Lung abscess is commonly caused by bacterial infections and these include bacteroides, peptostreptococcus and prevotella. Most of the lung abscess is caused by polymicrobial organisms,of which anaerobes play a crucial role. Less common include nocardia, actinomyces and fungi.

• Include conditions which may result in death or permanent disability within 24 hours if left untreated.
• Aerobic bacteria are most commonly associated with rapid and flumiant course with high grade fever and worsening symptoms. These bacteria Include Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Streptococcus pneumonia.

• About 90% of the lung abscess is caused by polymicrobial infection.^{[1] [2]}
• Anaerobes are the predominant pathogens involved in primary lung abscess, followed by Streptococcus pneumoniae.

• Klebsiella pneumoniae is the more commonly seen in alcoholics.^[3]

• Staphylococcus aureus is the most common pathogen responsible for lung abscess in children with cystic fibrosis.^[4]

The following table elaborates the most common etiological pathogens responsible for lung abscess ^[5]

• Bacteroides
• Fusobacterium
• Peptostreptococcus
• Prevotella
• Streptococcus milleri

• Legionella
• Lemierre’s syndrome
• Listeriosis
• Melioidosis

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