2b and c). The hot spring isolates, on the other hand, showed almost no variation; only

3 of the 12 occurring polymorphisms were present, with a preference for 14 repeat units (Fig. 2d). It was also observed that strains that had the same seven-gene SBT could still have a different copy number for the lcl VNTR region (data not shown). As addition of the seventh gene neuA to the previously used six-gene SBT scheme enhanced the discriminatory power (Ratzow et al., 2007), it is possible that additional genes can even further discriminate the presently established SBT types. Therefore, our sequencing data reinforce the observation made by Pourcel et al. (2007) that the VNTR region of lcl (lpms31) is very diverse and could be an additional tool to distinguish among isolates. However, we have to be cautious about its genetic variability. If this genetic variability is extremely large, the chance of PLX3397 in vivo two isolates of the same population being different is almost equal to the selleck screening library chance of two isolates of different locations being different. This problematic genetic variability was previously shown for three other L. pneumophila loci: fliC, proA and mompS (Coscolláet al., 2006). This emphasizes that attention

has to be paid when selecting a gene for discrimination purposes. More specifically, the genetic variability of the gene has to be high enough to discriminate between different isolates, but small enough to be stable in the period between the outbreak and epidemiological typing. Based on the knowledge that very mammalian collagen plays a role in cell adhesion (Kadler

et al., 2007), the role of Lcl in the adhesion of L. pneumophila Philadelphia to host cells was examined. For this, we attempted to prepare an Lcl-negative mutant. Notwithstanding many attempts, using (1) homologous recombination with a resistance cassette with flanking regions of the lcl gene of different sizes; (2) point mutagenesis; and (3) different resistance cassettes and shuttle vectors, a correct insertion was never obtained, even after screening thousands of colonies. Whether the failure of obtaining a deletion mutant is due to the presence of the VNTR regions present in the lcl gene is not known, but VNTR regions are known to have greater instability. Because we were not able to obtain an Lcl-negative mutant, the role of Lcl in L. pneumophila adhesion and invasion of host cells was determined indirectly by comparing the Philadelphia WT cells and the same cells preincubated with Lcl-specific antibodies. The preincubation of 5 × 107L. pneumophila Philadelphia-1 cells with 20 μg Lcl-specific antibodies for 30 min decreased the adhesion to A549 and macrophage-like cells by 59% (P=0.0015) and 39% (P=0.006), respectively (Fig. 3a and b). In contrast, adhesion and invasion of the amoebae A.