Bacteriocins and Their Impact on Our Lives and Agriculture - Essay Example

Bacteriocins and Their Impact on Our Lives and Agriculture Introduction Bacteriocins consist of a wide range of diverse ribosomally synthesized antimicrobial peptides that are produced either by bacteria or by archea. Our understanding of bacteriocins is still limited, yet growing, and the indications are that bacteriocins have the potential for several applications in increasing our immunity to microbial pathogens and in the food industry (Dobson et al., 2012) “Bacteriocins are bacterially produced antimicrobial peptides with narrow or broad host ranges” (Cotter, Hill & Ross, 2005, p. 777). Within this simple description of a set of proteins lies a new story in the continuing search for weapons in the fight against bacteria. The seeds for the possible antagonistic interaction between competing bacteria were planted by Pasteur and Joubert in 1877, through their observation of the inhibitory action of some strains of Escheria coli (E.coli) on the growth of Bacillus anthracis in infected animals. Andre Gratia was the first to uncover the inhibition property of bacteriocins in a compound he named colicin v, which was released by a virulent strain of E.coli bacteria. In 1954, Pierre Frederic uncovered the genetic determinates of colicin, as a conjugation transmissible element that is similar to the F factor. Since then a host of bacteriocins have been discovered, and our understanding of the usefulness of bacteriocins moves forward (Scienceray, 2012). Bacteriocins Bacteriocins are a constituent of the wide array of microbial defense systems. All bacteria produce bacteriocins (Riley & Chavan, 2007). These bacteriocins are proteinaceous compounds, which are lethal to bacteria other than the releasing strain. The spectrum of antibacterial activity can vary from narrow spectrum, with confined inhibition of closely related bacterial species or broad to include several of the other bacterial species (Joerger, 2003). Bacteriocins from gram positive bacteria are associated with the broader range of antibacterial range of activity. While initial studies were focused on colicins from E-coli and the bacteriocins from other gram negative bacteria, the current focus of studies on bacteriocins is on the bacteriocins from the gram positive bacteria, as they are assumed to have more application in humans and in foods and other products (Chen & Hoover, 2003). At first glance there may be a tendency to classify the bacteriocins as an extension of the traditional peptide antibiotics, because they are synthesized peptides. Yet, they are different, and it is in the essence of this difference that their utility lies. Unlike peptide antibiotics, which are synthesized by enzymes bacteriocins are ribosomally synthesized peptides. In addition, while typical antibiotics are active against a broad range of bacteria, bacteriocins have a narrow range of activity within its own bacteria species or closely related bacteria species. Furthermore, there is an important and unique difference in the potency. Within its narrow range of antibacterial activity it is potent in nanomolar concentrations, while in the case of antibiotics a much higher concentration is required for potent antibiotic activity. Though the initial origins and studies on bacteriocins pertain to those produced by gram negative bacteria, the current research on bacteriocins focuses more on the bacteriocins produced by gram positive bacteria, because of the greater potential utility seen in them. Any evaluation of bacteriocins produced by gram positive bacteria is best undertaken by studying them as two groups, namely the heat-stable lantibiotics and the nonmodified heat-stable bacteriocins (Nes, 2011). Bacteriocins from the gram positive lactobacillus are the most investigated group of bacteriocins. Class – I of these bacteriocins consist of the lantibiotics, which are heat stable. They comprise of post-transitionally modified peptides, having multiple rings, bridged by lanthiones or methyllanthionine residues (Zendo & Sonomoto, 2011). Class I bacteriocins are further subdivided into type A and type, essentially on structural modifications and mode of action. Nisin and subtilin are two important bacteriocides in type A. These lantibiotics feature elongated and catatonic amphiphilic polypeptides, with their mode of action based on disruption of the proton motive force at the cytoplasmic membrane. Type B bacteriocides are neutral and globular amphiphilic polypeptides. Their mode of action is based on enzyme inhibition and as immunoadjuvants. Duramycin and cinnamycin are two examples of type B bacteriocides (Hoover, 2000). The nonmodified heat stable bacteriocins make up Class II. These bacteriocins from lactic acid bacteria are small heat-stable membrane-active nonlanthione peptides. Leucocin is an example of a Class II bacteriocin (Hoover, 2000). The Class II bacteriocins have been mostly found to occur from lactic acid bacteria. This feature may be a result of either Class II bacteriocins being associated with lactic acid bacteria or because lactic acid bacteria have been most studied bacteria with regard to bacteriocins. The antimicrobial activity of lactic acid bacteria was traditionally believed to be due to the production of organic acid, predominantly lactic acid, However, the discovery of bacteriocins from lactic acid bacteria has caused a revision in the concept of antimicrobial activity of lactic acid bacteria. Between 1989 and 1991 several bacteriocins from lactic acid were uncovered and termed as lactococcins. Subsequently a large number of bacteriocins were chemically and genetically identified. Separation of the Class II bacteriocins into subtypes has proven to be a difficult task, because of the wide diversity present in them and the lack of unifying factors that can be used for grouping. Attempts have been made to subtype the Class II bacteriocins, but these attempts are still to receive universal acceptance (Nes, Brede & Holo, 2006). There are two other classes of bacteriocins. The Class III bacteriocins consist of heat-labile proteins. Millericin B is an example of a Class III bacteriocin. They are believed to act against susceptible bacteria by hydrolyzing specific peptide bonds in the stem or interpeptide bridges in the peptidoglycan layer of these bacteria. The identifying feature given to the Class IV bacteriocins is the presence of sugar or lipid moities. Details of the Class IV bacteriocins still remain uncovered, because no such bacteriocin has been purified, which also suggests the possible revision of this Class of bacteriocides (Zendo & Sonomoto, 2011). Bacteriocins from lactic acid bacteria constitute the most important bacteriocins from the perspective of their utility for several purposes to humans. Lactic acid is frequently found in the foods consumed by human beings, and also unconsciously added in the manufacture of fermented foods. It is an accepted fact that lactic acid bacteria assist in preserving food and also enhancing the taste of the food in which they are present. The food preserving action is the result of the bacteriocins from lactic acid bacteria inhibits the growth of bacteria that are responsible for spoiling food. In fact Nisin A bacteriocin from lactic acid bacteria has been used in food preservation for over three decades around the world. The efficacy and safety in the use of Nisin A has given rise to the promise of bacteriocins being of use to humans, which has led to the search for bacteriocins for several applications (Zendo & Sonomoto, 2011). Several events have contributed to the enhanced number of investigations into bacteriocins from lactic acid bacteria for applications. These events start with the effective and safe use of Nisin A, and move on to include Food and Drug Administration (FDA) approval of Nisin for certain applications in the food industry; growing consumer resistance to the use of traditional chemical preservatives by the food industry, and the growing clamor for the use of natural preservatives by the food industry; rational worries over the safety of the currently used preservatives like nitrates and sulfites; the growing awareness that bacteriocins and their bacteriogenecity are not a rarity in lactic acid bacteria; the feasibility the utilization bacteriocin generation and immunity for selected markers in starter culture bacteria; advances in microbiology techniques that permit transferring, cloning, and sequencing of the genetic determinants, and also engineering the genetic determinants of bacteriocins; and the financial support that is coming from federal funding agencies, food groups and associations of the food industry, and food processing industry for continued research in the basic as well as applications research on bacteriocins (Hoover, 2000). Applications in Humans In the recent past several bacteriocins produced by the lactic acid bacteria (LAB) have been found with either a narrow or broad spectrum of antibacterial activity against gram positive bacteria, with the potential to be developed as antibacterial agents for use in the human body. Bacteriocins of gram positive bacteria are mostly small, stable, and have a broad spectrum of anti-bacterial activity. Recent reviews of their antibacterial activity have been excellent, showing their potential for antibacterial therapy in humans (Nes, Deep & Holo, 2007). An example for potential use of bacteriocins in antibacterial therapy in humans is in the treatment of Clostridium difficile infections in the human distal colon. Antibiotics Vancomycin and Metronidazole, as also the bacteriocin lacticin 3147, are active against Clostridium difficile. However, their broad spectrum of activity poses a threat to the human gut microbiota. A narrow spectrum bacteriocin from Bacillus thuringiensis is equally effective against Clostridium difficile without the disadvantage of risk to the microbial flora in the human gut (Rea et al., 2011). A major area of concern in the treatment of bacterial infections in humans and animals is the dramatic rise in antibiotic resistant bacteria. As a consequence to this, currently the focus in the development of antibiotics pertains to the identification, development, and redesign of antibacterial agents against bacteria that have developed resistance to the antibiotics in the human armory to fight them. Bacteriocins have shown extreme promise as a novel approach in human health and veterinary medicine as replacements for the classical antibiotics that have lost their edge to resistant bacteria. Though, it is still early days in the evaluation of the evidence for the successful development of bacteriocins that can replace the traditional antibiotics in use, the increasing number of patents aimed at the use of bacteriocins is a clear indication of the expected role of bacteriocins in the new and novel designs in the battle against pathogenic bacteria and their development of resistance. A spin off in the novel development of bacteriocins in the fight against pathogenic bacteria is the possibility of their use in the treatment of tumors. The possibility of exploiting bacteriocins-based drugs that target and destroy prokaryotic as well as eukaryotic cells is the basis of the possible use of bacteriocins in the treatment of malignant tumors (Gillor & Ghazaryan, 2007). Staphylococcus aureus is the most common pathogen in skin infections, and methicillin-resistant staphylococcus aureus (MRSA) has become a major area of concern in health care institutions. Vancomycin is the last resort antibiotic used in the treatment of MRSA, but with limited success. Mercadin a lantibiotic from the bacillus species of bacteria has demonstrated the capacity to inhibit MRSA strains in vivo in mice, by inhibiting the cell wall synthesis in MRSA, offering a possible alternative to vancomycin in the treatment of MRSA. It is also active against propionibacterium acnes, demonstrating its possible use in personal care also (Dicks et al., 2011). Applications in Agriculture Consumers expect to receive health-promoting benefits, in addition to nutrition, from foods consumed by them. Reduction of adulteration and bio-preservation are other important features in consumer expectations. The use of bacteriocins offers these benefits to food consumers. For example, bacteriocins are the best available bio-preservatives (Mills et al., 2011). Bacteriocins offer the possibility to reduce the intensity of heat treatments to kill bacteria, thereby retaining the nutritional properties present in the food. Thus, consumer requirements of safe, fresh tasting, ready-to-eat, and minimally processed foods can be met. Narrow spectrum bacteriocins can be employed to destroy harmful bacteria without affecting the harmless microbiota present in the food. Immobilized bacteriocins can be used for bioactive food packaging applications. Currently, nisin and pediocin are commercially available as bacteriocins, with many more promising candidates in the pipeline (Galvez et al, 2007). Expected Major Advance in Bacteriocins Though only bacteriocins Nisin A and Pediocin PA-1 have found application in the food industry as agents to protect against spoilage and pathogenic organisms, in the future there is every reason to look forward to varied applications of bacteriocins in the food industry. These applications could see them being used as food processors, since it is possible to use them with hurdle approaches to enable better safety and quality, particularly in the light of the growing demand for such features in food and food products by reducing the processing of food and removal of artificial food preservatives . In the case of uncooked ready-to-eat vegetables, the future may witness inexpensive bacteriocin washes to preserve and retain the freshness in these vegetables. Bacteriocins have shown prowess in their ability to inhibit many pathogens resistant to traditional antibiotics. In the future it is quite likely that bacteriocins will be added singly or in combination to the arsenal to combat not juts deadly pathogens, but also tumors in the human body (Collins et al., 2010). (Word Count – 2124) References Chen, H., & Hoover, D. G. (2003). Bacteriocins and their food applications. Comprehensive Reviews in Food Science and Food Safety, 2, 82-100. 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