Human normal flora-Part 3 (Respiratory track)

A large number of bacterial species colonize the upper respiratory tract (nasopharynx). The nares (nostrils) are always heavily colonized, predominantly with Staphylococcus epidermidis and corynebacteria, and often (in about 20% of the general population) withStaphylococcus aureus, this being the main carrier site of this important pathogen. The healthy sinuses, in contrast are sterile.  The pharynx (throat) is normally colonized by streptococci and various Gram-negative cocci. Sometimes pathogens such as Streptococcus pneumoniae, Streptococcus pyogenes, Haemophilus influenzae and Neisseria meningitidis colonize the pharynx.

The lower respiratory tract (trachea, bronchi, and pulmonary tissues) is virtually free of microorganisms, mainly because of the efficient cleansing action of the ciliated epithelium which lines the tract. Any bacteria reaching the lower respiratory tract are swept upward by the action of the mucociliary blanket that lines the bronchi, to be removed subsequently by coughing, sneezing, swallowing, etc. If the respiratory tract epithelium becomes damaged, as in bronchitis or viral pneumonia, the individual may become susceptible to infection by pathogens such as H. influenzae or S. pneumoniae descending from the nasopharynx.  

BINOMIAL NAME	LOCATION
Acinetobacter spp	Nasopharynx
Burkholderia cepacia complex	Lung
Campylobacter sputorum	Nasopharynx
Candida albicans	Pharynx
Cardiobacterium spp	Nose
Chlamydophila pneumoniae	Lung
Citrobacter freundii	Throat
Eikenella corrodens	General distribution
Haemophilus parainfluenzae	Pharynx
Haemophilus paraphrophilus	Pharynx
Haemophilus spp	Nasopharynx
Kingella kingae	Upper respiratory Tract
Kingella spp	Upper respiratory Tract
Moraxella catarrhalis	Nasopharynx
Moraxella spp	Nasopharynx
Mycoplasma orale	Oropharynx
Mycoplasma pneumoniae	Respiratory epithelium
Neisseria cinerea	Nasopharynx
Neisseria elongata	Pharynx
Neisseria gonorrhoeae	Pharynx[citation needed
Neisseria lactamica	Nasopharynx
Neisseria meningitidis	Nasopharynx
Neisseria mucosa	Nasopharynx
Neisseria sicca	Nasopharynx
Neisseria spp	Nasopharynx
Peptococcus spp	Upper respiratory tract
Peptostreptococcus spp	Pharynx
Pseudomonas aeruginosa	Lung
Selenomonas sputigena	Nasopharynx
Staphylococcus aureus	Nose
Streptobacillus spp	Throat, nasopharynx
Streptococcus constellatus	Oropharynx
Streptococcus intermedius	Oropharynx
Streptococcus mitis	General distribution
Streptococcus pyogenes	Upper respiratory tract
Streptococcus viridans	Pharynx