Gram-Positive / Gram-Negative Bacteria

Controversy over the role of bacteria in exacerbations of COPD has been present for several decades. In the 1950s and 1960s, British researchers suggested that exacerbations of COPD were caused by bacterial infection and mucus hypersecretion. This hypothesis lost favor in the late 1960s and 1970s, when longitudinal studies did not find a significant difference in the bacteria cultured from stable COPD patients and those with an exacerbation. In the 1990s, new studies, diagnostic techniques, and research methods have revived the theory that bacterial infection is a cause of exacerbations of COPD.

Today, it is estimated that bacteria are present in approximately 50% of cases of exacerbation of COPD.  The 3 most common bacteria are nontypeable Gram-positive Streptococcus pneumoniae, the Gram-negative nontypeable Haemophilus influenzae, and Moraxella catarrhalis. The Gram-negative bacteria are sometimes present in cases of severe (stage III) COPD, with at least 4 exacerbations per year.

Hinfluenzae is present in 30% to 70% of all bacterial exacerba­tions of chronic bronchitis. It releases substances that stimu­late mucus production and activate enzymes (IgE proteases) that weaken the body’s defense system. It also causes an increase in the inflammatory process that leads to bronchial damage.

Spneumoniae and Mcatarrhalis are isolated in about 33% of COPD exacerbations. Interestingly, a shift in the prevalence of these 2 pathogens is occurring. In the past, Spneumoniae was more prevalent than Mcatarrhalis. More recent studies show that the incidence of Mcatarrhalis is increasing and Spneumoniae is decreasing. This shift may be caused by the availability of the pneumococcal vaccine. Antibiotic treatment of exacerbations caused by Spneumoniae may become more challenging as increasing antimicrobial resistance by this organism continues to emerge.