The detection of irradiated foods using the Direct Epifluorescent Filter Technique

A method was evaluated which has the potential to detect a food sample which has been irradiated. The technique will give an indication of the total number of viable micro-organisms present before irradiation. It is based on the comparison of an aerobic plate count (APC) with a count obtained using the Direct Epifluorescent Filter Technique (DEFT). When the APC of an irradiated sample was compared with the DEFT count on the same sample, the APC was considerably lower than that obtained by DEFT. The count of orange fluorescing cells after irradiation, however, correlated well with an APC of the same sample before irradiation. For the samples examined the DEFT count determined the viable microbial population in the sample before irradiation. The difference between the APC and the DEFT count gave the number of organisms rendered non-viable by the process.     

Learning invariant object recognition in the visual system with continuous transformations

The cerebral cortex utilizes spatiotemporal continuity in the world to help build invariant representations. In vision, these might be representations of objects. The temporal continuity typical of objects has been used in an associative learning rule with a short-term memory trace to help build invariant object representations. In this paper, we show that spatial continuity can also provide a basis for helping a system to self-organize invariant representations. We introduce a new learning paradigm “continuous transformation learning” which operates by mapping spatially similar input patterns to the same postsynaptic neurons in a competitive learning system. As the inputs move through the space of possible continuous transforms (e.g. translation, rotation, etc.), the active synapses are modified onto the set of postsynaptic neurons. Because other transforms of the same stimulus overlap with previously learned exemplars, a common set of postsynaptic neurons is activated by the new transforms, and learning of the new active inputs onto the same postsynaptic neurons is facilitated. We demonstrate that a hierarchical model of cortical processing in the ventral visual system can be trained with continuous transform learning, and highlight differences in the learning of invariant representations to those achieved by trace learning.     

Contrasting Effects of Heat Treatment and Incubation Temperature on Germination and Outgrowth of Individual Spores of Nonproteolytic Clostridium botulinum Bacteria

In this study, we determined the effects of incubation temperature and prior heat treatment on the lag-phase kinetics of individual spores of nonproteolytic Clostridium botulinum Eklund 17B. The times to germination (t_germ), one mature cell (t_C1), and two mature cells (t_C2) were measured for individual unheated spores incubated at 8, 10, 15, or 22°C and used to calculate the t_germ, the outgrowth time (t_C1 − t_germ), and the first doubling time (t_C2 − t_C1). Measurements were also made at 22°C of spores that had previously been heated at 80°C for 20 s. For unheated spores, outgrowth made a greater contribution to the duration and variability of the lag phase than germination. Decreasing incubation temperature affected germination less than outgrowth; thus, the proportion of lag associated with germination was less at lower incubation temperatures. Heat treatment at 80°C for 20 s increased the median germination time of surviving spores 16-fold and greatly increased the variability of spore germination times. The shape of the lag-time (t_C1) and outgrowth (t_C1 − t_germ) distributions were the same for unheated spores, but heat treatment altered the shape of the lag-time distribution, so it was no longer homogeneous with the outgrowth distribution. Although heat treatment mainly extended germination, there is also evidence of damage to systems required for outgrowth. However, this damage was quickly repaired and was not evident by the time the cells started to double. The results presented here combined with previous findings show that the stage of lag most affected, and the extent of any effect in terms of duration or variability, differs with both historical treatment and the growth conditions.Clostridium botulinum is a group of four physiologically and phylogenetically distinct anaerobic spore-forming bacteria (known as groups I, II, III, and IV) that produce the highly toxic botulinum neurotoxin (12). The severity of the intoxication, botulism, ensures considerable effort is directed at preventing the growth of this pathogen in food. Nonproteolytic (group II) C. botulinum is one of the two groups most frequently associated with food-borne botulism. It forms heat-resistant spores and can germinate, grow, and produce toxin at 3°C (8); thus, nonproteolytic C. botulinum is a particular concern in mild heat-treated chilled foods (16, 17).Spores formed by pathogens such as C. botulinum are a significant food safety issue since they are able to resist many of the processes, such as cooking, used to kill vegetative cells. Understanding the transformation from a dormant spore to active vegetative cells is an important part of quantifying the risk associated with such organisms. Considerable effort has been targeted at measuring and relating the kinetic responses of populations of C. botulinum to environmental conditions and such data have been used to create predictive models, for example, ComBase (www.combase.cc). Such approaches have made a considerable contribution to ensuring food safety but problems with using population based predictions may arise when an initial inoculum is very small or additional information beyond point values is required. Spores typically contaminate foods at low concentrations so that growth of C. botulinum, when it occurs, is likely to initiate from just a few spores. In these circumstances the distribution of times to growth in packs will reflect the heterogeneity of times to growth from the contaminating individual spores. There is an intrinsic variability between individual spores within a population, and the relationship between population lag and individual lag is complex. Consequently, individual lag times cannot be predicted from population measurements (3). Knowledge of the underlying distribution would allow greater refinement of risk assessments.The lag period between a spore being exposed to conditions suitable for growth and the start of exponential growth will reflect the combined times of germination, emergence, elongation, and first cell division. Currently, very little is known about the variability and duration of these stages and any relationships between them. Measuring the kinetics of spore germination is usually achieved by measuring a population to identify time to percent completion. Such germination curves represent the summation of responses by individual spores. Some authors have measured the biovariability associated with individual spores, but most studies have examined only germination (4-7, 11, 22) and not subsequent outgrowth. More recently, we have used phase-contrast microscopy and image analysis to follow individual spores of nonproteolytic C. botulinum from dormancy, through germination and emergence, to cell division (21, 23). These experiments showed there is very little, or no, relationship between the time spent in each stage by individual spores. We have now extended this work to determine distributions of times for different stages in lag phase as affected by heat treatment and incubation temperature.     

Identifying the neural circuitry of alcohol craving and relapse vulnerability

With no further intervention, relapse rates in detoxified alcoholics are high and usually exceed 80% of all detoxified patients. It has been suggested that stress and exposure to priming doses of alcohol and to alcohol-associated stimuli (cues) contribute to the relapse risk after detoxification. This article focuses on neuronal correlates of cue responses in detoxified alcoholics. Current brain imaging studies indicate that dysfunction of dopaminergic, glutamatergic and opioidergic neurotransmission in the brain reward system (ventral striatum including the nucleus accumbens) can be associated with alcohol craving and functional brain activation in neuronal systems that process attentional relevant stimuli, reward expectancy and experience. Increased functional brain activation elicited by such alcohol-associated cues predicted an increased relapse risk, whereas high brain activity elicited by affectively positive stimuli may represent a protective factor and was correlated with a decreased prospective relapse risk. These findings are discussed with respect to psychotherapeutic and pharmacological treatment options.     

Purification and sequencing of cyanogen bromide fragments from ribulosebisphosphate carboxylase/oxygenase from Rhodospirillum rubrum

As a part of the goal to determine the total sequence of Rhodospirillum rubrum ribulosebisphosphate carboxylase/oxygenase, the cyanogen bromide fragments were fractionated and sequenced (or partially sequenced). Twelve of the anticipated 14 peptides were obtained in highly purified form. The other two peptides were located, respectively, within a trytophanyl cleavage product (which overlapped with four CNBr fragments) and within an active-site peptide characterized earlier (which overlapped with three CNBr fragments). These overlaps coupled with amino and carboxyl terminal sequence information of the intact subunit and the availability of the sequence of the corresponding enzyme from higher plants permitted alignment of all fragments. Eight CNBr peptides were sequenced completely; four of the CNBr peptides consisted of more than 80 residues and were only partially sequenced as permitted by direct Edman degradation. Of the approximate 475 residues per subunit, 339 were placed in sequence. The lack of extensive conservation of primary structure between R. rubrum and higher plant carboxylases permits the tentative identifications of those regions likely to be functionally important.