In a healthy human, the internal tissues such as blood, brain, and muscle are generally free of microorganisms. On the other hand, the surface tissues, such as skin, all of the mucous membrane in the mouth, nasal cavity and intestinal tract can easily and readily become available for microorganism to colonize and grow. Depending on the location in the human body, different bacteria choose to grow on a specific location that provides the nutrition it needs, with optimum condition such as pH. There are many different bacteria that collectively are called normal flora, and live in the human body. Many of these bacteria are commensally living in humans, and some others are symbiotic. Commensal bacteria only obtain their food from the human, and do not harm or benefit the host, on the other hand symbiots not only get their food from the host, but in return they also become beneficial to the host in providing nutrition that human can not make, such as vitamin K. One of the most reco!.
gnized and extensively studied bacteria that often get more attention during the winter is Streptococcus. There are different strains of strep. Depending on their ability of hemolysis of blood agar, strep can be subdivided into a, b and g hemolytic (1-pp143). There are many different laboratory tests that can be done to distinguish one strep from the other. Different treatments also have been developed to fight each strain of strep.
The streptococci are a group of bacteria that infect human as well as animals. A very basic test to recognize strep is to perform blood agar plate (BAP) test. Hemolysis of the blood agar can indicate the presence of strep bacteria. Most strep bacteria are either a or b hemolytic on sheep blood agar. a-hemolytic strep partially lyses the red blood cells, creating a greenish zone around each colony, whereas, complete lyses of blood by b-hemolytic strep create a clear zone. g-hemolytic does not lyse red blood cells, and no change or zone is created (1-pp143).
