A study of the occurrence and distribution of bdellovibrios in estuarine sediment over an annual cycle

The recovery of bdellovibrios from estuarine sediments over an annual cycle was studied. Greater numbers of the predators were recovered in sediment than in the water column. Increases in the number of bdellovibrios recovered from sediment over various periods of time suggest that multiplication of the predators occurred. Sediment was observed to be an important ecosystem for the survival of bdellovibrios in the winter months. As has been observed in water, the number of bdellovibrios in sediment fluctuated, with seasonal and temperature changes declining to very low numbers during the winter months. In the colder months, low numbers of the predators appeared to winter-over in sediment, with greater numbers of the organisms being recovered from deeper sediment. As the water temperature warmed in the spring, increases in the number of bdellovibrios occurred first in sediment and subsequently in water. This increase of bdellovibrios in sediment may have resulted in the shedding of the organisms into the water column where their numbers subsequently increased. Population fluctuations of bdellovibrios were similar in both water and sediment. Although the temperature may account for much of the observed fluctuation in the number of bdellovibrios, other factors, including salinity and the number of host bacteria, may also play a major role. The number of bdellovibrios recovered from sediment correlated positively with the water temperature, and negatively with the water salinity and the number of bacterial colony-forming units from sediment. The results of this study revealed the significance of sediment to the seasonal cycle, survival, and growth of the bdellovibrios in an estuarine environment.     

Effects of Temperature, Salinity, and Substrate on the Colonization of Surfaces In Situ by Aquatic Bdellovibrios

Recent studies suggest that surfaces are a more conducive habitat than the water column for the proliferation of bdellovibrios in the aquatic environment. The effect of temperature and salinity on the colonization of bdellovibrios on oyster shell, glass, and polystyrene surfaces in situ was investigated over an annual cycle. Sterile surfaces were suspended in various bodies of water for intervals ranging from 24 to 120 h. The results revealed that bdellovibrios associated with different types of surfaces over a broad temperature and salinity range. After 24 h of submersion in waters with temperatures from 9.0 to 26.7(deg)C, the ranges in log(inf10) values per square centimeter for the three surfaces were as follows: oyster shell, 2.2 to 2.5; glass, 0.3 to 2.2; and polystyrene, 0.7 to 1.6. Bdellovibrios were not recovered from surfaces submerged in water at temperatures below 8(deg)C during the 120-h experimental cycle. The number of bdellovibrios and culturable bacteria on oyster shells was significantly higher than the numbers on glass and polystyrene at all time intervals. The number of bdellovibrios was positively correlated with temperature and salinity on all surfaces. A positive correlation between the number of recoverable bacteria and temperature was observed, but the results with respect to salinity were diverse. The numbers of bdellovibrios recovered from oyster shells (up to 48 h) and water samples were significantly increased at salinities greater than 11(permil) compared to those in lower-salinity environments. The results of this study reveal that like many other bacteria in the aquatic environment, bdellovibrios prefer to associate with surfaces. This association provides the predators a rich source of prey bacteria in surface biofilms and perhaps protection in the gel-like matrix of the biofilm.     

Recovery of bdellovibrios from submerged surfaces and other aquatic habitats

The distribution of bdellovibrios was investigated over a wide geographical area of the Chesapeake Bay including some tributaries and subestuaries. Bdellovibrios were recovered from five aquatic habitats; water, sediment, oyster shell surface biofilm, zooplankton, and plants over a wide range of temperature and salinity measurements. Consistently, the greatest number of the predators was recovered from samples of biofilm irrespective of temperature and salinity. A decrease in the numbers and frequency of predators recovered from all habitats was observed at temperatures below 10°C. Only the shell surface biofilm samples yielded bdellovibrios 100% of the time. The organisms were recovered from 79% of water samples and 44% of sediment samples. The results reveal that bdellovibrios are surface-associated organisms and that this association appears to provide some protection for the predators at low temperatures.     

Spatiotemporal shift in sulphide concentration in hypolimnic water column in Lake Hiruga,a saline lake in Japan

A 2-year study was designed to investigate the spatiotemporal distribution of sulphide in the water column of a saline lake, Lake Hiruga in Fukui, Japan. Water samples were collected in Lake Hiruga periodically between April 2014 and March 2016 at appropriate depths with simultaneous in situ measurements of physicochemical parameters such as temperature, salinity and dissolved oxygen (DO) concentration. Sulphide started accumulating in the hypolimnion in September 2014, whilst that did in June 2015. The sulphide concentrations increased toward the end of December in both 2014 and 2015. Then the sulphide disappeared from the hypolimnion in April 2015 and February 2016. The difference in starting season of the sulphide accumulation was closely connected with DO concentrations in the hypolimnion in circulation periods of winter season. The DO concentrations were regulated by water column stability before thermal stratification periods. Our analysis of the sulphide distribution for the 2 years of the study suggested that accumulation of sulphide in the hypolimnion during stratified periods appears to be associated with strength of water column stability in the winter-spring seasons before stagnant periods in Lake Hiruga.     

典型亚热带热分层水库秋季细菌群落垂直分布

水库在我国东南沿海地区是重要的饮用水水源地,对地区经济发展和社会稳定起到重要作用。选择亚热带地区典型的热分层水库——福建莆田东圳水库,于2011年秋季稳定分层期,以水体温度的垂直变化特征为依据进行分层采样。应用PCRDGGE和克隆测序的方法研究浮游细菌群落的垂直分布特征,利用多元统计分析揭示细菌群落与热分层水体理化指标之间的关系。结果显示:溶解氧、电导率、叶绿素a、总氮、氨氮及硝氮在上下层水体中的分布有显著差异,下层缺氧区细菌的ShannonWiener指数和DGGE条带数明显高于上层好氧区,表明东圳水库热分层水体中存在明显的物理、化学及生物分层现象。测序结果表明β-变形菌可能是东圳水库中占优势的细菌类群,统计结果提示溶解氧是显著影响细菌群落组成的环境因子。热分层水体的物理化学分层与水体细菌群落结构密切相关,提示水库生态学研究应对水体热分层给予重视。     

Efficiencies of Recovery of Bdellovibrios from Brackish- Water Environments by Using Various Bacterial Species as Prey

A total of 44 bacterial species subdivided into 10 trial experiments have been used as prey for the recovery of bdellovibrios from samples of water from a brackish tidal pond and an aquarium saltwater tank. In an initial investigation, the recovery efficiency of each of the test bacterial species was compared with that of a designated standard prey, Vibrio parahaemolyticus P-5. The results revealed that in each case strain P-5 yielded an equal or significantly greater number of plaques of bdellovibrios than the test prey with but a single exception, strain CS5. In repeat experiments, CS5 yielded fewer plaques than P-5. To determine whether the use of multiple bacterial species compared with a single species as prey would increase the number of PFU of bdellovibrios recovered, material from plaques appearing on each of the test prey in the respective trials was sequentially subcultured onto two respective agar plates, the first containing as prey V. parahaemolyticus P-5 and the second containing the initial test organism. In nearly every case, subculture of plaques from lawns of the test prey to P-5 resulted in plaque formation. On the basis of the results, the use of several test prey and P-5 did not result in the recovery of any more bdellovibrio PFU than the use of P-5 alone. In this study, V. parahaemolyticus P-5 was observed to be the most efficient prey for the recovery of bdellovibrios from moderate salt water.     

Biological,chemical and physical characteristics of downwelling and upwelling zones in the hyporheic zone of a north-temperate stream

Along a single stream riffle, there is a typical flow pattern in which surface water enters the hyporheic zone in a downwelling zone at the head of the riffle and hyporheic water returns to the stream surface in an upwelling zone at the tail of the riffle. Distinct patterns of physical and chemical conditions in the hyporheic zone are likely to determine patterns of microbial activity and occurrence of hyporheic fauna. Interstitial water and core samples were taken at three depths in the downwelling and upwelling zones of a single riffle in the Speed River, Southern Ontario, Canada. Physical and chemical characteristics of the hyporheic water, bacterial density, protein content, detritus content and faunal composition of the hyporheic sediment were analysed. The downwelling and upwelling zones differed significantly in temperature, pH, redox potential, dissolved oxygen and nitrate with significant positive correlations occurring among the latter three. There were no differences in bacterial density or detritus content between the two zones nor between depths in either zone, but protein content, considered to be a measure of biofilm biomass, was significantly higher in the downwelling zone. Total density of hyporheic fauna and the number of taxa decreased with increasing depth in both upwelling and downwelling zones, and were positively correlated with surface water characteristics (oxygen, temperature and nitrate), sediment protein content and detritus; however, only a weak correlation was found with zone. The composition of taxa differed between the two zones, and faunal distribution was correlated with dissolved oxygen, detritus, protein content and depth.     

Nitrification contributes to winter oxygen depletion in seasonally frozen forested lakes

In lakes that experience seasonal ice cover, understanding of nitrogen–oxygen coupling and nitrification has been dominated by observations during open water, ice-free conditions. To address knowledge gaps about nitrogen–oxygen linkages under ice, we examined long-term winter data (30 + years, 2–3 sample events per winter) in 7 temperate lakes of forested northern Wisconsin, USA. Across lakes and depths, there were strong negative relationships between dissolved oxygen (DO) and the number of days since ice-on, reflecting consistent DO consumption rates under ice. In two bog lakes that routinely experience prolonged winter DO concentrations below 1.0 mg L^?1, nitrate accumulated near the ice surface mainly in late winter, suggesting nitrification may depend on biogenic oxygen from photosynthesis. In contrast, within five oligotrophic-mesotrophic lakes, nitrate accumulated more consistently over winter and often throughout the water column, especially at intermediate depths. Exogenous inputs of nitrate to these lakes were minimal compared to rates of nitrate accumulation. To produce the nitrate via in-lake nitrification, substantial oxygen consumption by ammonium oxidizing microbes would be required. Among lakes and depths that had significant DO depletion over winter, the stoichiometric nitrifier oxygen demand ranged from 1 to 25% of the DO depletion rate. These estimates of nitrifier-driven DO decline are likely conservative because we did not account for nitrate consumed by algal uptake or denitrification. Our results provide an example of nitrification at temperatures < 5 degrees C having a substantial influence on ecosystem-level nitrogen and oxygen availability in seasonally-frozen, northern forested lakes. Consequently, models of under-ice dissolved oxygen dynamics may be advanced through consideration of nitrification, and more broadly, coupled nitrogen and oxygen cycling.     

Impact of Yangtze River Water Transfer on the Water Quality of the Lixia River Watershed,China

To improve water quality and reduce the negative impacts of sudden inputs of water pollution in the Lixia River watershed, China, a series of experimental water transfers from the Yangtze River to the Lixia River were conducted from 2 December 2006 to 7 January 2007. Water samples were collected every six days at 55 monitoring sites during this period. Eight water parameters (water temperature, pH, dissolved oxygen (DO), chemical oxygen demand (COD), potassium permanganate index (COD_Mn), ammonia nitrogen (NH₄ ⁺-N), electrical conductivity (EC), and water transparency (WT)) were analyzed to determine changes in nutrient concentrations during water transfers. The comprehensive pollution index (Pi) and single-factor (Si) evaluation methods were applied to evaluate spatio-temporal patterns of water quality during water transfers. Water quality parameters displayed different spatial and temporal distribution patterns within the watershed. Water quality was improved significantly by the water transfers, especially for sites closer to water intake points. The degree of improvement is positively related to rates of transfer inflow and drainage outflow. The effects differed for different water quality parameters at each site and at different water transfer times. There were notable decreases in NH₄ ⁺-N, DO, COD, and COD_Mn across the entire watershed. However, positive effects on EC and pH were not observed. It is concluded that freshwater transfers from the Yangtze River can be used as an emergency measure to flush pollutants from the Lixia River watershed. Improved understanding of the effects of water transfers on water quality can help the development and implementation of effective strategies to improve water quality within this watershed.     

Molecular diversity and distribution of marine fungi across 130 European environmental samples

Environmental DNA and culture-based analyses have suggested that fungi are present in low diversity and in low abundance in many marine environments, especially in the upper water column. Here, we use a dual approach involving high-throughput diversity tag sequencing from both DNA and RNA templates and fluorescent cell counts to evaluate the diversity and relative abundance of fungi across marine samples taken from six European near-shore sites. We removed very rare fungal operational taxonomic units (OTUs) selecting only OTUs recovered from multiple samples for a detailed analysis. This approach identified a set of 71 fungal ‘OTU clusters'' that account for 66% of all the sequences assigned to the Fungi. Phylogenetic analyses demonstrated that this diversity includes a significant number of chytrid-like lineages that had not been previously described, indicating that the marine environment encompasses a number of zoosporic fungi that are new to taxonomic inventories. Using the sequence datasets, we identified cases where fungal OTUs were sampled across multiple geographical sites and between different sampling depths. This was especially clear in one relatively abundant and diverse phylogroup tentatively named Novel Chytrid-Like-Clade 1 (NCLC1). For comparison, a subset of the water column samples was also investigated using fluorescent microscopy to examine the abundance of eukaryotes with chitin cell walls. Comparisons of relative abundance of RNA-derived fungal tag sequences and chitin cell-wall counts demonstrate that fungi constitute a low fraction of the eukaryotic community in these water column samples. Taken together, these results demonstrate the phylogenetic position and environmental distribution of 71 lineages, improving our understanding of the diversity and abundance of fungi in marine environments.     

High concentrations of viruses in the sediments of Lac Gilbert, Québec

Viruses were found to be very abundant in the top layer of the sediments of Lac Gilbert, Québec. Viruses were extracted from the sediments using pyrophosphate buffer, and viruses from the diluted extracts were pelleted onto grids and enumerated using transmission electron microscopy. Viral abundance in the sediments ranged from 6.5 × 10⁸ to 1.83 × 10¹⁰ ml^–1, which is 10- to 1,000-fold greater than the number observed in the water column. This increase corresponds well with the 100- to 1,000-fold increase in bacterial abundance in the sediments. Viral abundance differed significantly among the surface sediment samples taken at different bottom depths and among samples taken at different depths of the water column. Viral abundance also varied significantly between the oxic and anoxic zones of the water column and the sediments. The virus-to-bacteria ratio varied greatly among the different sediment sites but not among depths in the water column. Viral abundance in the water column was related to bacterial abundance and chlorophyll concentration, whereas viruses in the sediments were most abundant in sediments with high organic matter content. Elevated viral abundance and their erratic distribution in the sediments suggest that viruses might play an important role in sediment microbial dynamics. Correspondence to: Roxane Maranger     

三峡库区澎溪河鱼类时空分布特征的水声学研究

为了解三峡库区支流澎溪河鱼类时空分布变化,2009—2010年的秋季、冬季和春季,使用Simrad EY60鱼探仪对澎溪河的鱼类资源量及其时空分布特征进行3次声学调查。结果表明:3个季节鱼类水平分布不均匀,鱼类最大密度分别为67.07尾/1000 m3,19.66尾/1000m3,17.25尾/1000m3且不同季节上层、中层鱼类密度水平分布有显著性差异(P≤0.01,P=0.03);各季节鱼类密度垂直分布也有一定差异,冬季上层鱼类密度和下层鱼类密度差异较为显著(P=0.05);另外鱼类密度昼夜分布有显著性差异(P<0.05),造成该现象的原因主要是由于鱼类的昼夜垂直节律(Diel Vertical Migration,DVM)引起;3个季节的鱼类目标强度(TS值)的差异极其显著(P<0.01),其中秋季鱼类TS最高((-57.0±5.6)dB),春季TS值最低((-58.6±4.9)dB),造成该差异的原因是4—6月是长江上游鱼类繁殖季节,仔稚鱼居多。鱼类空间分布及其位点的水深关系分析显示,鱼类密度水平分布秋季、冬季与水深不相关(︱r︱<0.2),春季与水深中度负相关(r=-0.5,P≤0.05)。     

Influence of the uterine environment on rat sperm motility and swimming speed

The present study compared several rat sperm parameters in semen samples recovered from a natural uterine environment (i.e., intact estrous female) to those recovered from an artificially induced uterine environment (i.e., ovariectomized hormonally primed female). The sperm parameters measured were percent motile, percent exhibiting forward progressive motility, actual swimming speed, and linear swimming speed. The comparisons were conducted at four postcopulatory time points (0.25, 1.5, 3, and 6 hours) in order to detect differences as a function of residence time within the uterus. No significant differences (P less than 0.05) in the parameters were seen between the two types of uterine environments. Residence time within the reproductive tract had no significant effect on the parameters with the exception of percent motile, which was significantly increased (P less than 0.01) at the 1.5-hour postcopulatory time point.     

Biogeography of Southern Ocean prokaryotes: a comparison of the Indian and Pacific sectors

We investigated the Southern Ocean (SO) prokaryote community structure via zero-radius operational taxonomic unit (zOTU) libraries generated from 16S rRNA gene sequencing of 223 full water column profiles. Samples reveal the prokaryote diversity trend between discrete water masses across multiple depths and latitudes in Indian (71–99°E, summer) and Pacific (170–174°W, autumn-winter) sectors of the SO. At higher taxonomic levels (phylum-family) we observed water masses to harbour distinct communities across both sectors, but observed sectorial variations at lower taxonomic levels (genus-zOTU) and relative abundance shifts for key taxa such as Flavobacteria, SAR324/Marinimicrobia, Nitrosopumilus and Nitrosopelagicus at both epi- and bathy-abyssopelagic water masses. Common surface bacteria were abundant in several deep-water masses and vice-versa suggesting connectivity between surface and deep-water microbial assemblages. Bacteria from same-sector Antarctic Bottom Water samples showed patchy, high beta-diversity which did not correlate well with measured environmental parameters or geographical distance. Unconventional depth distribution patterns were observed for key archaeal groups: Crenarchaeota was found across all depths in the water column and persistent high relative abundances of common epipelagic archaeon Nitrosopelagicus was observed in deep-water masses. Our findings reveal substantial regional variability of SO prokaryote assemblages that we argue should be considered in wide-scale SO ecosystem microbial modelling.     

安徽省某酸性矿山废水坑湖中细菌群落的垂向分布特征及其影响因素

【目的】探究酸性矿山废水(acid mine drainage,AMD)坑湖中细菌群落沿垂向不同水深的分布规律及与环境因子之间的相互作用。【方法】采用16SrRNA基因高通量测序技术,对安徽省某AMD坑湖中6条采样垂线不同水深深度的细菌群落进行调查,同时测定水质理化指标,使用统计学软件分析细菌和地化参数间的联系。【结果】AMD坑湖中水质特征及细菌群落结构出现明显分层现象,自上而下溶解氧降低而pH和多种金属离子浓度增加,微生物群落结构发生变化,多样性和部分物种的丰度增大。细菌群落组成上,表层水域以Proteobacteria (Alpha、Gammaproteobacteria)和Acidobacteria占据主导地位;中下层水域则由Firmicutes、Acidobacteria、Actinobacteria、Gammaproteobacteria和Patescibacteria等共同主导。统计分析结果表明,TN、DO、ORP、pH、Fe、Mn、Al和Zn与嗜酸细菌丰度显著相关,是细菌空间分布的主要限制因素。【结论】AMD坑湖中水质理化特征和细菌群落分布在垂向空间上存在显著差异,群落的...     

The effects of water depth and density on the growth of a unionid clam*

SUMMARY. 1. Unionid clams from Narrow Lake, Alberta, were collected to quantify the natural variation in growth, to assess the natural variation in abundance, age and size distribution, and growth with water depth in the lake, and to conduct in situ experiments to directly test the effects of water depth (temperature) and clam abundance on clam growth. 2. The unionid clam, Anodonta grandis simpsoniana, showed wide variation in length at a given age. There were no significant differences in growth between clams collected at 1,3, 5, and 7m depths in the lake despite marked differences in water temperature. The wide variation in clam biomass within each depth zone may have masked possible effects of water depth. 3. The effect of water depth and variation in clam density on clam growth was tested directly by stocking clams into small enclosures at densities equivalent to 50, 150, 250, 350 and 450g m-2 (live weight) at each of 1, 3, 5 and 7 m depths in Narrow Lake (each depth and abundance treatment in triplicate). A uniform sandy substrate was used in all enclosures to eliminate any possible effect of substrate type on growth. 4. Mortality was negligible (0.9%) during the experiment. Clam density had no significant effect on clam growth which suggests that clam growth was not food limited in the lake. 5. Clams reared at 7 m grew more slowly than clams reared at 1, 3 and 5 m. Clams reared at 5 m grew more slowly than clams reared at 1 and 3m. Growth of clams reared at 1 and 3m did not differ. These differences in growth were strongly correlated with the measured differences in water temperature between depths. 6. Migration between depths probably accounts for the lack of a depth effect on clams growing in the natural habitat.     

黑藻对水体和沉积物理化性质的改善和营养元素的去除作用

通过人工模拟实验,研究了不同种植密度(50、100和150株/ m2)的黑藻(Hydrilla verticillata)对富营养湖泊水体和沉积物理化性质的改善和营养元素的去除作用。结果表明：种植黑藻能显著提高水体溶解氧(DO)和沉积物的氧化还原电位(Eh), DO由3.95mg/L提高到10.42mg/L;沉积物Eh提高了58.6-109.4mV。黑藻的生长有效地降低了水体和沉积物中的氮、磷含量,水体中TP降低了38.9%-57.1%;NH4+-N的含量降低了90.2%; 沉积物中TN的含量比试验前中期降低了70.0%。50、100和150株/ m2 三个种植密度间对水质和沉积物的改善效果差异不明显,说明当单位面积生物量达到一定程度后改善效果也趋于饱和,故在富营养湖泊的植被恢复中种植密度不宜过大。     

Bdellovibrios in Callinectus sapidus, the Blue Crab

Bdellovibrios were recovered from the gill tissue of all of 31 crabs sampled and from all samples of epibiota obtained from the ventral shell surface of 15 crabs. The results suggest that the blue crab is a reservoir for bdellovibrios. The association with crabs may be an important factor in the ecology of the bdellovibrios.     

Vertical and Horizontal Distribution of Bacterial Communities in Alluvial Groundwater of the Nakdong River Bank

As a collaborative effort to characterize a pilot test site for managed aquifer recharge (MAR), vertical and horizontal distributions of microbial communities in the river bank subsurface were investigated to assess the ecological effects after the operation of the MAR using the river water adjacent to the site. Along with a geochemical analysis, barcoded pyrosequencing was performed using the genomic DNAs extracted from the subsurface groundwater/sediment samples retrieved from three multilevel wells among the installed cluster of 14 boreholes. A total of 9 samples from 3 depths (10, 15–25, and 33 m below the ground surface) of each borehole showed higher bacterial abundance and diversity in the shallow (10 m) depths than in the deep (33 m) groundwater. In addition, there was a slight separation of the microbial communities between the depths based on the nonmetric multidimensional scaling analysis of the Yue and Clayton distance and the distance-weighted UniFrac analysis. The phylum Proteobacteria was dominant in all the samples at the sequence abundance of 64.0–97.8% with the total operational taxonomic units of 3375 at the species level, while among the total 288 genera, the genus Pseudomonas and an unclassified genus from Betaproteobacteria were the most abundant across the samples. The community separation between the shallow and the deep groundwater seemed to be correlated with depth differences, supported by differences in the dissolved oxygen (DO) concentration and oxidation-reduction potential (ORP). In the study site, unusually high values of electrical conductivity (EC) were found in the deep groundwater, but those values were unlikely to contribute to the community separation between the shallow and deep groundwater, unlike the DO and ORP values, which were found to influence the community differences.     

Comparison of selective and non-selective enrichment media in the detection of Listeria monocytogenes from meat containing Listeria innocua

AIMS: This study investigated whether the higher incidence of recovery from meat of Listeria innocua compared with L. monocytogenes could be due to the laboratory media used, leading to an artificially lower detection of the pathogenic species, L. monocytogenes. METHODS AND RESULTS: Minced beef was inoculated with L. monocytogenes, L. innocua, or a mixture of these species, and stored at 0 or 10 degrees C under vacuum or aerobic conditions for up to 28 days. Listeria were recovered from the minced beef using selective (University of Vermont Medium, UVM) and non-selective (Buffered Peptone Water, BPW) enrichment broths after 0, 14, and 28 days of storage. In general, there were no significant differences (P < 0.05) between the numbers of L. monocytogenes recovered from minced beef samples after 24 h enrichment in BPW and the numbers recovered using UVM. In addition, the presence of L. innocua in meat samples containing L. monocytogenes did not significantly (P < 0.05) affect the numbers of L. monocytogenes recovered using either enrichment broth. In most cases there were no significant differences (P < 0.05) between the numbers of L. innocua recovered from minced beef samples after 24 h enrichment in BPW compared with numbers recovered using UVM. CONCLUSION: Listeria innocua was found to have no significant competitive advantage over L. monocytogenes in selective or non-selective enrichment media. SIGNIFICANCE AND IMPACT OF THE STUDY: The results suggest that, in some instances, the use of a selective enrichment broth offers no advantage over a non-selective enrichment broth for the recovery of Listeria species from minced beef.