矿泉水中铜绿假单胞菌的测定能力验证结果分析

目的分析矿泉水中铜绿假单胞菌检测能力验证(ACAS-PT 736(2019))的结果。方法根据能力验证指导书,并参照GB 4789.2-2016《食品安全国家标准食品微生物学检验菌落总数测定》对样品进行稀释,依据GB 8538-2016《食品安全国家标准饮用天然矿泉水检验方法》对可疑菌落进行鉴定,同时对可疑菌落使用VITEK2进行辅助鉴定。结果样品19-P383检测结果为7800 CFU/250 mL,样品19-Q333检测结果为8800 CFU/250 mL。本次能力验证Z值分别为?0.8、?0.1、|Z|均小于2,检测结果满意。结论本实验室具备检测铜绿假单胞菌的能力, VITEK2对可疑菌落进行辅助鉴定的准确性也得到了验证。     

Effects of ice-nucleation active bacteria on the freezing of some model food systems

Cells of ice-nucleation active (INA) bacteria, Pseudomonas syringae and Erwinia herbicola , were cultured at 18°C with media of nutrient broth and/or yeast extract and harvested at late log phase for maximum ice nucleation activity. These cells were able to nucleate water to freeze at temperatures as high as −2°C. They were incorporated into model food systems, including sugar, protein solutions and oil/water suspensions, representing all major components of foods, to investigate their effects on freezing. The nucleation temperatures of all the treated models were significantly raised by between 3.0 and 5.9°C compared with controls when the freezer temperature was set at −6 to −7°C. The application of the INA cells also caused freezing of certain model solutions at −6°C, such as sucrose solution (10%), which did not freeze at the same conditions without INA bacterial cells. Additions of INA cells also shortened the total freezing time of the model systems by between 20 and 38%. These results suggest that with the application of bacterial ice nucleation, some current food freezing processes may be modified to operate at higher subzero temperatures to provide guaranteed freezing, energy savings and improvement of efficiency and product quality.     

抗铜绿假单胞菌南极微生物的筛选、鉴定及其抑菌谱研究

该研究采用稀释涂布平板法从南极团结湖沉积物中分离、纯化南极微生物,采用双层平板法和琼脂扩散法从中筛选铜绿假单胞菌的拮抗菌,通过形态观察、生理生化试验及16S rDNA序列分析对筛选菌株进行菌种鉴定,并测定其抑菌谱。结果表明,共分离纯化出64株南极微生物,8株对铜绿假单胞菌具有抑制作用,其中菌株NO.TJ31的抑制效果最好,抑菌圈直径达（22.3±0.7） mm,经鉴定,其为弗氏甲基杆菌（Methylobacterium frigidaeris）,菌株NO.TJ31对大肠杆菌、金黄色葡萄球菌、白色念珠菌、副溶血弧菌、鼠伤寒沙门氏菌、鲍曼不动杆菌、屎肠球菌、肺炎克雷伯氏菌都具有一定的抑制作用,具有较广的抑菌谱。     

Antagonistic intestinal microflora produces antimicrobial substance inhibitory to Pseudomonas species and other spoilage organisms

Chicken intestine harbors a vast number of bacterial strains. In the present study, antimicrobial substance produced by lactic acid bacteria (LAB) isolated from the gastrointestinal tract of healthy chicken was detected, characterized, and purified. Based on 16S rRNA sequencing, the bacteria were identified as Lactobacillus plantarum vN. The antimicrobial substance produced by this bacterium was designated vN-1 and exhibited a broad-spectrum of activity against many important pathogenic and spoilage microorganisms, including Pseudomonas aeruginosa, Staphylococcus aureus, Micrococcus luteus, Salmonella Typhimurium, and Erwinia amylovova. vN-1 was determined to be thermostable, insensitive to pH values ranging from 2.0 to 8.0, resistant to various organic solvents and to enzymatic inactivation. The inhibition kinetics displayed a bactericidal mode of action. This study revealed an antimicrobial substance with low molecular mass of less than 1 kDa as determined by ultrafiltration and having features not previously reported for LAB isolated from chicken intestines. The detection of this antimicrobial substance addresses an important aspect of biotechnological control agents of spoilage caused by Pseudomonas spp. and promises the possibility for preservation of refrigerated poultry meat. Practical Application: The newly characterized antimicrobial substance and designated as vN-1 may have the potential to be used in food preservation.     

Uranium biomineralization by a metal resistant Pseudomonas aeruginosa strain isolated from contaminated mine waste

Uranium biomineralization by a metal-resistant Pseudomonas aeruginosa strain isolated from uranium mine waste was characterized for its potential in bioremediation. Uranium resistance, its cellular localization and chemical nature of uranium-bacteria interaction were elucidated. Survival and uranium biomineralization from mine water were investigated using microcosm experiments. The selected bacterium showed U resistance and accumulation (maximum of 275 mg U g(-1)cell dry wt.) following incubation in 100 mg U L(-1), pH 4.0, for 6 h. Transmission electron microscopy and X-ray diffraction analyses revealed that bioaccumulated uranium was deposited within the cell envelope as needle shaped U-phosphate compounds that attain crystallinity only at pH 4.0. A synergistic involvement of deprotonated phosphate and carboxyl moieties in facilitating bioprecipitation of uranium was evident from FTIR analysis. Based on these findings we attribute the localized U sequestration by this bacterium as innocuous complex to its possible mechanism of uranium resistance. Microcosm data confirmed that the strain can remove soluble uranium (99%) and sequester it as U oxide and phosphate minerals while maintaining its viability. The study showed that indigenous bacteria from contaminated site that can survive uranium and other heavy metal toxicity and sequester soluble uranium as biominerals could play important role in uranium bioremediation.     

61株水源性铜绿假单胞菌耐药分析及其16S rRNA系统发育学研究

目的 采用16S rRNA基因序列分析法对2018~2020年间分离自广东地区桶装水中的61株铜绿假单胞菌进行同源性分析,并探讨其对11种不同抗生素的耐药性。方法 采用27F/1492R通用引物对目标菌的16S rRNA基因序列扩增,测序后,采用Clustal X软件进行序列比对,利用MEGA 7.0软件构建系统发生树;药敏实验应用微生物全自动鉴定及药敏系统检测。结果 系统发育分析结果表明：61株共可分为3个分支,分别包含15株一支、1株一支、45株和铜绿假单胞菌标准菌株ATCC 27853一支;药敏结果显示61株铜绿假单胞菌处于较低耐药水平,对所有测试抗生素的耐药率均低于2%,但仍发现一株6重耐药菌株。结论 本研究初步建立了广东地区水源性铜绿假单胞菌的菌株资源库及药敏数据库,为之后的污染溯源工作提供了数据支持,从而保障广大消费群众的饮水安全。     

固定化酵母菌和醋酸杆菌发酵食醋工艺研究

用海藻酸钠包埋酵母菌，滴入1％～9％的钙离子液固化，固定时间4h，连续酒精发酵凝胶颗粒的完整性和弹性尚好。用2．5％的海藻酸纳与4％的PVA混合作醋酸杆菌包埋剂，滴入2％～4％的钙离子硼酸液制备凝胶球，固化9h～10h，成型性和机械强度很好。固定化醋酸杆菌分批发酵50h，产醋酸达4．06g／100mL，重复使用25d，固定化细胞保持高的活力。     

松油烯-4-醇对荧光假单胞菌抑菌能力及作用机理

本实验通过测定最小抑菌剂量(minimum inhibitory concentration,MIC)及生长曲线,评价松油烯-4-醇对荧光假单胞菌的抑菌能力;随后通过碱性磷酸酶活力、电导率测定,二乙酸荧光素染色实验分析以及扫描电子显微镜观察评价松油烯-4-醇对细胞壁及细胞膜通透性的影响;最后通过测定DNA、总蛋白与胞内钠、钾离子三磷酸腺苷(adenosine triphosphate,ATP)酶活力,来进一步探究松油烯-4-醇对细胞内大分子及细胞代谢的影响。结果表明:松油烯-4-醇对荧光假单胞菌的MIC为2μL/mL;松油烯-4-醇可有效破坏荧光假单胞菌的细胞壁,破坏程度随剂量的升高而增强;松油烯-4-醇会使细胞膜的通透性增强,导致细胞内离子的外渗;扫描电子显微镜观察结果表明松油烯-4-醇能对细胞膜产生不可逆的破坏;凝胶阻滞电泳分析结果表明,松油烯-4-醇会使大分子的DNA泄露;通过测定总蛋白含量与Na+、K+-ATP酶活力可知,松油烯-4-醇能降低细胞内蛋白质的含量并能阻滞蛋白质的表达与ATP酶的合成,造成细胞凋亡。综上,松油烯-4-醇有望成为新型水产品保鲜剂,本实验可为拓展天然防腐剂在水产品的应用提供理论依据。     

利用根霉发酵制作腊八豆的研究

对毛霉和根霉最适温度及产蛋白酶、淀粉酶情况进行了研究，同时对毛霉、根霉作为发酵剂对腊八豆制作从发酵到成品的总酸、氨基酸态氯及游离氨基酸的含量变化进行了探讨。结果表明：根霉、毛霉发酵腊八豆的氨基酸态氮及游离氨基酸含量都很接近，而且根霉可以在高温下发酵，因此利用根霉代替毛霉发酵制作腊八豆，不受季节的限制，还能改善腊八豆的风味，提高了劳动生产率及设备利用率。