Resumen de Dynamics of Streptococcus pneumoniae in patients with Chronic Obstructive Pulmonary Disease
Arnau Domenech Pena
It is estimated that within a few years chronic obstructive pulmonary disease (COPD) will be the third leading cause of death worldwide. The morbidity and mortality associated with COPD are due, in part to acute exacerbation episodes (AECOPD), mainly caused by microbial pathogens such as Haemophilus influenzae, Streptococcus pneumoniae and Pseudomonas aeruginosa. Moreover, COPD is the main underlying disease associated with pneumococcal pneumonia episodes. This thesis describes four studies performed to gain insights into the role of pneumococci and their closely-related species S. pseudopneumoniae in causing acute exacerbation and pneumonia episodes in COPD patients. In the first study, a total of 188 sputum samples were obtained from AECOPD episodes occurring in severe COPD patients during a 1-year period. Samples were quantitatively cultured; of them, S. pneumoniae was isolated in 31 (16.5%) episodes and S. pseudopneumoniae in 9 (4.8%) episodes. S. pneumoniae was the third most frequent cause after Pseudomonas aeruginosa (28.8%) and Haemophilus influenzae (19.7%). There are major differences in the invasiveness potential of pneumococci, depending on their serotype and genotype. Indeed, in our second study (from 2001 to 2008) we found an association of certain serotypes, and their related genotypes, with different pneumococcal infections. Serotypes 4 (ST2474), 5 (Colombia5-ST289) and 8 (Netherlands8-ST53) were associated with bacteraemic pneumonia, serotypes 1 (Sweden1-ST306) and 3 (Netherlands3-ST180 and ST2603) with bacteraemic and non-bacteraemic pneumonia, and serotypes 16F (ST3016F), 11A and non-typeable pneumococci with AECOPD episodes (P<0.05). Finally, in our experience, serotype 3 pneumococcus was the most frequent cause of pneumonia and acute exacerbations in COPD patients. Moreover, the implementation of pneumococcal conjugate vaccine PCV7 for children in 2001 in Spain has been shown to be highly effective in reducing invasive pneumococcal disease in children, and in adults as well due to the phenomenon of herd protection. This effect was also observed among pneumococci causing acute exacerbations in adults: PCV7 serotypes decreased from 39.4% in the 2001-04 period to 11.2% in the 2009-12 period. In parallel, the prevalence of multi-drug resistant serotypes 15A and 6C has dramatically increased in recent years. For this reason, although the resistance rates of ?-lactams decreased over time, macrolides and multi-drug resistance remained stable throughout the study period. The presence of bacteria colonizing the lower airways of most severe COPD patients results in bronchial epithelial injury and increases morbidity among these patients. In the third study (1995-2010 period), it was found that a third of recurrent pneumococcal acute exacerbations were relapses (caused by a pre-existing strain), mainly associated with serotypes 9V and 19F (P<0.02). This suggests an important role for capsular type in pneumococcal persistence. In view of these results, we analysed the impact of antimicrobial consumption in the development of pneumococcal resistance to ?-lactams and fluoroquinolones in 13 patients with a long-time persistence of pneumococci (average time: 582 days, SD ±362). Changes in quinolone-resistant determining regions (QRDR) involved in fluoroquinolone resistance were frequently observed in persistent strains after fluoroquinolone treatment; however, the penicillin-binding protein (PBP) sequences were stable over time, even though all but two patients received multiple courses of ?-lactam treatment. These results suggest that an optimal combination of pbp genes is maintained to compensate for the fitness cost imposed by additional changes in these genes. Despite the genetic stability of these persistent strains, S. pneumoniae is naturally transformable and is able to acquire exogenous DNA, resulting in a dynamic and complex epidemiology of pneumococcal diseases. This genetic diversity was also observed among the 36 S. pseudopneumoniae strains analysed. Altogether, our studies can help to improve the understanding of the dynamics of S. pneumoniae and S. pseudopneumoniae populations causing disease in COPD patients.
