Reduction In Bacterial Population Research Articles

Antimicrobial Nitric Oxide Releasing Contact Lens Gels for the Treatment of Microbial Keratitis.

Microbial keratitis is a serious sight threatening infection affecting approximately two million individuals worldwide annually. While antibiotic eye drops remain the gold standard treatment for these infections, the significant problems associated with eye drop drug delivery and the alarming rise in antimicrobial resistance has meant that there is an urgent need to develop alternative treatments. In this work, a nitric oxide releasing contact lens gel displaying broad spectrum antimicrobial activity against two of the most common causative pathogens of microbial keratitis is described. The contact lens gel is composed of poly-ε-lysine (pεK) functionalized with nitric oxide (NO) releasing diazeniumdiolate moieties which enables the controlled and sustained release of bactericidal concentrations of NO at physiological pH over a period of 15 h. Diazeniumdiolate functionalization was confirmed by Fourier transform infrared (FTIR), and the concentration of NO released from the gels was determined by chemiluminescence. The bactericidal efficacy of the gels against Pseudomonas aeruginosa and Staphylococcus aureus was ascertained, and between 1 and 4 log reductions in bacterial populations were observed over 24 h. Additional cell cytotoxicity studies with human corneal epithelial cells (hCE-T) also demonstrated that the contact lens gels were not cytotoxic, suggesting that the developed technology could be a viable alternative treatment for microbial keratitis.

Improving Wastewater Treatment Using Dried Banana Leaves and Bacteriophage Cocktail

WATER pollution is a serious problem resulting from introduction of hazardous biological waste, organic materials and heavy metals into the natural environment. This study aimed for improving the quality of wastewater as measured by the physicochemical parameters and controlling microbial pollution using dried banana leaves with phage cocktail. Different wastewater samples were collected from New Cairo, Gabal El-Asfar and Helwan, Egypt, and were used for isolation of Escherichia coli, Pseudomonas. aeruginosa and Salmonella Typhi and their specific phages. Fine dried powder of banana leaves was prepared to improve the physicochemical characteristics and reduce microbial populations; the treatment of wastewater was performed using fine powder of banana leaves, phage cocktail individually and in combination. Before treatment, the physical and chemical parameters showed higher levels, dissolved oxygen was depleted and the counts of total coliforms, fecal coliforms and fecal streptococci exceeded the permissible limits. However, using banana leaves, there was improvement in physicochemical parameters and slight reduction of bacterial populations. Individual application of phage cocktail resulted in a significant reduction of bacterial growth as well as adsorption of wastewater pollutants. Furthermore, using combination of phage cocktail specific to E. coli, P. aeruginosa and S. Typhi and fine powder of banana leaves, enhanced the microbial inactivation and removal of water pollutants. Thus, this study indicated the capability of using ecofriendly approach comprising of fine dried powder banana leaves and phage cocktail for wastewater treatment and pave the way for further research to enable reusing wastewater.

Antimicrobial effects of pyruvic and succinic acids on Salmonella survival in ground chicken

This study was designed to assess the antimicrobial effect of pyruvic or succinic acid with oregano essential oil on Salmonella survival, composition of natural microflora, and resultant ground meat quality. Various concentrations of pyruvic (PA) and succinic acids (SA) with 0.5% essential oil (EO) were applied as immersion treatments for broiler breast meat. Salmonella Typhimurium was inoculated on breast meat to evaluate its post-treatment reduction in ground meat. For assessing impact of antimicrobial treatments on ground product, non-inoculated meat was treated with antimicrobials, ground, and stored for retail display in foam trays. Treated ground product was further evaluated for natural microbial counts, instrumental color, pH, and expressible moisture over 8 days of retail display. A combination of 3 g/100 ml SS + 0.5 ml/100 ml EO showed a maximum reduction of 1.52 log CFU/g for Salmonella on ground chicken. The same treatment (3 g/100 ml SS + 0.5 ml/100 ml EO) resulted in reduction of bacterial population ca. 1.2 log CFU/g aerobic plate count and lower pH and L* variation over the 8 d of storage. (P < 0.05) than all other treatments. Results obtained from this study indicate that broiler meat treatment with PA or SA with EO will provide effective reduction of Salmonella and improved raw ground meat quality.

The synergistic antimicrobial effect of a simultaneous UV‐A light and propyl paraben (4‐hydroxybenzoic acid propyl ester) treatment and its application in washing spinach leaves

AbstractSynergistic antimicrobial effect of a simultaneous UV‐A light and propyl paraben (PP) treatment against Escherichia coli O157:H7 is demonstrated. While other parabens with shorter chain length (methyl and ethyl) showed minimal antimicrobial effect, 3 mM PP with UV‐A light achieved more than 5 log [CFU/ml] reduction in bacterial population within 30 min in aqueous solution with a D‐value of 4.89 ± 0.66 min. Neither UV‐A light or 3 mM PP was able to achieve more than 1.5 logarithmic reduction, underscoring the synergy of the simultaneous treatment. Membrane damage as detected via propidium iodide assay was a dominant mechanism of action. The simultaneous treatment could reduce the risk of cross‐contamination during washing of spinach without negatively impairing its color, chlorophyll content, or total phenolic content. Approximately, 75% of the paraben residue from the treatment could be effectively removed with a subsequent rinsing step. The proposed technology is an attractive approach to improve the safety of fresh produce.Practical applicationsCross‐contamination during washing process may increase the food safety risk of fresh produce. Many conventional antimicrobial treatments have limited efficacy, need constant replenishment, and pose a potential health concerns for the line workers. Therefore, new antimicrobial treatments are necessary. This study demonstrates the antimicrobial effect of a simultaneous UV‐A light and propyl paraben treatment against Escherichia coli O157:H7 in water and its ability in reducing the risk of cross‐contamination during washing of spinach (Spinacia oleracea) leaves without negatively impairing its color, chlorophyll content, or total phenolic content. Majority of paraben residue on the spinach after the treatment could be effectively removed with a subsequent rinsing step making it less of an issue for consumers. Overall, proposed technology may be an attractive alternative to conventional antimicrobial used in produce industry.

Efficacy of plant-derived antimicrobials for controlling Salmonella Schwarzengrund on dry pet food

Salmonella enterica is a major human pathogen that is responsible for 23,000 hospitalizations annually in the United States. Contact with contaminated pet food and infected companion animals can transmit salmonellosis to humans. Recent multistate human outbreaks of salmonellosis linked to commercial contaminated dry dog foods underscore the need for controlling the pathogen in pet foods for protecting pet and public health. In this study, the efficacy of five Generally Recognized as Safe (GRAS) status, plant-derived antimicrobials (PDAs), namely trans-cinnamaldehyde (TC), carvacrol (CR), thymol (TY), eugenol (EG), and caprylic acid (CA) applied as a vegetable oil or chitosan based antimicrobial spray on dry pet food for reducing Salmonella Schwarzengrund was investigated. Three hundred gram portions of a commercial dry dog food were inoculated with a two-strain mixture of nalidixic acid (NA) resistant S. Schwarzengrund (~6 log CFU/g), followed by a spray treatment with 0%, 0.5%, 1% or 2% of TC, CR, TY, EG or CA in combination with 5% vegetable oil or 1% chitosan as a carrier. The control and treated dog food samples were stored at 25 °C for 28 days. On days 0, 1, 3, 5, 7, 14, 21, and 28, Salmonella on pet food was enumerated by serial dilution and plating on xylose lysine desoxycholate (XLD) agar. All PDAs at 1% and 2% applied in vegetable oil or chitosan reduced S. Schwarzengrund by at least ~2 log CFU/g on day 3 of storage when compared to control (P < 0.05). No significant reductions in Salmonella were observed on feed sprayed with only vegetable oil or chitosan (P > 0.05). Overall, 2% TC in vegetable oil or chitosan was the most effective treatment, where at least 3 to 3.5 log CFU/g reduction in bacterial populations was observed during storage (P < 0.05). Results suggest that the aforementioned PDAs could potentially be used as an antimicrobial spray to reduce S. Schwarzengrund on dry dog food. However, further studies on the acceptance of PDA-treated dry food by dogs are needed.

Chlorine dioxide inactivation of Pseudomonas aeruginosa and Staphylococcus aureus in water: The kinetics and mechanism

This study evaluated the inactivation kinetics and the bactericidal mechanism of chlorine dioxide towards Pseudomonas aeruginosa (ATCC 27853) and Staphylococcus aureus (ATCC 29213) on a laboratory scale with the view of determining the optimal operational conditions of its application as an alternative disinfectant in water treatment. Bacteria inactivation was conducted in batch reactors at varied disinfectant concentrations, pH, temperature and initial bacteria densities in buffered disinfectant demand free water. The bactericidal mechanism in terms of the effect on the permeability of the outer and cytoplasmic cell membranes and the morphology of the cells were explored. At the highest studied concentration (5.0 mg/L), at least 5-log reductions in bacterial population were observed for each strain of bacteria. Chlorine dioxide inactivation showed a stronger sensitivity to changes in water pH conditions with the inactivation rate at 8.5 being at least 4-fold of what pertained at 6.5 but efficiency was less impacted by changes in the initial bacteria density. A rise in temperature from 4 °C to 15 °C resulted in approximately 56% increase in the inactivation rate of S. aureus. Chlorine dioxide was found to increase the permeability of outer and cytoplasmic cell membranes and consequently resulting in the release of vital nuclear materials which strongly correlated with loss of cell activity or death. However, from TEM micrographs significant morphological damages or cells lysis was not observed. These results provide vital data on operational strategies to enhance efficient disinfection of water with chlorine dioxide whilst monitoring regulatory requirements on disinfection by-products.

Non-thermal atmospheric pressure plasma jet for the bacterial inactivation in an aqueous medium

This study reports the potential of non-thermal atmospheric pressure plasma jet for the bacterial inactivation in an aqueous medium. All experiments were conducted in a reactor containing aqueous solution i.e., water, pre-inoculated with bacterial suspensions and after plasma exposure solution is inoculated in Petrifilm to know the viable count. The plasma jet exposure to the bacterial aqueous solution was carried out under various gases such as helium, argon, air and also in combination as Argon + Air and Helium + Air. In each case, the oxidizing species such as hydrogen peroxide, nitric acid, hydroxyl radicals and ozone formed in the reactor during the plasma exposure were quantified. The effect of applied voltage and gas flow rate were studied to optimize the conditions for its efficacy. The solution pH plays a prominent role in bacterial inactivation, as the process is effective at low pH exhibiting 7 log reduction of bacterial population. The bacterial inactivation is efficient at below the critical pH (<4.7) and the inactivation process becomes less effective if the pH goes above 4.7. Plasma treatment of deionized water produces some reactive species such as hydrogen peroxide and nitrates, this plasma treated water is used to test the bacterial inactivation. Addition of Fe2+ salt to the plasma treated water improves the efficacy by converting hydrogen peroxide to hydroxyl radicals, which serves to be a major contributor to the bacterial inactivation. Especially, Non-thermal plasma offers an alternative way to sterilize vacuum sensitive and thermo-labile living tissues.

Plasma-activated water: a new and effective alternative for duodenoscope reprocessing.

IntroductionDuodenoscopes have been widely used for both diagnostic and therapeutic endoscopic retrograde cholangiopancreatography procedures. Numerous outbreaks of duodenoscope-associated infections involving multidrug-resistant bacteria have recently been reported. Plasma activated water (PAW) has been widely considered an effective agent for surface decontamination and is increasingly used for disinfection of medical equipment. The aim of this study was to evaluate whether the duodenoscopes currently on market are suited for the repeated use of PAW and to test the efficacy of PAW for their disinfection.Materials and methodsIn order to evaluate the disinfection efficacy and the required time of contact, the duodenoscope samples were contaminated by immersing them in fasted-state simulated intestinal fluid containing Escherichia coli, Klebsiella pneumoniae, Acinetobacter baumannii, and Pseudomonas aeruginosa, prior to PAW exposure. In order to test the duodenoscope polymer compatibility with PAW, a challenge test was conducted by immersing the samples in PAW for 30 minutes daily for 45 consecutive days.ResultsSignificant reductions in bacterial populations were achieved after 30 minutes of PAW treatment, indicating a high-level disinfection. Atomic force microscopy and scanning electron microscopy were used to demonstrate that repeated PAW treatment of duodenoscope coating polymer samples did not result in significant differences in morphological surface between the treated and untreated samples. Energy-dispersive X-ray spectroscopy analysis also showed no significant differences between the elemental composition of the duodenoscope coating polymer samples before and after repeated PAW treatment.ConclusionConsidering these preliminary results, PAW could be considered as a new alternative for duodenoscope reprocessing.

Combined effect of sodium hypochlorite and gamma-irradiation for the control of Vibrio vulnificus in fresh oyster and clam

This study investigated the synergistic bactericidal effects of treatment with a combination of sodium hypochlorite (NaOCl) and gamma irradiation against Vibrio vulnificus on shucked oysters and clams. The V. vulnificus population decreased to 1.1–4.8 and 1.2–4.8 log10 colony forming units/g in oysters and clams, respectively, after treatment with a combination of NaOCl (20–80 ppm) and gamma irradiation (0.1–2.0 kGy). V. vulnificus was not detected on oysters or clams after exposure to 60–80 ppm NaOCl and then 2.0 kGy gamma irradiation, where a >2-log synergistic reduction in bacterial population was observed. Based on the Weibull model, 5D-values for 5-log reductions were calculated for treatment with 60 ppm NaOCl with 1.1 kGy irradiation and 80 ppm NaOCl with 0.9–1.0 kGy gamma irradiation. These results indicate treating V. vulnificus populations 5 logs in size with a combination of 60 or 80 ppm NaOCl and 0.9–1.1 kGy gamma irradiation could be a strategy used in post-harvest processing of seafood and distribution to enhance the microbial safety of molluscan shellfish.

Bactericidal Effect of Needle Plasma System on Pseudomonas aeruginosa

Thirty Pseudomonas aeruginosa isolates identified using the API 20E system, biochemical and morphological characteristics then treated with needle plasma system (NPS) at different times. Pseudomonas aeruginosa isolates were tested by disk diffusion method to profile antibiotic susceptibility after and before NPS treatment. Our results of CFU show reduction in bacterial population by an average of (~ 3.1) log CFU from an initial (~ 23.3) log CFU. The percentage reduction (R%) was 100% which gave a very good indication of killing bacteria, for all isolates. The D-value was the average between 0.5 and 2.9 for all isolates according to treatment time 10–60 min. Antimicrobial sensitivity after NPS treatment has been increased. From this study, the NPS improved the high efficiency as physical bactericidal effects. The specific primer pairs (PA-SS forward, PA-SS reverse) were used to amplify (956) bp 16S rRNA region before and after NPS, then sequenced, the results of the locally clinical nosocomial bacteria isolates (query) were (99%) identical to 16S rRNA P. aeruginosa, and have no much difference in their 16S rRNA before and after PNS treatment but have an increase in the number of mutation after PNS: 2 G > T, 3,4 deletion G, 5 deletion C, 6 deletion A, 9,10 A > G, 13 G > T, 14 T > A, 17 deletion A, 21 T > G, 22 C > A, 23 A > T, 31 A > T, 34 C > G, 925, 926 deletion T, 927, 928 deletion A, 931 G > A.

Validation of Biofilm Assays to Assess Antibiofilm Efficacy in Instrumented Root Canals after Syringe Irrigation and Sonic Agitation

IntroductionDifferent methods to characterize bacterial biofilms have been established, each presenting with distinct advantages and shortcomings. The aim of this study was to validate the ability of microbiological culture, the adenosine-5′-triphosphate (luminescence) assay, molecular, and microscopic methods to assess antibiofilm efficacy. MethodsThirty-nine extracted single-rooted teeth were selected. Enterococcus faecalis biofilms were grown for 21 days and randomly distributed into 3 groups. All canals were instrumented (F3 ProTaper Universal; Dentsply Sirona, Johnson City, TN) and irrigated (ProRinse needles, Dentsply Sirona) as follows: group 1, sodium hypochlorite and EDTA irrigation; group 2, supplemented with sonic agitation of NaOCl, and group 3, sterile distilled water irrigation. Bacteriologic samples were collected before (S1) and after canal preparation (S2) and subjected to quantification by culture methods, quantitative reverse transcriptase real-time PCR (qRT-PCR), and luminescence assay. The biofilm structure and bacterial cell viability were evaluated under scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). Data were subjected to statistical analysis to determine the statistical significance (P < .05). ResultsS1 samples showed approximately 8-log colony-forming-units of bacteria using both culture and qRT-PCR. The reduction in bacterial population and relative luminescence was highly significant in the S2 samples from groups 1 and 2 (P < .001). SEM and CLSM showed well-matured root canal biofilms in the pretreatment samples that were reduced after treatment. Irrigation with NaOCl combined with sonic agitation significantly decreased the percentage of live cells (P < .05) but was not able to eliminate the biofilm structure. ConclusionsThis study highlighted the maximum reduction of microbes after instrumentation-syringe irrigation. Although supplementary sonic agitation reduced the root canal biofilm further, it did not completely eliminate the biofilm from a single root canal model. The merits of combining microbiological and molecular quantification methods with CLSM for the comprehensive assessment of antibiofilm efficacy in root canals were emphasized.

Green water technology for the production of pacific white shrimp, Penaeus vannamei (Boone, 1931)

A study was conducted to assess the efficiency of green water culture strategy for production of Pacific white shrimp Penaeus vannamei (Boone, 1931) in high density polyethylene (HDPE) lined ponds (300 m2) for a period of 96 days. Green water from a broodstock fish pond was used for rearing shrimp in treatment ponds; whereas, filtered seawater was used for growing shrimp in control ponds, with both treatment and control in triplicates. Shrimp juveniles (specific pathogen free, SPF) of uniform size (1.74±0.46 g) were stocked at the rate of 100 nos. m-2 per pond. Feeding, water exchange, sampling and water quality analysis were done as per standard shrimp growout procedure. Shrimp health status and microbial load in culture ponds were recorded periodically. Water quality parameters did not show significant variations between control and treatment ponds. Enhanced growth, survival (19.7%) and biomass (23.3%) were observed in treatment ponds when compared to control. Significant reduction in bacterial population and improved shrimp health status were also noticed in treatment ponds. Green water culture technique reduced harmful bacterial population in culture ponds and enhanced shrimp growth, survival, health and production.

ZnO nanoparticles combined radio frequency heating: A novel method to control microorganism and improve product quality of prepared carrots

Abstract Effects of ZnO nanoparticles combined radio frequency (RF) heating on the sterilization and product quality attributes (hardness, color, carotenoids and microstructure) of prepared carrots were investigated comparing to ZnO nanoparticles or RF heating treatment alone. The results showed that the combined sterilization effect of ZnO nanoparticles with radio frequency treatments was superior to ZnO nanoparticles or RF heating treatment alone and extended the shelf life of prepared carrots up to 60 days. ZnO nanoparticles combining RF heating 20 mm/20 min (plate spacing/RF heating time) reduced the loss of hardness, color difference value (ΔE), and carotenoids of prepared carrots. The Scanning electron micrographs (SEM) showed that the cell microstructure of prepared carrots that treated by RF treatments within 20 min was most closely integrated with each other. Therefore, the experimental results of ZnO nanoparticles combined with radio frequency heating could be helpful for food processing industries to produce high quality sterilized prepared carrots. Industrial relevance ZnO nanoparticles combined with radio frequency heating achieved logarithmic reduction of bacterial population and met China's national standard while preserving the color, texture and nutrition better. This information can be helpful for food processing industries to produce high quality sterilized prepared carrots and this same approach can be applied to many other prepared food formulations.

Activation and inactivation of Bacillus pumilus spores by kiloelectron volt X-ray irradiation.

In this study, we investigated the inactivation efficacy of endospore-forming bacteria, Bacillus pumilus, irradiated by low-energy X-rays of different beam qualities. The different low-energy X-rays studied had cut-off energies of 50, 100 and 150 keV. Bacillus pumilus spores (in biological indicator strips) were irradiated at step doses between 6.5 to 390 Gy. The resulting bacteria populations were then quantified by a pour plate method. Results showed that X-rays of lower energies were more effective in inactivating bacterial spores. In addition, an increment in bacterial population was observed at doses below 13Gy. We attributed this increase to a radiation-induced activation of bacterial spores. Four kinetic models were then evaluated for their prediction of bacterial spore behavior under irradiation. This included: (i) first-order kinetics model; (ii) Shull model; (iii) Sapru model; and (iv) probabilistic model. From R2 and AIC analyses, we noted that the probabilistic model performed the best, followed by the Sapru model. We highlighted that for simplicity in curve fitting the Sapru model should be used instead of the probabilistic model. A 12-log reduction in bacterial population (corresponding to a sterility assurance level of 10−6 as required in the sterilization of medical devices) was computed to be achievable at doses of 1000, 1600 and 2300 Gy for the three different X-ray cut-off energies respectively. These doses are an order in magnitude lesser than that required in gamma irradiation. This highlights the applicability of cheaper and safer table-top X-ray sources for sterilization application.

Microorganisms (AMF and PSB) interaction on linseed productivity under water-deficit condition.

The relationship between arbuscular mycorrhizal fungi (AMF) and their associated bacteriacan be has great importance for sustainable agriculture especially in the case of highlymycorrhizal plants such as linseed. To evaluate the possible effect of AMF in association withphosphate solubilizing bacteria (PSB) on linseed plants, a 2-yr factorial experiment wasconducted based on a randomized complete block design with three replications at UrmiaUniversity, Urmia, Iran (37° 39′ 24.82″ N 44° 58′ 12.42″ E). The treatments included two AMFspecies (Glomus mosseae, G. intraradices and non-mycorrhizal control), PSB (Pseudomonasputida P13 and non-inoculated control) and various irrigation regimes (irrigation after 60, 120and 180 mm of evaporation from Class A pan). A significant increase in mycorrhizal linseedplants yield indicated the effectiveness of the two AMF species more than bacterial inoculation.The cumulative (second year) soil spores were maximally observed in mycorrhizal (single AMFand dually inoculation) treatments. The reduction in bacterial population was found with anincrease in water deficit. Dual infections caused an increase in leaf P content more than the onein PSB and AMF inoculations. Drought stress-induced yield reduction in seed and in oil wassignificantly compensated by mycorrhizal symbiosis for all irrigation levels. We found over25% increase for seed yield and 30% for oil yield in mycorrhizal plants as well as co-inoculatedplants. The yields improvements in mycorrhizal treatments (single and dually inoculated)leading to the highest water use efficiency.

Assessment of chlorine tolerance profile of Citrobacter species recovered from wastewater treatment plants in Eastern Cape, South Africa.

This present study assessed the chlorine tolerance of some Citrobacter species recovered from secondary effluents from the clarifiers of two wastewater treatment plants in the Eastern Cape, South Africa. The bacterial survival, chlorine lethal dose and inactivation kinetics at lethal doses were examined. Inactivation of the test bacteria (n=20) at the recommended dose of 0.5mg/l for 30min exposure showed a progressive reduction in bacterial population from 4 to 5 log reduction and residuals ranged between 0.12 and 0.46mg/l. The bactericidal activity of chlorine increased at higher dosages with a substantial reduction in viability of the bacteria and complete inactivation of the bacterial population at a lethal dose of 0.75 and 1.0mg/l in 30min. For the inactivation kinetics, bactericidal activity of chlorine increased with time showing a 3.67-5.4 log reduction in 10min, 4.0-5.6 log reduction in 20min and above 6.3 log reductions to complete sterilization of bacterial population over 30min for all the entire test Citrobacter isolates used in this study. Furthermore, there was a strong correlation (R 2>0.84) between bacteria inactivation and increase in contact time. This study appears to have provided support for laboratory evidence of bacterial tolerance to chlorine disinfection at current recommended dose (0.5mg/l for 30min), and chlorine concentration between 0.75 and 1.0mg/l was found to have a better disinfecting capacity to check tolerance of Citrobacter species.

Characterisation of polyamide 11/copper antimicrobial composites for medical device applications

Direct incorporation of antimicrobial additive into the polymer matrix is a cost effective approach for the development of polymer/metal antimicrobial composites. Application of these antimicrobial composite systems for manufacturing medical devices addresses the issue of device related infections. In the present study, commercially available inorganic copper based additive, Plasticopper, was incorporated into a Polyamide 11(PA 11) matrix during the polymer processing stage. These polymer composites were evaluated for their morphological, mechanical, antimicrobial and ion release properties. Isothermal crystallisation studies showed that the copper additive acted as a nucleating agent and promoted faster crystallisation. Short term mechanical studies confirmed that the incorporation of copper has reinforcing effect on the composites with 5 and 10% copper loadings and did not adversely affect the short-term mechanical performance of the polymer composites. These composite systems were shown to be active against Escherichia coli ATCC 8739 with >99.99% reduction in bacterial population. Corresponding ion release profiles for these composites indicated long term antimicrobial activity.

Development of a novel strategy for controlled release of lysozyme from whey protein isolate based active food packaging films

The purpose of this study is to develop a novel controlled release system based on pH-responsive polyacrylic acid (PAA)/lysozyme (LYS) complexes incorporated within a hydrophilic whey protein isolate (WPI) film matrix for active food packaging applications. Complex formation is simple under benign conditions that are suitable for preserving antimicrobial activity of the lysozyme. In addition, the pH-dependent charge density of complexes allowed a uniform distribution in the matrix. The properties of the complexes such as size, surface charge and hydrophilicity were varied by changing PAA/LYS ratio (0.1 and 0.3 w/w) and PAA molecular weight (2 kDa and 450 kDa). The effects of complex properties as well as mode of lysozyme incorporation into the films (100%-free, 50%-free+50%-PAA/LYS complex and 100%-PAA/LYS complex) on the LYS release rate, activity and antimicrobial efficacy of the films were investigated. The results have shown that ∼100% LYS loading into the complexes is possible regardless of PAA molecular weight or PAA/LYS ratio. Incorporating lysozyme into the film in complexed form extended its release time from less than 24 h up to 500 h and reduced its diffusivity from ∼10−9 to ∼10−13 cm2/s. The films including 50%-free-LYS+50%-PAA/LYS complex showed a 5.7 log reduction in bacterial population within 72 h whereas 100%-free-LYS containing film could not suppress Listeria innocua growth after 24 h. Overall, the results suggest that complexation of lysozyme with weak polyelectrolytes can be used as an effective strategy to achieve a long-lasting antimicrobial effect and that films prepared with such complexes have great potential as food packaging materials.

Application of mathematical models for bacterial inactivation curves using Hypericin-based photosensitization.

The aim of this study was to evaluate which of the three mathematical models (Weibull, Geeraerd and Logistic) makes the best approximation for Hypericin-based photosensitization bacterial inactivation. The inactivation of common food-borne pathogens Listeria monocytogenes and Bacillus cereus has been analysed. Three models, Weibull, Logistic and Geeraerd, have been used for different treatment conditions (10(-7) moll(-1) and 10(-8) moll(-1) Hypericin concentrations and 2 and 60min incubation time). The Logistic method showed better correspondence (estimated R(2) ≥0·98, RMSE≤0·41), than the Weibull (estimated R(2) ≥0·91, RMSE≤0·90) and the Geeraerd model (R(2) ≥0·83, RMSE≤1·27). After evaluation of best fitting model for the dependence of bacterial population reduction on irradiation time, the parameters describing treatment efficiency have been calculated. Our results indicate that the Logistic model described in the best way the inactivation of B.cereus and L.monocytogenes by Hypericin-based photosensitization. This study identified a best model for describing bacterial inactivation by hypericin-based photosensitization, which provides a way to evaluate the efficacy of different treatment conditions for this novel decontamination technique.

Highly Efficient F, Cu doped TiO2 anti-bacterial visible light active photocatalytic coatings to combat hospital-acquired infections.

Bacterial infections are a major threat to the health of patients in healthcare facilities including hospitals. One of the major causes of patient morbidity is infection with Staphylococcus aureus. One of the the most dominant nosocomial bacteria, Methicillin Resistant Staphylococcus aureus (MRSA) have been reported to survive on hospital surfaces (e.g. privacy window glasses) for up to 5 months. None of the current anti-bacterial technology is efficient in eliminating Staphylococcus aureus. A novel transparent, immobilised and superhydrophilic coating of titanium dioxide, co-doped with fluorine and copper has been prepared on float glass substrates. Antibacterial activity has demonstrated (by using Staphylococcus aureus), resulting from a combination of visible light activated (VLA) photocatalysis and copper ion toxicity. Co-doping with copper and fluorine has been shown to improve the performance of the coating, relative to a purely fluorine-doped VLA photocatalyst. Reductions in bacterial population of log10 = 4.2 under visible light irradiation and log10 = 1.8 in darkness have been achieved, compared with log10 = 1.8 under visible light irradiation and no activity, for a purely fluorine-doped titania. Generation of reactive oxygen species from the photocatalytic coatings is the major factor that significantly reduces the bacterial growth on the glass surfaces.