HETEROGENEITY IN LEVELS OF VACUOLATING CYTOTOXIN GENE (VACA) TRANSCRIPTION AMONG HELICOBACTER-PYLORI STRAINS

Broth culture supernatants from Tox(+) Helicobacter pylori strains ind uce vacuolation of HeLa cells in vitro and contain VacA in concentrati ons that are higher than those found in supernatants from Tox(-) H. py lori strains. To investigate the basis for this phenomenon, we analyze d the transcription of the vacuolating cytotoxin gene (vacA) in eight Tox(+) strains (each with a type s1/m1 vacA genotype) and nine Tox- st rains (each with a type s2/m2 vacA genotype). Most of the Tox(+) and T os(-) strains tested used the same vacA transcriptional start point, b ut Tox(+) strains yielded significantly stronger primer extension sign al intensities than did Tox- strains (mean densitometry values of 15.8 +/- 1.9 versus 8.9 +/- 1.7, P = 0.0016). Correspondingly, when we int roduced vacA:: xylE transcriptional fusions into the chromosomes of a Tox(+) strain (60190) and a Tox- strain (86-313), the level of XylE ac tivity in 60190 vacA::xylE was about 30-fold higher than that in 86-31 3 vacA::xylE. Sequence analysis and promoter exchange experiments indi cated that the different levels of vacA transcription in these two str ains cannot be explained solely by a difference in promoter strength. These data indicate that Tox+ and Tox- H. pylori strains typically dif fer not only in the VacA amino acid sequence but also in the level of vacA transcription.