Approche moléculaire de la résistance à la méticilline de Staphylococcus aureus

Staphylococcus aureus is one of the most common species met in medical microbiology laboratories. It causes many infectious diseases, and some of them are severe. Today, it can resist to many antibiotics, that were initially fully active, such as G or A group penicillin, by producing a penicillinase. Hospital strains can also resist to M group penicillins (methicillin, oxacillin) by modifying the β-lactam target: penicillin binding protein (PBP). Indeed, these strains produce a new PBP, called PBP 2a, of which affinity for β-lactams is much lower than the one of common Staphylococcus PBP. This PBP2a is encoded by mecA gene, of which expression is under control of several regulation genes. The expression of methicillin-resistance can be homogeneous or heterogeneous. Some strains can resist to methicillin using other mechanisms (penicillinase overproduction, methicillin-specific hydrolytic enzyme, PBP modifications). Particular methods are needed for the phenotypic detection of methicillin-resistance: antibiograms on NaCl-supplemented agar or incubated at 30 °C. Molecular detection of mecA gene by PCR permits to detect that resistance on strains for which phenotypic detection has failed.     

Intérêt de l'hémovigilance dans l'amélioration de la démarche diagnostique et dans la prévention des incidents transfusionnels liés à la contamination bactérienne des produits sanguins

Through the hemovigilance system implemented in France in 1994, 185 cases of transfusion reactions due to the bacterial contamination (TRBC) of blood components (BC) have been recorded over 5 years, thus confirming the frequency and severity of bacterial risks in transfusion medicine. Activation of the hemovigilance network and awareness raising among the virus actors involved (clinicians, nurses…) have made it possible to both prevent possible related TRBCs (due to the transfusion of a BC derived from the same donation) and improve case reporting. The first results obtained through the alert system thus developed have led the Agence Française du Sang to assess and better understand, in a joint study, transfusion-related risks as well as determine factors likely to prevent them. Continuous analysis, in real time, of the reported cases have improved prevention strategies at every stage of the transfusion chain, from blood collection to blood component transfusion.     

Apport de la biologie moléculaire au diagnostic de la tuberculose

Reducing delays in diagnosing tuberculosis should contribute to lower the lethality and to reduce the transmission. Microscopy examination is an easy to perform and rapid technique, but lacks sensitivity and specificity. Culture and biochemical identification are sensitive and specific, but require two to eight weeks DNA probes performed on solid or liquid media are very efficient for M. tuberculosis complex strains identification. Nucleic acid amplification techniques are available to directly detect the M. tuberculosis complex in clinical samples. Performances are variable. Very good results are obtained with experienced teams who scrupulously follow the specified guidelines.