Pseudomonas aeruginosa is the key bacterial agent of cystic fibrosis (CF) lung infections, and the most important pathogen in progressive and severe CF lung disease. This aerobic, gram-negative, opportunistic pathogen can grow and proliferate in patients, and exposure can occur in hospitals and other healthcare settings. CF is a genetic disorder, and P. aeruginosa infections tend to set in due to the production of mucoid secretions (as a result of the defective CFTR gene, a protein that acts as a channel for mucus production and other body fluids) clogging the lung airways, reducing mucociliary clearance of inhaled microbes, and leading to the formation of bacterial biofilms with mucoid layers as their habitat. Once these sticky biofilms are formed, inflammation results and, in some cases, lead to chronic infections that can last for months or years. Early symptoms of infection can include incessant coughing and phlegm production, and hemosptysis (bloody mucus), followed by such serious complications as exacerbations, bronchiectasis, hypoxia, and pulmonary hypertension. The severity of lung disease in CF patients is considered a major determinant of life quality and length.
P. aeruginosa infections are difficult to treat, because it is a resilient and resistant infectious agent. According to a study published in the journal Allergy & Immunology, the bacteria produces many virulence factors, including secreted factors — such as elastase, proteases, phospholipase C, hydrogen cyanide, exotoxin A, and exoenzyme S — and cell-associated factors, such as lipopolysaccharide, flagella, and pili. These factors are controlled in a cell density-dependent manner known as quorum sensing (QS), which is thought to play a role in both the development and the protection of P. aeruginosa biofilms. These biofilms, or communities of cells (secreted proteins, polysaccharides, nucleic acids, and cellular debris) encased in an extracellular matrix, act in a coordinated way and show adaptive mechanisms, and their growth is associated both with antimicrobial resistance and resistance to host defenses. Extracellular DNA is also a major component of the biofilm matrix, especially in its earlier stages.
P. aeruginosa infections often become chronic, and strains undergo a phenotypic change that is characterized by the production of a polysaccharide known as alginate. According to another study, this bacterial phenotype, known as the mucoid phenotype, is associated with considerable difficulty in eradicating the pathogen, eliciting strong inflammatory responses and resulting in an accelerated loss of lung function and a poorer prognosis.
Expert care is necessary to treat CF patients with P. aeruginosa infections. In its early stages, when the pathogen is most susceptible to antimicrobials, inhaled and, possibly, systematic treatments with prophylactic antibiotics are a must, followed by chronic suppressive therapy. Antibiotics currently marketed for inhalation include nebulized and dry powder forms of tobramycin and colistin and nebulized aztreonam. The prevalence of antibiotic resistance remains a cause of concern, however, and new treatments are needed.
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