THE INLA GENE REQUIRED FOR CELL INVASION IS CONSERVED AND SPECIFIC TOLISTERIA-MONOCYTOGENES

The Gram-positive bacterium Listeria monocytogenes can actively induce its own uptake by epithelial cells and fibroblasts through a surface- exposed 80 kDa protein, internalin (InlA), encoded by inlA. We studied the distribution and the DNA polymorphism of inlA sequences in a wide variety of wild strains of L. monocytogenes as compared to other List eria species. This was done by PCR-amplifying inlA sequences encoding the fifteen repeats A and the three repeats B of InlA. inlA-repeated s equences were only found in L. monocytogenes. The amplified fragment o f inlA encoding the repeats A displayed an Alul DNA polymorphism which arises from point mutations. These results indicate that inlA require d for cell invasion is specific to L. monocytogenes and that the intra genic repeats only exhibit a genetic heterogeneity due to point mutati ons and not to recombinations.