Pork meat and processed pork products have been the sources of outbreaks of listeriosis in France and in other European countries during the last decade. The aim of this review is to understand how ...contamination, survival and growth of Listeria monocytogenes can occur in pork meat products. This study discusses the presence of L. monocytogenes in raw pork meat, in the processing environment and in finished products. The prevalence of L. monocytogenes generally increases from the farm to the manufacturing plants and this mainly due to cross-contamination. In many cases, this pathogen is present in raw pork meat at low or moderate levels, but foods involved in listeriosis outbreaks are those in which the organism has multiplied to reach levels significantly higher than 1000 CFU g⁻¹. In such cases, L. monocytogenes has been able to survive and/or to grow despite the hurdles encountered during the manufacturing and conservation processes. Accordingly, attention must be paid to the design of food-processing equipment and to the effectiveness of the cleaning and disinfecting procedures in factories. Finally, the production of safe pork meat products is based on the implementation of general preventive measures such as Good Hygiene Practices, Good Manufacturing and the Hazard Analysis Critical Control Point.
Experimental manipulation of protein abundance in living cells or organisms is an essential strategy for investigation of biological regulatory mechanisms. Whereas powerful techniques for protein ...expression have been developed in Caenorhabditis elegans, existing tools for conditional disruption of protein function are far more limited. To address this, we have adapted the auxin-inducible degradation (AID) system discovered in plants to enable conditional protein depletion in C. elegans. We report that expression of a modified Arabidopsis TIR1 F-box protein mediates robust auxin-dependent depletion of degron-tagged targets. We document the effectiveness of this system for depletion of nuclear and cytoplasmic proteins in diverse somatic and germline tissues throughout development. Target proteins were depleted in as little as 20-30 min, and their expression could be re-established upon auxin removal. We have engineered strains expressing TIR1 under the control of various promoter and 3' UTR sequences to drive tissue-specific or temporally regulated expression. The degron tag can be efficiently introduced by CRISPR/Cas9-based genome editing. We have harnessed this system to explore the roles of dynamically expressed nuclear hormone receptors in molting, and to analyze meiosis-specific roles for proteins required for germ line proliferation. Together, our results demonstrate that the AID system provides a powerful new tool for spatiotemporal regulation and analysis of protein function in a metazoan model organism.
Chromosome segregation at meiosis I depends on pairing and crossing-over between homologs. In most eukaryotes, pairing culminates with formation of the proteinaceous synaptonemal complex (SC). In ...budding yeast, recombination initiates through double-strand DNA breaks (DSBs) and is thought to be essential for SC formation. Here, we examine whether this mechanism for initiating meiotic recombination is conserved, and we test the dependence of homologous chromosome synapsis on recombination in
C. elegans. We find that a homolog of the yeast DSB-generating enzyme, Spo11p, is required for meiotic exchange in this metazoan, and that radiation-induced breaks partially alleviate this dependence. Thus, initiation of recombination by DSBs is apparently conserved. However, homologous synapsis is independent of recombination in the nematode, since it occurs normally in a
C. elegans spo-11 null mutant.
Health organizations worldwide have advocated that treatment records be required to show that antibiotics are used prudently by veterinarians and farmers alike. In 2000, the French government passed ...legislation making a farm register mandatory for all farms that raise animals for food production. The farm register is a comprehensive record designed to track all animal movements, treatments, and veterinary interventions on the farm. We conducted a survey to assess the knowledge, attitudes, and behaviors of dairy farmers toward the farm register, with particular emphasis on recording of antibiotic treatments. The 43 farmers interviewed belonged to veterinary health cooperatives. All farmers correctly named an antibiotic or antibiotic preparation, yet only 2 recognized the 5 components of the farm register. Farmer attitudes toward the register were globally positive, even though they named a wide variety of constraints. Nevertheless, 72% of farmers interviewed had a permanent health record, and approximately half had recorded either the last treatment (irrespective of drug class) or the last intramammary tube administered. Results were discussed in the light of health behavior change models that are applied in human medicine. We suggest that programs that seek compliance with the farm register should focus on educational interventions and bonus incentives.
Germline maintenance in the nematode C. elegans requires global repressive mechanisms that involve chromatin organization. During meiosis, the X chromosome in both sexes exhibits a striking reduction ...of histone modifications that correlate with transcriptional activation when compared with the genome as a whole. The histone modification spectrum on the X chromosome corresponds with a lack of transcriptional competence, as measured by reporter transgene arrays. The X chromosome in XO males is structurally analogous to the sex body in mammals, contains a histone modification associated with heterochromatin in other species and is inactivated throughout meiosis. The synapsed X chromosomes in hermaphrodites also appear to be silenced in early meiosis, but genes on the X chromosome are detectably expressed at later stages of oocyte meiosis. Silencing of the sex chromosome during early meiosis is a conserved feature throughout the nematode phylum, and is not limited to hermaphroditic species.
Dernburg discusses the theory that many components and mechanisms underlying kinetochore function are highly conserved between holocentric and monocentric chromosomes. She explores how a chromosome ...function as basic and essential as microtubule attachment has assumed such distinct evolutionary forms.
Structural studies of fixed cells have revealed that interphase chromosomes are highly organized into specific arrangements in the nucleus, and have led to a picture of the nucleus as a static ...structure with immobile chromosomes held in fixed positions, an impression apparently confirmed by recent photobleaching studies. Functional studies of chromosome behavior, however, suggest that many essential processes, such as recombination, require interphase chromosomes to move around within the nucleus.
To reconcile these contradictory views, we exploited methods for tagging specific chromosome sites in living cells of Saccharomyces cerevisiae with green fluorescent protein and in Drosophila melanogaster with fluorescently labeled topoisomerase ll. Combining these techniques with submicrometer single-particle tracking, we directly measured the motion of interphase chromatin, at high resolution and in three dimensions. We found that chromatin does indeed undergo significant diffusive motion within the nucleus, but this motion is constrained such that a given chromatin segment is free to move within only a limited subregion of the nucleus. Chromatin diffusion was found to be insensitive to metabolic inhibitors, suggesting that it results from classical Brownian motion rather than from active motility. Nocodazole greatly reduced chromatin confinement, suggesting a role for the cytoskeleton in the maintenance of nuclear architecture.
We conclude that chromatin is free to undergo substantial Brownian motion, but that a given chromatin segment is confined to a subregion of the nucleus. This constrained diffusion is consistent with a highly defined nuclear architecture, but also allows enough motion for processes requiring chromosome motility to take place. These results lead to a model for the regulation of chromosome interactions by nuclear architecture.
Crossing over and chiasma formation during Caenorhabditis elegans meiosis require msh-5, which encodes a conserved germline-specific MutS family member. msh-5 mutant oocytes lack chiasmata between ...homologous chromosomes, and crossover frequencies are severely reduced in both oocyte and spermatocyte meiosis. Artificially induced DNA breaks do not bypass the requirement for msh-5, suggesting that msh-5 functions after the initiation step of meiotic recombination. msh-5 mutants are apparently competent to repair breaks induced during meiosis, but accomplish repair in a way that does not lead to crossovers between homologs. These results combine with data from budding yeast to establish a conserved role for Msh5 proteins in promoting the crossover outcome of meiotic recombination events. Apart from the crossover deficit, progression through meiotic prophase is largely unperturbed in msh-5 mutants. Homologous chromosomes are fully aligned at the pachytene stage, and germ cells survive to complete meiosis and gametogenesis with high efficiency. Our demonstration that artificially induced breaks generate crossovers and chiasmata using the normal meiotic recombination machinery suggests (1) that association of breaks with a preinitiation complex is not a prerequisite for entering the meiotic recombination pathway and (2) that the decision for a subset of recombination events to become crossovers is made after the initiation step.
We have investigated the mechanism that enables achiasmate chromosomes to segregate from each other at meiosis I in D. melanogaster oocytes. Using novel cytological methods, we asked whether ...nonexchange chromosomes are paired prior to disjunction. Our results show that the heterochromatin of homologous chromosomes remains associated throughout prophase until metaphase I regardless of whether they undergo exchange, suggesting that homologous recognition can lead to segregation even in the absence of chiasmata. However, partner chromosomes lacking homology do not pair prior to disjunction. Furthermore, euchromatic synapsis is not maintained throughout prophase. These observations provide a physical demonstration that homologous and heterologous achiasmate segregations occur by different mechanisms and establish a role for heterochromatin in maintaining the alignment of chromosomes during meiosis.
The behaviour of
Escherichia coli O157:H7 was studied during the manufacture and ripening of raw goat milk lactic cheeses. Cheese was manufactured from raw milk in the laboratory and inoculated with
...E. coli O157:H7 to a final concentration of 10, 100 and 1000 cfu ml
−
1.
E. coli O157:H7 was counted by CT-SMAC (Mac Conkey Sorbitol Agar with cefixim and tellurite) and O157:H7 ID throughout the manufacturing and ripening processes. When the milk was inoculated with 10, 100 or 1000 cfu ml
−
1, counts decreased to less than 1 log
10 g
−
1 in curds just prior to moulding. However, viable
E. coli O157:H7 were found in cheeses throughout processing, and even after 42 days of ripening. Results indicate that
E. coli O157:H7 survives the lactic cheese manufacturing process. Thus, the presence of low numbers of
E. coli O157:H7 in milk destined for the production of raw milk lactic cheeses can constitute a threat to the consumer.
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