The most common way in which tuberculosis is acquired is via the

Organisms may be transmitted in a number of ways, such as by air, food, hands, sexual contact, and infected needles. However, for each disease or disease category, there is usually a portal of entry not always unique to the organism. The respiratory tract is a common portal of entry to such airborne organisms as M. tuberculosis. This is why respiratory precautions must be taken when patients are harboring viable M. tuberculosis.The gastrointestinal tract is usually infected from ingestion of contaminated food or water (Shigella, Salmonella, Campylobacter) or by an alteration of the normal microbial flora such as with C. difficile disease. The skin is a tough integument and intact, is resistant to most infectious organisms except those that may break down human skin. Breaches of the skin as by wounds, burns, and the like predispose patients to a variety of infections such as tetanus caused by wound contamination with spores of C. tetani, or direct infection by Staphylococcus, Streptococcus, or Gram-negative rods (such as Serratia or Pseudomonas).The genital tract may become infected either by sexual contact or by alteration of the genital environment as often occurs with yeast infections. Several bacteria such as N. gonorrhoeae, Chlamydia, and Treponema pallidum are transmitted by direct sexual contact with infected partners.