This approach was first successfully applied to identify vaccine candidates in Neisseria meningitidis [2] and has since been applied to identify vaccine candidates for other bacterial pathogens including Streptococcus pneumoniae [4], Streptococcus agalactiae [5], Staphylococcus aureus [6], Porphyromonas gingivalis [7], Chlamydia pneumoniae [8], Bacillus anthracis [9], Streptococcus suis [10] and E