Properties

Pathogenesis

Clinical findings

Laboratory diagnosis

Treatment & Prevention

Species most often involved in human infections.

K.pneumoniae has a very large capsule which gives its colonies a striking mucoid appearance.

S.marcescens produces red-pigmented colonies.

Predisposing conditions to K.pneumoniae infections:

- advanced age

- chronic respiratory disease

- diabetes

- alcoholism

K.pneumoniae is carried in the respiratory tracts of about 10% of normal people, who are prone to pneumonia if host defenses are lowered.

Enterobacter and Serratia infections are related to hospitalization, especially to invasive procedures such as intravenous catheterization, respiratory intubation, & urinary tract manipulations.

Diseases:

- urinary tract infections

- pneumonia

- bacteremia & secondary spread to other areas such as the meninges.

Pneumonia caused by Klebsiella produces a thick, bloody sputum & can progress to necrosis & abscess formation.

Organisms of this group produce lactose-fermenting (colored) colonies on differential agar such as MacConkey’s or EMB.

Serratia, a late lactose fermenter, can give a negative reaction.

These organisms are separated by the use of biochemical tests.

An aminoglycoside, e.g. gentamicine & a cephalosporin, e.g. cefotaxime, are used empirically until the results of the testing are known.

Prevention:

- changing the site of intravenous catheters.

- removing urinary catheters when they are no longer needed.

- taking proper care of respiratory therapy devices.

No vaccine.