Microbiology of bacterial respiratory infections.

The upper respiratory tract may become susceptible to bacterial infection as a result of health conditions such as allergies and viral infections, as well as the effects of smoking and airborne environmental pollutants. Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis are the most common bacterial pathogens in upper and lower respiratory tract infections. Streptococcus pyogenes is the predominant bacterial pathogen in pharyngitis and tonsillitis. Bacterial pathogens adhere to mucous membranes and colonization ensues. In an otherwise healthy individual the host immune system responds to the invading bacteria resulting in edema and swelling. If antimicrobial treatment does not eradicate the invading organisms and successfully interrupt the progress of the infection, the patient may develop recurrent or chronic disease. S. pneumoniae and other pathogens once susceptible to penicillin and other antibiotics are now becoming resistant. Bacterial resistance has developed and disseminated because of the widespread use of antibiotics. Major mechanisms of bacterial resistance to antimicrobials in upper respiratory tract infections include enzymatic inhibition, membrane impermeability, alteration of target enzymes, active pumping out of antibiotic and alteration of the ribosomal target.