Additive Antimicrobial Effect Research Articles

Photodynamic inactivation of antibiotic‐resistant Gram‐positive bacteria: Challenges and opportunities

AbstractThe growing numbers of pathogenic bacteria acquiring multidrug resistance are posing the challenges to develop novel therapeutic approaches. Photodynamic bacterial inactivation assaults multiple subcellular targets of pathogenic bacteria, including Staphylococcus aureus, with low tendency to induce further resistance. A wide range of aPDI photosensitizers were investigated for localized infections, including endogenous porphyrins and encapsulated sensitizers in nanoparticles. This mini review presents the concepts of aPDI, a field consisting of more than 3000 research articles published over 30 years. Mutated PBP membrane enzymes of multiantibiotic resistant S. aureus are plausible targets of aPDI. Synergistic aPDI using simultaneously DP, light irradiation and the antibiotic oxacillin, was recently described, eliminating temporarily oxacillin resistance. Additive antimicrobial effects were achieved with DP‐aPDI combined with additional classes of antibiotics. We propose that mutual aPDI adjuvant with antibiotics or other toxic molecules is opening a new therapeutic window for topical life‐threatening infections, without induction of further resistance.

Antimicrobial activity of Citrus spp. and Anethum graveolens components against Candida metapsilosis in ranch sauce.

In this paper, a study was carried out to test the inhibitory effect of a natural food compound (NFC), based on flavonoids (naringenin, hesperetin, tangeritin, luteolin, apigenin and kaempferol) from citrus and dill, in ranch sauce. A strain of C. metapsilosis, isolated from a spoiled sample of ranch sauce, was used as target pathogen microorganism. The inhibitory effect of NFC was compared with a common mixture of chemical preservatives used in this type of sauces: potassium sorbate and sodium benzoate (S/B). An in vitro test was performed by the microtiter plate assay at 10, 25 and 37°C for 24h in modified Tryptic Soy Broth. An additive antimicrobial effect had been observed in the combination of acetic acid and NFC. The results of the microtiter assay were validated in a challenge test in ranch sauce at 5, 25 and 37°C for 10weeks. NFC showed partial fungicidal effect against C. metapsilosis, reducing two logarithmic units at 5°C for 10weeks. At 5°C, the traditional doses of S/B used in ranch sauce decreased viable cells to non-detectable counts from the second week of the experiment. At 25 and 37°C, the use of S/B mixture or the use of NFC showed the same fungicidal effect. The incorporation of NFC, alone or in combination with acetic acid, opens the possibility of formulating clean label sauces with good protection against the development of the acid resistant yeast C. metapsilosis.

Inactivation of foodborne pathogens based on synergistic effects of ultrasound and natural compounds during fresh produce washing.

Ultrasound has potential to be used for disinfection, and its antimicrobial effectiveness can be enhanced in presence of natural compounds. In this study, we compared the antimicrobial effects of ultrasound at 20kHz (US 20kHz) or 1MHz (US 1MHz) in combination with carvacrol, citral, cinnamic acid, geraniol, gallic acid, lactic acid, or limonene against E. coli K12 and Listeria innocua at a constant power density in water. Compared to the cumulative effect of the individual treatments, the combined treatment of US 1MHz and 10mM citral generated >1.5 log CFU/mL additional inactivation of E. coli K12. Similarly, combined treatments of US 1MHz and 2mM carvacrol (30min), US 20kHz and 2mM carvacrol, 10mM citral, or 5mM geraniol (15min) generated >0.5-2.0 log CFU/mL additional inactivation in L. innocua. The synergistic effect of citral, as a presentative compound, and US 20kHz treatment was determined to be a result of enhanced dispersion of insoluble citral droplets in combination with physical impact on bacterial membrane structures, whereas the inactivation by US 1MHz was likely due to generation of oxidative stress within the bacteria. Combined ultrasound and citral treatments improved the bacterial inactivation in simulated wash water in presence of organic matter or during washing of inoculated blueberries but only additive antimicrobial effects were observed. Findings in this study will be useful to enhance fresh produce safety and shelf-life and design other alternative ultrasound based sanitation processes.

Comparative evaluation of 2% turmeric extract with nanocarrier and 1% chlorhexidine gel as an adjunct to scaling and root planing in patients with chronic periodontitis: A pilot randomized controlled clinical trial.

Context:Nanoparticles, owing to their smaller size, penetrate regions inaccessible to other delivery systems, such as periodontal pockets. Thus, the present study aimed to comparatively evaluate efficacy of 2% curcumin with nanocarrier and 1% chlorhexidine gel as a local drug delivery (LDD) in the treatment of periodontal pockets.Materials and Methods:Forty-five chronic periodontitis patients with pocket depth 5–7 mm in two or more teeth were selected. Full-mouth scaling and root planing (SRP) was done for all patients followed by random allocation to the three treatment groups, namely SRP group (Group 1), 2% curcumin with nanogel (Group 2), and 1% chlorhexidine gel (Group 3). Clinical parameter assessment and microbiological analysis of subgingival plaque samples for Aggregatibacter actinomycetemcomitans (Aa), Porphyromonas gingivalis (Pg), and Tannerella forsythia (Tf) was done at baseline, 21st day, and 45th day.Results:The results showed that when the two LDD agents were used as an adjunct to SRP in chronic periodontitis, there was an improvement in all clinical parameters. Evaluation of microbiological parameters also showed a significant reduction in Aa, Pg, and Tf levels. Comparison of 2% turmeric extract with a nanocarrier system with 1% chlorhexidine gel showed that both the agents had a comparable antibacterial effect on the three selected periodontopathic bacteria.Conclusion:The present study showed that both the LDD agents showed an effective improvement of clinical and microbiologic parameters. 2% curcumin delivered with a nanocarrier system showed results comparable to chlorhexidine gel and hence shows promising future as an LDD agent in the treatment of periodontal pockets.

Adjunctive transferrin to reduce the emergence of antibiotic resistance in Gram-negative bacteria.

BackgroundNew strategies are needed to slow the emergence of antibiotic resistance among bacterial pathogens. In particular, society is experiencing a crisis of antibiotic-resistant infections caused by Gram-negative bacterial pathogens and novel therapeutics are desperately needed to combat such diseases. Acquisition of iron from the host is a nearly universal requirement for microbial pathogens—including Gram-negative bacteria—to cause infection. We have previously reported that apo-transferrin (lacking iron) can inhibit the growth of Staphylococcus aureus in culture and diminish emergence of resistance to rifampicin.ObjectivesTo define the potential of apo-transferrin to inhibit in vitro growth of Klebsiella pneumoniae and Acinetobacter baumannii, key Gram-negative pathogens, and to reduce emergence of resistance to antibiotics.MethodsThe efficacy of apo-transferrin alone or in combination with meropenem or ciprofloxacin against K. pneumoniae and A. baumannii clinical isolates was tested by MIC assay, time–kill assay and assays for the selection of resistant mutants.ResultsWe confirmed that apo-transferrin had detectable MICs for all strains tested of both pathogens. Apo-transferrin mediated an additive antimicrobial effect for both antibiotics against multiple strains in time–kill assays. Finally, adding apo-transferrin to ciprofloxacin or meropenem reduced the emergence of resistant mutants during 20 day serial passaging of both species.ConclusionsThese results suggest that apo-transferrin may have promise to suppress the emergence of antibiotic-resistant mutants when treating infections caused by Gram-negative bacteria.

The pH-dependent effect of cationic and non-ionic delmopinol on planktonic and biofilm bacteria

ObjectivesThe primary purpose was to evaluate the antimicrobial effects of cationic and non-ionic delmopinol on planktonic and biofilm bacteria. MethodsDetermination of the minimum inhibitory concentrations on planktonic and biofilm bacteria was performed below and above the pKa-value of delmopinol. Test bacteria were Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli and Pseudomonas aeruginosa. Comparisons were made with three antimicrobial agents and “quaternary” delmopinol. Synergy testing of delmopinol was determined with serial dilutions of delmopinol with the other compounds in a checkerboard fashion, and the fractional inhibitory concentration index (FIC) was calculated. ResultsDelmopinol showed minor differences between its MIC- and MBEC-values for all bacterial strains (MBEC/MIC-ratios of 1–2). For the other compounds the difference between their MIC- and MBEC-values were higher and varied considerably between the bacteria. The MIC- and MBEC-concentrations were lower at pH where the non-ionic form of delmopinol dominates. “Quaternary” delmopinol showed the same MIC-concentrations as delmopinol, but needed much higher concentrations to kill biofilm bacteria. Synergy testing showed FIC-indices of 0.5–1. ConclusionsThe biofilm penetration of non-ionic delmopinol is better than for cationic delmopinol. Likewise, the cationic test reference samples exerted limited biofilm penetration. The increased efficacy of non-ionic delmopinol is probably due to reduced binding to negative groups in the extracellular matrix of polymeric substances surrounding biofilm bacteria. It is also proposed that the non-ionised form of delmopinol deposits on the biofilm surface. Higher amounts of delmopinol than expected will therefore accumulate. Combinations of delmopinol with other compounds suggests an additive antimicrobial effect.

Evaluation of the Antimicrobial Efficacy of Herbal Extracts Added to Root Canal Sealers of Different Bases: An In Vitro Study.

ABSTRACTAimThis study aimed to evaluate and compare the antimicrobial efficacy of root canal sealers of different bases when mixed with herbal extracts.Materials and methodsAn evaluation of three sealers (Endomethasone, AH plus, Apexit plus) mixed with three herbal extracts [Emblica officinalis (Amla), Myristica fragrans (Nutmeg) and Salvadora persica (Miswak)] was done against nine strains of bacteria at various time intervals using the agar diffusion test. Moreover, measurement of the mean zones of inhibition was done.ResultsThe largest zones of bacterial growth inhibition were observed with Endomethasone mixed with Myristica fragrans (Nutmeg) followed in the descending order by AH plus mixed with Salvadora persica (Miswak) and Apexit plus mixed with Salvadora persica (Miswak) respectively. The differences between zones of inhibition among different groups were found to be statistically significant.ConclusionZinc-oxide-eugenol-based sealer (Endomethasone) mixed with herbal extracts produced the largest inhibitory zones followed in the descending order by resin-based sealer (AH plus) and calcium-hydroxide-based sealer (Apexit plus), respectively.Clinical significanceHerbal plants such as [Emblica officinalis (Amla), Myristica fragrans (Nutmeg) and Salvadora persica (Miswak)] are rich sources of bioactive compounds that possess antimicrobial properties. Mixing their extracts with endodontic sealers can produce additive antimicrobial effect against microbes found in inflamed pulp.How to cite this articleDevi MT, Saha S, Tripathi AM, et al. Evaluation of the Antimicrobial Efficacy of Herbal Extracts Added to Root Canal Sealers of Different Bases: An In Vitro Study. Int J Clin Pediatr Dent 2019;12(5):398–404.

Compositions of essential oils with antimicrobial properties against isolates from oral cavities of patients with inflammatory diseases of the periodontium

The significant spread of antibiotic-resistant microorganisms which are part of microbial associations of the oral cavity is considered one of the main causes for the complications and relapses of inflammatory diseases of the periodontium. This problem underlines the importance of constant monitoring of the circulation of polyantibiotic-resistant isolates, and development of new approaches and means of correction for the microbiocoenosis of the oral cavity affected by inflammatory processes. The paper is dedicated to research of antimicrobial properties of essential oil compositions against opportunistic pathogenic microorganisms, agents of inflammatory diseases of the periodontium. Out of the microorganisms isolated from the nidus of inflammation, the extra antibiotic-resistant ones were chosen. For the purpose of antibiotic susceptibility and antimicrobial activity testing, the disc diffusion method was used. The following compositions were manufactured from essential oils: Hyssopus officinalis L. + Rossmarinus officinalis L.; Menta piperita L. + H. officinalis; R. officinalis + Coriandrum sativum L.; R. officinalis + M. piperita + H. officinalis. The compositions H. officinalis + R. officinalis; M. piperita + H. officinalis were shown to have the highest level of antibacterial activity against clinical and typical isolates. Combinations of essential oils demonstrated a broader spectrum of activity against microorganisms than their components taken separately. Certain essential oils and the compositions H. officinalis + R. officinalis; M. piperita + H. officinalis were ascertained to have a high anti-mycotic activity against Candida genus microscopic fungi. This fact proves the advantage of application of combinations of essential oils compared to the use of their separate components. However, not all variants reviewed showed additive antimicrobial effect of the use of combinations of essential oils. The compositions that showed high antibacterial properties against the reviewed isolates may be used for oral hygiene products.

Efficacy of Feracrylum as Topical Hemostatic Agent in Therapeutically Anticoagulated Patients Undergoing Dental Extraction: A Comparative Study.

To compare the efficacy of feracrylum with tranexamic acid (TXA), following dental extraction in patients who are therapeutically anticoagulated with warfarin. Sixty patients on warfarin were randomly divided into three groups. Groups 1 and 2 patients were given feracrylum (1%), and TXA (5%) solution pressure pack and a control group (Group 3) was given normal saline (NS) pressure pack after extraction. Postoperative bleeding was assessed and graded numerically and periodically (0, 1, 2, 5 and 7days). The values were statistically analyzed. Sixty patients (M:F::37:23) with a mean age of 56years who were therapeutically anticoagulated for different medical conditions were included. The mean warfarin dosage was 3.5mg, and the mean INR was 2.83. Out of 27 patients who showed bleeding on day of extraction, eight, ten and nine patients belonged to groups I, II and III, respectively, and the difference was nonsignificant. Out of 15 patients who showed bleeding on post-extraction day 1, one, five and nine patients belonged to groups I, II and III, respectively. The difference was statistically significant on day 1 and nonsignificant in the next follow-ups. Local hemostatic agents like TXA and feracrylum arrest bleeding without having any systemic action and without the necessity of altering the anticoagulant regimen. Feracrylum has an added advantage of a single application, formation of a mechanical barrier and an additional antimicrobial effect. These agents should be incorporated in the protocol for managing patients on oral anticoagulants.

Evaluation of in vitro growth-inhibitory effect of carvacrol and thymol combination against Staphylococcus aureus in liquid and vapour phase using new broth volatilization chequerboard method

Carvacrol and thymol, both plant-derived volatile compounds, have extensively been studied individually as well as in combination with other agents for their antimicrobial activity in liquid phase. However, in contrast to well-established assays for testing of antimicrobial combinatory effects in liquid media, there are no standardized methods for evaluation of interactions between volatile compounds in vapour phase. The objective of this study was to verify new broth volatilization chequerboard method by testing the combination of carvacrol and thymol and to determine in vitro inhibitory effect of these compounds in liquid and vapour phase against twelve Staphylococcus aureus strains. The new method, based on combination of standard microdilution chequerboard and new broth volatilization tests allowing calculation of fractional inhibitory concentrations (FICs), was used. Combination of carvacrol and thymol produced the additive antimicrobial effect against all strains tested. In several cases, they reached ΣFIC values lower than 0.6, which can be considered as a strong additive interaction. The best result was found in vapour phase against one standard strain at combination of 128 μg/mL of carvacrol and 16–256 μg/mL of thymol (ΣFIC = 0.51) and in liquid phase against one clinical isolate at combination of 256 μg/mL of carvacrol and 256 μg/mL of thymol (ΣFIC = 0.53). The study verified that the new technique is suitable for simple and rapid high-throughput combinatory antimicrobial screening of volatile compounds simultaneously in vapour and liquid phase and that it allows determination and comparison of MIC and FIC values in both, liquid and solid media.

Nonphotodynamic Roles of Methylene Blue: Display of Distinct Antimycobacterial and Anticandidal Mode of Actions.

Significance of methylene blue (MB) in photodynamic therapy against microbes is well established. Previously, we have reported the antifungal potential of MB against Candida albicans. The present study attempts to identify additional antimicrobial effect of MB against another prevalent human pathogen, Mycobacterium tuberculosis (MTB). We explored that MB is efficiently inhibiting the growth of Mycobacterium at 15.62 μg/ml albeit in bacteriostatic manner similar to its fungistatic nature. We uncovered additional cell surface phenotypes (colony morphology and cell sedimentation rate) which were impaired only in Mycobacterium. Mechanistic insights revealed that MB causes energy dependent membrane perturbation in both C. albicans and Mycobacterium. We also confirmed that MB leads to enhanced reactive oxygen species generation in both organisms that could be reversed upon antioxidant supplementation; however, DNA damage could only be observed in Mycobacterium. We provided evidence that although biofilm formation was disrupted in both organisms, cell adherence to human epithelial cells was inhibited only in Mycobacterium. Lastly, RT-PCR results showed good correlation with the biochemical assay. Together, apart from the well-established role of MB in photodynamic therapy, this study provides insights into the distinct antimicrobial mode of actions in two significant human pathogens, Candida and Mycobacterium, which can be extrapolated to improve our understanding of finding novel therapeutic options.

A Retrospective Cohort Analysis Shows that Coadministration of Minocycline with Colistin in Critically Ill Patients Is Associated with Reduced Frequency of Acute Renal Failure

ABSTRACTNonclinical studies have suggested that oxidative damage, caspase-mediated apoptosis, and inducible nitric oxide synthase levels may be involved in the pathogenesis of colistin (CST)-associated acute renal failure. MIN inhibits caspase 1, caspase 3, and inducible nitric oxide synthase, leading to the hypothesis that coadministration of CST with MIN (CST-MIN) may reduce the incidence of acute renal failure as well as produce additive or synergistic antimicrobial effects. A multicenter retrospective cohort study was conducted using the Premier Research database to examine the impact of CST-MIN on acute renal failure. Inclusion criteria were as follows: age of ≥18 years, intensive care unit admission at CST initiation, primary International Classification of Diseases 9 (ICD-9) diagnosis of pneumonia or sepsis, nondialysis at hospital admission, and discharge between January 2010 and December 2015. ICD-9 code 584.XX or ICD-10 code N17 was used to define acute renal failure. Baseline comparisons, 1:8 propensity score matching, and confirmatory logistic regression analyses were conducted. In total, 4,817 patients received CST and met inclusion criteria; 93 received CST-MIN. Unadjusted frequency of acute renal failure was significantly lower in patients receiving CST-MIN than CST (11.8% versus 23.7%, P = 0.007). Similar results were seen in propensity score matching (12.0% versus 22.3%, P = 0.031) and logistic regression analyses (odds ratio of 0.403, P = 0.006). Mortalities and 30-day readmission rates were similar between groups. The acute renal failure rate was not impacted by prevalence of baseline renal disease. CST-MIN in critically ill patients may reduce CST-associated acute renal failure. Further evaluation of this combination in prospective clinical studies is warranted.

Exploring bacterial interspecific interactions for discovery of novel antimicrobial compounds.

SummaryRecent studies indicated that the production of secondary metabolites by soil bacteria can be triggered by interspecific interactions. However, little is known to date about interspecific interactions between Gram‐positive and Gram‐negative bacteria. In this study, we aimed to understand how the interspecific interaction between the Gram‐positive Paenibacillus sp. AD87 and the Gram‐negative Burkholderia sp. AD24 affects the fitness, gene expression and the production of soluble and volatile secondary metabolites of both bacteria. To obtain better insight into this interaction, transcriptome and metabolome analyses were performed. Our results revealed that the interaction between the two bacteria affected their fitness, gene expression and the production of secondary metabolites. During interaction, the growth of Paenibacillus was not affected, whereas the growth of Burkholderia was inhibited at 48 and 72 h. Transcriptome analysis revealed that the interaction between Burkholderia and Paenibacillus caused significant transcriptional changes in both bacteria as compared to the monocultures. The metabolomic analysis revealed that the interaction increased the production of specific volatile and soluble antimicrobial compounds such as 2,5‐bis(1‐methylethyl)‐pyrazine and an unknown Pederin‐like compound. The pyrazine volatile compound produced by Paenibacillus was subjected to bioassays and showed strong inhibitory activity against Burkholderia and a range of plant and human pathogens. Moreover, strong additive antimicrobial effects were observed when soluble extracts from the interacting bacteria were combined with the pure 2,5‐bis(1‐methylethyl)‐pyrazine. The results obtained in this study highlight the importance to explore bacterial interspecific interactions to discover novel secondary metabolites and to perform simultaneously metabolomics of both, soluble and volatile compounds.

Microbicidal activity of N-chlorotaurine in combination with hydrogen peroxide

N-chlorotaurine (NCT) and hydrogen peroxide are powerful endogenous antiseptics. In vivo, the reaction between hydrogen peroxide and metal ions leads to the formation of free hydroxyl radicals, which have an increased bactericidal activity. This study examined whether there is an additive antimicrobial effect of NCT combined with hydrogen peroxide. Additionally, it was tested if the additive effect is based on the formation of free radicals. We found by luminometry that, in the presence of H2O2, NCT caused a slow and long-lasting production of singlet oxygen in contrast to HOCl, where this burst occurred instantaneously. Both NCT and hydrogen peroxide (1.0 and 0.1%) demonstrated bactericidal and fungicidal activity. At pH 7.1 and 37 °C, hydrogen peroxide (1%, 294 mM) showed a stronger bactericidal and particularly fungicidal activity than NCT (1%, 55 mM), whereas at pH 4.0 and also in the presence of 5.0% peptone NCT revealed a stronger bactericidal activity. A combination of NCT and hydrogen peroxide led to an increased bactericidal but no increased fungicidal activity compared to both substances alone. The additive effect against bacteria was not removed in the presence of the radical scavengers NaN3, DMSO, or peptone. As a conclusion, NCT and hydrogen peroxide used concurrently interact additive against a range of microorganisms. However, the results of this study suggest that the additive effect of NCT combined with hydrogen peroxide is rather not based on the formation of free radicals.

Japanese internet-based patient registration system for hereditary angioedema: Results of genetic analysis

Zein films assimilated with 1% monolaurin (ML) and 2 or 3% Zataria multiflora Boiss. essential oil (ZEO) were developed and their antimicrobial effects against Listeria monocytogenes and E. coli O157: H7 in vitro and in minced beef meat were determined. Zein films were developed using casting method. Films containing 1% ML + 3% ZEO had the highest swelling index (52.3%). Only ZEO containing films had a remarkable phenolic (13.53 mg gallic acid/g film) and plain zein films had no phenolic contents. Similar improvement were obtained for antioxidant activity of films containing ZEO. Antimicrobial activity was significantly increased by adding ZEO and ML which influenced by the concentrations of agents as well as type of bacteria, which L. monocytogenes was more susceptible than E. coli. In minced meat, the growth of L. monocytogenes was significantly inhibited by ML and/or ZEO containing films during 3 days of storage at 4 °C, whereas the growth of E. coli was only inhibited by films containing ZEO. The results showed the antimicrobial and antioxidant activity of zein film by addition of ZEO and ML. In the case of combination, ZEO and ML had no additive or synergistic antimicrobial effects.

Antioxidant and antimicrobial effects of zein edible film impregnated with Zataria multiflora Boiss. essential oil and monolaurin

Zein films assimilated with 1% monolaurin (ML) and 2 or 3% Zataria multiflora Boiss. essential oil (ZEO) were developed and their antimicrobial effects against Listeria monocytogenes and E. coli O157: H7 in vitro and in minced beef meat were determined. Zein films were developed using casting method. Films containing 1% ML + 3% ZEO had the highest swelling index (52.3%). Only ZEO containing films had a remarkable phenolic (13.53 mg gallic acid/g film) and plain zein films had no phenolic contents. Similar improvement were obtained for antioxidant activity of films containing ZEO. Antimicrobial activity was significantly increased by adding ZEO and ML which influenced by the concentrations of agents as well as type of bacteria, which L. monocytogenes was more susceptible than E. coli. In minced meat, the growth of L. monocytogenes was significantly inhibited by ML and/or ZEO containing films during 3 days of storage at 4 °C, whereas the growth of E. coli was only inhibited by films containing ZEO. The results showed the antimicrobial and antioxidant activity of zein film by addition of ZEO and ML. In the case of combination, ZEO and ML had no additive or synergistic antimicrobial effects.

Synergistic and Additive Antimicrobial Activities of Curcumin, Manuka Honey and Whey Proteins

Antimicrobial activity of curcumin, Manuka honey (MH, Leptospermum scoparium) and Whey protein isolate (WPI) and their synergistic and/or additive effects were tested against various Gram positive and negative bacterial strains for development of functional foods. Curcumin and MH each displayed 100% inhibition against all the tested strains of bacteria. The minimum inhibitory concentration values of curcumin and honey against different strains ranged from 100 to 250 µg/mL and 5–20% respectively. Except Bacillus subtilis, all other tested pathogens were completely inhibited by the mixture of subinhibitory concentrations of curcumin and MH. At these levels, the mixture of MH and WPI was more effective against Streptococcus pyogenes, Shigella soneii and Proteus vulgaris. Mixture of curcumin and WPI completely inhibited the growth of Listeria monocytogenes and Staphylococcus aureus. Combinations of curcumin, MH and WPI had additive and/or synergistic antimicrobial activities and various combinations could be used in food formulations and pharmacological applications. Practical Applications Turmeric, honey and whey proteins are widely consumed all over the world, and have been associated with multiple health benefits. Synergistic and/or additive antimicrobial effects of curcumin, Manuka honey (MH) and whey protein isolate (WPI) were tested against various Gram positive and negative bacterial strains for development of functional foods. Curcumin and MH each showed complete inhibition against all the tested bacterial strains. These in vitro investigations demonstrate that combinations of curcumin, MH and WPI have potent antibacterial activities. To our knowledge, this is the first of such outcomes to be reported. The implication of the results of this study is that Curcumin, MH and WPI in various combinations could be used as a food supplement and also in pharmacological applications.

Antibacterial and physical effects of modified chitosan based-coating containing nanoemulsion of mandarin essential oil and three non-thermal treatments against Listeria innocua in green beans

The antimicrobial activity against Listeria innocua of three different combined non-thermal treatments, along with the impact on color and texture on green bean samples, was evaluated. In this study a bioactive coating formulation based on modified chitosan containing 0.05% nanoemulsion of mandarin essential oil was tested in combination with γ-irradiation, UV-C and ozonated water treatments, and the results in terms of antimicrobial activity, color and texture changes, were evaluated during 14days storage. The combined coating and γ-irradiation treatment gave promising results, showing 3.3 log CFU/g initial microbial reduction, and exhibiting a strong synergistic antimicrobial effect. The treatment based on UV-C and coating formulation allowed a 3 log CFU/g reduction of initial L. innocua population on samples, showing a good residual antimicrobial activity and preventing loss of firmness and color changes during storage. The combined treatment of coating and ozonated water did not show any synergistic or additive antimicrobial effect, but they showed an impact on firmness and color. In conclusion UV-C and γ-irradiation treatments, in combination with the bioactive coating, represent an effective approach to control the growth of L. innocua on vegetable foods.

Antimicrobial Polylactic Acid Packaging Films against Listeria and Salmonella in Culture Medium and on Ready-to-Eat Meat

The contamination of Listeria monocytogenes and Salmonella spp. in ready-to-eat (RTE) meat products has been a concern for the meat industry. In this study, edible chitosan-acid solutions incorporating lauric arginate ester (LAE), sodium lactate (NaL), and sorbic acid (SA) alone or in combinations were developed and coated on polylactic acid (PLA) packaging films. Antimicrobial effects of coated PLA films on the growth of Listeria innocua, L. monocytogenes, and Salmonella Typhimurium in a culture medium (tryptic soy broth, TSB) and on the surface of meat samples were investigated. Antimicrobial PLA films containing 1.94 mg/cm2 of chitosan and 1.94 μg/cm2 of LAE were the most effective against both Listeria and Salmonella in TSB and reduced them to undetectable level (<0.69 log CFU/ml). The same PLA films with LAE significantly (p < 0.05) reduced the growth of L. innocua, L. monocytogenes, and S. Typhimurium on RTE meat during 3 and 5 weeks’ storage at 10 °C, achieving 2–3 log reduction of Listeria and 1–1.5 log reduction of Salmonella as compared with controls. PLA films coated with 1.94 mg/cm2 of chitosan, 0.78 mg/cm2 of NaL, and 0.12 mg/cm2 of SA significantly reduced the growth of L. innocua but were less effective against Salmonella. The combination of NaL (0.78 mg/cm2) and SA (0.12 mg/cm2) with LAE (1.94 μg/cm2) did not generate additional or synergetic antimicrobial effect against Listeria or Salmonella on the meat surface. L. innocua had a similar sensitivity to the film treatments as L. monocytogenes, suggesting that L. innocua may be used as a surrogate of L. monocytogenes for further scaleup and validation studies. The film treatments were more effective against the microorganisms in TSB culture medium than in RTE meat, which suggests that in vivo studies are a necessary step to develop antimicrobial packaging for applications in foods.

Combinatorial antimicrobial effect of curcumin with selected phytochemicals on Staphylococcus epidermidis

Staphylococcus epidermidis is reported to be the main causative agent of nosocomial infections. It has become increasingly difficult to treat this micro-organism because of the emergence of new antibiotic-resistant strains and its ability to form biofilm on medical associated devices. Phytochemicals acting in synergy are effective in killing the micro-organisms by lowering the doses, and synergistic compounds evade the development of resistance due to different mechanism of action. This study aims to determine the synergistic antimicrobial potential of curcumin with cinnamaldehyde, eugenol, and ellagic acid against S. epidermidis. Curcumin with ellagic acid as well as eugenol were found to have additive antimicrobial effect, whereas, in combination, curcumin and cinnamaldehyde were found to have synergistic effect against S. epidermidis (fractional inhibitory concentration index (FICI) = 0.5). Synergy between curcumin and cinnamaldehyde was established by time–kill kinetics and was further evaluated for antibiofilm activity. The dose required to inhibit biofilm formation was reduced to half than that needed to inhibit its planktonic culture (minimal inhibitory concentration (MIC) of curcumin = 3.12 μg/ml; MIC of cinnamaldehyde = 15.62 μg/ml; FICI = 0.248). Both curcumin and cinnamaldehyde disrupted the bacterial membrane for killing the bacteria as determined by permeability studies on Escherichia coli ML-35p.