pleuropneumoniae ��-Nicotinamide molecular weight  and loss of the ability in colonizing in the gastric mucosa in Helicobacter pylori after frdA genes were inactivated. Furthermore, Joseph et al. described FrdA as an antigen in Brucella abortus . FepA, FrpB and HbpA are important components in check details several ABC transport pathways for obtaining iron or regulating iron utilization in vivo or vitro. The immunogenic activity of FepA and FrpB was shown in Klebsiella pneumoniae  and Neisseria meningitides
 respectively, and HbpA was widely conserved and served as an antigen in Leptospira interrogans. Moreover, homologous analysis of these proteins at NCBI revealed a high level identity (>98%) with the sequenced serotype Selleckchem JQ1 1, 5 and 7 strains respectively. These suggest that they might be new common antigens for A. pleuropneumoniae. High-affinity zinc uptake system protein ZnuA precursor, was essential of B. abortus for intracellular survival and virulence in mice and shown immunogenic in Streptococcus suis. PsaA is needed for the adherence of pneumococcal cells and antibodies to PsaA contributed to reduce the nasopharyngeal colonization
of challenged pneumococcal cells [32, 33]. DegPs, a member of the widely conserved HtrA family of serine proteases, were frequently identified as antigens in other pathogens, such as B. abortus  and Chlamydia trachomatis . Besides, trigger factor (TIG) has been demonstrated to be an excellent candidate for vaccination against Brucella melitensis  and a virulence-related protein in Listeria monocytogenes , and similar findings were described about malate dehydrogenase (MDH) of Candida albicans  and spermidine/putrescine-binding
periplasmic protein (PotD) of Streptococcus pneumoniae . Glyceraldehyde 3-phosphate dehydrogenase (GapA) has been proven to be antigenically conserved proteins, suggesting potential for vaccines in several microorganisms . Homologous protein of translation elongation factor EF-Tu (TufB), a very abundant protein, had been detected ROS1 in immunological researches of other bacteria, such as C. trachomatis and Shigella flexneri. The periplasm of gram-negative bacteria is well equipped with ATP-independent chaperones and folding catalysts, including peptidyl-prolyl isomerases (FkpA). It is reported recently that FkpA was found to be immunogenic in Bordetella pertussis. Phosphate acetyltransferase (PTA), an enzyme that catalyzes the reversible transfer of the acetyl group from acetyl phosphate to coenzyme A plays a major role in the energy-yielding metabolism and recently has been reported to be immunogenic in S. suis.