What specific micro organism gain enty via the following routes skin, gastointestinal tract, respiratory tract and genitourinary tract?
Theoretically, any microorganism can enter the body through any portal of entry if we come into contact with that organism. But just because an organism enters doesn't mean it will cause disease. Different areas of the body have what are called normal flora. These are bacteria that normally live in that area. The skin is a good example, it has several species of bacteria that normally live there like strep. and staph. Even though these bacteria live on the skin (on all of us) they may or may not be pathogenic. Pathogenicity depends on many different factors including the susceptibility of the host.
Disease processes have specific pathogens that most commonly cause the disease. For example, tuberculosis is caused by mycobacterium tuberculosis. TB is primarily a lung problem, so the mycobacteria do gain entry to the respiratory tract by inhalation and cause disease. However, this same pathogen is found in other parts of the body and it can gain access from other portals of entry other than the respiratory tract, but the reason you don't hear about this is because it doesn't cause disease when entering from a site other than the respiratory tract.