Bacteriocin Resistance

In order to effectively exploit the potential of bacteriocin applications we have to learn more about their mode of action since it becomes increasingly evident that the presumption that bacteriocins act by directly forming pores in the cytoplasmic membrane is not always true. The mechanisms by which these antimicrobial peptides act appear to be nearly as diverse as their structures and physicochemical properties. 

Bacteria can also develop resistance in a susceptible strain upon long exposure to bacteriocins. However, the frequency of resistance development varies greatly depending on both the type of bacteriocins and the sensitive bacteria, which likely reflects their different modes of action (Gravesen et al. 2002a). There are also examples of intrinsic resistance mechanisms (Collins et al. 2010 McBride and Sonenshein 2011). 

It is well known that transporters play a role in bacteriocin producer self-immunity for different classes of bacteriocins, including lantibiotics (Draper et al. 2008) and circular bacteriocins (Martinez-Bueno et al. 1998 Kempaman et al. 2003). Different transporter complexes have also been shown 

There are several reasons for the limited success in commercial application of bacteriocins. Their physiochemical properties seem to be an obstacle when applied in a chemically complex environment such as food and feed. Being positively charged and hydrophobic/anphiphilic they will attach to negatively charged and/or lipophilic surfaces/molecules that will actually make the bacteriocins less available to reach target bacteria. There have been a great number of excellent works and reviews in recent years that directly deal with applications of bactoiocins in foods, therefore this field will not be treated in this review. We will focus on medical-related applications of bacteriocins and the potential of bacteriocin-producing bacteria as probiotics. 

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Gravesen, A., Jydegaard Axelsen, A.M., Mendes da Silva, J., et al. (2002a). Frequency of bacteriocin resistance development and associated fitness costs in Listeria monocytogenes. Appl Environ Microbiol 68, 756—764. 

Vadyvaloo, V, Hastings, J.W., van der Merwe, M.J., and Rautenbach, M. (2002b). Membranes of class 11a bacteriocin-resistant Listeria manacytagenes cells contain increased levels of desaturated and short-acyl-chain phosphatidylglyc-erols. Appl Enviran Micrabial 68, 5223—5230. 

Because of mounting consumer resistance to the excessive use of sulfur dioxide and other chemical preservatives in wine, the use of bacteriocins as preservatives has generated interest among researchers. In a study by Schoeman et al (1999), bactericidal yeast strains were developed by... 

Plasmids are autonomous, circular DNA molecules (from around 1 kilobase pairs (kb) to several hundreds of kb in size) that are capable of self-replication within a bacterial cell (Figure 1). Plasmids contain some genes involved in their own replication and transfer between bacteria, but can also harbor additional genes that can impart such biochemical capabilities as antibiotic resistance, utilization of additional nutrients, production of pathogenic factors, nitrogen fixation, or the production of bacteriocins. 

Consumer resistance to the use of synthetic additives in foods has stimulated interest in natural additives and preservatives. The principal natural additive used in cheese is the bacteriocin, nisin. Bacteriocins are peptides which inhibit a limited range of bacteria, usually closely related to the producer organism. The potential of nisin, produced by Lactococcus lactis, as a food preservative was first demonstrated using nisin-producing cultures in the manufacturer of Swiss-type cheese to prevent spoilage by Clostridia (Hirsch et ai, 1951). To date, nisin is the only purified bacteriocin commercially exploited as a food preservative. It can be added to processed cheese products to prevent late blowing by Clostridia, the spores of which, if present in the natural cheese, survive pasteurization (Barnby-Smith, 1992). 

Three important phenotypes can confer non-sensitivity to bacteriocins (i) immunity is genetically linked with bacteriocin production and exerts the strongest level of non-sensitivity, (ii) resistance can occur as the appearance of spontaneous mutants following selection on the bacteriocin and (iii) resistance conferred by a gene that is not genetically linked with bacteriocin production. These three categories of resistance are likely to be similar for any bacteriocin [21]. 

Bernhard, K., Schrempf, H., and Goebel, W. (1978) Bacteriocin and antibiotic resistance plasmids in... 

Curing of plasmids pRGOl, pRG02 and pRG05 from the respective strains had no effect on their capacity to synthesize bacteriocin, or to ferment 21 carbohydrates, as well as on their resistance to 21 antibiotics, including ampicillin, bacitracin, cephalotin, chloramphenicol, cloxacillin, erythromycin, fusidic acid, gentamycin, kanamycin, lyncomycin, metycillin, nalidixic acid, neomycin, novobiocin, oxacycline, penicillin, rifampicin, streptomycin, tetracycline, trimethoprim, and vancomycin. 

Jensenin P is a bacteriocin produced by P. jensenii B1264- which inhibits closely related propionibacteria and lactic acid bacteria. It was shown that jensenin P is a new anionic bacteriocin (Ratnam et al., 1998). Jensenin P is stable at lOOT for 45 min, at pH 2 to 10 for 225 min, and in 0.1 to 0.3M NaCl (pH 10) for 225 min (Barefoot et al., 1995). The resistance of jensenins to the extremes of pH and high temperature, their wide inhibitory spectrum allows to consider them as useful natural preservatives in thermal food processing. P. jensenii strain DFl was found (Miesher et al., 1998) to markedly inhibit other P. jensenii strains and to suppress 15 out of 24 yeasts and 3 out of 4 molds tested. From the culture broth of P. jensenii DFl an inhibitory protein substance, named SMI, was isolated and partially purified (Miesher et al., 1998). Crude propionicin SMI was sensitive to proteolytic enzymes and stable to incubation at 30°C (more than 14 days), cold storage (more than 6 months at 4 C) and heat treatment (15 min, 100 C). 

Bacteriocin sensitivity Protection by physicochemical barriers Development of resistance mechanisms... 

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