GltT ABC-type transporter: potential candidate for development of vaccine against Neisseria meningitidis.

Introduction Neisseria meningitidis is a Gram-negative encapsulated diplococcus, the major cause of meningitis and sepsis. During the infectious cycle, N. meningitidis is able to utilize only few compounds as energy sources. In intracellular milieu, the main energy sources for meningococci are pyruvate, lactate, and certain aminoacid, such as L-glutamate. The meningococcus possesses a L-glutamate ABC-type transporter, GltT. Literature data demonstrated that the GltT transporter is required for bacterial survival within epithelial cells, and survival in human whole blood, and in a meningococcal meningitis murine model. In order to evaluate whether the GltT transporter may represent a potential candidate for vaccine development, protein components of the transporter have been induced in in vitro expression system, purified, and, after active immunization assay, specific antibodies were tested for their bactericidal activity. Materials and Methods The NMC1935 gene, encoding for the periplasmic protein of GltT transporter was cloned in expression vector. The periplasmic protein with Glutathione S-transferase (GST) tag was over-expressed in E. coli and then purified by affinity chromatography. Therefore we proceeded with specific antibodies production by active immunization assay in vivo. ELISA analysis determined the titer of immune anti-sera. To investigate the capacity for serum bactericidal killing of meningococci, serogroup C 93/4286 strain was grown with different dilution of the anti-GltT antiserum and rabbit complement. Results The anti-GltT antiserum analyzed showed a bactericidal activity of 93/4286 strain with all dilution tested compared to the control where bacteria were incubated alone or with rabbit complement. Discussion and Conclusion Although early diagnosis and antibiotic treatment enhance survival, prevention through vaccination would appear the best way to limit meningococcal disease. In this study we evaluated the GltT transporter as potential vaccinal candidate. The GltT transporter is a glutamate uptake system highly conserved between meningococcal strain, in vitro and in vivo data demonstrated that this component is essential to meningococcal infection and survival. The anti-GltT antiserum tested showed a promising bactericidal activity, passive immunization assay will be performed.