What are the most common organisms in cystic fibrosis (CF)?

Most Common Organisms in Cystic Fibrosis

Pseudomonas aeruginosa is the most frequent pathogen isolated from cystic fibrosis (CF) sputum or bronchoalveolar lavage samples across all age groups, followed by Staphylococcus aureus. 1

Prevalence of Major Pathogens in CF

Pseudomonas aeruginosa

• P. aeruginosa is the most frequently described opportunistic pathogen in CF patients 1
• Prevalence increases with age: 29.8% in children aged 2-5 years and 81.3% in adults aged 26-30 years 1
• Overall incidence of P. aeruginosa infections in CF is estimated at 8% 1
• Chronic P. aeruginosa infection is associated with more rapid reduction in lung function and poorer prognosis 1
• Conversion to mucoid phenotype is common in chronic infection and contributes to antibiotic resistance and biofilm formation 2

Staphylococcus aureus

• S. aureus is one of the first and most common pathogens isolated from the respiratory tract of CF patients 3
• More prevalent during infancy and early childhood, with declining incidence as P. aeruginosa becomes more prominent with increasing age 4
• Both methicillin-susceptible and methicillin-resistant S. aureus (MRSA) prevalence has increased over the past decade 3
• Small colony variant (SCV) S. aureus has been associated with persistent infection and co-infection with P. aeruginosa 4

Other Common Pathogens

• Stenotrophomonas maltophilia 5
• Mycobacterium abscessus 5
• Achromobacter species 5
• Obligate anaerobes, most commonly Prevotella species 5

Microbial Interactions in CF Airways

P. aeruginosa and S. aureus Interactions

• P. aeruginosa secretes respiratory inhibitors (hydrogen cyanide, pyocyanin, quinoline N-oxides) that suppress S. aureus growth 4
• S. aureus can adapt to these attacks by developing small colony variants (SCVs) that are more resistant to antibiotics 4
• S. aureus can increase the risk of subsequent chronic P. aeruginosa respiratory infection 6
• Protein A from S. aureus can inhibit P. aeruginosa biofilm formation while protecting both bacteria from phagocytosis 4

Diagnosis of Bacterial Colonization/Infection

• P. aeruginosa lung infection should be assessed by collecting sputum with minimal saliva contamination 1
• In non-sputum producers, hypopharyngeal or endolaryngeal suctions should be taken, preferably after lung physiotherapy or hypertonic saline inhalation 1
• P. aeruginosa grows well on standard laboratory media such as 5% sheep blood agar or chocolate agar 1
• Selective media, such as cetrimide agar, facilitate the isolation of P. aeruginosa from other bacterial species 1
• Periodic serological tests for P. aeruginosa antigens should be used in non-sputum producers to avoid false-negative results 1
• Colonization/infection should be assessed as early as possible, at least every three months 1

Clinical Implications

• The majority of CF patients carrying mucoid P. aeruginosa experience an immediate and more rapid reduction of lung function compared to those without P. aeruginosa infection 1
• Pulmonary infection has been recognized as having the greatest role in morbidity and mortality, leading to premature death in 90% of CF patients 1
• Antipseudomonal therapy is generally warranted in CF patients and affects survival to an extent that is not fully quantified 1
• S. aureus colonization can promote severe lesions including abscess formation and increase the risk of subsequent chronic P. aeruginosa infection 6

Prevention and Management Considerations

• CF centers have implemented separation of patients with and without P. aeruginosa infection to limit cross-infection 1
• Hygienic measures to decontaminate environmental reservoirs of P. aeruginosa (nebulizers, medical equipment, sinks, toilets) are recommended 1
• Hand disinfection for CF patients and hospital personnel is important 1
• Combination antibiotic therapy with two different drugs is preferred over monotherapy to delay development of antibiotic resistance 1