Organisms That Inhabit The Oral Cavity--
The oral cavity
is a complex environment that contains both aerobic and anaerobic conditions.
If is hard to classify oral bacteria as commensals because many species
can aid in the formation of plaque and dental carries, cause periodontal
disease, or become potential pathogens as they invade other body tissue.
Some also present mutualistic benefits such as vitamin synthesis and the
suppression of no indigenous potential pathogens. Species of
Streptococcus, Neisseria, Lactobacillus, and Staphylococcus
up just a few of the many bacteria present in the oral cavity.
Organisms That Inhabit The Upper Respertory Tract--
upper respertory tract consists of the nostrils, nasal cavities
and throat. The most common commensalistic inhabitants are:
Neisseria sp., Staphylococcus epidermidis
avirulant strains of Streptococcus pneumonea,
Many other species such as Staphylococcus aureus
the upper respitory tract but are potential pathgens. The lower respitory
system is virtually free of bacteria in a healthy person.
Culture of nasal flora containing Staphylococcus
aureus and Corynebacterium on blood agar
Organisms That Inhabit The Lower GI Tract
-- More organisms inhabit
the lower GI tract than anywhere else on or in the human body. Bifidobacterium,
Bacteroides, Lactobacillus, Enterococcus, Escherichia coli
and other anaerobic bacteria dominate this habitat. Populations in the small
intestine can reach 10^11 cells per ml feces. As in other cases many of these
organisms cannot be classified as pure commensalists. Many of them provide
nutritional benefits such as vitaman production, the break down of
non-digestible materials, and competitive exclusion of pathogens. Some
intestinal inhabitants such as Bacteroides
can become opportunistic