Involvement of the mpo operon in resistance to class IIa bacteriocins in Listeria monocytogenes.

High resistance to class IIa bacteriocins in Listeria monocytogenes has been clearly linked to lack of expression of the mptACD operon, encoding the EIIt Man mannose PTS permease. Also, intermediate resistance has been associated with membrane phospholipid modifications in the spontaneous mutants L. monocytogenes B73-V1 and B73-V2. We constructed a new mutant of L. monocytogenes that was interrupted in mpoA, and which also exhibited an intermediate resistance phenotype. The mpoABCD operon putatively encodes a PTS permease of the mannose family similar to that encoded by the mpt operon. In silico analysis indicated that mpo transcription might be dependent on sigma54. Our study demonstrated that the three intermediate resistant mutants have a slight decrease in mptACD expression, showing that the level of sensitivity is correlated to the level of mpt expression. We show a cross-regulation between mpo and mpt. In particular, the mpo mutant has a defect in mpt expression that possibly could explain its intermediate resistance phenotype.