一种能同时富集沙门氏菌、金黄色葡萄球菌和单增李斯特菌的培乔基

[目的]设计制备一种能够同时富集沙门氏菌、金黄色葡萄球菌及单增李斯特菌的复合增菌肉汤.[方法]挑选合适的添加剂进行单因素实验,确定增菌肉汤的成分及配比,采用平板计数法及三重荧光PCR技术验证肉汤的增菌效果.[结果]结果得到一种能同时富集沙门氏菌、金黄色葡萄球菌及单增李斯特菌的选择性增菌肉汤(SSL),经验证SSL可使得3种目标菌以相对一致的速度进行富集,经过37℃ 150 r/min振荡培养24 h后,菌体浓度到达10~7～10~8 CFU/mL,非目标菌生长受到抑制.应用荧光PCR扩增样品,可同时得到3种目标菌的扩增曲线.在710份实际样品检测中,无假阳性及假阴性报告.[结论]研究结果表明,SSL肉汤可用于沙门氏菌、金黄色葡萄球菌及单增李斯特菌的共增菌,可用于多重PCR检测的前增菌.     

A multipathogen selective enrichment broth for simultaneous growth of Salmonella spp., Vibrio parahaemolyticus, and Vibrio cholerae

A selective enrichment broth (SVV) was formulated to allow concurrent growth of Salmonella spp., V. parahaemolyticus, and V. cholerae. Potassium tellurite and sodium citrate were added as the inhibitors, while glucose, mannitol, anhydrous sodium sulfite and sodium pyruvate were employed as the growth-promoters. When mixed in equal or varied proportions, the target pathogens in SVV had a great accumulation (10(5)-10(8) CFU/ml) and effectively inhibited the growth of competitive microflora. In the artificially contaminated samples, a high recovery of these 3 target pathogens was obtained in SVV. Finally, Salmonella spp., V. parahaemolyticus, and V. cholerae were detected from 608 suspicious food samples by SVV with real-time PCR, and no false-positive or -negative results were reported. In summary, SVV has been shown to be a suitable broth for the simultaneous detection of the 3 pathogens by multipathogen detection on a single-assay platform.     

选择性富集沙门氏菌、副溶血弧菌和霍乱弧菌的共增菌培养基SVV

本研究通过单因素试验和响应面分析试验建立了能够选择性富集沙门氏菌、副溶血弧菌和霍乱弧菌的共增菌培养基SVV,采用平板计数法及三重荧光PCR技术验证了SVV的增菌效果。结果表明:SVV能同时富集以不同浓度比例混合的3种目标菌,37oC振荡培养18h后,菌体浓度达到105~108CFU/mL;SVV强烈抑制大部分的非目标菌;用荧光PCR方法检测经过37oC振荡培养18h的10份人工接种样品和608份实际样品,结果表明目标菌在SVV中增殖18h后菌量达到检测限以上,SVV联合荧光PCR检测方法的检出率为4.06%,比传统检测方法(3.78%)高,无假阴性和假阳性。SVV可望应用于水产品中沙门氏菌、副溶血弧菌和霍乱弧菌检测前的增菌处理,可简化检测过程,有效克服漏检,提高检出率。     

Experimental study on the growth of Salmonella and coli-aerogenes bacteria in pure and mixed cultures,in a fermentor,in two different enrichment media: Sodium selenite and tetrathionate broth

Summary Different serotypes of Salmonella and coli-aerogenes bacteria were grown in a fermentor at +43°C. The Culture media used were composed of two different nutrient broths, one supplemented with sodium selenite, the other with potassium tetrathionate. The growth of both bacteria and the following types of mixed bacteria was studied: Escherichia coli-Salmonella brancaster and Klebsiella pneumoniae-Salmonella brancaster. During the first 10 h of incubation, sodium tetrathionate broth inhibited the multiplication of coli-aerogenes bacteria. Similar results were obtained when these bacteria were grown with S. brancaster and incubated for 18 h, regardless of the original concentration of each of the bacteria. In the presence of sodium selenite, after 18 h of incubation growth was inhibited in E. coli, but not in the other coli-aerogenes bacteria.     

Resuscitation of a defective prophage in Salmonella cocultures

Widely studied Salmonella enterica serovar Typhimurium strains ATCC 14028s and SL1344 harbor a cryptic ST64B prophage unable to produce infectious virions. We found that coculturing either strain with an isogenic sibling lacking the prophage leads to the appearance of active forms of the virus. Active phage originates from reversion of a +1 frameshift mutation at a monotonous G:C run in a presumptive tail assembly pseudogene.     

Influence of pectinase treatment on fruit spirits from apple mash, juice and pomace

The current investigation was conducted to determine the influence of pectinase treatment on fruit spirits produced from apple mash, juice, and pomace. Crispin apples were processed into apple mash, juice, and pomace in our pilot-plant, and fermented with a commercial Red Star wine yeast (Sachharomyces cerevisiae Davis 904). After fermentation, the samples of fermented apple mash, juice, and pomace were distilled, and the distillates were analyzed by HPLC with a Bio-Rad Aminex HPX 87H column and a refractive index detector. Methanol, ethanol, n-propanol, iso-butanol, and iso-amyl alcohol were identified as the major alcohols in all the apple spirits. Student's t-test results indicate that there are significant differences between the methanol concentrations of pectinase treated and non-pectinase treated apple spirits. Duncan's multiple range tests show significant differences in the concentrations of methanol of the fruit spirits made from apple mash, juice, and pomace. Apple pomace yielded significantly higher methanol concentrations than apple mash and juice. Pectinase treatment had little effect on the concentrations of n-propanol, iso-butanol, and iso-amyl alcohol. It is concluded that fruit spirits made from the pectinase treated mash, juice, and pomace of Crispin apples had methanol concentrations significantly above the United States FDA guidance of 0.35% by volume or 280 mg/100 mL of fruit brandy containing 40% ethanol.     

Microbiological quality of walnut kernels and apple juice concentrate

In the present study, we have evaluated the microbiological quality of walnut kernels and pasteurized apple juice concentrate and the application of PCR for quality control of these important horticultural products. PCR assays for the detection of Bacillus cereus, Salmonella, Escherichia coli and E. coli O157:H7 were standardized using minimum time for each step of the reaction. The protocols were effective for their detection in these products after pre-enrichment for 6–12 h. 2, 68 and 30% of the samples of walnut kernels were respectively found satisfactory, acceptable and unsatisfactory on the basis of their viable count. Only 15% of the samples of pasteurized apple juice concentrate were found to possess the desired viable count of less than 100 c.f.u./ml. The predominant contaminants of walnut kernels were found to be the species of Bacillus, Klebsiella, Enterobacter and Staphylococcus. Samples of apple juice concentrate were predominantly found contaminated with species of Bacillus, Staphylococcus and Micrococcus. However, B. cereus, Salmonella and E. coli were also isolated from some of the samples of walnut kernels. Bacillus cereus was also obtained from some of the samples of pasteurized apple juice concentrate in high numbers. Among the moulds Penicillium, Aspergillus, Cladosporium, Rhizopus and Mucor were isolated from these products.     

Limitations of lysine-iron-cystine-neutral red broth in the presumptive identification of Salmonella.

Lysine-iron-cystine-neutral red broth performed satisfactorily in the presumptive identification of Salmonella in preenriched food and animal feed samples enriched in tetrathionate-brilliant green broth. Homologous results from selenite-cystine enrichment broths yielded unacceptably high numbers of false negative reactions.     

Growth of yeast and alcohol production in apple juice containing patulin

Apple juice containing 0, 50, 100, 250, and 500 g of patulin per liter was fermented with Saccharomyces cereviseae var. Montrochet. Numbers of yeast and amount of alcohol in the juice were determined daily for 10 days. No appreciable differences in either numbers of yeast or alcohol production were noted between samples with and without patulin.     

Effect of sunlight on the survival of Salmonella on surfaces

AIMS: To investigate the effect of simulated full-spectrum tropical sunlight on the survival of Salmonella in droplets on surfaces. MATERIALS AND RESULTS: The survival on surfaces of three Zambian strains of Salmonella enterica serovars Enteritidis and Heidelberg was compared with that of a strain of S. enterica serovar Enteritidis phage type (PT) 4 with known characteristics which had been isolated from poultry in the UK. Samples were taken from surfaces every hour for 3 h and after 24 h exposure in either dark or 12 h light/12 h dark cycle conditions. Differences were analysed for significance using a one-way analysis of variance (anova). Results show that there were a significantly higher number of cells surviving on surfaces after 24 h in the dark when compared with populations exposed to a 12 h light/12 h dark cycle. Significantly more cells also survived exposure to sunlight under dirty than clean conditions. CONCLUSIONS: Exposure to sunlight results in a significant decrease in numbers of Salmonella on surfaces. SIGNIFICANCE AND IMPACT OF THE STUDY: Under field conditions exposure of contaminated surfaces to sunlight could be used in place of chemical methods of control as a cheaper way to reduce Salmonella contamination of surfaces.     

Inhibitory effects of high pressure and heat on Alicyclobacillus acidoterrestris spores in apple juice

The effectiveness of combined high pressure and heat treatment for reducing spore levels of Alicyclobacillus acidoterrestris, a thermoacidophilic spore-forming bacterium, in commercial pasteurized apple juice was investigated. Spores suspended in apple juice were successfully destroyed by combining high pressure with a mild or high temperature (45, 71, or 90 degrees C).     

Population biology of Aureobasidium pullulans on apple leaf surfaces

Colonization of apple leaves by the yeast-like fungus Aureobasidium pullulans was studied in the field on eight dates over 2 years. Population densities from adaxial leaf surfaces were approximately log10 0.5-2.6 U higher when enumerated directly along line transects as microscopic counts of A. pullulans cells specifically identified by fluorescence in situ hybridization (FISH) than indirectly as CFU obtained by plating leaf washings from comparable surfaces onto nutrient media. Site-specific mapping of the leaf landscape colonized by A. pullulans was facilitated by use of geographic information system (GIS) software. Colonization was plotted and analyzed both qualitatively (as occupancy) and quantitatively (as density). Overall, when expressed as mean occupancy per date, 22-42% of the microscope fields (each 0.196 mm2) contained > or = 1 A. pullulans cell. Occupancy on a microscope field basis was greater over the midvein (47-89%) or smaller veins (49-65%) than over interveinal regions (11-21%). Intensity of colonization, whether expressed as percentage of total A. pullulans cells associated with a particular leaf feature or as cell density per unit area, was also significantly greater (P < 0.05) over the veinal areas compared with the interveinal areas. The primary fungal morphotypes involved in colonization were blastospores, swollen cells, and chlamydospores; only infrequently were hyphae or pseudohyphae seen. Numbers of microcolonies (> or = 10 clustered cells) and percentage of total A. pullulans cells that occurred as microcolonies increased over the growing season and were significantly greater (P < 0.05) over veinal regions compared with interveinal regions. Locally high concentrations of A. pullulans were associated with naturally occurring micro-wounds in interveinal areas. We conclude that A. pullulans colonizes the phylloplane predominantly as single cells and groups thereof in a highly heterogeneous fashion and that sites exist that are relatively conducive (veins; wounds) or nonconducive (unwounded interveinal areas) for epiphytic fungal growth.