Analysis of expression of CagA and VacA virulence factors in 43 strains of Helicobacter pylori reveals that clinical isolates can be divided in two major types and that CagA is not necessary for expression of the vacuolating cytotoxin - Xiang,Z.; Censini,S.; Bayeli,P.; Telford,J.L.; Figura,N.; Rappuoli,R.; Covacci,A. (Infect Immun, 1995)