Ex-vivo passive protection bacteremia assay

1. A method of detection of bactericidal antibodies effective against a Gram-negative pathogenic bacterium of interest in a biological sample, the method comprising:

combining in a reaction mixture:

a biological sample suspected of containing bactericidal antibodies effective against a Gram-negative pathogenic bacterium of interest, wherein the biological sample is human serum or human plasma that is heated to inactivate endogenous complement;

the Gram-negative pathogenic bacterium of interest, wherein the Gram-negative pathogenic bacterium is viable; and

fresh human whole blood obtained from a non-immune human donor which does not contain detectable bactericidal antibodies effective against the Gram-negative pathogenic bacterium of interest, wherein the human from which the human serum or the human plasma was obtained is not the non-immune human donor, and wherein said fresh human whole blood contains an anticoagulant that does not significantly affect complement activation or complement activity; and

detecting the presence or the absence of the bactericidal antibodies in said sample by assessing viability of said Gram-negative pathogenic bacterium, wherein decreased viability of said Gram-negative pathogenic bacterium in the presence of said biological sample indicates the sample contains the bactericidal antibodies.

2. The method of claim 1 , wherein said biological sample is the human serum.

3. The method of claim 1 , wherein said biological sample is the human plasma.

4. The method of claim 1 , wherein said biological sample in the reaction mixture is a biological pre-immune sample and wherein the method further comprises:

combining in a separate reaction mixture:

a biological post-immune sample suspected of containing the bactericidal antibodies, wherein the post-immune sample and the pre-immune sample are obtained from the same human and wherein the post-immune sample is obtained after administration of an immunogenic composition intended to elicit bactericidal antibodies effective against the Gram-negative pathogenic bacterium to the human, wherein the pre-immune sample and the post-immune sample are heated to inactivate endogenous complement;

the Gram-negative pathogenic bacterium, wherein the Gram-negative pathogenic bacterium is viable; and

fresh human whole blood which does not contain detectable bactericidal antibodies effective against the Gram-negative pathogenic bacterium of interest, wherein the fresh human whole blood is obtained from a non-immune human donor, wherein the human from which the human serum or the human plasma was obtained is not the non- immune human donor, and wherein said fresh human whole blood contains an anticoagulant that does not significantly affect complement activation or complement activity; and

detecting the presence or the absence of the bactericidal antibodies in said pre-immune sample and in said post-immune sample by assessing viability of said Gram-negative pathogenic bacterium in said samples,

wherein the presence of the bactericidal antibodies in the post-immune sample as compared to the pre-immune sample is indicative of the ability of the immunogenic composition administered to the human to elicit the bactericidal antibodies.

5. The method of claim 4 , wherein said Gram-negative pathogenic bacterium is a Neisseria bacterium and said immunogenic composition comprises a Neisserial antigen.

6. The method of claim 5 , wherein said Neisseria bacterium is Neisseria meningitidis.

7. The method of claim 4 , wherein said pre-immune sample and said post-immune sample are a pre-immune serum sample and a post-immune serum sample, respectively.

8. The method of claim 4 , wherein the combining of the pre-immune sample in the reaction mixture and the combining of the post-immune sample in the separate reaction mixture is carried out in parallel.

9. A method of screening for an immunogenic composition intended to elicit bactericidal antibodies effective against a Gram-negative pathogenic bacterium of interest, said method comprising:

combining in a first reaction mixture:

a pre-immune biological sample obtained from a human prior to administration of an immunogenic composition intended to elicit bactericidal antibodies effective against a Gram-negative pathogenic bacterium of interest;

the Gram-negative pathogenic bacterium, wherein the Gram-negative pathogenic bacterium is viable; and

fresh human whole blood obtained from a non-immune human donor, which does not contain detectable bactericidal antibodies effective against the Gram-negative pathogenic bacterium, wherein the human from which the pre-immune biological sample is obtained is not the non-immune human donor, and wherein said flesh human whole blood contains an anticoagulant that does not significantly affect complement activation or complement activity;

combining in a second reaction mixture:

a post-immune biological sample obtained from said human subject following administration of the immunogenic composition; said fresh human whole blood; and said Gram negative pathogenic bacterium, wherein said Gram-negative pathogenic bacterium is viable; and

detecting the presence or the absence of the bactericidal antibodies effective against the Gram-negative pathogenic bacterium in each of the pre-immune and the post-immune biological samples by assessing viability of the Gram-negative pathogenic bacterium:

wherein the pre-immune and the post-immune biological samples are human serum samples or human plasma samples; and

wherein the presence of the bactericidal antibodies in the post-immune sample as compared to the pre-immune sample is indicative of the ability of the immunogenic composition administered to the human to elicit the bactericidal antibodies.

10. The method of claim 9 , wherein the pre-immune biological sample and the post-immune biological sample are the human serum samples.

11. The method of claim 9 , wherein said Gram negative pathogenic bacterium is Neisseria bacterium.

12. The method of claim 11 , wherein said Neisseria bacterium is Neisseria meningitidis.