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International audience; Rhodococcus equi is one of the most important causes of mortality in foals between 1 and 6 months of age. Although rare, infection also occurs in a variety of other mammals including humans, often following immunosuppression of various causes. Secreted proteins are known to mediate important pathogen-host interactions and consequently are favored candidates for vaccine development as they are the most easily accessible microbial antigens to the immune system. Here, we describe the results of a proteomic analysis based on SDS-PAGE, immunoblot and mass spectrometry, which was carried out aiming the identification of secreted proteins that are differently expressed at 30 degrees C versus 37 degrees C and at mid-exponential versus early-stationary growth phase and antigenic proteins from R. equi ATCC 33701. A total of 48 proteins was identified regardless of growth conditions. The cholesterol oxidase ChoE appears to be the major secretory protein. Moreover, four proteins revealed high homologies with the mycolyl transferases of the Ag85 complex from Mycobacterium tuberculosis. The sequence analysis predicted that 24 proteins are transported by a signal peptide-dependent pathway. Moreover, five antigenic proteins of R. equi were identified by immunoblot, including a novel strongly immunoreactive protein of unknown function. In conclusion, the elucidation of the secretome of R. equi identified several proteins with different biological functions and a new candidate for developing vaccines against R. equi infection in horse.

Mycoplasma meleagridis, a turkey pathogen, can be detected by PCR directly from tracheal or genital swabs. However, up to 40% samples may contain inhibitory substances. A DNA fragment, that can be amplified with M. meleagridis primers and in the same cycling conditions, was constructed to use as an internal control (IC) to check for these inhibitors. This IC can easily be distinguished from the M. meleagridis amplicon after agarose gel electrophoresis since it is longer. Use of this IC in PCR amplifications revealed that more than 35% of turkey tracheal swabs and more than 45% of turkey cloacal swabs contained inhibitors. In most cases, dilution (1:100) of swab lysates allowed amplification of the internal control but DNA purification may be necessary to eliminate inhibitors (20% of tracheal swabs and 5% of cloacal swabs). Use of this internal control DNA allowed assessment of the efficiency of each individual reaction and ensured that the reaction was not inhibited by interfering substances.

Successful detection of Mycoplasma synoviae (MS) by culture and PCR from samples collected in the environment of experimentally infected chickens and turkeys, or under field conditions, is described. Results showed that in the experimental infection, 10/96 and 46/96 samples of food, drinking water, feathers, droppings or dust were positive by culture and Mycoplasma-PCR. In field conditions, the number of positive results for environmental samples were respectively 7/28 and 17/28. These observations highlight the high disseminating capacities of this mycoplasma and show the usefulness of the PCR method for epidemiological studies.