Synergistic effect of nisin and cone essential oil of Metasequoia glyptostroboides Miki ex Hu against Listeria monocytogenes in milk samples

Study of the Resistance of Staphylococcus aureus Biofilm, Biofilm-Detached Cells, and Planktonic Cells to Microencapsulated Carvacrol Used Alone or Combined with Low-pH Treatment

Microbial biofilms pose severe problems in the medical field and food industry, as they are the cause of many serious infections and food-borne diseases. The extreme biofilms' resistance to conventional anti-microbial treatments presents a major challenge to their elimination. In this study, the difference in resistance between Staphylococcus aureus DSMZ 12463 biofilms, biofilm-detached cells, and planktonic cells against microcapsules containing carvacrol was assessed. The antimicrobial/antibiofilm activity of low pH disinfection medium containing the microencapsulated carvacrol was also studied. In addition, the effect of low pH on the in vitro carvacrol release from microcapsules was investigated. The minimum inhibitory concentration of microencapsulated carvacrol was 0.625 mg mL-1. The results showed that biofilms exhibited greater resistance to microencapsulated carvacrol than the biofilm-detached cells and planktonic cells. Low pH treatment alone, by hydrochloric acid addition, showed no bactericidal effect on any of the three states of S. aureus strain. However, microencapsulated carvacrol was able to significantly reduce the planktonic cells and biofilm-detached cells below the detection limit (no bacterial counts), and the biofilm by approximatively 3 log CFU mL-1. In addition, results showed that microencapsulated carvacrol combined with low pH treatment reduced biofilm by more than 5 log CFU mL-1. Thus, the use of microencapsulated carvacrol in acidic environment could be a promising approach to combat biofilms from abiotic surfaces.

Essential Oils and Their Combination with Lactic Acid Bacteria and Bacteriocins to Improve the Safety and Shelf Life of Foods: A Review

The use of plant extracts (e.g., essential oils and their active compounds) represents an interesting alternative to chemical additives and preservatives applied to delay the alteration and oxidation of foods during their storage. Essential oils (EO) are nowadays considered valuable sources of food preservatives as they provide a healthier alternative to synthetic chemicals while serving the same purpose without affecting food quality parameters. The natural antimicrobial molecules found in medicinal plants represent a possible solution against drug-resistant bacteria, which represent a global health problem, especially for foodborne infections. Several solutions related to their application on food have been described, such as incorporation in active packaging or edible film and direct encapsulation. However, the use of bioactive concentrations of plant derivatives may negatively impact the sensorial characteristics of the final product, and to solve this problem, their application has been proposed in combination with other hurdles, including biocontrol agents. Biocontrol agents are microbial cultures capable of producing natural antimicrobials, including bacteriocins, organic acids, volatile organic compounds, and hydrolytic enzymes. The major effect of bacteriocins or bacteriocin-producing LAB (lactic acid bacteria) on food is obtained when their use is combined with other preservation methods. The combined use of EOs and biocontrol agents in fruit and vegetables, meat, and dairy products is becoming more and more important due to growing concerns about potentially dangerous and toxic synthetic additives. The combination of these two hurdles can improve the safety and shelf life (inactivation of spoilage or pathogenic microorganisms) of the final products while maintaining or stabilizing their sensory and nutritional quality. This review critically describes and collects the most updated works regarding the application of EOs in different food sectors and their combination with biocontrol agents and bacteriocins.

Impact of tannic acid on nisin encapsulation in chitosan particles

This study investigates the effect of addition of tannic acid on nisin encapsulated in chitosan matrices. Composite materials were prepared using a mild, environmentally friendly procedure, ionotropic gelation of chitosan by sodium tripolyphosphate in the presence of nisin (N) at different concentrations. In two parallel sets of preparations, tannic acid (TA) was added at 10:1 and 5:1 N:TA, respectively. The obtained particles were characterized by FTIR, SEM, size, zeta potential, encapsulation efficiency, loading capacity, and ratio of residual free amino groups. The kinetics of nisin release from the particles was studied to assess the role of TA as a potential modulator thereof. Its addition resulted in enhanced release, higher at lower N:TA ratio. An additional benefit was that TA, a strong antioxidant, imparted antioxidant activity to the composites. Antimicrobial turbidimetric tests were performed against one gram-positive bacterium (Staphylococcus aureus) and two gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa), all relevant for the food, pharmaceutical, and cosmetic industries. All the composites showed synergistic effects against all the bacteria tested. The positive coaction was stronger against the gram-negative species. This is remarkable since nisin by itself has not known activity against them.

A review of potential antibacterial activities of nisin against Listeria monocytogenes: the combined use of nisin shows more advantages than single use

Listeria monocytogenes is a foodborne pathogen causing serious public health problems. Nisin is a natural antimicrobial agent produced by Lactococcus lactis and widely used in the food industry. However, the anti-L. monocytogenes efficiency of nisin might be decreased due to natural or acquired resistance of L. monocytogenes to nisin, or complexity of the food environment. The limitation of nisin as a bacteriostatic agent in food could be improved using a combination of methods. In this review, the physiochemical characteristics, species, bioengineered mutants, and antimicrobial mechanism of nisin are reviewed. Strategies of nisin combined with other antibacterial methods, including physical, chemical, and natural substances, and nanotechnology to enhance antibacterial effect are highlighted and discussed. Additionally, the antibacterial efficiency of nisin applied in real meat, dairy, and aquatic products is evaluated and analyzed. Among the various binding treatments, the combination with natural substances is more effective than the combination with physical and chemical methods. However, the combination of nisin and nanotechnology has more potential in terms of the impact on food quality.

Essential oils and their active components applied as: free, encapsulated and in hurdle technology to fight microbial contaminations. A review

Microbial contaminations are responsible for many chronic, healthcare, persistent microbial infections and illnesses in the food sector, therefore their control is an important public health challenge. Over the past few years, essential oils (EOs) have emerged as interesting alternatives to synthetic antimicrobials as they are biodegradable, extracted from natural sources and potent antimicrobials. Through their multiple mechanisms of actions and target sites, no microbial resistance has been developed against them till present. Although extensive documentation has been reported on the antimicrobial activity of EOs, comparisons between the use of whole EOs or their active components alone for an antimicrobial treatment are less abundant. It is also essential to have a good knowledge about EOs to be used as alternatives to the conventional antimicrobial products such as chemical disinfectants. Moreover, it is important to focus not only on planktonic vegetative microorganisms, but to study also the effect on more resistant forms like spores and biofilms. The present article reviews the current knowledge on the mechanisms of antimicrobial activities of EOs and their active components on microorganisms in different forms. Additionally, in this review, the ultimate advantages of encapsulating EOs or combining them with other hurdles for enhanced antimicrobial treatments are discussed.

Conditions of nisin production by Lactococcus lactis subsp. lactis and its main uses as a food preservative

Nisin is a small peptide produced by Lactococcus lactis ssp lactis that is currently industrially produced. This preservative is often used for growth prevention of pathogenic bacteria contaminating the food products. However, the use of nisin as a food preservative is limited by its low production during fermentation. This low production is mainly attributed to the multitude of parameters influencing the fermentation progress such as bacterial cells activity, growth medium composition (namely carbon and nitrogen sources), pH, ionic strength, temperature, and aeration. This review article focuses on the main parameters that affect nisin production by Lactococcus lactis bacteria. Moreover, nisin applications as a food preservative and the main strategies generally used are also discussed.

Antibacterial activity and mechanism of linalool against Pseudomonas aeruginosa

The purpose of this study was to evaluate the antibacterial activity and mechanism of linalool against Pseudomonas aeruginosa. The determination of antibacterial activity was based on the minimum inhibitory concentration (MIC) and the minimum bactericide concentration (MBC). Further, the antibacterial mechanism was explored by a growth curve assay, scanning electron microscopy (SEM), cell membrane permeability, membrane potential and respiratory chain dehydrogenase determination. The MIC and the MBC of linalool were 431 μg/mL and 862 μg/mL, respectively. The growth curve assay showed that the growth of P. aeruginosa was inhibited. The results of SEM revealed that linalool disrupted the normal morphology of the cell. The release of nucleic acids as well as the decrease in the membrane potential proved that the membrane integrity of P. aeruginosa was destroyed. Moreover, the respiratory chain was damaged by respiratory chain dehydrogenase determination as the absorbance at 490 nm decreased. This research suggested that it was possible for linalool to become a preservative of food by destroying the cell membrane, resulting in cell death.

Invited review: Advances in nisin use for preservation of dairy products

Dairy product safety is a global public health issue that demands new approaches and technologies to control foodborne pathogenic microorganisms. Natural antimicrobial agents such as nisin can be added to control the growth of pathogens of concern in dairy foods, namely Listeria monocytogenes and Staphylococcus aureus. However, several factors affect the antimicrobial efficacy of nisin when directly added into the food matrix such as lack of stability at neutral pH, interaction with fat globules, casein, and divalent cations. To overcome these limitations, new and advanced strategies are discussed including nisin encapsulation technology, addition to active packaging, bioengineering, and combination with other antimicrobials. This review highlights advanced technologies with potential to expand and improve the use of nisin as a dairy preservative.

Inhibitory effect of bacteriocins againstEscherichia coliO157:H7

The purpose of this study was to explore the activity of bacteriocin enterocin KP and lactococcin BZ against Escherichia coli O157:H7, a Gram-negative foodborne pathogen, in ultra-high temperature (UHT) milks with different fat ratios. Enterocin KP and lactococcin BZ were produced from two bacteriocinogenic strains, isolated in previous studies from White cheese and Boza. Full fat (3.0%), half fat (1.5%), and low fat (<0.1% fat) UHT milks inoculated with 102, 104, and 106CFU/ml of E. coli O157:H7 were treated with different concentrations (400, 800, 1600, and 2500 AU/ml) of lactococcin BZ, enterocin KP, or a combination of both and stored at 4 or 20 ℃ for 20 days. The survival of E. coli O157:H7 was determined at both storage temperatures during the storage period of 20 days. Lactococcin BZ and enterocin KP had a bactericidal impact on E. coli O157:H7 in all UHT milk samples either separately or in combination. However, antibacterial activity of the bacteriocins decreased with increasing fat content of milk and inoculum levels of bacterium. The results of this study indicate that lactococcin BZ and enterocin KP may be useful candidates either separately or in combination as biopreservatives for use in the dairy industry to control the growth of pathogenic microorganisms.

Effect of nisin and perilla oil combination against Listeria monocytogenes and Staphylococcus aureus in milk

In the present study, in vitro interaction of nisin and perilla oil (PO) against 20 food-borne isolates of L. monocytogenes and S. aureus were assessed using a checkerboard microdilution method. Synergism was observed in tested strains with the fractional inhibitory concentration indexs (FICIs) ranges from 0.125-0.25 and 0.19-0.375, respectively. Scanning electron microscopy was carried out to investigate the effect of nisin and PO on the integrity of cell wall and membrane of L. monocytogenes and S. aureus. The results showed that nisin and PO were more effective in damaging cell wall and membrane in combination.

Essential oils in combination and their antimicrobial properties

Essential oils (EOs) have been long recognized for their antibacterial, antifungal, antiviral, insecticidal and antioxidant properties. They are widely used in medicine and the food industry for these purposes. The increased interest in alternative natural substances is driving the research community to find new uses and applications of these substances. EOs and their components show promising activities against many food-borne pathogens and spoilage microorganisms when tested in vitro. In food systems, higher concentrations of EOs are needed to exert similar antibacterial effects as those obtained in in vitro assays. The use of combinations of EOs and their isolated components are thus new approaches to increase the efficacy of EOs in foods, taking advantage of their synergistic and additive effects. The purpose of this review is to provide an overview on the antimicrobial efficacy of these combinations. A survey of the methods used for the determination of the interactions and mechanisms involved in the antimicrobial activities of these combinations are also reported.