Molecular analysis of a Listeria monocytogenes strain that is resistant to leucocin A.
Leucocin A is a class 11a bacteriocin produced by Leuconostoc mesenteroides TA33a that was previously shown to inhibit Listeria monocytogenes. A spontaneous resistant mutant of L. monocytogenes was isolated, and found to be resistant to leucocin A at levels in excess of 2 mg/ml. The resistant mutant had an eight-fold increased binding capacity for leucocin A in comparison to the parental strain. The mutant showed no significant cross resistance to nisaplin or ESFI-7GR. The resistant phenotype had a similar growth rate in monoculture, to the sensitive phenotype. DNA and protein analysis of the resistant and susceptible strains were carried out using silver stained amplified fragment length polymorphism (ssAFLP) and one and two dimensional (2D) SDS polyacrylamide gel electrophoresis (PAGE). Two-dimensional SDS PAGE revealed two differences. The first was a 35 kDa protein which was present in the sensitive but absent from the resistant phenotype and, secondly there was a higher level of expression of a 18 kDa protein in the resistant phenotype compared with the sensitive phenotype. The 35 kDa protein was found to have a 83% homology to the mannose-specific phosphotransferase system IIAB of Streptococcus salivarius.