What bacteria cause yellow to greenish sputum production?

Yellow to Greenish Sputum: Bacterial Causes

Yellow to greenish sputum is most commonly caused by Haemophilus influenzae, followed by Streptococcus pneumoniae, Moraxella catarrhalis, and in severe disease or specific risk factors, Pseudomonas aeruginosa. 1

Primary Bacterial Pathogens

The color of sputum reflects myeloperoxidase content from neutrophils rather than specific bacterial species, but certain organisms are consistently associated with purulent (yellow-green) sputum production:

Most Common Organisms

• H. influenzae is the predominant pathogen isolated in patients with purulent sputum, particularly in COPD exacerbations and bronchiectasis (20-40% of cases) 1
• S. pneumoniae is the second most frequent organism, especially in mild disease with FEV1 >50% (46% of Gram-positive isolates) 1
• M. catarrhalis accounts for approximately 23% of bacterial isolates in patients with colored sputum 1

Severity-Dependent Pathogens

The bacterial profile shifts based on disease severity:

• Mild disease (FEV1 >50%): S. pneumoniae predominates (46%), with H. influenzae and M. catarrhalis less common (23%) 1
• Severe disease (FEV1 <50%): Gram-negative organisms become preponderant (63%), with P. aeruginosa and Enterobacteriaceae increasingly isolated 1

Pseudomonas aeruginosa: High-Risk Scenarios

P. aeruginosa causes 10-30% of infections producing purulent sputum in specific high-risk populations and requires distinct consideration: 1, 2

Risk Factors for P. aeruginosa

P. aeruginosa should be suspected when patients have two or more of the following: 1

• Recent hospitalization
• Frequent antibiotic use (>4 courses per year or within last 3 months)
• Severe airway disease (FEV1 <30%)
• Previous P. aeruginosa isolation or known colonization

Clinical Significance

• P. aeruginosa colonization correlates with more extensive lung damage, worse lung function, and more intense inflammatory responses 1, 3
• This organism develops antibiotic resistance rapidly, particularly in chronic infections with frequent antimicrobial exposure 4
• Mortality increases significantly if anti-pseudomonal antibiotics are not initiated early in severe infections 1, 2

Sputum Color and Bacterial Load Correlation

Green purulent sputum demonstrates 94.4% sensitivity and 77.0% specificity for high bacterial loads (≥10^7 CFU/mL), though color alone should not dictate antibiotic decisions: 1

• Median bacterial load in mucoid sputum: 7.5 × 10^6 CFU/mL 1
• Median bacterial load in purulent sputum: 10^7-10^8 CFU/mL 1
• In 92% of high bacterial load specimens, one bacterial species predominates 1

Important Clinical Caveats

Sputum color alone is not a reliable indicator of bacterial infection and should not be the sole basis for antibiotic treatment decisions. 5 The purulent appearance results from inflammatory cells and sloughed epithelial cells, not necessarily bacteria. 5

When to Consider Antibiotics

Rather than relying on sputum color, base antibiotic decisions on: 5

• COPD exacerbations: All three Anthonisen criteria (increased dyspnea, increased sputum volume, increased sputum purulence) or mechanical ventilation requirement
• Pneumonia: Fever, tachycardia, tachypnea, abnormal chest examination
• Acute bronchitis in healthy adults: Generally avoid antibiotics regardless of sputum color (>90% are viral)

Microbiological Testing Recommendations

• Severe COPD exacerbations (FEV1 <30%, >4 exacerbations/year, prior antibiotics/steroids): Obtain sputum cultures before initiating antibiotics 1
• Bronchiectasis exacerbations: Sputum cultures recommended in most cases due to diverse flora and resistance patterns 1
• Sputum cultures correlate well (75% agreement) with bronchoscopic specimens in these populations 1