Can I Get Rid Of It?
First of all, I think it is generally accepted that once a PWCF has acquired P. aeruginosa it is pretty difficult if not impossible to completely eradicate from the lung. Here one has to make the distinction between obtaining negative sputum cultures after antibiotic treatment (which is usually fairly easy to achieve for a varying period of time) and the complete eradication of the organism. I believe several studies have shown that when the organism does reappear in sputum culture, it is invariably the same strain type as previous indicating regrowth of the original infection rather than re-infection.(see J Infec Dis 1994:170;1616-21 for example)
One model of P. aeruginosa infection that has been proposed and I find creditable is that put forward by Niels Hoiby. He suggests that after infection and binding to the respiratory epithelium, alginate (mucoid polysaccharide) is produced effectively trapping the bacteria within a ‘Bio-film’. This bio-film which is probably only 20% bacteria tends to slow down the growth of the bacteria but on the other hand, gives the bacteria extra protection from antibiotics and scavenging immune cells. What is being detected in sputum cultures is bacteria that has been shed from this Bio film. The reason antibiotic therapy does appear to be effective, is that probably the free living or shed aeruginosa (what Niels calls the Planktonic bacteria) are the major cause of lung inflammation. They are also much easier to eliminate.
The bacteria in the bio-film are much more difficult to eliminate and after ‘playing possum’ will eventually reappear in sputum culture. This model also explains why P. aeruginosa can often appear sensitive to antibiotics in the laboratory but are apparently resistant in the lung.