Anaerobic infection.

Many of the infections are polymicrobial. 

Anaerobic bacteria are found in 60% to 85% of the cases.

50% of patients have only anaerobic organisms, while the other 50% have a combination of aerobic and anaerobic organisms with and anaerobic predominance.

Anaerobes that are frequently found include:

Aerobes that my be found in predominant anaerobic infection include:

Normal person 

50% of healthy persons aspirate during sleep, usually goes unrecognized, and has few sequelae.

Determinants who gets infection?

The frequency, volume, and character of the aspirated material will determine whether or not a pulmonary infection will develop.

Predisposing factors for aspiration

Factors associated with increased frequency of aspiration include.

His alcoholism and seizures probably are the predisposing factors for him. Gingivitis and caries provided a bigger bacterial inoculum for aspiration.

Pathogenesis of this pneumonia.

Common sites for aspiration lung abscess 

The superior segments of RLL, LLL and axillary subsegments of anterior and posterior segments of RUL are common sites for aspiration and will account for 85% of all Lung abscesses. 

Gravitational forces determine the site of aspiration. Position of the patient at the time of aspiration determines the segment the aspiration is most likely to occur. 

Clinical picture of lung abscess

Most of the patients present with sub acute onset of illness and do not seek medical attention for three to four weeks since the onset of illness. 
Patients complain of cough, low grade fever, anorexia and weight loss of few weeks duration . 
Patients often have cough with large amounts of foul smelling sputum. 
Lack of foul smell does not exclude lung abscess, as 50% of anaerobic infections do not produce a foul smell. 

Other routes besides aspiration by which anaerobes can reach lungs

Less common mechanisms by which anaerobic bacteria reach the lung include:

Complications are associated with this infection

If aspiration pneumonia goes untreated, progressive tissue necrosis may ensue. This results in

Therapeutic strategy

Hospital acquired aspiration pneumonia

Patients with nosocomial aspiration pneumonia are more likely to have a mixed aerobic-anaerobic infection, in which the aerobic component (gram-negative bacilli) predominates.

Aerobic organisms:

Anaerobic organisms: