Assessment of different selective agar media for enumeration and isolation of Listeria from dairy products

Different selective agar media were compared for the recovery and isolation of five species of Listeria from raw milk and cheese. The selective media examined were Beerens medium, MacBride medium and that described by Dominguez et al. (1984) with 6 mg/l acriflavine, listeria selective agar medium (LSAM), and LSAM with 12 mg/l acriflavine (LSAM X 2A); a non-selective yeast glucose Lemco agar was included for comparison. When the difference between listeria and the natural microflora of raw milk and cheese was 10(2) cfu/ml, listeria could be isolated by direct plating on all media tested. When it was lower than 10(3)-10(4) cfu/ml, listeria were isolated by direct plating only on LSAM and LSAM X 2A. When the difference was greater than 10(4) cfu/ml, a previous enrichment was necessary to isolate them. LSAM and LSAM X 2A media performed better than the other media tested for isolating listeria by direct plating and improved their isolation from dairy products. This superior performance was evaluated by the ability of these media to support colony formation of different species of Listeria tested, the easy recognition of these colonies from those formed by other microorganisms and by their capacity to inhibit the natural microflora of these foods.     

Performance comparison of the BioSys optical assay and the violet red bile agar method for detecting coliforms in food products

Coliform counts in a variety of foods, including dairy products (raw milk, pasteurized milk, yogurt, butter, and ice cream), meats (pork sausage, ground beef, and raw chicken), raw eggs, and chocolate, were performed by the rapid automated BioSys optical assay and the conventional method with violet red bile agar (VRBA). The standard deviation (SD) among five replicate counts for the optical assay was similar to or better than that obtained with VRBA plates for all foods tested. The average SD for all foods tested was 0.21 for the optical assay and 0.30 for the VRBA plates. At very low concentrations of coliforms (1 to 10 CFU/ml for liquid products and 10 to 100 CFU/g for solid samples), the average SDs were 0.26 and 0.47, respectively. The optical assay was less susceptible to interference by noncoliform organisms. In naturally contaminated samples, bacteria such as Serratia liquefaciens, Pantoea spp., Vibrio fluvialis, Aeromonas hydrophilia, and Pseudomonas spp. formed typical colonies in VRBA, resulting in false-positive results or a need to verify colonies in brilliant green lactose broth. The optical assay appeared to be more selective than the VRBA conventional method, detecting fewer noncoliforms. There was close agreement in test results between the two methods, as indicated by correlation coefficients of 0.92 to 0.99 obtained for the regression analysis of the two methods. In most cases both methods distinguished accurately between positive samples containing coliforms and negative controls. All products tested using the automated BioSys Optical Assay for coliforms yielded results more quickly (typically 10 to 12 h) than did those tested with the conventional VRBA method (24 to 72 h with confirmation).     

Lithium chloride-sodium propionate agar for the enumeration of bifidobacteria in fermented dairy products.

Lithium chloride-sodium propionate agar has been developed for the enumeration of bifidobacteria in fermented dairy products. The medium contains lithium chloride and sodium propionate to inhibit the growth of other lactic acid bacteria. Pure cultures of bifidobacteria, lactobacilli, and streptococci were tested for growth in this medium. With one exception, all bifidobacteria were able to grow in this medium and in a nonselective agar with a difference not exceeding .4 log units. However, none of the lactobacilli tested and only one strain each of Streptococcus salivarius ssp. thermophilus and Lactococcus lactis ssp. cremoris grew in lithium chloride-sodium propionate agar. In those cases, the numbers of colonies were lower in lithium chloride-sodium propionate agar by 1.26 and 2.51 log units, respectively, compared with a nonselective agar. Bifidobacteria were also selectively isolated from all fermented milks and cheeses analyzed.     

Twenty-four-hour direct presumptive enumeration of Listeria monocytogenes in food and environmental samples using the ISO-GRID method with LM-137 agar

A new culture medium, LM-137 agar, was developed for use with the ISO-GRID hydrophobic grid membrane filter system for direct presumptive enumeration of Listeria monocytogenes in 24 h. The method was validated against three-replicate, three-dilution most probable number procedures based on enrichment methods specified by the U.S. Department of Agriculture, the Association of Official Analytical Chemists International and the U.S. Food and Drug Administration. The study encompassed meats, dairy products, egg, produce, seafood, and environmental samples. The ISO-GRID filter method produced significantly higher recovery of L. monocytogenes from fermented sausage, hot dogs, pasteurized and raw milk, raw shrimp, and environmental swab samples (P < 0.05). The reference methods yielded significantly higher counts from frozen raw pork and cole slaw (P < 0.05). Confirmation rates of presumptive positive isolates from the filter method ranged from a low of 92% (frozen raw pork) to 100% (most other products). Neither the recovery efficiency nor the confirmation rate were affected by the presence of competing aerobic flora.     

整鸡中弯曲菌定量检测方法的建立与优化

目的建立一种简便、灵敏、稳定的整鸡中弯曲菌定量检测方法,并用北京地区市售整鸡样品进行验证。方法分别对37株鸡肉中常污染的背景杂菌、24株弯曲菌菌株进行抗生素敏感性测试,对弯曲菌分离用选择性培养基及抗生素添加剂进行优化和改进;用77份人工定量污染弯曲菌的鸡淋洗液进行添加回收实验,以生长指数评价选择性平板对鸡肉样品中背景杂菌的抑制情况和弯曲菌生长状况影响。结果在改良后的Karmali和Preston选择性平板上,弯曲菌生长状态稳定,并可有效抑制鸡肉样品中常见的背景干扰杂菌的生长繁殖,此方法对鸡肉中弯曲菌检出的灵敏度可达2.5 CFU/g。结论所建方法灵敏度高、操作简便、计数准确,Karmali和Preston平板组合后可有效提高鸡肉中弯曲菌的检出率,适用于禽类食品中弯曲菌的定量检测。     

Development of a selective differential agar for isolation and enumeration of Campylobacter spp.

Direct plating is an effective technique for isolation and enumeration of Campylobacters from a variety of sample types; however, distinguishing Campylobacters from non-Campylobacter contaminants that frequently grow on many existing agars is difficult. In this study, it was determined that exposing Campylobacters to low levels (200 mg/liter) of triphenyltetrazolium chloride (TTC) was not inhibitory to growth yet was sufficient to give a deep-red to magenta color to the colonies. The new agars (Campy-Line agar [CLAI and Campy-Line blood agar [CLBA]) are translucent. The contrast of deep-red colonies on a translucent background greatly facilitates Campylobacter isolation and makes enumeration on light boxes or by electronic means possible. Direct plating of broiler carcass rinse samples (n = 20) was compared on Campy-Cefex agar and CLA. Recovery of Campylobacter populations was not significantly different between the agars (P < 0.05); however, enumeration was much less labor intensive with the CLA. No contaminants were observed on the CLA, whereas the Cefex agar supported the growth of approximately 14 contaminating (non-Campylobacter) CFU/ml. In a separate trial, recovery of Campylobacters from carcass rinses (n = 25) was similarly compared on Cefex, CLA, and CLBA. Again, recovery of Campylobacters was not significantly different between the agars (Pearson correlation coefficient = 0.988), whereas about nine contaminating (non-Campylobacter) CFU/ml were observed on Cefex agar and none on CLA or CLBA. Although some contaminants can still grow on CLA and CLBA and can present red colonies, most of these contaminants are easily distinguished from Campylobacter by differences in colony morphology.     

社会呼唤绿色食品

<正> 绿色食品是无污染的安全、优质、营养类食品的统称。这个命名,一是由于与环境保护有关的事物通常冠之以“绿色”,以突出这类食品出自良好的生态环境;二是由于绿色象征着生命、健康和活力,对于饱受环境污染毒害的人们,将“绿色”寓意于食品中,体现出自我保护意识和回归自然的愿望。     

Automated turbidimetry for the rapid differentiation and enumeration of bacteria in food

A fully automated analysis system has been used to determine bacterial contamination in food, both qualitatively and quantitatively. Growth curves of bacterial flora were monitored using differential media, and a correlation was established between growth curve parameters and colony-forming units derived from drop-plating as the reference method. Optimal correlation was reached by multiple linear regression. The results were already obtained 16 h.     

Automated turbidimetry for the rapid differentiation and enumeration of bacteria in food

A fully automated analysis system has been used to determine bacterial contamination in food, both qualitatively and quantitatively. Growth curves of bacterial flora were monitored using differential media, and a correlation was established between growth curve parameters and colony-forming units derived from drop-plating as the reference method. Optimal correlation was reached by multiple linear regression. The results were already obtained 16 h.

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Automatische Turbidimetrie als Methode zur Schnellbestimmung von Bakterien in Lebensmitteln

Zusammenfassung Mit Hilfe eines automatisierten Analysensystems kann die Keimflora von Nahrungsmitteln qualitativ und quantitativ bestimmt werden. Dazu wurden Wachstumskurven der Bakterienflora in Differentialnährmedien aufgenommen und Korrelationen zwischen Wachstumskurvenparametern und Koloniezählwerten (KBE) aus dem Tropfplattenverfahren als Referenzverfahren erstellt. Optimale Korrelation wurde dabei durch multiple lineare Regression erreicht. Die Ergebnisse lagen schon nach 16 h vor.

     

食品中菌落总数测定方法探讨

食品中茵落总数测定方法有多种。笔者对其中最主要的2种方法(国家标准和IDF国际标准中的方法)在理论和实践上进行深入的分析和探讨，并用实验进行结果比对。结果表明，国际标准优于国家标准，检出率高，营养全面，计数公式科学，茵落易于分辨。缺点是检验周期较长。     

食品检验中改良SS琼脂配方的研究

SS琼脂是食品检验中肠道致病菌沙门氏菌、志贺氏菌的选择性培养基,为了增加检测的准确性,我们对市售SS琼脂进行质量检测,不尽符合质控标准.改良SS琼脂培养基是在原有配方的基础上,调整一些关键试剂的用量,使用效果明显好于市售产品.     

Comparison of a simple butterfat agar medium with other media used for isolation and enumeration of lipolytic bacteria from dairy products

A nutrient agar medium containing 0.1% of a low melting point fraction of butterfat was shown to be suitable for detection, enumeration and isolation of lipolytic bacteria from milk. Bacterial growth was not inhibited by the butterfat and lipolytic reactions were clearly visible and easily interpreted. Lipolytic counts on the butterfat agar compared favourably with lipolytic counts obtained with other commonly used media.     

Prevalence and resistance to antibiotics for Aeromonas species from retail fish in Malaysia

A total of 87 market fish samples representing five types of fish were evaluated for the presence of Aeromonas spp. Of the samples examined, 69%, 55%, 11.5% and 2.3% harbored Aeromonas spp., A. veronii biovar sobria, A. hydrophila and A. caviae, respectively. The 60 isolated Aeromonas spp. strains were further examined for hemolytic activity, resistance to antimicrobial agents and presence of plasmids. Hemolytic activity varied widely among the isolated strains. Though all the isolates demonstrated resistance to three or more of the antibiotics tested, all were susceptible to ceptazidime. Thirty-four (56.7%) of the sixty isolates harbored plasmids, with sizes ranging from 2.3 to 15.7 kb. These results indicate that hemolytic, multiple antibiotic resistant and genetically diverse aeromonads are easily recovered from fish in this region.     

MC与M17琼脂在嗜热链球菌计数中的比对研究

目的评价国标中使用的MC琼脂与ISO标准中使用的M17琼脂在嗜热链球菌计数中的优劣。方法按照GB 4789.35-2016,使用MC琼脂与M17琼脂对2种以嗜热链球菌为主要成分的菌粉,以及含有嗜热链球菌的发酵乳,进行了计数比对。结果使用M17琼脂对菌粉和发酵乳中嗜热链球菌计数,其计数值均高于采用MC琼脂的计数值,对于2种菌粉样品和发酵乳样品, M17琼脂计数值较MC琼脂分别高出116%、89%和30%;对配对计数结果进行了t检验分析,差异具有极显著性(P0.01)。且分组数据的方差分析表明,与MC琼脂计数结果相比, M17琼脂计数结果的方差更小,精密度更高。结论对于嗜热链球菌的计数, M17琼脂在回收率、精密度和实用性方面显著优于MC琼脂。     

绿色食品的生产技术要求

对绿色食品生产过程中涉及到的原料产地环境质量、生产过程管理、食品添加剂使用、加工场所及生产工艺、原料收购和贮存及包装等环节的技术要求进行了综合论述．为绿色食品生产提供了较完整的技术参考。     

谱写绿色环保包装的新篇章——记环宝科技集团开发绿色环保BOPP瓶的成功之路

<正> 改革开放以来,我国经济飞速发展。由于我国人口众多和资源的无限度使用,在人们物质生活水平不断提高的同时,人们的生态环境遭到严重的破坏。森林砍伐、物种减少、大气污染、河流枯竭,使我国经济的可持续性发展面临严峻的考验。     

发展绿色食品和有机食品丰富食物构成

<正> 针对食品污染的状况和严峻的现实,早在20世纪60年代国际上就开始了生态农业的尝试。在1972年斯德哥尔摩联合国人类环境会议上,首次提出了生态农业的概念。随后,生态农业在许多国家兴起,提倡在食品原料生产、加工过程中树立“食品安全”的思想,生产无公害污染的食品。欧美国家称之为有机食品、生态食品,日本则称为自然食品。叫法称谓虽不同,但基本上都是指在产品生产过程中限制了化学肥料、农药和其他化学物质的使用的食品。 我国的绿色食品始于1990年。开发绿色食品首先要从改善农业生态环境     

纤维素纳米晶体胆甾相液晶形成与应用

纤维素纳米晶体（Cellulose nanocrystal,CNC）在特定浓度下可自组装排列,赋予体系独特的光学性能。为阐明CNC薄膜形成过程中CNC自组装行为机制,本文通过分析CNC薄膜在宏观颜色、紫外可见光谱、偏振光学、微观形貌以及晶体结构等方面的变化,探究了密封沉积时间和CNC浓度对自然蒸发干燥薄膜内部胆甾相液晶形成与排列的影响。结果表明,当密封沉积时间延长至48 h后,CNC薄膜的结构色显色范围、胆甾相结构的长程有序性均得到明显提升。随着浓度的升高,CNC颗粒间距减小,相邻颗粒间扭转角增大,螺距被压缩,从480 nm减小至344 nm。此外,密封沉积处理对高浓度CNC悬浮液形成长程有序性胆甾相结构具有明显优势。本研究结果表明,延长密封沉积时间和提高CNC浓度可以提高薄膜中长程有序性的提高,并促进胆甾相结构域的形成。这进一步完善了CNC基智能包装材料制备的科学基础,对于新型可视化食品包装和检测材料的开发具有积极作用。

     

食品检测用木糖赖氨酸脱氧胆盐琼脂培养基标准物质的研制

目的 研制食品检测用木糖赖氨酸脱氧胆盐琼脂(xylose lysine deoxycholate agar,XLD)培养基标准物质.方法 将XLD培养基各成分按比例称量、球磨后分装制成标准物质.倾注平板后观察培养基形态,检测pH.根据GB 4789.28—2013《食品安全国家标准食品微生物学检验培养基和试剂的质量要求...     

Behavior of Aeromonas species at refrigeration temperatures

The ability of many strains of Aeromonas hydrophila and A. sobria to produce several types of virulence factors has been documented. The presence of Aeromonas in drinking water, as well as in river and saline waters and on various finfish and shellfish taken from them, has caused some concern relative to the role this bacterium plays as a causative agent of human gastroenteritis. The fairly common occurrence of Aeromonas on red meats, poultry and fresh produce and its ability to grow at 4 degrees C gives rise to further concern over public health risks which may be associated with consumption of these foods. A brief overview of the behavior of Aeromonas species at refrigeration temperatures is presented.