Pseudomonas aeruginosa, one of the most common types of bacteria present in severe lung infections, infects cystic fibrosis (CF) patients differently than those with non-cystic fibrosis bronchiectasis, according to a long-term study.
Researchers observed that these bacteria are more stable in CF patients than in non-CF bronchiectasis patients, and that the appearance of new strains was not necessarily associated with bronchiectasis exacerbations, as opposed to CF.
The study, “Epidemiology and natural history of Pseudomonas aeruginosa airway infections in non-cystic fibrosis bronchiectasis,” was published in the journal ERJ Open Research.
Infection with P. aeruginosa has been thoroughly studied in CF patients, since it is one of the main causes of lung deterioration and death in this patient population.
In non-CF bronchiectasis, the presence of these bacteria in patients’ airways has also been associated with worse lung function, poorer quality of life, and an increased death and complications. However, little is known about the evolution of P. aeruginosa infection in non-CF bronchiectasis patients, and what is currently known, has mainly been inferred from data on CF patients.
To better understand the infection process in non-CF bronchiectasis patients, researchers investigated the history and incidence of the disease, known as disease epidemiology, as well as the transmission characteristics and clinical outcomes associated with P. aeruginosa infections.
Bacterial samples that had been collected from patients between 1986 and 2011 were used in the study. Researchers included patients older than 18, who had two or more infections with P. aeruginosa over a minimum of six months.
In total, the team collected 203 samples of bacteria (isolates) from 39 patients. The genetic information within each isolate was analyzed, and the results compared with a large collection of CF types (strains) and other non-CF isolates.
Researchers were able to identify four patterns of infection in non-CF bronchiectasis that are not common in CF cases, including persistence of a single P. aeruginosa strain, in 67% of the patients; a change in the type of P. aeruginosa over the course of the infection, a process known as strain displacement, in 20% of patients; temporary disruption of the infection in 8%; and chaotic airway infection found in 5%.
However, these patterns were not significant predictors of lung function decline or disease progression. The acquisition of new strains was also not linked to the occurrence of lung exacerbations.
Genetic analysis indicated that the types of P. aeruginosa present in the airways of non-CF bronchiectasis patients appeared only in a few cases of CF patients and other non-CF diseases. Moreover, there was no patient-patient transmission of the bacteria among non-CF bronchiectasis patients.
Most notably, researchers highlighted the higher chances of strain displacement in the non-CF bronchiectasis group than those observed in CF studies. Nonetheless, this had no impact in clinical outcomes.
“While a majority of non-CF bronchiectasis patients experience persistent colonization by an individual P. aeruginosa strain, a higher than expected number of individuals were observed who experienced strain displacement over the course of their disease,” although “strain displacement was not linked with episodes of [pulmonary exacerbations],” the researchers wrote.
“Our longitudinal study of non-CF bronchiectasis patients has observed several distinctions in the epidemiology of P. aeruginosa infections as compared to CF, … whereas P. aeruginosa infections in CF adults are known to be relatively stable, strain displacement with unique strains was observed commonly in non-CF bronchiectasis,” they concluded.
“Furthermore, when new strains were observed, they were not necessarily associated with pulmonary exacerbation events, in a similar fashion to what has been previously observed in CF,” the team said, adding that “whereas cross-infection of P. aeruginosa has been observed in CF, we did not find any evidence of cross-infection amongst non-CF bronchiectasis patients.”
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