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P. Aeruginosa in COPD Shows Two Distinct Patterns of Carriage
By Michelle Rizzo
NEW YORK (Reuters Health) May 08 - In a recent study, researchers identified two distinct patterns of Pseudomonas aeruginosa colonization in patients with chronic obstructive pulmonary disease (COPD) -- short-term colonization followed by clearance, and long-term, persistent carriage.
"Pseudomonas aeruginosa is isolated from adults with COPD in cross-sectional studies," Dr. Timothy F. Murphy of Buffalo Veterans Affairs Medical Center, New York, and colleagues write in the April 15th issue of the American Journal of Respiratory and Critical Care Medicine. "However, patterns of carriage and the role of P. aeruginosa in COPD are unknown."
In a 10-year prospective study, the researchers sought to elucidate carriage patterns of P. aeruginosa in 126 adults with COPD who were enrolled between April 1994 and December 2004, and to characterize bacterial strain phenotypes.
In addition, the team examined the clinical consequences of P. aeruginosa infection, and evaluated the antibody response to P. aeruginosa in COPD.
The researchers identified 57 episodes P. aeruginosa acquisition in 39 of the 126 patients over 10 years. An association was observed between acquisition of a new strain of P. aeruginosa and the occurrence of an exacerbation.
Thirty-one episodes were followed by clearance of the strain. Of these, 16 were of short duration (less than 1 month) and 15 were of longer duration (2 to 22 months). Thirteen strains exhibited persistent carriage, and 13 were of indeterminate duration.
The authors note that six strains of P. aeruginosa demonstrated a mucoid phenotype. These strains were more likely to persist than non-mucoid strains (100% versus 22.5%, p = 0.005). Overall, 53.8% of persistent carriage episodes were associated with the development of an antibody response, compared with 9.7% of short-term carriage episodes (p = 0.003). Antibody responses did not mediate clearance of P. aeruginosa from the respiratory tracts of patients with COPD.
"The practical implication is that P. aeruginosa causes some acute exacerbations of COPD and thus are likely benefited by antibiotic therapy," Dr. Murphy said in an interview with Reuters Health. "The challenge is distinguishing those situations where P. aeruginosa is causing infection from those situations where the organism is simply a colonizer and another virus or bacterium is causing the exacerbation."
"Right now there is not a reliable way to make this distinction so clinicians need to use clinical judgment," Dr. Murphy explained. "This question is particularly important because P. aeruginosa is resistant to many of the antibiotics that are used routinely to treat patients with exacerbations."
The author said his team is currently investigating these strains "to determine whether infecting strains are different from colonizing strains with regard to genome content; i.e., do infecting strains have specific genes that allow them to cause infection that are absent in colonizing strains?"
Am J Respir Crit Care Med 2008;177:853-860.
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