安石榴苷的纯化及对金黄色葡萄球菌抑菌作用的研究

采用超声波辅助法从石榴皮中提取单宁类物质,并用Amberlite XAD-16大孔吸附树脂进行柱层析,以甲醇梯度洗脱法进行纯化,经高效液相色谱对其组分进行分析后,以安石榴苷含量最高的组分对金黄色葡萄球菌进行抑菌实验,分别测得抑菌圈直径和最小抑菌浓度,并检测了安石榴苷对金黄色葡萄球菌生长曲线的影响。液相结果表明,随着洗脱剂浓度的升高,安石榴苷的含量呈现先升高后降低的趋势,最高含量达79.6%;抑菌结果表明,安石榴苷纯化物对金黄色葡萄球菌有明显的抑菌效果,最小抑菌浓度为0.1mg/m L,安石榴苷纯化物以剂量依赖的形式抑制金黄色葡萄球菌的生长。      

Factors affecting the susceptibility of Staphylococcus aureus CCRC 12657 to water soluble lactose chitosan derivative

In this study, the susceptibility of Staphylococcus aureus CCRC 12657 to water-soluble lactose chitosan derivative as influenced by pH, temperature and cell age were investigated. Besides, the effect of this chitosan derivative on enterotoxin production and cell leakage of S. aureus CCRC 12657 was also examined.It was found that the susceptibility of S. aureus CCRC 12657 to lactose chitosan derivative varied with incubation temperature, pH and cell age. The lactose chitosan derivative exerted a higher antibacterial activity against S. aureus CCRC 12657 at 37°C than at 22 and 5°C. At pH 6.5–7.0, S. aureus CCRC 12657 was more susceptible to the chitosan derivative than at pH 6.0 or 7.5. Besides, cells of S. aureus CCRC 12657 in the late-exponential phase (12 h) were most susceptible to the chitosan derivative followed by cells in the stationary phase (24 h) and mid-exponential phase (6 h). Supernatant of cell suspension showed a marked increase in absorbance at 280 nm after the cells of the test organism were exposed to deionized water-containing lactose chitosan derivative. Furthermore, it was also noted that the lactose chitosan derivative not only caused the death of S. aureus CCRC 12657 but also inhibited enterotoxin production in Brain–Heart infusion broth.     

Antioxidative and antimicrobial effects of low molecular weight shrimp chitosan and its derivatives on seasoned-dried Pangasius fillets

This study was performed to evaluate the efficacy and applicability of low molecular weight shrimp chitosan (LMWC) and its derivatives (chitosan nanoparticles, CN; chitosan hydrochloride salt, CHS) as a preservative against lipid oxidation and microbial growth in seasoned-dried Pangasius hypophthalmus fillets during storage. All chitosans exhibited antioxidant activity in vitro (2,2-diphenyl-1-picrylhydrazyl radical scavenging activity, total reducing power ability and lipid peroxidation inhibition activity). The lipid oxidation in dried pangasius fillets that were seasoned by immersing in a solution containing 1.5% chitosan was suppressed during the 8-week storage; such effect was more effective than immersing in a solution containing 0.05% vitamin C. Likewise, LMWC and its derivatives were more effective in inhibiting microbial growth (lower total viable count and yeast/mould counts) than the control. These results clearly show that LMWC and its derivatives could be a potent antioxidant and antimicrobial preservative in seasoned-dried pangasius fillets during 8-week storage at 20 °C.     

柑橘精油纳米乳的制备及对金黄色葡萄球菌的抑制活性研究

以抑菌圈直径试验筛选出的对金黄色葡萄球菌抑制效果较好的3种柑橘(佛手柑、甜橙、蜜柚)精油为油相,以吐温80为乳化剂,去离子水为水相,通过相转变法制备纳米乳.结果表明,3种柑橘精油纳米乳的配方:精油质量分数为6％、吐温80质量分数为24％、去离子水质量分数为70％,此条件下制备的纳米乳平均粒径为10～20 nm,粒径分布...     

Prevalence,antimicrobial susceptibility,and molecular characterization of Staphylococcus aureus isolated from dairy herds in northern China

Staphylococcus aureus is one of the main pathogens involved in dairy cow mastitis. Monitoring of antibiotic use would prove useful to assess the risk of Staph. aureus in raw milk. The objective of this work was to investigate the prevalence of Staph. aureus strais isolated from raw milk in northern China, and to characterize antimicrobial susceptibility of these strains and their key virulence genes. In total, 195 raw milk samples were collected from 195 dairy farms located in 4 cities of northern China from May to September 2015. Out of 195 samples, 54 (27.7%) were positive for Staph. aureus. Among these 54 samples, 54 strains of Staph. aureus were isolated, and 16 strains were identified as methicillin-resistant Staph. aureus. The strains exhibited high percentages of resistance to penicillin G (85.2%), ampicillin (79.6%), and erythromycin (46.3%). Moreover, 72% of the strains showed resistance to more than one antimicrobial agent. Overall, 63% of penicillin-resistant strains possessed the blaZ gene, and 60% of the erythromycin-resistant strains possessed erm(A), erm(B), erm(C), msr(A), or msr(B) genes with 8 different gene patterns. All isolates resistant to gentamicin, kanamycin, and oxacillin carried the aac6'-aph2”, ant(4')-Ia, and mecA genes, respectively. Two tet(M)-positive isolates carried specific genes of the Tn916-Tn1545 transposon. The most predominant virulence genes were sec, sea, and pvl, which encode staphylococcal enterotoxins (sec and sea) and Panton-Valentine leukocidin, respectively. Thirty-two isolates (59.2%) harbored one or more virulence genes. The majority of Staph. aureus strains were multidrug resistant and carried multiple virulence genes, which may pose a risk to public health. Our data indicated that antimicrobial resistance of Staph. aureus was prevalent in dairy herds in northern China, and that antibiotics, especially penicillin G and ampicillin, to treat mastitis caused by Staph. aureus should be used with caution in northern China.     

Antimicrobial edible packaging based on cellulosic ethers, fatty acids, and nisin incorporation to inhibit Listeria innocua and Staphylococcus aureus

Edible cellulosic films made with hydroxypropylmethylcellulose (HPMC) have proven to be inadequate moisture barriers. To improve its water vapor barrier properties, different hydrophobic compounds were incorporated into the HPMC matrix. Some fatty acids and derivatives were included into the film-forming solution prior to film formation. Stearic acid was chosen because of its high capacity to reduce significantly the water vapor transmission rate. Antimicrobial activity of edible HPMC film was obtained by the incorporation of nisin into the film-forming solution. Nisin is an antimicrobial peptide effective against gram-positive bacteria. The inhibitory activity of this bacteriocin was tested for inhibition of Listeria innocua and Staphylococcus aureus. The use of stearic acid was observed to reduce the inhibitory activity of active HPMC film against both selected strains. This phenomenon may be explained by electrostatic interactions between the cationic nisin and the anionic stearic acid. Further studies showed that antimicrobial activity of film varied with the nature of the hydrophobic compound incorporated, in decreasing order: film without lipid, methylstearate film, and stearic acid film. This corroborated the idea of electrostatic interactions.     

Low molecular weight chitosan prepared with the aid of cellulase,lysozyme and chitinase: Characterisation and antibacterial activity

A continuous set of low molecular weight chitosan (LMWC) products was successfully made for this study by coordinating three enzymes (chitinase, lysozyme and cellulase) and two different deacetylated chitosan substrates (80% and 92%). It was observed that the intrinsic viscosity molecular weight (M_V) and SEC-HPLC-determined M_W distribution of LMWC were directed by both the used enzyme and the degree of chitosan substrate acetylation. LMWC prepared using lysozyme and 92%-deacetylated chitosan had larger M_W and, therefore, possessed higher antibacterial activity, as compared to other combinations. LMWC enzyme-directed properties suggest chitinase is more predictable and flexible to produce the specified M_V of LMWC. LMWC’s solubility and antibacterial activity, determined as minimum inhibitory concentration (MIC), against Escherichia coli exhibited a negative linear relationship with log M_V. E. coli strains showed much higher susceptibility to LMWCs than Staphylococcus aureus strains did. Both species also showed intra-species sensitivity diversity toward LMWC.     

Identification and molecular mechanism of action of antibacterial peptides from Flavourzyme-hydrolyzed yak casein against Staphylococcus aureus

Antibacterial peptides can be released from yak milk casein. To date, the amino acid sequences and mechanism of action of yak casein–derived antibacterial peptides remain unknown. The current study identified antibacterial peptides from yak casein and their molecular mechanism of action. Our results showed that yak α-casein, β-casein, and κ-casein could be effectively hydrolyzed by Flavourzyme (Solarbio Science and Technology Co. Ltd.), and the 2-h hydrolysate showed the highest antibacterial rate of 43.07 ± 2.59% against Staphylococcus aureus. The 1,000 to 3,000 Da fraction accounted for 23.61% of the 2-h hydrolysate and had an antibacterial rate of 62.64 ± 4.40%. Three novel peptides with antibacterial activity were identified from this fraction, and the β-casein–derived peptide APKHKEMPFPKYP showed the strongest antibacterial effect (half-maximal inhibitory concentration = 0.397 mg/mL). Molecular docking predicted that APKHKEMPFPKYP interacted with 2 important enzymes of Staph. aureus, dihydrofolate reductase and DNA gyrase, through hydrophobic, hydrogen bonding, salt bridge, and π-π stacking interactions. Our findings suggest that the yak casein–derived peptides may serve as a potential source of natural preservatives to inhibit Staph. aureus.     

高分子质量阳离子聚丙烯酰胺的合成及其对漂白麦草浆的助留助滤性能

研究采用无机氧化还原引发体系,以阳离子单体DMC和丙烯酰胺(州)为共聚单体合成出一系列不同分子量和不同单体配此的阳离子聚丙烯酰胺(CPAM).与有机引发体系相比,无机引发体系具有反应平缓,可操作性强等优点.将所得产品应用于造纸湿部,结果表明,自制阳离子聚丙烯酰胺具有良好的助留助滤性能.     

Antibacterial effects of chitosan solution against Legionella pneumophila, Escherichia coli, and Staphylococcus aureus

Chitosan has been shown to have antibacterial activities on the growth of a wide variety of bacteria. Chitosan solution has been sold commercially for use as an antibacterial agent. Chitosan solution contains not only chitosan but also organic acids as solvents and desalted Japan Sea Proper Water (dJSPW). We aimed to clarify whether chitosan solution has antibacterial activity against bacteria invading bath water, and then to explore the causative factor among these ingredients. The antibacterial activity of full-strength chitosan solution and of 10(2)- and 10(4)-fold chitosan solution diluted with purified water was studied against Legionella pneumophila serogroups 1 (L. pneumophila SG1) and 6 (L. pneumophila SG6), Escherichia coli (E. coli), and Staphylococcus aureus (S. aureus) for 7 days at 37 degrees C. To clarify the causative factor in the antibacterial activity against E. coli, the antibacterial activities of the full-strength and diluted chitosan solutions for 24 h were examined. L. pneumophila SG1 and SG6, and E. coli could not survive in the chitosan solution or in the 10(2)-fold dilute solution for over a day at 37 degrees C. The cells of S. aureus were found to have decreased more than 2.46 log cfu/ml after 1 day of incubation, not only in the chitosan solutions, but also in phosphate buffer solution as a control. No inhibitory effect of dJSPW on the growth of the bacteria was observed. The antibacterial activity of the chitosan solution was lower compared with those of the organic acids solutions, and it increased with decreasing pH value. We observed the antibacterial activity of chitosan solution against L. pneumophila SG1 and SG6, and E. coli, suggesting it may be due to the decreased pH value derived from organic acids rather than from chitosan itself or dJSPW.     

Synergetic effects of high-pressure carbon dioxide and nisin on the inactivation of Escherichia coli and Staphylococcus aureus

Synergetic effects of high-pressure carbon dioxide (HPCD) and nisin on Escherichia coli and Staphylococcus aureus were evaluated. Changes in morphology, interior structure, and membrane permeability were analyzed by scanning and transmission electron microscopy, and flow cytometry. Synergetic effects were found, especially in S. aureus. HPCD alone or with nisin led to morphological and intracellular alterations in both bacteria, but nisin alone led to these damages only in S. aureus. A positive correlation between membrane damage and inactivation was found, but ratios of inactivation were higher, probably because of viable but non-culturable state. Mechanisms were proposed for synergism: for E. coli, outer membrane was damaged first by HPCD, and then HPCD and nisin jointly acted on and destroyed the cytoplasmic membrane, leading to further intracellular damage by HPCD; for S. aureus, HPCD and nisin acted on the cytoplasmic membrane together leading to cell death.Industrial RelevanceEscherichia coli and Staphylococcus aureus are two common microorganisms, which exist widely in the environment and easily contaminate food such as vegetables and dairy products, respectively. Considering heat treatment may destroy some heat-sensitive quality of the products, this study evaluated synergetic effects of high-pressure carbon dioxide (HPCD) combined with the bacteriocin nisin. The investigations provided evidence for potentially combined application of HPCD and nisin to help keep food safe in the industry.     

Effect of molecular weight, type of chitosan, and chitosan solution pH on the shelf-life and quality of coated eggs

ABSTRACT:  Effects of the molecular weight and type of chitosans and pH of chitosan solution on antibacterial activity against Salmonella enterica Enteritidis and on internal quality of chitosan-coated eggs were evaluated during 4 wk of storage at 25 °C. Two types of chitosans were studied: α-chitosans with 4 different molecular weights (Mw = 282, 440, 746, and 1110 kDa) and β-chitosan (Mw = 577 kDa). The α-chitosan with 282 kDa exhibited stronger bactericidal effects than did other α- and β-chitosans. The weight loss, Haugh unit, and yolk index values suggested that coating of eggs with α-chitosan with 282 kDa increased the shelf-life of eggs by almost 3 wk at 25 °C compared with noncoated eggs. The pH (4.5, 5.0, and 5.5) of the α-chitosan (282 kDa) solution did not affect the internal quality of chitosan-coated eggs. Therefore, coating of eggs with 282 kDa α-chitosan without pH adjustment (initial pH of 4.5) may offer a protective barrier against contamination of S. Enteritidis while simultaneously preserving the internal quality of eggs.     

Inhibition of selected pathogens inoculated on the surface of catfish fillets by high molecular weight chitosan coating

Antibacterial activity of high molecular weight water-soluble (HMWWS) chitosan (800 kDa) was investigated against four Gram-negative (Escherichia coli, Salmonella typhimurium, Vibrio cholerae and Vibrio parahaemolyticus) and two Gram-positive (Staphylococcus aureus and Listeria monocytogenes) bacteria. Catfish fillets were surface-inoculated with these food-borne pathogens and coated with chitosan dissolved in aspartic acid (AS) or acetic acid (AC) solution at different concentrations (1% or 3%). Samples were stored at 4 °C for 8 days, except for those inoculated with Vibrio species (10 °C for 6 days). Overall, the most effective coating treatment was the 3% HMWWS chitosan in AS solution (800AS3%). Compared with the control, significant (P < 0.05) reductions caused by 800AS3% were observed for all tested pathogens at the end of storage. The growth of V. parahaemolyticus was completely suppressed by 800AS3%. This study demonstrated that HMWWS chitosan in AS solution could be used as an alternative antimicrobial coating for catfish fillets.     

餐饮具表面的大肠杆菌和金黄色葡萄球菌活性研究

目的研究温度、湿度及餐饮具材质对餐饮具表面大肠杆菌和金黄色葡萄球菌活性的影响。方法分别在同一湿度50%、不同温度(25℃、37℃和60℃)下及同一温度25℃、不同湿度(20%、50%)条件下接种大肠杆菌和金黄色葡萄球菌到陶瓷餐饮具表面,在10、30、60和120 min后检测两种细菌的存活数量;在25℃、湿度50%的条件下分别接种两种细菌到陶瓷、木质、不锈钢和铜合金的餐饮具上,在10、30 min后检测两种细菌的存活数量。结果在同一湿度(50%),25℃时,两种细菌活性均较好;37℃时,存活的大肠杆菌数量比金黄色葡萄球菌低10~2 CFU/m L;60℃时,大肠杆菌10 min后失活,金黄色葡萄球菌60 min后失活。在25℃,湿度20%时,存活的大肠杆菌数量10 min后下降103 CFU/m L,120 min后失活;湿度50%时,存活的大肠杆菌数量120 min后仅下降10~2 CFU/m L。而金黄色葡萄球菌在两种湿度条件下,存活的细菌数量120 min后仅下降10 CFU/m L。在25℃、湿度50%的条件下接种10 min后,铜合金餐饮具上的两种细菌比其他材质的低10~2CFU/m L,30 min后,铜合金餐饮具上的两种细菌均失活。结论大肠杆菌对高温和干燥的耐受性比金黄色葡萄球菌弱。陶瓷、木质和不锈钢餐饮具对大肠杆菌和金黄色葡萄球菌均无抑菌性,而铜合金餐饮具对两种细菌均有抑菌性。     

低分子量透明质酸的制备及其抗氧化活性的研究

首先研究了Fe2+-S2O2-8氧化体系硫酸根自由基(SO-4·)对透明质酸(HA)的氧化降解作用,初步确定了SO-4·氧化降解HA制备低分子量透明质酸(LMWHA)的实验条件。接着HA降解产物经过乙醇沉淀以及凝胶柱层析纯化,采用高效凝胶过滤色谱法(HPGFC)测得纯化后LMWHA分子量为1.45×105Da。最后采用不同的体外抗氧化实验,并以HA为对照,研究了LMWHA的抗氧化活性,发现SO-4·降解后生成的LMWHA的抗氧化活性高于降解前的。本实验说明用SO-4·降解HA制备具有抗氧化活性LMWHA是可行的,为LMWHA抗氧化药物的开发提供了理论依据。     

乌药叶多酚提取工艺优化及其对金黄色葡萄球菌的抑菌作用

目的 优化乌药叶多酚的提取工艺,并评估其对金黄色葡萄球菌的抑菌作用。方法 采用超声辅助乙醇提取法提取多酚类物质,利用单因素和响应面试验优化提取工艺;利用牛津杯法、二倍稀释法和透射电镜试验分析乌药叶多酚对金黄色葡萄球菌的抑菌作用。结果 乌药叶多酚最佳的提取工艺条件为:乙醇浓度59%,料液比1:30 (g/mL),超声时间42 min,超声功率360 W,该条件下乌药叶多酚提取率为4.73%。乌药叶多酚对金黄色葡萄球菌的抑菌圈直径、最小抑菌浓度和最小杀菌浓度分别为(13.10±0.29)mm、2.50和5.00mg/mL。在乌药叶多酚的作用下,金黄色葡萄球菌细胞形态被严重破坏,使出现严重的变形、塌陷和细胞质泄漏等现象。结论 在本试验优化的最优提取工艺下,乌药叶多酚的提取率较高,所得的乌药叶多酚对金黄色葡萄球菌有明显的抑菌效果,为天然防腐剂的开发提供了新思路。     

Tolerance of Salmonella Enteritidis and Staphylococcus aureus to surface cleaning and household bleach

Effective cleaning and sanitizing of food preparation sites is important because pathogens are readily spread to food contact surfaces after preparation of contaminated raw products. Tolerance of Salmonella Enteritidis and Staphylococcus aureus to surface cleaning by wiping with regular, microfiber, and antibacterial-treated cloths was investigated. Wiping with cleaning cloths resulted in a considerable reduction of microorganisms from surfaces, despite the greater difficulty in removing S. aureus than Salmonella Enteritidis. Depending on the cloth type, S. aureus were reduced on surfaces from initial numbers of approximately 10(5) CFU/100 cm2 to numbers from less than 4 CFU/100 cm2 (below the detection limit) to 100 CFU/100 cm2. Directly after the cloths were used to clean the contaminated surfaces, they contained high numbers of bacteria (10(4) to 10(5) CFU/100 cm2), except for the disposable antibacterial-treated cloths, in which no bacteria could be detected. The tolerance of these pathogens to sodium hypochlorite was studied in the suspension test and in cloths. S. aureus showed a better tolerance for sodium hypochlorite than Salmonella Enteritidis. Inactivation of microorganisms in cloths required a higher concentration of sodium hypochlorite than was needed in the suspension test. Repeated exposure to sodium hypochlorite, however, resulted in an increase in susceptibility to this compound. This study provides essential information about the transfer of bacteria when wiping surfaces and highlights the need for a hygiene procedure with cleaning cloths that sufficiently avoids cross-contamination in the household environment.     

Evaluation of molecular methods to determine enterotoxigenic status and molecular genotype of bovine, ovine, human and food isolates of Staphylococcus aureus

This study evaluated the use of PFGE and single enzyme AFLP techniques for the determination of the genetic relationships between Staphyloccocus aureus isolates from human, bovine, ovine and food related sources and reports the prevalence of 'classic' (sea to see) and 'new' (seg, seh, sei, sej, sem, sen and seo) staphylococcal enterotoxin (se) genes in 92 S. aureus strains. A sub-set of the se genotyping results was confirmed by ELISA and the presence of SE toxin determined in isolates from different sources. A 100% correlation was observed, between detection of enterotoxin genes sea-see and expression of corresponding enterotoxin proteins in vitro. The se genotyping data generated from 90 of the S. aureus isolates showed that many of the S. aureus strains producing identical se genotypes correlated with both AFLP and PFGE pattern types. However, single enzyme AFLP technique did not possess the discriminatory power of the PFGE method, but similar clonal relationships were observed by both techniques in many of the isolates tested. Results reported here include the first comprehensive study using a single enzyme AFLP technique to investigate the genetic background of S. aureus isolates from a wide distribution including animal, human and food related sources.