Systèmes de sécrétion des protéines de type IV et virulence bactérienne

La virulence bactérienne est liée à la synthèse de macromolécules interférant avec des fonctions physiologiques de l’organisme infecté, aux niveaux moléculaire, cellulaire et tissulaire. D’importants progrès ont été faits dans la compréhension du mécanisme d’action de nombreux facteurs de pathogénicité. En revanche, l’étude des relations précoces entre bactéries et cellules autres que des phagocytes professionnels n’a été que récemment abordée. Ces recherches ont renouvelé nos idées en infectiologie, conduisant à l’émergence d’une nouvelle discipline, la microbiologie cellulaire. Elles ont mis en lumière l’existence d’interactions entre protéines bactériennes et structures cellulaires, d’où résultent soit l’internalisation de la bactérie, soit, au contraire, une résistance à l’internalisation. Elles ont aussi démontré que certains gènes bactériens impliqués dans la virulence sont dérivés d’autres gènes ayant des rôles différents dans la physiologie des bactéries. C’est le cas des gènes impliqués dans la sécrétion de protéines chez les bactéries à Gram négatif. Ces nouvelles données permettent d’envisager d’autres abords thérapeutiques pour certaines maladies infectieuses

Spondylodiscitis Due to Clostridium ramosum Infection in an Immunocompetent Elderly Patient

The first ever case of spondylodiscitis caused by Clostridium ramosum in an elderly immunocompetent patient has been reported. C. ramosum is usually an intestinal bacterium but may occasionally be isolated in clinical specimens as an opportunistic pathogen. This report shows that this anaerobic organism can cause bone tropism without there having been any contamination due to spinal surgery. The infection cleared after empirical therapy using intravenous amoxicillin and oral metronidazole

Identification of a New Virulence Factor, BvfA, in Brucella suis

We report the identification of BvfA (for Brucella virulence factor A), a small periplasmic protein unique to the genus Brucella, which is essential for the virulence of Brucella suis. A BvfA knockout mutant was highly attenuated both in in vitro macrophage infection assays and in vivo in the murine model of brucellosis. Fluorescence-activated cell sorting analysis with green fluorescent protein fusions showed that the expression of bvfA is induced within macrophages by phagosome acidification and coregulated with the B. suis virB operon, suggesting that it too may play a role in the establishment of the intracellular replication niche

A review of a 13-month period of FilmArray Meningitis/Encephalitis panel implementation as a first-line diagnosis tool at a university hospital

International audienceEarly diagnosis and treatment of meningitis and encephalitis is essential for reducing both their morbidity and mortality. The FilmArray® Meningitis/Encephalitis (FA-M/E) panel is a recently available molecular tool allowing the simultaneous detection of 14 pathogens in about one hour. We evaluated its routine use over a 13-month period at Nîmes University Hospital, France. Cerebrospinal fluid (CSF) specimens were prospectively analyzed, independently of cell count; results were retrospectively analyzed and positive results compared to clinical and microbiological data. Among the 708 patients included (734 CSF samples), 89 (12.6%) had a positive FA-M/E panel, 71 (80%) for a viral pathogen and 18 (20%) for a bacterial pathogen. Enterovirus and HHV-6 were the main detected pathogens. Mean time-to-results was 1h46mn. Four non-clinically relevant results were detected (3 HHV-6 and 1 Haemophilus influenzae) on the basis of inconsistent clinical and/or biological data, and/or after visualization of melting curves. No CSF pleocytosis was observed in 11% of the patients with a positive FA-M/E panel. For the 18 patients with a positive FA-M/E panel for a bacterial pathogen, five (28%) had CSF samples showing a positive Gram stain allowing an early diagnosis of bacterial infection and 67% had CSF displaying a positive culture. Altogether the panel detected 5 cases of bacterial M/E (29%) not diagnosed by culture. Despite undeniable advantages, mainly ease of use, quick result availability, and an extremely low rate of invalid results, measures should be implemented to limit false-positive results due to contamination and a careful interpretation based on the overall data for each patient is required