The Listeria transcriptional landscape from saprophytism to virulence.

The bacterium Listeria monocytogenes is ubiquitous in the environment and can lead to severe food-borne infections. It has recently emerged as a multifaceted model in pathogenesis. However, how this bacterium switches from a saprophyte to a pathogen is largely unknown. Here, using tiling arrays and RNAs from wild-type and mutant bacteria grown in vitro, ex vivo and in vivo, we have analysed the transcription of its entire genome. We provide the complete Listeria operon map and have uncovered far more diverse types of RNAs than expected: in addition to 50 small RNAs (<500 nucleotides), at least two of which are involved in virulence in mice, we have identified antisense RNAs covering several open-reading frames and long overlapping 5' and 3' untranslated regions. We discovered that riboswitches can act as terminators for upstream genes. When Listeria reaches the host intestinal lumen, an extensive transcriptional reshaping occurs with a SigB-mediated activation of virulence genes. In contrast, in the blood, PrfA controls transcription of virulence genes. Remarkably, several non-coding RNAs absent in the non-pathogenic species Listeria innocua exhibit the same expression patterns as the virulence genes. Together, our data unravel successive and coordinated global transcriptional changes during infection and point to previously unknown regulatory mechanisms in bacteria.

Molecular and serological evidence of Pneumocystis circulation in a social organization of healthy macaques (Macaca fascicularis).

Simian populations represent valuable models for understanding the epidemiology of human pneumocystosis. The present study aims to describe the circulation of Pneumocystis organisms within a social organization of healthy crab-eating macaques (Macaca fascicularis) living in a natural setting in France. Animals were followed for up to 2 years. Deep nasal swab and blood samples were collected monthly from each animal under general anaesthesia. Environmental air was sampled for a 1 week period every month in the park where the macaques dwelt. Pneumocystis DNA was detected by nested-PCR of mitochondrial large subunit rRNA (mtLSU) gene in nasal swab and air samples. Anti-Pneumocystis IgG antibodies were detected in serum samples by indirect immuno-fluorescence assay. Pneumocystis DNA was detected in 168 of 500 swab samples examined (33.6 %). The number of macaques with detectable Pneumocystis DNA was highly variable from one month to another. Positive detection of Pneumocystis DNA was not related to the detection of serum anti-Pneumocystis antibody. During the second year of the study, Pneumocystis DNA was amplified more frequently from unweaned macaques than from adults or subadults. The mtLSU sequence showed marked polymorphism with eight Pneumocystis sequence types representing two distinct groups. On the whole, a constant and intensive circulation of Pneumocystis organisms within the community was observed. However, the implication of the various members of the colony was probably different and several levels of colonization by Pneumocystis may occur in immunocompetent macaques.

Spectrographic analysis of the ultrasonic vocalisations of adult male and female BALB/c mice.

In this study, a spectrographic analysis was designed to improve the description of the shape, the modulations, the rate, length and frequencies of BALB/c mouse calls in different behavioural situations. Male and female calls emitted during investigation of cages with clean bedding, soiled with male or female bedding, and during same-sex encounters, were recorded and described. BALB/c male mice uttered different types of vocalisations both when investigating counterpart odour cues and when interacting with same-sex counterparts. BALB/c female mice vocalised solely during same-sex counterpart encounters and it appeared that calls were uttered mainly by the resident females. Male and female mice present a complex array of calls, which seem to be linked to particular behavioural situations. Further studies using this technology may help to improve our understanding of the role of vocal communication in natural rodent populations.

Reduction in testosterone concentration and its effect on the reproductive output of chronic malaria-infected male mice.

An experimental host-parasite association involving BALB/c male mice infected with Plasmodium chabaudi chabaudi was used in order to investigate the influence of the parasite on the sexual physiology and behavior of infected hosts. Infected males displayed complete courtship behavior leading to ejaculation and sired litters on several occasions. A weekly assay of testosterone and corticosterone plasma concentrations revealed a twofold decrease in the testosterone level at 4 and 5 weeks post-injection, during recrudescence. This imbalance was accompanied by a decrease in the overall duration of the social investigation contacts occurring during courtship and by a reduction in the fertilization rate of the infected animals. These physiological perturbations can be regarded as an adaptive response of the host to the recrudescing parasites, which illustrates the rodents' capacity for regulating the testosterone profiles needed to balance the competing demands of immunity and reproduction.

Influence of the female sexual cycle on BALB/c mouse calling behaviour during mating.

Real-time recording technology was used in this study to analyse calling activity during heterosexual encounters in BALB/c mice. The spectrographic analyses revealed distinct types of calls that could be linked to a precise pre-ejaculatory behavioural sequence. In addition, the oestrous cycle of the female was observed to influence the vocalization emission pattern. The recording technology used in this study provides numerous improvements in the characterization description of mice calling behaviour during mating and is expected to be useful in studies of vocal communication in many rodent species.

Oestrus cycle perturbations and hypotrophy of clitoral glands in malaria-infected female BALB/c mice.

An experimental host-parasite association involving BALB/c female mice infected with Plasmodium vinckei petteri was used with the aim of investigating the morphological and physiological alterations induced by the parasite in the genital tract of the host. The vaginal oestrous cycle was monitored as a daily clue to the sexual physiology of the female mice, and a complete histological analysis of the genital tract was performed 36 days following parasite inoculation. The oestrous cycle showed strong transitory alterations during the first 30 days following infection. The occurrence of oestrus days increased during the first 10 days post-infection and then decreased to a subnormal value during the following 20 days. Infected mice also showed a remarkable hypotrophy of their clitoral glands 30 days after the beginning of the malarial infection. A probable cause of such perturbations is a significant hormonal imbalance triggered by the erythrocytic proliferation of the Plasmodium. The relationship between the immune response of the host and these physiological and morphological alterations, as well as the outcomes of these alterations on the sexuality of the rodent host are discussed.