Abstract: The current invention relates to the diagnosis and treatment of diseases resulting from infections by Mycobacterium avium subsp. paratuberculosis. In particular the invention relates to the use of an antigen selected among (a) a synthetic peptide 5P having the following formula: DPhe-NMeVal-Ile-Phe-Ala-OMe (SEQ ID NO: 1); (b) a lipopeptide L5P consisting of the synthetic peptide a) wherein the N-terminal phenylalanine residue is N-acylated with an eicosanoic acid acyl chain; (c) a variant of peptide a) or lipopeptide b) able to react with anti-Mycobacterium paratuberculosis antibodies; for in vitro detection or quantification of specific anti-Mycobacterium paratuberculosis antibodies in a biological sample.

Abstract: A process for replacing a nucleotide sequence in the genome of a mycobacterium strain comprises the steps of:a) providing a vector containing SacB gene coding for levane saccharase enzyme and a nucleotide sequence of interest;b) transfecting the mycobacterium strain with the vector;c) selecting clones of the resulting transfected mycobacteria for replacement of the nucleotide sequence of interest by propagating the transfected clones in a culture medium supplemented with sucrose; andd) isolating the recombinant strain.The process is useful for positive selection of allelic exchange mutants, such as in Mycobacterium tuberculosis complex.

Abstract: A process for replacing a nucleotide sequence in the genome of a mycobacterium strain comprises the steps of:a) providing a vector containing SacB gene coding for levane saccharase enzyme and a nucleotide sequence of interest;b) transfecting the mycobacterium strain with the vector;c) selecting clones of the resulting transfected mycobacteria for replacement of the nucleotide sequence of interest by propagating the transfected clones in a culture medium supplemented with sucrose; andd) isolating the recombinant strain.The process is useful for positive selection of allelic exchange mutants, such as in Mycobacterium tuberculosis complex.