In a human body normal flora a normally harmless bacteria that lives primarily on the skin and in the eyes, mouth, upper respiratory system, the gastrointestinal tract mainly in the large intestine (colon) and urogenital tract; however under certain conditions some of the normal flora may be become pathogenic then by causing opportunistic infections
The co-existence of bacteria and the human hosts is called symbiosis; normal flora existing one of three symbiotic relationships with the human hosts.
In commensalism the bacteria benefit from the relationship and the human host is neither harm nor benefit it; examples of commensals include the corynebacterium species that inhabit the tissues surrounding the eye and mycobacterium species that normally lives in the ear and external genitals; these bacteria use normal body secretions and died cells as nutrients and cause no harm to the host.
In mutualism both the bacteria and the host benefit; examples of mutualistic bacteria include the E. coli species that inhabit the large intestine; these bacteria live on the nutrients that pass through intestine and in return they produce essential vitamins use such as K and B for the human host.
In parasitism the bacteria benefit at the expense of the host; parasites in the human body are pathogenic bacteria that responsible for many diseases; the important bacterial sub-types that frequently cause diseases in humans are:-
· Cocci and Bacilli.
· Mycoplasmas.
· Mycobacteria.
· Spirochetes.
· Rickettsias.
· Nocardia Forms.
Cocci are round bacteria and the bacilli are rod shaped; pathogenic cocci and bacilli include gram positive, gram negative, aerobic or anaerobic sub-types.
Staphylococcus aureus which are gram positive aerobe cocci cause skin and lung infections; Pseudomonas aeruginosa which are gram negative aerobic bacilli cause numerous respiratory and urinary tract infections.
In contrast Mycoplasmas are very small bacteria that lake cell walls as a result they are irregularly shaped, they atypically facultative anaerobe; mycoplasmas such as Mycoplasma pneumoniae are primarily associated with respiratory infections.
Mycobacteria are a group of aerobic non-motile, non-endospore-forming rods; mycobacterium tuberculosis is responsible for tuberculosis and Mycobacterium leprae causes leprosy; the Mycobacterium avium, Mycobacterium intracellulare complex a group of microorganisms that rarely infect humans but it has now classified as one of the leading opportunistic infections associated with AIDS.
Spirochetes are motile bacteria with coiled shapes since they lack flagella they moved by rotating in a corkscrew fashion spirochetes can be an aerobic or anaerobic; the pathogenic species of spirochetes cause syphilis and Lyme disease.
Rickettsias are gram negative and non motile and can be either the rods or cocci; they also parasites since they most inhabit another organism to survive a and cannot reproduce outside a host cell; rickettsias are almost always transmitted to humans via insect and tick bite; vehicles diseases such as epidemic typhus and Rocky Mountains spotted fever
Chlamydia trachomatis are coccoid rickettsia is that can cause blindness and two types of sexually transmitted diseases (STDs) one of which Non-Gonococcal Urethritis is probably the most common STD in the U.S.
Finally Nocardia forms are aerobic rods; Nocardia asteroides can cause chronic tuberculosis like respiratory infection.
