Pseudomonas colonization

Question

Hello,
Could you please define what is Pseudomonas colonization ? When Pseudomonas is observed for the first time in sputum sample, that it’s treated, that it’s disappeared for a long period, is it colonization ? Is it a primo-colonization? If Pseudomonas is not found in the following sputum samples, is the Pseudomoans always in the patient’s bronchi ?

Answer

Hello and thanks for your question.
First of all we have to distinguish between "colonization" and "infection". If we only find a micro-organism in the sputum, we talk first about colonization or primo-colonization. If the patient shows additionaly direct signs of infection (inflammation, fever, etc) or indirect signs of an immune response (Pseudomonas antibodies), we talk about an infection instead of colonization. After the first finding an eradication therapy is initiated and often successful. But in the long runs, P. aeruginosa often reappears in spite of antibiotic therapy. Then we talk about the stage of chronic colonization/infection.
There is no uniform definition of this chronic colonization, it can be defined by the isolation of the same germ from at least 2 out of 4 distinct sputum samples per year. Other sources (such as the EuroCareCF working group) recommend to take at least 6 sputum samples per year and 50% or more have to be positive in order to fulfill the definition of a chronic P. aeruginosa infection.
When Pseudomonas has already been found in the sputum, it is possible that the further sputum samples are Pseudomonas-free whereas few colonies are present in the bronchi. Indeed, a sputum sample reflects only the microbial flora from the beginning of the lower airways (trachea, and maybe the main bronchi). That’s why, very often, antibiotics, when necessary, are adapted to the results of the 3 or 4 last sputum samples.
With my best regards,
Prof Jean-Christophe Dubus

09.07.2012