Inhibition of Salmonella Typhimurium by bovicin HC5 associated with chelating agents and surfactants

Mathematical Model of Interaction Between Bacteriocin-Producing Lactic Acid Bacteria and Listeria. Part 2: Bifurcations and Applications

The big challenge for the food industry is the attending to demands for minimally processed foods, avoiding intense heat treatments and reducing the addition of chemical preservatives, but at the same time ensuring microbiological safety of these products. Lactic acid bacteria are traditionally used in the production of fermented foods. They are responsible for the production of antimicrobial compounds, such as organic acids and bacteriocins, which are protein compounds with bactericidal effect against related species and bacteria such as Listeria monocytogenes and Staphylococcus aureus. Aiming to study quantitatively the biological control as a technique of conservation, we developed a mathematical model to describe the interaction between lactic acid bacteria and Listeria in the food. The steady state and dynamical trajectories analyses of the model permit us to study the suitability of including lactic acid bacteria in order to reduce the growth of Listeria in food.

Strategies for the use of bacteriocins in Gram-negative bacteria: relevance in food microbiology

Bacteriocins are ribosomally synthesized peptides that have bacteriostatic or bactericidal effects on other bacteria. The use of bacteriocins has emerged as an important strategy to increase food security and to minimize the incidence of foodborne diseases, due to its minimal impact on the nutritional and sensory properties of food products. Gram-negative bacteria are naturally resistant to the action of bacteriocins produced by Gram-positive bacteria, which are widely explored in foods. However, these microorganisms can be sensitized by mild treatments, such as the use of chelating agents, by treatment with plant essential oils or by physical treatments such as heating, freezing or high pressure processing. This sensitization is important in food microbiology, because most pathogens that cause foodborne diseases are Gram-negative bacteria. However, the effectiveness of these treatments is influenced by several factors, such as pH, temperature, the composition of the food and target microbiota. In this review, we comment on the main methods used for the sensitization of Gram-negative bacteria, especially Salmonella, to improve the action of bacteriocins produced by Gram-positive bacteria.

Stress enhances the sensitivity of Salmonella enterica serovar Typhimurium to bacteriocins

AIMS

The aim of this study was to evaluate the potential application of bacteriocins against Gram-negative bacteria when associated with others food preservation methods.

METHODS AND RESULTS

Salmonella was subjected to heat, cold, acid and chemical (with ethylenediaminetetracetate and trisodium phosphate) stresses. Then, the cells were recovered and subjected to treatment with bacteriocins (500 AU ml(-1) ) for 6 h. Heat and cold stress were those that promoted more sensitization to bactericidal activity of nisin. Under the same conditions, bovicin HC5 acted more rapidly than nisin reducing the number of viable cells to undetectable levels after 20 min of treatment. Similar results with use of nisin only were observed after 6 h of treatment.

CONCLUSIONS

Stress conditions used in food industry, such as temperature and pH, and use of chelating agents or membrane disruptors, sensitized Salmonella Typhimurium cells to bacteriocins produced by lactic acid bacteria, such as nisin and bovicin HC5.

SIGNIFICANCE AND IMPACT OF THE STUDY

Food preservation methods sensitized Gram-negative bacteria to bacteriocins activity, which demonstrate the potential of nisin and bovicin HC5 to inhibit the growth of Salmonella.

Differences in the antibacterial activity of nisin and bovicin HC5 against Salmonella Typhimurium under different temperature and pH conditions

AIMS

To compare the action of nisin and bovicin HC5 in combination with EDTA on Salmonella Typhimurium under different environmental conditions.

METHODS AND RESULTS

Salmonella Typhimurium was treated in BHI broth containing EDTA (1·5 mmol l(-1)) and nisin or bovicin HC5 (200 AU ml(-1)) under different pH and temperature conditions, and according to a central composite design with two factors (temperature and pH). Cell viability was evaluated on plate count agar for 48 h. The combination of nisin or bovicin HC5 with EDTA was able to inhibit the growth of Salmonella, but the temperature and pH conditions promoting inhibition were distinct for each bacteriocin. Nisin was bactericidal over a broad range of temperature and pH, while bovicin HC5 was bacteriostatic in most conditions and bactericidal only in specific conditions (pH >6·0 and temperature >30°C). Salmonella Typhimurium did not show tolerance to bovicin HC5 or cross-tolerance between these lantibiotics.

CONCLUSIONS

Nisin and bovicin HC5 both inhibited the growth of Salmonella, but the activity of each bacteriocin was differently influenced by environmental conditions.

SIGNIFICANCE AND IMPACT OF THE STUDY

Nisin and bovicin HC5 have the potential to inhibit the growth of Salmonella, but environmental conditions should be considered to establish optimal conditions for its application.