxicity Assessment of Antimicrobial Peptides (AMPs LR14) Derived from Lactobacillus plantarum Strain LR/14 in Drosophila melanogaster

Lactic acid bacteria are known to produce antimicrobial peptides (AMPs) such as bacteriocins which can be employed to control pathogens and food spoilage microorganisms. However, their possible role as toxic agents against a eukaryotic system still remains unexplored. The present study deals with the in vivo evaluation of acute toxic effect of AMPs LR14, a mixture of AMPs isolated from Lactobacillus plantarum LR/14 on Drosophila melanogaster. The fly was used as a model system to measure the extent of toxicity of these peptides. The results showed that concentrations below 10 mg/ml are not significantly effective. When exposed to 10 mg/ml of AMPs LR14, acute toxic effect and a significant delay in the developmental cycle of the fly could be observed. Also, the weight and size of the flies were significantly reduced upon ingestion of these peptides. Higher concentrations (beyond 15 mg/ml) exerted a strong larvicidal effect. Detailed analysis on larval tissues and adult germ cells of the insect revealed deformity in cellular architecture, DNA fragmentation, and premature apoptosis, confirming that the peptides have a dose-dependent toxic property. Our studies provide the first information on the role of AMPs LR14 as an insecticidal agent.

Probiotic Potential of Lactobacillus plantarum LD1 Isolated from Batter of Dosa, a South Indian Fermented Food

Lactobacillus plantarum LD1 was isolated from dosa batter and identified by biochemical, physiological and genetic methods. Species level identification was done by 16S rDNA amplification and sequencing. The probiotic potential of strain LD1 was assessed by different standard parameters. Cell surface hydrophobicity was recorded to be 62% with SAT value <0.007 M. Seventy-eight percent of viable count was found after treatment with simulated gastric juice containing pepsin (pH 2.0). Bile salt tolerance and bile salt hydrolase activity were also demonstrated by strain LD1. The culture supernatant was able to inhibit food-borne as well as clinical pathogenic microorganisms such as Staphylococcus aureus, Salmonella typhimurium, Shigella flexneri, Pseudomonas aeruginosa, urogenic Escherichia coli and Vibrio sp. Strain LD1 was found to be sensitive to most of the antibiotics used in the study. Since strain has been isolated from food source that is most typical of Southern India, it would be safe for further consumption in probiotic products.

Plantaricin IIA-1A5 from Lactobacillus plantarum IIA-1A5 displays bactericidal activity against Staphylococcus aureus

Plantaricin IIA-1A5 is a bacteriocin produced by Lactobacillus plantarum IIA-1A5 isolated from Indonesian beef. This research aimed to identify the genes involved in plantaricin IIA-1A5 production and examine its mode of action against Staphylococcus aureus. It has been reported that a bacteriocin structural gene, plnW, is present in genome of L. plantarum IIA-1A5. Here, we reported the presence of additional genes responsible for plantaricin precursor (plnA and plnEF) and a gene encoding the quorum sensor of histidine kinase (plnB). It indicates that genes involved in production of plantaricin IIA-1A5 are organized in at least two bacteriocin operons (plnABCD, plnEFI) and a structural plnW gene. Purified plantaricin IIA-1A5 yielded a single band in SDS-PAGE with apparent size of 6.4 kDa. Amino acid composition of purified plantaricin IIA-1A5 was mainly composed of cationic glutamic acid and cysteine that allowed the formation of disulphide bonds, suggesting plantaricin IIA-1A5 belongs to the pediocin-subclass of class II bacteriocins. Plantaricin IIA-1A5 displayed remarkable antibacterial activity against S. aureus, which was initiated by the adsorption of plantaricin IIA-1A5 onto the cell membrane of S. aureus. The adsorption is hypothesised to be facilitated by non-ionic interactions as it is reduced by the presence of organic solvents or detergents. This adsorption promoted leakage of cellular metabolites through the cell membrane of S. aureus, as indicated by the release of genetic and proteinaceous material of S. aureus observed at 260 and 280 nm, respectively. The leakage also promoted the release of divalent (Ca2+, Mg2+) and monovalent (K+) cations. The release of these intracellular components might be due to pores formed in the cell membrane of S. aureus by plantaricin IIA-1A5 as shown by scanning electron microscopy. Altogether, the mode of action of plantaricin IIA-1A5 against S. aureus seems to be bactericidal as indicated by lysis of the cell membrane.

Assessment of anti-plasmodial activity of non-hemolytic, non-immunogenic, non-toxic antimicrobial peptides (AMPs LR14) produced by Lactobacillus plantarum LR/14

BACKGROUND AND OBJECTIVES

Lactobacillus plantarum strains are known to exhibit an antimicrobial property against bacteria and fungi. In the present investigation, AMPs LR14, antimicrobial peptides produced by L. plantarum strain LR/14, were tested against a protozoan system, Plasmodium falciparum and its non-toxic nature was envisaged on a mammalian system.

METHODS

Human erythrocytes infected with chloroquine-sensitive and -resistant strains of P. falciparum were treated with purified AMPs LR14. The loss in cell viability was assessed by monitoring the incorporation of [(3)H]-hypoxanthine in the nucleic acid of the parasite. The hemolytic activity of AMPs LR14 was monitored at different concentrations and the investigations into the in vivo toxicity of AMPs LR14 were carried out on a mammalian system (Wistar rat). The level of toxicity in the tissues was visualized by histopathological studies conducted on the liver and kidney of the test and control rats. A study was also undertaken to see the production of antibodies in an animal (rabbit) after it was immunized with AMPs LR14.

RESULTS

A loss in cell viability was observed in both test strains of P. falciparum. However, the dose required for inhibition of the chloroquine-resistant strain was ~2 times the dose required for the chloroquine-sensitive strain. At these concentrations, no hemolysis of human erythrocytes was observed. The studies conducted on in vivo toxicity of AMPs LR14 suggest that the lethal dose (LD50) is beyond 1,000 mg/kg body weight, suggesting its safe use against microbes and protozoans. Antibodies were also not detected against these peptides, indicating a non-immunogenic nature.

CONCLUSION

The data indicate that AMPs LR14 are non-toxic, potent anti-plasmodial peptides causing growth inhibition of P. falciparum without causing hemolysis. These results pave the way for the development of bioactive peptides as therapeutics.

Improved antimicrobial activities of synthetic-hybrid bacteriocins designed from enterocin E50-52 and pediocin PA-1

Two hybrid bacteriocins, enterocin E50-52/pediocin PA-1 (EP) and pediocin PA-1/enterocin E50-52 (PE), were designed by combining the N terminus of enterocin E50-52 and the C terminus of pediocin PA-1 and by combining the C terminus of pediocin PA-1 and the N terminus of enterocin E50-52, respectively. Both hybrid bacteriocins showed reduced MICs compared to those of their natural counterparts. The MICs of hybrid PE and EP were 64- and 32-fold lower, respectively, than the MIC of pediocin PA-1 and 8- and 4-fold lower, respectively, than the MIC of enterocin E50-52. In this study, the effect of hybrid as well as wild-type (WT) bacteriocins on the transmembrane electrical potential (ΔΨ) and their ability to induce the efflux of intracellular ATP were investigated. Enterocin E50-52, pediocin PA-1, and hybrid bacteriocin PE were able to dissipate ΔΨ, but EP was unable to deplete this component. Both hybrid bacteriocins caused a loss of the intracellular concentration of ATP. EP, however, caused a faster efflux than PE and enterocin E50-52. Enterocin E50-52 and hybrids PE and EP were active against the Gram-positive and Gram-negative bacteria tested, such as Micrococcus luteus, Salmonella enterica serovar Enteritidis 20E1090, and Escherichia coli O157:H7. The hybrid bacteriocins designed and described herein are antimicrobial peptides with MICs lower those of their natural counterparts. Both hybrid peptides induce the loss of intracellular ATP and are capable of inhibiting Gram-negative bacteria, and PE dissipates the electrical potential. In this study, the MIC of hybrid bacteriocin PE decreased 64-fold compared to the MIC of its natural peptide counterpart, pediocin PA-1. Inhibition of Gram-negative pathogens confers an additional advantage for the application of these peptides in therapeutics.

Purification and characterisation of plantaricin ZJ008, a novel bacteriocin against Staphylococcus spp. from Lactobacillus plantarum ZJ008

A novel bacteriocin, plantaricin ZJ008 produced by Lactobacillus plantarum ZJ008 isolated from fresh milk, was purified by XAD 2, cation exchange chromatograph, gel chromatograph, and RP-HPLC. Mass spectrometry based on MALDI-TOF indicated that the bacteriocin had a molecular of 1334.77 Da. Only five of twenty amino acids could be identified by Edman degradation. This bacteriocin was highly thermostable (121°C, 30 min) and exhibited narrow pH stability (pH 4.0-5.0). It was sensitive to α-Chymotrypsin, trypsin, papain, and pepsin. However it still had 80% of activity after treatment by proteinase K. The action mode of this peptide functioned as bactericidal, but it did not lead to lysis of cells. This bacteriocin exhibited broad-spectrum antimicrobial activity against tested Gram-positive and Gram-negative bacteria, especially Staphylococcus spp. These results suggested that this bacteriocin appears potentially very useful to control and inhibit Staphylococcus spp. in the food industry.

Anti-Candida activity of two-peptide bacteriocins, plantaricins (Pln E/F and J/K) and their mode of action

The fungicidal effect of plantaricin peptides PlnE, -F, -J, and -K was studied against pathogenic yeast, Candida albicans. Dose-dependent inhibitory effect was observed by drop in cell viability, further demonstrated by measuring the fluorescence intensity of cells by exposing them to 5, (6)-carboxyfluorescein diacetate (CFDA). Live/dead staining by CFDA and propidium iodide (PI) also suggested the viability loss response. Also, the PI uptake by treated cells suggested the membrane damage. PlnJ was identified as most inhibitory among different plantaricins tested. PlnJ not only induced membrane potential dissipation but also resulted in the release of K(+). In addition, enhanced production of reactive oxygen species (ROS) was also observed by fluorometry using 2',7'-Dichlorodihydrofluorescein diacetate (DCFH-DA). Dual staining with Hoechst stain and PI depicted both early apoptotic and necrotic cells in the treated population. Terminal deoxynucleotidyl transferase dUTP nick-end labelling (TUNEL) positive staining further confirmed the ROS-mediated apoptosis. Scanning electron microscopy and transmission electron microscopy also revealed characteristic apoptotic features such as appearance of blebs, indentations, and wrinkling of the cell wall, discontinuity of cell membrane, undefined and damaged nuclei, and shrinkage of protoplasm. Taken together the results suggest that Pln-treatment initiate the apoptosis cell death which may lead to necrosis due to toxicity of the plantaricin peptides.

Anti-Candida activity of spent culture filtrate of Lactobacillus plantarum strain LR/14

OBJECTIVES

This study was undertaken to understand the effect of antimicrobial compounds produced by an environmental isolate of lactic acid bacterium, Lactobacillus plantarum strain LR/14, on growth, viability and biofilm forming ability of the pathogenic yeast, Candida albicans SC5314 and to identify the mode of action of such compounds.

MATERIAL AND METHODS

L. plantarum LR14 was grown at 37°C for 18 h in MRS broth. The spent culture filtrate (SCF) was collected by centrifugation and checked for anti-Candida activity. Live/dead staining followed by fluorescence microscopy was done to study the membrane damage. Increased membrane permeability was confirmed by measuring the release of ions and macromolecules (ATP) using atomic absorption spectrophotometer and luminometer, respectively. Effect on biofilm formation was quantified by MTT reduction assay.

RESULTS

The viability of yeast cells was affected by SCF LR14 treatment in a dose-dependent manner, exerting a fungicidal effect. The active compound was identified as a pH-dependent thermostable proteinaceous metabolite. The fungicidal activity was further confirmed by PI staining, suggesting compromised membrane as the cause of cell death. Leakage of intracellular contents such as, K+ ions and ATP, as a cause of its inhibitory action further confirmed the membrane disruption. Moreover, significant reduction in biofilm formation was also confirmed.

CONCLUSIONS

SCF LR14 showed potent anti-Candida activity, affecting cell viability, membrane permeability, and biofilm formation and leading to cell death, thereby suggested a probable candidate as a natural therapeutic agent.

Enhanced production, purification, characterization and mechanism of action of salivaricin 9 lantibiotic produced by Streptococcus salivarius NU10

Background

Lantibiotics are small lanthionine-containing bacteriocins produced by lactic acid bacteria. Salivaricin 9 is a newly discovered lantibiotic produced by Streptococcus salivarius. In this study we present the mechanism of action of salivaricin 9 and some of its properties. Also we developed new methods to produce and purify the lantibiotic from strain NU10.

Methodology / Principal Findings

Salivaricin 9 was found to be auto-regulated when an induction assay was applied and this finding was used to develop a successful salivaricin 9 production system in liquid medium. A combination of XAD-16 and cation exchange chromatography was used to purify the secondary metabolite which was shown to have a molecular weight of approximately 3000 Da by SDS-PAGE. MALDI-TOF MS analysis indicated the presence of salivaricin 9, a 2560 Da lantibiotic. Salivaricin 9 is a bactericidal molecule targeting the cytoplasmic membrane of sensitive cells. The membrane permeabilization assay showed that salivaricin 9 penetrated the cytoplasmic membrane and induced pore formation which resulted in cell death. The morphological changes of test bacterial strains incubated with salivaricin 9 were visualized using Scanning Electron Microscopy which confirmed a pore forming mechanism of inhibition. Salivaricin 9 retained biological stability when exposed to high temperature (90-100°C) and stayed bioactive at pH ranging 2 to 10. When treated with proteinase K or peptidase, salivaricin 9 lost all antimicrobial activity, while it remained active when treated with lyticase, catalase and certain detergents.

Conclusion

The mechanism of antimicrobial action of a newly discovered lantibiotic salivaricin 9 was elucidated in this study. Salivaricin 9 penetrated the cytoplasmic membrane of its targeted cells and induced pore formation. This project has given new insights on lantibiotic peptides produced by S. salivarius isolated from the oral cavities of Malaysian subjects.

Cloning and heterologous expression of plnE, -F, -J and -K genes derived from soil metagenome and purification of active plantaricin peptides

Plantaricin gene-specific primers were used to obtain plnE, -F, -J and -K structural gene amplicons from soil metagenome. These amplicons were cloned and expressed in pET32a (+) vector in Escherichia coli BL21 (DE3). PlnE, -F, -J and -K peptides were expressed as His-tagged-fusion proteins and were separated by Ni(2+) -chelating affinity chromatography. The peptides were released from the fusion by enterokinase cleavage and separated from the carrier thioredoxin. The cleaved peptides were further analysed for antimicrobial activity and found to be active against Listeria innocua NRRL B33314, Micrococcus luteus MTCC 106 and lactic acid bacteria, such as Enterococcus casseliflavus NRRL B3502, Lactococcus lactis lactis NRRL 1821, Lactobacillus curvatus NRRL B4562 and Lactobacillus plantarum NRRL B4496. E. coli has been successfully exploited as a host for heterologous expression with a significant yield of fused and cleaved peptides in the range of 8-12 and 1-1.5 mg/l of the culture, respectively. Heterologous expression, therefore, can be used to overcome the constraints of low yield often reported from a native strain.

Purification and characterization of enterocin MC13 produced by a potential aquaculture probiontEnterococcus faeciumMC13 isolated from the gut ofMugil cephalus

A bacteriocin producer strain MC13 was isolated from the gut of Mugil cephalus (grey mullet) and identified as Enterococcus faecium . The bacteriocin of E. faecium MC13 was purified to homogeneity, as confirmed by Tricine sodium dodecyl sulphate – polyacrylamide gel electrophoresis (SDS–PAGE). Reverse-phase high-performance liquid chromatography (HPLC) analysis showed a single active fraction eluted at 26 min, and matrix-assisted laser desorption ionization time of flight (MALDI-TOF) mass spectrometry analysis showed the molecular mass to be 2.148 kDa. The clear zone in native PAGE corresponding to enterocin MC13 band further substantiated its molecular mass. A dialyzed sample (semicrude preparation) of enterocin MC13 was broad spectrum in its action and inhibited important seafood-borne pathogens: Listeria monocytogenes , Vibrio parahaemolyticus , and Vibrio vulnificus . This antibacterial substance was sensitive to proteolytic enzymes: trypsin, protease, and chymotrypsin but insensitive to catalase and lipase, confirming that inhibition was due to the proteinaceous molecule, i.e., bacteriocin, and not due to hydrogen peroxide. Enterocin MC13 tolerated heat treatment (up to 90 °C for 20 min). Enterococcus faecium MC13 was effective in bile salt tolerance, acid tolerance, and adhesion to the HT-29 cell line. These properties reveal the potential of E. faecium MC13 to be a probiotic bacterium. Enterococcus faecium MC13 could be used as potential fish probiotic against pathogens such as V. parahaemolyticus, Vibrio harveyi , and Aeromonas hydrophila in fisheries. Also, this could be a valuable seafood biopreservative against L. monocytogenes.

Skin microbiota: microbial community structure and its potential association with health and disease

Skin, the largest human organ, is a complex and dynamic ecosystem inhabited by a multitude of microorganisms. Host demographics and genetics, human behavior, local and regional environmental characteristics, and transmission events may all potentially drive human skin microbiota variability, resulting in an alteration of microbial community structure. This alteration may have important consequences regarding health and disease outcomes among individuals. More specifically, certain diversity patterns of human microbiota may be predictive or diagnostic of disease. The purpose of this review is to briefly describe the skin microbiota, outline the potential determining factors driving its variability, posit the likelihood of an association between the resulting microbial community structure on the skin with disease outcomes among individuals, and finally, to present some challenges and implications for studying the skin microbiota.

Characterization and structure identification of an antimicrobial peptide, hominicin, produced by Staphylococcus hominis MBBL 2-9

Hominicin, antimicrobial peptide displaying potent activity against Staphylococcus aureus ATCC 25923, methicillin-resistant S. aureus (MRSA) ATCC 11435 and vancomycin-intermediate S. aureus (VISA) CCARM 3501, was purified by chloroform extraction, ion-exchange column chromatography and reverse-phase HPLC from culture supernatant of Staphylococcushominis MBBL 2-9. Hominicin exhibited heat stability up to 121 degrees C for 15min and activity under both acidic and basic conditions (from pH 2.0 to 10.0). Hominicin was cleaved into two fragments after treatment with proteinase K, resulting in the loss of its antibacterial activity, while it was resistant to trypsin, alpha-chymotrypsin, pepsin and lipase. The molecular mass of hominicin determined by mass spectrometry was 2038.4Da. LC-mass spectrometry and NMR spectroscopy analyses of the two fragments revealed the sequence of hominicin as DmIle-Dhb-Pro-Ala-Dhb-Pro-Phe-Dhb-Pro-Ala-Ile-Thr-Glu-Ile-Dhb-Ala-Ala-Val-Ile-Ala-Dmp, which had no similarity with other antimicrobial peptides previously reported. The present study is the first report of this novel antimicrobial peptide, which has uncommon amino acid residues like the ones in Class I group and shows potent activity against clinically relevant S. aureus, MRSA and VISA.

Activity assay for nisin-like acidic bacteriocins using an optimal pH-conditioned gel matrix

A new zymography for detecting nisin-like acidic bacteriocins was developed using a tricine-sodium dodecyl sulfate (SDS) gel and an acidic gel matrix (pH 4.0). After electrophoresis, proteins in the tricine gel were electrotransferred to an optimal pH-conditioned gel matrix (OP-CGM). The OP-CGM was overlaid with indicator cells (Bacillus cereus) embedded in nutrient broth soft agar (0.8%, w/v). Antibacterial activity shown as a growth inhibition using B. cereus was detected at approximately 3.8kDa. Because nisin is unstable in buffers at pH values over 6.0, the common electrophoretic systems, SDS-polyacrylamide gel electrophoresis and tricine gel, are not suitable for detection of nisin-like acidic bacteriocins.

Identification of a bacteriocin and its cognate immunity factor expressed by Moraxella catarrhalis

Background

Bacteriocins are antimicrobial proteins and peptides ribosomally synthesized by some bacteria which can effect both intraspecies and interspecies killing.

Results

Moraxella catarrhalis strain E22 containing plasmid pLQ510 was shown to inhibit the growth of M. catarrhalis strain O35E. Two genes (mcbA and mcbB) in pLQ510 encoded proteins predicted to be involved in the secretion of a bacteriocin. Immediately downstream from these two genes, a very short ORF (mcbC) encoded a protein which had some homology to double-glycine bacteriocins produced by other bacteria. A second very short ORF (mcbI) immediately downstream from mcbC encoded a protein which had no significant similarity to other proteins in the databases. Cloning and expression of the mcbI gene in M. catarrhalis O35E indicated that this gene encoded the cognate immunity factor. Reverse transcriptase-PCR was used to show that the mcbA, mcbB, mcbC, and mcbI ORFs were transcriptionally linked. This four-gene cluster was subsequently shown to be present in the chromosome of several M. catarrhalis strains including O12E. Inactivation of the mcbA, mcbB, or mcbC ORFs in M. catarrhalis O12E eliminated the ability of this strain to inhibit the growth of M. catarrhalis O35E. In co-culture experiments involving a M. catarrhalis strain containing the mcbABCI locus and one which lacked this locus, the former strain became the predominant member of the culture after overnight growth in broth.

Conclusion

This is the first description of a bacteriocin and its cognate immunity factor produced by M. catarrhalis. The killing activity of the McbC protein raises the possibility that it might serve to lyse other M. catarrhalis strains that lack the mcbABCI locus, thereby making their DNA available for lateral gene transfer.