Development of Wide-Spectrum Hybrid Bacteriocins for Food Biopreservation

Synergy Assessment of Four Antimicrobial Bioactive Compounds for the Combinational Treatment of Bacterial Pathogens

Antimicrobial resistance (AMR) has become a topic of great concern in recent years, with much effort being committed to developing alternative treatments for resistant bacterial pathogens. Drug combinational therapies have been a major area of research for several years, with modern iterations using combining well-established antibiotics and other antimicrobials with the aim of discovering complementary mechanisms. Previously, we characterised four GRAS antimicrobials that can withstand thermal polymer extrusion processes for novel medical device-based and therapeutic applications. In the present study, four antimicrobial bioactive-silver nitrate, nisin, chitosan and zinc oxide-were assessed for their potential combined use as an alternative synergistic treatment for AMR bacteria via a broth microdilution assay based on a checkerboard format. The bioactives were tested in arrangements of two-, three- and four-drug combinations, and their interactions were determined and expressed in terms of a synergy score. Results have revealed interesting interactions based on treatments against recognised test bacterial strains that cause human and animal infections, namely E. coli, S. aureus and S. epidermidis. Silver nitrate was seen to greatly enhance the efficacy of its paired treatment. Combinations with nisin, which is a lantibiotic, exhibited the most interesting results, as nisin has no effect against Gram-negative bacteria when used alone; however, it demonstrated antimicrobial effects when combined with silver nitrate or chitosan. This study constitutes the first study to both report on practical three- and four-drug combinational assays and utilise these methods for the assessment of established and emerging antimicrobials. The novel methods and results presented in this study show the potential to explore previously unknown drug combination compatibility measures in an ease-of-use- and high-throughput-based format, which can greatly help future research that aims to identify appropriate alternative treatments for AMR, including the screening of potential new bioactives biorefined from various sources.

Understanding the Necessity of Regulatory Protein Machinery in Heterologous Expression of Class-III Type of Ocins

To date, there have been no or just a few reports of successful cloning and expression to create biologically active ocins or bacteriocins. Cloning, expression, and production of class I ocins are problematic because of their structural arrangements, coordinated functions, size, and posttranslational modifications. Mass synthesis of these molecules is necessary for commercialization and to restrict the excessive use of conventional antibiotics, which encourages the development of antibiotic-resistant bacteria. In the case of class III ocins, there are no reports of obtaining biological active proteins to date. Being able to obtain biologically active proteins requires an understanding of mechanistic features due to their expanding importance and broad spectrum of activity. As a result, we intend to clone and express the class III type. The class I types that are devoid of posttranslational modifications were transformed into class III through fusion. Therefore, this construct resembles a class III type ocin. With the exception of Zoocin, expression of the proteins was found to be physiologically ineffective after cloning. But, few cell morphological changes such as elongation, aggregation, and the formation of terminal hyphae were observed. However, it was discovered that the target indicator had been altered to Vibrio spp. in a few. All the three ocins were subjected to in-silico structure prediction/analysis. Finally, we confirm the existence of unidentified additional intrinsic factors for successful expression to obtain biologically active protein.

Probiotics, prebiotics and synbiotics: Safe options for next-generation therapeutics

Abstract

Probiotics have been considered as an economical and safe alternative for the treatment of a large number of chronic diseases and improvement of human health. They are known to modulate the host immunity and protect from several infectious and non-infectious diseases. The colonization, killing of pathogens and induction of host cells are few of the important probiotic attributes which affect several functions of the host. In addition, prebiotics and non-digestible food substances selectively promote the growth of probiotics and human health through nutrient enrichment, and modulation of gut microbiota and immune system. This review highlights the role of probiotics and prebiotics alone and in combination (synbiotics) in the modulation of immune system, treatment of infections, management of inflammatory bowel disease and cancer therapy.

Key points

• Probiotics and their derivatives against several human diseases.

• Prebiotics feed probiotics and induce several functions in the host.

• Discovery of novel and biosafe products needs attention for human health.

Antibacterial Activity of Pediocin and Pediocin-Producing Bacteria Against Listeria monocytogenes in Meat Products

One of the most important challenges in the food industry is to produce healthy and safe food products, and this could be achieved through various processes as well as the use of different additives, especially chemical preservatives. However, consumer awareness and concern about chemical preservatives have led researchers to focus on the use of natural antimicrobial compounds such as bacteriocins. Pediocins, which belong to subclass IIa of bacteriocin characterized as small unmodified peptides with a low molecular weight (2.7-17 kDa), are produced by some of the Pediococcus bacteria. Pediocin and pediocin-like bacteriocins exert a broad spectrum of antimicrobial activity against Gram-positive bacteria, especially against pathogenic bacteria, such as Listeria monocytogenes through formation of pores in the cytoplasmic membrane and cell membrane dysfunction. Pediocins are sensitive to most protease enzymes such as papain, pepsin, and trypsin; however, they keep their antimicrobial activity during heat treatment, at low temperatures even at -80°C, and after treatment with lipase, lysozyme, phospholipase C, DNase, or RNase. Due to the anti-listeria activity of pediocin on the one hand and the potential health hazards associated with consumption of meat products on the other hand, this review aimed to investigate the possible application of pediocin in preservation of meat and meat products against L. monocytogenes.

Overview of Nanocellulose in Food Packaging

BACKGROUND

The rising concern with environmental preservation has led to increasing interest in biodegradable polymer composites from renewable sources, such as cellulose and its derivatives. The use of nanocellulose is an innovative food packaging trend.

DISCUSSION

This paper presents an overview and discusses the state of the art of different nanocellulose materials used in food and food packaging, and identifies important patents related to them. It is important to consider that before marketing, new products must be proven safe for consumers and the environment.

CONCLUSION

Several packaging materials using nanocellulose have been developed and shown to be promising for use as active and intelligent materials for food packaging. Other nanocellulose products are under investigation for packaging and may enter the market in the near future. Many countries have been adjusting their regulatory frameworks to deal with nanotechnologies, including nanocellulose packaging.

Antimicrobial activity of MccJ25(G12Y) against gram-negative foodborne pathogens in vitro and in food models

The use of bacteriocins is a promising alternative to improve food security through the biocontrol of food pathogens and spoilage microorganisms. Gram-negative produced microcin J25(G12Y), known as (MccJ25(G12Y)) is a variant of the well-studied and characterized antimicrobial peptide, microcin J25 (MccJ25). In the present work, we explored the activity of this microcin against Gram-negative bacteria linked to foodborne diseases. We evaluated the in vitro antimicrobial activity of MccJ25(G12Y) in solid medium against a collection of pathogenic and food-altering strains and studied its activity and stability in meat and dairy food systems. We show that MccJ25(G12Y) exhibited the same in vitro antimicrobial spectrum as its parental microcin (MccJ25) against different Gram-negative foodborne pathogens and spoilage strains. We highlight that low concentrations of MccJ25(G12Y) between 0.45 and 29.4 μM were able to inhibit a substantial number of pathogens, including Salmonella, Escherichia, Shigella and Enterobacter genus. We also demonstrate the antimicrobial effectiveness of the peptide against Escherichia coli O157:H7 NCTC 12900, Enterobacter cloacae CECT 194, and Salmonella enterica CECT 4396 in fish and beef burgers and yogurt. MccJ25(G12Y) was added or not to food matrices inoculated with the foodborne pathogens at 10⁵ CFU/g or mL. Afterward, food products were stored at 4 °C and selective media for the specific enumeration were used to determine the antimicrobial susceptibility of each pathogen to MccJ25(G12Y). The viability of the three pathogens was significantly reduced in the different food biological environments. In yogurt, the peptide decreased E. coli numbers on day 5 by about 4 log 10 CFU/mL as compared to non-treated samples. For S. enterica and E. cloacae no viable cells were detected at the end of the treatment. Adding MccJ25(G12Y) to fish burgers decreased E. cloacae numbers during storage 2 log₁₀ CFU/g on the first day, reaching a difference of about 5 log 10 CFU/g after 10 days compared to non-treated control. Finally, the peptide decreased E. coli O157:H7 numbers on the beef burgers samples during storage on day 10 by about 3 log 10 CFU/g as compared to non-treated samples. The stability analysis demonstrated that MccJ25(G12Y) is capable of remaining active in these food matrices for a considerable time during the storage at refrigeration temperatures. These results reinforce the studies on the potential applicability of this microcin as a biopreservative in the food industry.

Mining and Statistical Modeling of Natural and Variant Class IIa Bacteriocins Elucidate Activity and Selectivity Profiles across Species

Class IIa bacteriocin antimicrobial peptides (AMPs) are a compelling alternative to current antimicrobials because of potential specific activity toward antibiotic-resistant bacteria, including vancomycin-resistant enterococci. Engineering of these molecules would be enhanced by a better understanding of AMP sequence-activity relationships to improve efficacy in vivo and limit effects of off-target activity. Toward this goal, we experimentally evaluated 210 natural and variant class IIa bacteriocins for antimicrobial activity against six strains of enterococci. Inhibitory activity was ridge regressed to AMP sequence to predict performance, achieving an area under the curve of 0.70 and demonstrating the potential of statistical models for identifying and designing AMPs. Active AMPs were individually produced and evaluated against eight enterococcus strains and four Listeria strains to elucidate trends in susceptibility. It was determined that the mannose phosphotransferase system (manPTS) sequence is informative of susceptibility to class IIa bacteriocins, yet other factors, such as membrane composition, also contribute strongly to susceptibility. A broadly potent bacteriocin variant (lactocin DT1) from a Lactobacillus ruminis genome was identified as the only variant with inhibitory activity toward all tested strains, while a novel enterocin variant (DT2) from an Enterococcus faecium genome demonstrated specificity toward Listeria strains. Eight AMPs were evaluated for proteolytic stability to trypsin, chymotrypsin, and pepsin, and three C-terminal disulfide-containing variants, including divercin V41, were identified as compelling for future in vivo studies, given their high potency and proteolytic stability.IMPORTANCE Class IIa bacteriocin antimicrobial peptides (AMPs), an alternative to traditional small-molecule antibiotics, are capable of selective activity toward various Gram-positive bacteria, limiting negative side effects associated with broad-spectrum activity. This selective activity is achieved through targeting of the mannose phosphotransferase system (manPTS) of a subset of Gram-positive bacteria, although factors affecting this mechanism are not entirely understood. Peptides identified from genomic data, as well as variants of previously characterized AMPs, can offer insight into how peptide sequence affects activity and selectivity. The experimental methods presented here identify promising potent and selective bacteriocins for further evaluation, highlight the potential of simple computational modeling for prediction of AMP performance, and demonstrate that factors beyond manPTS sequence affect bacterial susceptibility to class IIa bacteriocins.

Bacteriocin-like inhibitory substance of Pediococcus pentosaceus as a biopreservative for Listeria sp. control in ready-to-eat pork ham

The growing demand of consumers for synthetic chemical-free foods has increased the search for natural preservatives such as bacteriocins and bacteriocin-like inhibitory substances (BLIS) to give them adequate microbiological safety, sensory characteristics, and shelf life. In this study, the antimicrobial activity of BLIS produced by Pediococcus pentosaceus ATCC 43200 was compared with that of nisin. Lactobacillus sakei ATCC 15521, Listeria seeligeri NCTC 11289, Enterococcus En2052 and En2865, and Listeria monocytogenes CECT 934 and NADC 2045 exhibited larger inhibition halos in BLIS-treated than in Nisaplin-treated samples, unlike Listeria innocua NCTC 11288. In artificially contaminated ready-to-eat pork ham, BLIS was effective in inhibiting the growth of L. seeligeri NCTC 11289 for 6 days (counts from 1.74 to 0.00 log CFU/g) and ensured lower weight loss (2.7%) and lipid peroxidation (0.63 mg MDA/kg) of samples compared with the control (3.0%; 1.25 mg MDA/kg). At the same time, coloration of ham samples in terms of luminosity, redness, and yellowness as well as discoloration throughout cold storage was not influenced by BLIS or Nisaplin taken as a control. These results suggest the potential use of P. pentosaceus BLIS as a biopreservative in meat and other food processing industries.

Features and applications of Ent35-MccV hybrid bacteriocin: current state and perspectives

Bacteriocins are peptides of ribosomal synthesis that are active against bacteria related to the producing strain. They have been widely used in the food industry as biopreservatives. The generation of hybrid peptides by combining the genes that encode two different bacteriocins has made it possible to study the mechanisms of action of the bacteriocins that compose them and also develop new peptides with improved biotechnological applications. Hybrid bacteriocins may be obtained in several ways. In our laboratory, by combining enterocin CRL35 and microcin V (Ent35-MccV), we obtained a broad-spectrum peptide that is active against both Gram-positive and Gram-negative bacteria. Ent35-MccV is sensitive to the action of intestinal proteases and is heat resistant, which makes it a good candidate for use as a biopreservative. For this reason, the peptide was tested in skim milk and beef burgers as food models. We also obtained more potent variants of the hybrid by modifying the central amino acid of the hinge region that connects the two bacteriocins. This review also discusses future applications and perspectives regarding the Ent35-MccV and other hybrid peptides.Key Points• Ent35-MccV is a new broad-spectrum bacteriocin.• The mechanism of action of bacteriocins can be studied using hybrid peptides.• Genetic engineering allows obtaining improved bacteriocin derivatives.• Hybrid peptides can be used in the food, pharmaceutical, and veterinary applications.

Obtaining an Ent35-MccV derivative with mutated hinge region that exhibits increased activity against Listeria monocytogenes and Escherichia coli

The present paper describes the generation of derivatives from the hybrid peptide called Ent35-MccV, active against Gram-positive and Gram-negative bacteria. This peptide has a triple glycine hinge region between enterocin CRL35 and microcin V. In order to obtain variants of Ent35-MccV with greater biotechnological potential, a saturation mutagenesis was carried out in the hinge region. As a result, we obtained a bank of E. coli strains expressing different mutated hybrid bacteriocins in the central position of the hinge region. From all these variants, we found that the one bearing a tyrosine in the central region of the hinge (Ent35-GYG-MccV) is 2-fold more active against E. coli and 4-fold more active against Listeria than the original peptide Ent35-MccV. This derivative was purified and characterized. The development and evaluation of alternative hinges for Ent35-MccV represents a step forward in the bioengineering of antimicrobial peptides. This approach fosters the rational design of peptides with enhanced antimicrobial activity.

An active indirect solar system for food products drying

An energy independent active indirect solar drying system for the study of food products drying at specific climate conditions was developed and tested. As a model material, sliced tomato was selected because of its short shelf live, high humidity and potential to be a high value dried product. Indirect solar dryer enabled complete protection of the dried material against sunlight, birds, insects, rain and dust during the drying process. The solar dryer system design includes a rectangular section (1000 × 600 × 400) mm chamber and a flat solar collector (1500 × 600 × 100) mm with the surface area of 0.9 m2. Air flow was induced by a fan installed at the inlet of the collector and powered by a photovoltaic solar panel and a battery system. Temperature and humidity of air were monitored at the collector inlet, collector outlet and the drying chamber outlet. The key element of the collector is a 10.5 m long rectangular section aluminum pipe (55 × 35) mm coated with an absorption layer. The maximum dryer capacity is around 3 kg of wet material (sliced tomato) per batch. Average air temperature increase in the collector was measured to be 30 °C during the winter season. Air relative humidity decreased from 21 % to 15 % after passing through the collector. The moisture of tomato slices decreased from the initial value of 92 % down to 22 % during the time of the experiment (30 h). Quality of tomatoes dried using the designed solar dryer differed significantly in color as well as in texture from those dried by the commonly used methods, like an open sun drying system. Equilibrium moisture content of the product was reached after 30 h in December when the maximum outside temperature was 17.6 °C. The tomato mass decreased from 333 g to 33.15 g; the mass loss being approximately 90 %. The heated air temperature and humidity at the dryer inlet and outlet were influenced by the change of the ambient temperature and humidity during the day. Variation of the drying rate with the change of the ambient temperature and humidity was observed. During summer, when the sun radiation increases, the drying time for sliced tomato with 9 mm thickness decreased from 25 h to 15 h. The sample thickness also has an impact on the drying process. When the sample thickness increased from 9 mm to 12 mm, the drying time increased from 15 h to 20 h of active device time.

Bactericidal Activity and Synergy Studies of Peptide AP-CECT7121 Against Multi-resistant Bacteria Isolated from Human and Animal Soft Tissue Infections

AP-CECT7121 is an antimicrobial peptide, produced by Enterococcus faecalis CECT7121, with bactericidal activity against Gram-positive bacteria. The aim of this study was to evaluate the bactericidal activity of AP-CECT7121, alone and with gentamicin, against multi-resistant bacteria isolated from human and animals with soft tissue infections. During the period 2014-2015, bacterial strains producing human and animal soft tissue infections were studied. Samples from patients attended at a general hospital and cattle from four dairies in the Province of Buenos Aires (Argentina) were included. Twenty-two methicillin-resistant Staphylococcus aureus (11, human blood samples; 11, cow milk) and five vancomycin-resistant Ent. faecium strains isolated from four mastitic dairy cows were tested. AP-CECT7121 (12 mg/L) potency was assessed by time-kill curves alone or with sub-inhibitory concentrations of gentamicin. All staphylococcal strains were susceptible to gentamicin; enterococci did not show high-level gentamicin resistance. Colony counts were carried out at 0, 2, 4, 8, and 24 h of incubation. AP-CECT7121 showed bactericidal activity against all the enterococcal strains. In addition, AP-CECT7121 had a bactericidal effect on most staphylococci (16/22). Early AP-CECT7121/gentamicin synergy (4-8 h) for all staphylococci was detected. At 24 h, synergy (19/22) and indifference (3/22) were observed. Synergy with gentamicin was detected for staphylococci. AP-CECT7121 constitutes an attractive candidate for its use as a natural therapeutic tool for the treatment of infections produced by multi-resistant Staph. aureus and vancomycin-resistant Ent. faecium isolated from humans and animals.

Bacteriocin Produced from Lactobacillus plantarum ATM11: Kinetic and Thermodynamic Studies

In the present study, the effect of heat treatment on the activity of bacteriocin from Lactobacillus plantarum ATM11 was studied. The kinetic and thermodynamic parameters were calculated for the thermal inactivation of the bacteriocin over a time–temperature combinations in the range of 30, 45, 60 and 90 min and 60, 65, 70, 75 and 80 °C. Understanding the thermal inactivation of biopreservatives in a food matrix is essential to allow their proper utilization in food industry, enabling the reduction of heating times and optimization of heating temperature. The results indicate the different thermal stabilities with k-values between 0.0159 and 0.0225 min−1. D-values decreased with increase in temperature, indicating faster inactivation of the bacteriocin at higher temperatures. These results suggest that bacteriocin is relatively heat stable with a z-value of 22.85 °C.

Antimicrobial peptides targeting Gram-negative pathogens, produced and delivered by lactic acid bacteria

We present results of tests with recombinant Lactococcus lactis that produce and secrete heterologous antimicrobial peptides with activity against Gram-negative pathogenic Escherichia coli and Salmonella . In an initial screening, the activities of numerous candidate antimicrobial peptides, made by solid state synthesis, were assessed against several indicator pathogenic E. coli and Salmonella strains. Peptides A3APO and Alyteserin were selected as top performers based on high antimicrobial activity against the pathogens tested and on significantly lower antimicrobial activity against L. lactis . Expression cassettes containing the signal peptide of the protein Usp45 fused to the codon-optimized sequence of mature A3APO and Alyteserin were cloned under the control of a nisin-inducible promoter PnisA and transformed into L. lactis IL1403. The resulting recombinant strains were induced to express and secrete both peptides. A3APO- and Alyteserin-containing supernatants from these recombinant L. lactis inhibited the growth of pathogenic E. coli and Salmonella by up to 20-fold, while maintaining the host's viability. This system may serve as a model for the production and delivery of antimicrobial peptides by lactic acid bacteria to target Gram-negative pathogenic bacteria populations.

Class IIa bacteriocins: diversity and new developments

Class IIa bacteriocins are heat-stable, unmodified peptides with a conserved amino acids sequence YGNGV on their N-terminal domains, and have received much attention due to their generally recognized as safe (GRAS) status, their high biological activity, and their excellent heat stability. They are promising and attractive agents that could function as biopreservatives in the food industry. This review summarizes the new developments in the area of class IIa bacteriocins and aims to provide uptodate information that can be used in designing future research.

A new hybrid bacteriocin, Ent35-MccV, displays antimicrobial activity against pathogenic Gram-positive and Gram-negative bacteria

Bacteriocins and microcins are ribosomally synthesized antimicrobial peptides that are usually active against phylogenetically related bacteria. Thus, bacteriocins are active against Gram-positive while microcins are active against Gram-negative bacteria. The narrow spectrum of action generally displayed by bacteriocins from lactic acid bacteria represents an important limitation for the application of these peptides as clinical drugs or as food biopreservatives. The present study describes the design and expression of a novel recombinant hybrid peptide combining enterocin CRL35 and microcin V named Ent35–MccV. The chimerical bacteriocin displayed antimicrobial activity against enterohemorrhagic Escherichia coli and Listeria monocytogenes clinical isolates, among other pathogenic bacteria. Therefore, Ent35–MccV may find important applications in food or pharmaceutical industries.