Antibody

Antibody is a protein in animals body to fight against specific types of antigen. Antigen is foreign living pathogen that usually harms body.  

Antibody made inside the body kills foreign particles. Foreign particles should be bacteria, virus or fungus.

Antibody is the active part of our immune system. It is also indicator of immunity. Who gained antibody against specific disease he gained immunity against specific disease.

Bacteria

 Bacteria is a living microorganism that is unicellular and consist with nucleus protoplasm surrounded it. 

The basic difference of bacteria and virus is that it is independently alive. But virus is alive when it hosted by living organism. Otherwise it is particle.

According to gram staining experiment bacteria is gram positive and gram negative. 

According to survival capabilities in presence of Oxygen bacteria classified into aerobic bacteria and anaerobic bacteria. 

According to infection capabilities bacteria are classified into pathogenic bacteria and non pathogenic bacteria.