Bacteriocins are bacterially produced antimicrobial peptides with narrow or broad host ranges. Many bacteriocins are produced by food-grade lactic acid bacteria, a phenomenon which offers food scientists the possibility of directing or preventing the development of specific bacterial species in food. This can be particularly useful in preservation or food safety applications, but also has implications for the development of desirable flora in fermented food. In this sense, bacteriocins can be used to confer a rudimentary form of innate immunity to foodstuffs, helping processors extend their control over the food flora long after manufacture.

Bacteriocins: developing innate immunity for food

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

Bacteriocins — a viable alternative to antibiotics?

Microbes produce an extraordinary array of microbial defense systems. These include classical antibiotics, metabolic by-products, lytic agents, numerous types of protein exotoxins, and bacteriocins. The abundance and diversity of this potent arsenal of weapons are clear. Less clear are their evolutionary origins and the role they play in mediating microbial interactions. The goal of this review is to explore what we know about the evolution and ecology of the most abundant and diverse family of microbial defense systems: the bacteriocins. We summarize current knowledge of how such extraordinary protein diversity arose and is maintained in microbial populations and what role these toxins play in mediating microbial population-level and community-level dynamics. In the latter half of this review we focus on the potential role bacteriocins may play in addressing human health concerns and the current role they serve in food preservation.

Bacteriocins: evolution, ecology, and application.

Listeria monocytogenes is a Gram positive, aerobic, facultative anaerobic and nonacid fast bacterium, which can cause the disease listeriosis in both human and animals. It is widely distributed thoroughout the environment and has been isolated from various plant and animal food products associated with listeriosis outbreaks.

Contaminated ready-to-eat food products such as gravad and cold-smoked salmon and rainbow trout have been associated with human listeriosis in Sweden. The aim of this study was to analyse the occurrence and level of L. monocytogenes in
gravad and cold-smoked salmon (Salmo salar) products packed under vacuum or modified atmosphere from retail outlets in Sweden. Isolated strains were characterized by serotyping and the diversity of the strains within and between
producers were determined with PFGE (Pulsed-field gel electrophoresis). The characterized fish isolates were compared with previously characterized human strains.
L. monocytogenes was isolated from 11 (three manufacturers) of 56 products analysed. This included gravad salmon products from three manufacturers and cold-smoked salmon from one manufacturer. The highest level of L. monocytogenes found was 1500 cfu/g from a cold-smoked salmon product but the level was low (<100 cfu/g) in most of the products. Serovar 1/2a was predominant,
followed by 4b. Three products of gravad salmon harboured more than one serovar. PFGE typing of the 56 salmon isolates detected five Asc I types: four types were identical to human clinical strains with Asc I and one was identical and one was closely related to human clinical strains with Apa I. Isolation of identical or closely related L. monocytogenes strains from human clinical cases of listeriosis and gravad and cold-smoked salmon suggested that these kinds of products are possible sources of listeriosis in Sweden. Therefore, these products should be considered risk products for human listeriosis.

Listeria monocytogenes, a food-borne pathogen

Lactic acid bacteria of foods and their current taxonomy.

Nisin-curvaticin 13 combinations for avoiding the regrowth of bacteriocin resistant cells of Listeria monocytogenes ATCC 15313.

Strain C19, isolated from fermented cucumbers and identified as Lactobacillus plantarum, produced a bacteriocin. This bacteriocin, named plantaricin C19, was stable at acidic pH, was relatively the...

Detection and characterization of a bacteriocin produced by Lactobacillus plantarum C19

Carnobacterium maltaromaticum: Identification, isolation tools, ecology and technological aspects in dairy products

The effects of nisin and monolaurin, alone and in combination, were investigated on Bacillus licheniformis spores in milk at 37 degrees C. In the absence of inhibitors, germinated spores developed into growing vegetative cells and started sporulation at the end of the exponential phase. In the presence of nisin (25 IU ml-1), spore outgrowth was inhibited (4 log10 reduction at 10 h). Regrowth appeared between 10 and 24 h and reached a high population level (1.25 x 10(8) cfu ml-1) after 7 d. Monolaurin (250 micrograms ml-1) had a bacteriostatic effect during the first 10 h but thereafter, regrowth occurred slowly with a population level after 7 d (4 x 10(5) cfu ml-1) lower than that of nisin. Different combined effects of nisin (between 0 and 42 IU ml-1), monolaurin (ranging from 0 to 300 micrograms ml-1), pH values (between 5.0 and 7.0) and spore loads (10(3), 10(4), 10(5) spores ml-1) were investigated using a Doehlert matrix in order to study the main effects of these factors and the different interactions. Results were analysed using the Response Surface Methodology (RSM) and indicated that nisin and monolaurin had no action on spores before germination; only pH values had a significant effect (P < or = 0.001), i.e. spore count decreased as the pH value increased in relation to germination. Sublethal concentrations of nisin (30 IU ml-1) and monolaurin (100 micrograms ml-1) in combination acted synergistically on outgrown spores and vegetative cells, showing total inhibition at pH 6.0, without regrowth, within 7 d at 37 degrees C.

Jean-Bernard Millière

Papers

Nisin-curvaticin 13 combinations for avoiding the regrowth of bacteriocin resistant cells of Listeria monocytogenes ATCC 15313.

Detection and characterization of a bacteriocin produced by Lactobacillus plantarum C19

Carnobacterium maltaromaticum: Identification, isolation tools, ecology and technological aspects in dairy products

Inhibition of Bacillus licheniformis spore growth in milk by nisin, monolaurin, and pH combinations

Inhibitory combinations of nisin, sodium chloride, and pH on Listeria monocytogenes ATCC 15313 in broth by an experimental design approach.