Absence of a putative mannose-specific phosphotransferase system enzyme IIAB component in a leucocin A-resistant strain of Listeria monocytogenes, asshown by two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis

Leucocin A is a class IIa bacteriocin produced by Leuconostoc spp. that has preciously been shown to inhibit the growth of Listeria monocytogenes. A s pontaneous resistant mutant of L. monocytogenes was isolated and found to b e resistant to leucocin A at levels in excess of 2 mg/ml. The mutant showed no significant cross-resistance to nontype IIa bacteriocins including nisa plin and ESF1-7GR. However, there were no inhibition zones found on a lawn of the mutant when challenged with an extract containing 51,200 AU of pedio cin PA-2 per ml as determined by a simultaneous assay on the sensitive wild -type strain. DNA and protein analysis of the resistant and susceptible str ains were carried out using silver-stained amplified fragment length polymo rphism (ssAFLP) and one- and two-dimensional sodium dodecyl sulfate-polyacr ylamide gel electrophoresis (SDS-PAGE), respectively. Two-dimensional SDS-P AGE clearly showed a 35-kDa protein which was present in the sensitive but absent from the resistant strain. The N-terminal end of the 35-kDa protein was sequenced and found to have an 83% homology to the mannose-specific pho sphotransferase system enzyme IIAB of Streptococcus salivarius.