Combination Of Nisin Research Articles

Effects of Nisin Treatment on the Shelf Life of Ready-to-Eat Roasted Shrimp (<i>Penaeus vannamei</i>)

The microbiological, biochemical, and physicochemical changes of ready-to-eat shrimps (Penaeus vannamei) with high water content, subjected to nisin treatment in combination of hurdle technology, were investigated. The ready-to-eat shrimps were processed by boiling, drying, treatment with nisin solution, seasoning, and roasting, followed by vacuum packaging, sterilization, and storage at room temperature (25°C). The results showed that the samples treated with nisin in combination with other hurdles resulted in a significant decrease in bacterial counts (Bacillus cereus and native microflora) compared to the control samples. Additionally, the nisin-treated samples possessed better biochemical and physicochemical properties, as well as better sensory patterns. According to the safety guidelines for roasted shrimp (SC/T 3305-2003), the shelf life of ready-to-eat shrimp with 48–53% moisture content was extended by nisin application at concentrations of 60 and 100 mg/kg of nisin; specifically, ready-to-eat shrimp maintained good quality from 4–6 days up to 6–12 and 8–14 days corresponding to 60 and 100 mg/kg of nisin treatments, respectively. Nisin treatment combined with hurdle technology in the production of ready-to-eat shrimp provides a highly valued product in China.

Effect of AHL-lactonase and nisin on microbiological, chemical and sensory quality of vacuum packaged sturgeon storage at 4ºC

ABSTRACT Quorum sensing (QS) has been reported to be involved in bacterial food spoilage. Acetylated homoserine lactones (AHLs) are QS signals of Gram-negative bacteria. AHL lactonases AiiAAI96 is a QS inhibitor, and thus can theoretically be applied to control the Gram-negative bacteria caused sturgeon spoilage by inhibiting their AHL-based QS system. As Gram-negative bacteria and Gram-positive bacteria were both found in spoilage sturgeon, the combination of AiiAAI96 and nisin, which is an effective bactericide to control the Gram-positive bacteria, was used to control the bacteria spoilage of sturgeon. The results showed that AiiAAI96 at 6.6 × 10−2, 6.6 × 10−1 and 6.6 U/mL could suppress the growth of microflora and delayed the increase of TVB-N, sensory score and biogenic amine levels of sturgeon. In addition, 6.6 U/mL AiiAAI96 coupled with 2000 AU/mL nisin exhibited the strongest inhibition effect on spoilage and extended their shelf life by about 5 days. In conclusion, AiiAAI96 combined with nisin could be used as a suitable biological preservative for chilled sturgeon fillets.

Application of Natural Antimicrobial Additives and Protective Culture to Control Aerobic Spore Forming Bacteria in Low Salt Soft Cheese

There is an increasing interest in the application of natural antimicrobials instead of chemical ones to enhance the microbiological quality of dairy products. The objective of this study was to assess the effect of some natural antimicrobial additives and protective culture for reducing the usage of chemical preservatives, shelf-life extension, retarding microbial spoilage in low-salt soft cheese. The antimicrobial agents (protective culture, nisin, lysozyme, and natamycin) were studied on the activity of 28 isolates of spore-forming bacteria. Inhibitory effect of different natural antimicrobial additives as protective culture (Lactobacillus rhamnosus, 40 mg kg -1), nisin (25 mg kg -1), lysozyme (100 mg kg -1), combination of nisin and lysozyme (25 mg kg -1/100 mg kg -1), and combination of protective culture and natamycin (40 mg kg -1/25 mg kg -1) were studied on the growth of aerobic spore-forming bacteria in low-salt soft cheese during the storage period (30 days) at 4±1°C. The results revealed that the addition of different natural antibacterial additives with various concentrations had a significant effect on aerobic spore-forming bacteria, compared to other treatments and control. The growth pattern of aerobic spore-forming bacteria gradually decreased in all treatments along the storage period with variable reduction percentages in comparison with control cheese which was in continuous increment. The application of a combination of nisin and lysozyme had the most significant reduction of aerobic spore-forming bacteria, compared to control and other treatments.

Synergistic effect of two antimicrobial peptides, Nisin and P10 with conventional antibiotics against extensively drug-resistant Acinetobacter baumannii and colistin-resistant Pseudomonas aeruginosa isolates

BackgroundInfections caused by drug-resistant strains of Acinetobacter baumannii and Pseudomonas aeruginosa are now a global problem that requires the immediate development of new antimicrobial drugs. Combination therapy and using antimicrobial peptides are two strategies with high potential to solve this issue. By these strategies, this study aimed to determine the antimicrobial effect of Nisin and P10 antimicrobial peptides on extensively drug-resistant Acinetobacter baumannii and colistin-resistant Pseudomonas aeruginosa isolates, and investigate the most effective combination of an antimicrobial peptide with an antibiotic. Material and methodsThis study was performed on five resistant clinical isolates and one standard strain for each kind of bacterium. First, the minimum inhibitory concentrations of two antimicrobial peptides (Nisin and P10) and five common antibiotics for the treatment of Gram-negative bacteria (ceftazidime, tobramycin, ciprofloxacin, doripenem, and colistin) was determined using Scanner-Assisted Colorimetric MIC Method. Then, the combination effect of P10+Nisin, P10+antibiotics, Nisin + antibiotics was investigated using checkerboard method. ResultsThe MIC value of Nisin and P10 against studied pathogens were 64–256 and 8–32 μg/ml, respectively. P10+Nisin combination showed synergistic effect against standard strains and additive effect against drug-resistant clinical isolates. It was also found that the combination effect of P10+ceftazidim, P10+doripenem, and Nisin + colistin was synergistic in most cases. Nisin + tobramycin combination showed synergistic effect in exposure to standard strains, while the synergy is strain-dependent against drug-resistant clinical isolates. ConclusionIn conclusion, the synergism of Nisin + colistin and P10+ceftazidime/doripenem could be of great therapeutic value as antimicrobial drugs against infections caused by colistin-resistant P.aeruginosa and XDR A. baumannii.

Antimicrobial efficacy of nisin, oregano and ultrasound against Escherichia coli O157:H7 and Listeria monocytogenes on lettuce

Ready-to-eat vegetables such as lettuce are prone to bacterial contamination, predominantly from Escherichia coli and Listeria monocytogenes, the leading causes of foodborne illnesses globally. Chlorine is widely used as a decontaminant in the fresh produce industry, however, potential carcinogenic risks limit its usage. As an alternative, green methods and hurdle technology are gaining interest. In this paper, the efficacy of a combination of nisin, oregano and ultrasound on the reduction of E. coli and L. monocytogenes on lettuce was studied using response surface methodology/Box-Behnken model design, and was found to be reliable (p < 0.05). A combination of 771.2 IU/g nisin, 0.185% v/v oregano and 14.65 min ultrasound was the most effective treatment on both pathogens, showing log reductions of 3.43 and 9.20 CFU/mL for E. coli and L. monocytogenes, respectively. The treated lettuce samples did not show any significant differences in textural properties; however, mild colour changes and a slight increase in the electrolyte leakage rate was observed, within permissible limits. Interestingly this is the first report on the combination of nisin, oregano and ultrasound, as a promising alternative to chemical treatments for the reduction of E. coli and L. monocytogenes on lettuce, without compromising its appearance and quality.

The impact of food model system structure on the inactivation of Listeria innocua by cold atmospheric plasma and nisin combined treatments

Novel processing methods such as cold atmospheric plasma (CAP) and natural antimicrobials like nisin, are of interest to replace traditional food decontamination approaches as, due to their mild nature, they can maintain desirable food characteristics, i.e., taste, texture, and nutritional content. However, the microbial growth characteristics (planktonic growth/surface colonies) and/or the food structure itself (liquid/solid surface) can impact the inactivation efficacy of these novel processing methods. More specifically, cells grown as colonies on a solid(like) surface experience a completely different growth environment to cells grown planktonically in liquid, and thus could display a different response to novel processing treatments through stress adaptation and/or cross protection mechanisms. The order in which combined treatments are applied could also impact their efficacy, especially if the mechanisms of action are complementary.This work presents a fundamental study on the efficacy of CAP and nisin, alone and combined, as affected by food system structure. More specifically, Listeria innocua was grown planktonically (liquid broth) or on a viscoelastic Xanthan gum gel system (1.5% w/v) and treated with CAP, nisin, or a combination of the two. Both the inactivation system, i.e., liquid versus solid(like) surface and the growth characteristics, i.e., planktonic versus colony growth, were shown to impact the treatment efficacy. The combination of nisin and CAP was more effective than individual treatments, but only when nisin was applied before the CAP treatment.This study provides insight into the environmental stress response/adaptation of L. innocua grown on structured systems in response to natural antimicrobials and novel processing technologies, and is a step towards the faster delivery of these food decontamination methods from the bench to the food industry.

Antilisterial effects of lysozyme-nisin combination at temperature and pH ranges optimal for lysozyme activity: Test of key findings to inactivate Listeria in raw milk

This study aimed to determine antilisterial potential of lysozyme (LYS)-nisin (NIS) combination at temperatures and pHs optimal for LYS activity. Tests in buffers at pH 4.5 and 6.0 showed that heating at 50 or 60 °C combined with LYS-NIS caused higher Listeria innocua inactivation (- 6.2 to >6.6 log) than heating alone (- 0.05 to 5.5 log), or heating combined with LYS (- 4.34 to 6.0 log) or NIS (3.9 to >6.6). The antimicrobial performance of LYS-NIS in buffer at 50 °C was not pH-dependant (5.8–5.9 logs) while heating at 60 °C with LYS-NIS at pH 6.0 (>6.6 logs) caused higher Listeria reduction than that at pH 4.5 (5.7 logs). Heating at 50 °C for 45 min alone or in combination with LYS-NIS caused 0 and 5.5 logs Listeria reduction in milk, respectively. In contrast, Listeria inactivation in milk at 60 °C occurred mainly by heat (5.5 logs) with limited contribution of LYS and/or NIS. Milk heated at 50 °C maintained 73% of NIS and 63% of LYS activity. Application of LYS-NIS at 50 °C provides an opportunity to improve milk safety with less destruction of milk enzyme and microbial flora necessary to obtain desired ripening periods, and aroma and flavour in traditional cheeses.

Evaluation of combinations of nisin, lauric arginate, and ε-polylysine to control Listeria monocytogenes in queso fresco

Listeria monocytogenes contamination is of great concern in queso fresco (QF), and listeriosis outbreaks linked to consumption of QF continue to happen. Hurdle approaches such as combining antimicrobials provide an alternative to improve QF safety. In this work, the efficacy of antimicrobial combinations of nisin (NIS), lauric arginate (LAE), and ε-polylysine (EPL) to inhibit L. monocytogenes growth in QF was evaluated. First, antimicrobials were screened for potential synergy in vitro. Later, antimicrobial treatments were challenged in QF inoculated with ∼4 log10 cfu/g of L. monocytogenes 5-strain cocktail and stored for 28 d at 4°C. Our results showed that combinations of NIS-LAE and EPL-LAE were synergistic in vitro. Limited antilisterial control was observed in QF treated with NIS, LAE, and NIS-LAE; however, EPL and EPL-LAE exhibited listeristatic effect in QF for up to 14 and 28 d of cold storage, respectively. Additionally, L. monocytogenes QF isolates had similar susceptibility to EPL or LAE. A consumer panel was able to distinguish between QF added with EPL (250 µg/g) + LAE (66.66 µg/g) and control QF, most likely associated with manufacturing and storage rather than antimicrobials' taste. Our results support the use of EPL-LAE combination to control L. monocytogenes growth in QF.

Characterizing bacterial strains of spoiled Jinhua ham and evaluating the effect of antimicrobial agents on these isolated bacterial strains

In order to explore effective measures to control the microbes responsible for the spoilage in Jinhua ham, spoiled ham was sampled and used to characterize bacterial strains; NaCl tolerance and ability to produce biogenic amines of bacteria strains were further determined. Total of 80 strains were isolated from spoiled ham, which 6 strains and 18 strains were identified at family level and species level, respectively; C. farmei CDC 2991–81, B. cereus ATCC 14579 and E. faecalis ATCC 19433 were main spoilage microorganisms of Jinhua ham. E. faecalis ATCC 19433 and E. faecium DSM 20477 showed higher NaCl resistance and production capacity of 2-phenylethylamine and tyramine, compared with other bacterial strains. The main producers of putrescine were strains of C. farmei CDC 2991–81 and B. cereus ATCC 14579. Nisin, sodium diacetate, citric acid, potassium lactate and potassium sorbate were active against the tested strains but at high levels. Antimicrobial interactions between binary mixtures showed that the combination of nisin and sodium diacetate had the best preservative effect on above bacteria based on the changes of fractional inhibitory concentrations index. These results indicated that the combination of nisin and sodium diacetate could be the best preservative effect against all tested strains.

Improved control of Listeria monocytogenes during storage of raw salmon by treatment with the fermentate Verdad N6 and nisin

Fresh Atlantic salmon (Salmo salar) represents a healthy, nutritious food with global distribution and increasing consumption and economic value. Contaminating Listeria monocytogenes in fresh salmon represents a health hazard to consumers, is linked to extensive product recalls and is a major challenge for salmon processors. Verdad N6, a commercially available buffered vinegar, was evaluated as a treatment for raw salmon fillets either alone or in combination with the antimicrobial peptide nisin, with regard to anti-listerial effects under processing and storage, and influence on sensory quality and background microbiota. Salmon fillets were surface contaminated with L. monocytogenes and immersed in solutions of Verdad N6 or treated with nisin or a combination of these two treatments. Levels of L. monocytogenes were determined during vacuum-pack refrigerated storage. The use of Verdad N6 resulted in increased lag times and substantially reduced growth of L. monocytogenes. The inhibitory effects were dependent on Verdad N6 levels, immersion time, and storage time and temperature. A 5 s immersion in 10% Verdad N6 solution at 4 °C reduced growth of L. monocytogenes from log 2.8 to log 1 after 12 days of storage. Nisin (0.2–1 ppm) had listericidal effects up to 1 log but did not inhibit regrowth when used alone. Appropriate combinations of Verdad N6 and nisin led to L. monocytogenes levels no higher after 12 days of storage than the initial levels. The inhibitory effects were markedly lower at 7 °C than at 4 °C. Salmon with Verdad N6 showed reduced levels of total counts during storage indicating a longer shelf-life, and a shift in the dominating bacteria with reduced and increased relative levels of Enterobacteriaceae and lactic acid bacteria, respectively. Sensory analyses of raw and cooked Verdad N6 treated a non-treated salmon resulted in small differences. In summary, Verdad N6 is an option for production of high-quality raw salmon with increased shelf-life and enhanced food safety through its Listeria inhibiting effects. The application of Verdad N6 in combination with nisin treatment can further reduce the listeria-risks of these products.

Control of the growth of Alicyclobacillus acidoterrestris in industrialized orange juice using rosemary essential oil and nisin.

The use of rosemary essential oil (RO) and its combination with nisin (RO+N) in preventing the multiplication of Alicyclobacillus acidoterrestris in orange juice was evaluated. The minimum inhibitory and bactericidal concentrations (MIC and MBC) for RO were both 125μgml-1 while RO+N displayed a synergistic effect. The use of RO and RO+N at concentrations of 1, 4 and 8× MIC in orange juice for 96h was evaluated in terms of their sporicidal effectiveness. With regard to the action against A. acidoterrestris spores, RO at 8× MIC was sporostatic, whereas RO+N at 1× MIC was sporicidal. Morphological changes in the structure of the micro-organism after treatment were also observed by microscopy. Furthermore, flow cytometric analysis showed that most cells were damaged or killed after treatment. In general, the antioxidant activity after addition of RO+N decreased with time. The results demonstrate that using the combination of RO and nisin can prevent the A. acidoterrestris growth in orange juice.

Antimicrobial activity of Baccharis dracunculifolia DC and its synergistic interaction with nisin against food-related bacteria.

The antimicrobial activities of Baccharis dracunculifolia DC essential oil (EO) and hydroalcoholic extract (HE) were evaluated. The EO showed broad antimicrobial activity and its synergistic combination with nisin was tested. Major components of EO were nerolidol, beta-pinene and D-limonene, while artepillin C, rutin and cafeic acid were major phenolics of HE. EO and HE were tested by agar diffusion assay against several strains of bacteria and yeasts, and mixed cultures of bacterial strains. The EO presented the largest spectrum of antimicrobial activity inhibiting all Gram-positive bacteria tested. Yeasts were not inhibited. The effect of EO against mixtures of sensitive and non-sensitive bacteria was tested on milk agar, being the inhibitory effect only observed on mixtures containing susceptible strains. The combination of EO and nisin at ½ MIC was evaluated on the growth curve of Staphylococcus aureus, Bacillus cereus, Listeria monocytogenes and Salmonella Enteritidis during 24h at 37°C. The combination EO-nisin was effective and no viable counts of B. cereus, L. monocytogenes and S.Enteritidis was observed, while the individual antimicrobials caused no inhibition. The counts of S. aureus were about 4 log CFU/mL lower in comparison with EO or nisin alone. B. dracunculifolia DC may be a potential source of natural antimicrobials, and its synergistic effect with nisin would reduce the working concentration, minimizing the organoleptic effects associated with this plant antimicrobial.

Changes in the Microbial Content and Quality Attributes of Carrot Juice Treated by a Combination of Ultrasound and Nisin During Storage

The objective of the article was to study the effects of ultrasound (US) and 80 ppm nisin-assisted US (US + nisin) on the inactivation of microorganisms and the nutritional quality of fresh carrot juice. Fresh carrot juice was exposed to HT (60 °C, 10 min), US, and US + nisin at 271 W and 30 °C for 10 min since the treatments had a similar microbial inactivation effect. Results showed that nisin exhibited an additional inactivation effect on the total aerobic bacteria (TAB) with US, while having no obvious effect on the yeast and mold (YM). The TAB was increased by 2.56, 2.20, and 4.28 log10 cycles, while the YM was increased by 4.67, 4.75, and 6.84 log10 cycles in carrot juice treated by US, US + nisin, and HT, respectively, after 20 days’ storage at 4 °C, indicating that US + nisin had a better post-inhibition effect on TAB than US and HT. Moreover, no significant changes occurred in the total suspended solids (TSS), viscosity, turbidity, or color, while carotenoid content was increased by 22.4%, 34.6%, and 21.4% in the carrot juice treated by US, US + nisin, and HT, respectively. In conclusion, the study ascertained that US + nisin is able to ensure both the microbial safety and the quality of carrot juice more effectively than HT alone.

Biocompatible combinations of nisin and licorice polyphenols exert synergistic bactericidal effects against Enterococcus faecalis and inhibit NF-\u03baB activation in monocytes

Enterococcus faecalis is one of the bacterial species most frequently isolated from persistent endodontic and apical periodontal infections. The aim of the present study was to evaluate the synergistic antibacterial effects of nisin and selected licorice polyphenols (glabridin, licoricidin, licochalcone A) against planktonic and biofilm-embedded E. faecalis cells. The biocompatibility and anti-inflammatory properties of the nisin/licorice polyphenol combinations were also investigated. The lantibiotic bacteriocin (nisin), the two isoflavonoids (glabridin, licoricidin), and the chalcone (licochalcone A) efficiently inhibited the growth of E. faecalis, with MICs ranging from 6.25 to 25 µg/mL. Combining nisin with each licorice polyphenol individually resulted in a significant synergistic antibacterial effect. Following a 30-min contact, nisin in combination with either glabridin, licoricidin, or licochalcone A caused significant biofilm killing. The nisin/licorice polyphenol combinations had no cytotoxic effects (oral epithelial cells, gingival fibroblasts, and stem cells of the apical papilla), with the exception of nisin/glabridin, when used at their MICs. Lastly, we showed that nisin/glabridin, nisin/licoricidin, and nisin/licochalcone A inhibit NF-κB activation induced by E. faecalis in a monocyte model, suggesting that these combinations possess anti-inflammatory properties. The present study provides evidence that combinations of nisin and glabridin, licoricidin, or licochalcone A show promise as root canal disinfection agents.

Combination of Antibiotics-Nisin Reduces the Formation of Persister Cell in Listeria monocytogenes.

Persister cells are a subpopulation of bacteria with the ability of survival when exposed to lethal doses of antibiotics, and are responsible for antibiotic therapy failure and infection recurrences. In this study, we investigated persister cell formation and the role of nisin in combination with antibiotics in reducing persistence in Listeria monocytogenes. We also examined the expression of toxin-antitoxin (TA) systems in persister cells of L. monocytogenes to gain a better understanding of the effect of TA systems on persister cell formation. To induce persistence, L. monocytogenes were exposed to high doses of different antibiotics over a period of 24 hr, and the expression levels of TA system was genes were measured 5 hr after the addition of antibiotics by the quantitative reverse transcription-polymerase chain reaction (qRT-PCR) method. To investigate the effect of nisin, L. monocytogenes was exposed to a combination of nisin and antibiotics. According to our results, L. monocytogenes was highly capable of persister cell formation, and the combination of nisin and antibiotics resulted in reduced persistence. qRT-PCR results showed a significant increase in GNAT/RHH expression among the studied systems. Overall, our results demonstrated the potential of the combination of nisin and antibiotics in reducing persister cell formation, and emphasized the role of the GNAT/RHH system in bacterial persistence.

Isolation and application of bacteriophages alone or in combination with nisin against planktonic and biofilm cells of Staphylococcus aureus.

Staphylococcus aureus is a notorious foodborne pathogen since it has ability to produce variety of toxins including heat-stable enterotoxin, form biofilm, and acquire resistance to antibiotics. Biocontrol of foodborne pathogens by lytic bacteriophages garners increasing interest from both researchers and food industry. In the present study, 29 phages against S. aureus were successfully isolated from chicken, pork, and fish. Characterization of the isolates revealed that phage SA46-CTH2 belonging to Podoviridae family had a number of features suitable for food industry applications such as wide host range, short latent period, large burst size, high stress tolerance, and a genome free of virulence genes. Furthermore, phage SA46-CTH2 alone or in combination with nisin exhibited great efficacy in reducing planktonic and biofilm cells of S. aureus at various conditions tested. The combination of phage SA46-CTH2 and nisin was also found to be able to inhibit the regrowth of S. aureus at both 37 and 24°C.Key points• A total of 29 S. aureus phages were successfully isolated from fish, pork, and chicken products. • Phage SA46-CTH2 was characterized by host range, morphology, and genome sequencing. • SA46-CTH2 significantly reduced both planktonic and biofilm cells of S. aureus. • Combination of SA46-CTH2 and nisin inhibited the regrowth of S. aureus.

Antimicrobial kinetics of nisin and grape seed extract against inoculated Listeria monocytogenes on cooked shrimps: Survival and residual effects

The antimicrobial effects of nisin (2000 IU/mL) and grape seed extract (GSE, 1%) against Listeria monocytogenes (SSA184, SSA97 and LM10) inoculated on cooked shrimps (Litopenaeus vannamei) were investigated. Notable reductions (1.7–1.9 log CFU/g reduction) of L. monocytogenes were observed after 15-min treatment of combined nisin and GSE while SSA184 showed the highest susceptibility to the activity of nisin and GSE as compared to other strains. The atomic force microscopy results indicated that greater morphological changes were found in combination treated cells of SSA184, whose width (0.47 μm) and height (0.25 μm) were decreased while the surface roughness (10.12 nm) was increased significantly (P < 0.05). Residual nisin and GSE further inhibited the listerial growth during storage (0.4–0.8 log CFU/g increment). Based on the fitting goodness, Weibull and Baranyi models were verified as the best ones to describe inactivation kinetics of L. monocytogenes and growth dynamics during storage, respectively. Additionally, the colour of cooked shrimpsafter combined treatment were not negatively affected and even protected during storage. In conclusion, the antimicrobial treatment of combined nisin and GSE could be a potential antilisterial strategy for shrimps.

Synergistic antibacterial effect of nisin, ethylenediaminetetraacetic acid, and sulfite on native microflora of fresh white shrimp during ice storage

AbstractThis study aims to investigate the effectiveness of using nisin, ethylenediaminetetraacetic acid (EDTA), and sulfite alone or in combination in reducing Vibrio parahaemolyticus, Salmonella enterica, and Pseudomonas fluorescens in broth and native microflora on raw Pacific white shrimp during ice storage. Nisin (50 ppm), EDTA (20 mM), alone or in combination were used to test on the growth of V. parahaemolyticus, S. enterica, and P. fluorescens in broth. Nisin (50 ppm), EDTA (20 mM), sodium metabisulfite (1.25 and 0.625%), ice; alone or in combination were used on shrimps during 1°C storage for 10 days. Microbial and chemical changes were analyzed during shrimp storage. First, the combination of nisin and EDTA exhibited antibacterial effects against V. parahaemolyticus, S. enterica, and P. fluorescens in broth. Second, in shrimp preservation, the combination of nisin, EDTA, and sulfite at a low dose of 0.625% exhibited higher antimicrobial activity than did a high dose of sulfite (1.25%). Based on aerobic bacteria counts, psychrotrophic bacteria, and TVB‐N, shrimp treatment with combination of nisin, EDTA, and low‐dose sulfite were still acceptable within 10 days of storage. Based on our findings, nisin and EDTA can be used to reduce uses of sulfite for shrimp preservation in the future.

Effect of the lantibiotic nisin on inhibitory and bactericidal activities of antibiotics used against vancomycin-resistant enterococci

ObjectivesAntibiotic resistance is a serious issue facing clinicians all over the world. Vancomycin-resistant enterococci (VRE) are amongst the most common resistant pathogens that are isolated from patients suffering from infections in our locality. New antimicrobial agents such as the lantibiotic nisin have been previously examined against resistant bacteria as it has strong antibacterial action with no chance of resistance development. This study aimed to explore the effect of nisin in combination with the conventional antibiotics against VRE, with a view to using it as an auxiliary therapy with such antibiotics for combating resistant isolates. MethodsTwenty-three VRE had been examined for the combined effect of nisin with the routine sets of antibiotics using the microplate dilution technique for minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) testing. Checkerboard microbroth assay was conducted for inspection of synergism between nisin and either ampicillin or chloramphenicol. ResultsAn obvious improvement of inhibitory and bactericidal activities of the tested antibiotics after addition of lantibiotic nisin was observed, with a remarkable reduction in the MIC values of vancomycin against all of the isolates. Nisin recorded a synergistic outcome when combined with either ampicillin or chloramphenicol using the checkerboard assay. ConclusionNisin could be effectively considered as a supplementary agent to traditional antibiotics in the management of VRE-associated infections, as it had a synergistic outcome with commonly prescribed antibiotics such as ampicillin and chloramphenicol.

Antibacterial effects of Lactobacillus acidophilus surface-layer protein in combination with nisin against Staphylococcus aureus

The objective of this study was to evaluate the bactericidal effects of surface-layer protein (Slp) derived from Lactobacillus acidophilus NCFM, L. acidophilus CGMCC1.1878 in combination with nisin against Staphylococcus aureus and investigate their antibacterial mechanism. Compared with the nisin (MIC, 300 IU/mL) alone treatment, the Slps (50 μg/mL) + nisin (1/2 MIC, 150 IU/mL) treatment effectively inhibited S. aureus growth and significantly enhanced its cell membrane permeability (P < 0.05). This combination treatment did not evidently accelerate the leakage of nucleic acids in the cytoplasm, but flow cytometry results showed that the proportion of damaged bacterial cells (including dead and sublethally injured cells) was almost 96.8%, and this combination inactivated intracellular enzymes and decreased the cell membrane potential. Our results showed that Slps enhanced the effect of nisin (1/2 MIC) and reduced the dosage of nisin required for inhibiting S. aureus growth. These results indicate that Slp is a promising combined agent that enhances the antibacterial actions of nisin. The Slps + nisin combination can also be used as a potential antibacterial treatment for food preservation.