Listeria monocytogenes

Gram Stain

• Gram positive bacilli regular short (singly or short chains) (facultative anaerobic)

Clinical Significance

This organism is widely distributed in nature especially soil and decaying vegetable matter.

It is a cause of meningitis, encephalitis, brain abscesses, bacteremia/septicemia, lymphadenitis, empyema, myocarditis, endocarditis (native/prosthetic valves), and septic arthritis (especially if rheumatoid arthritis) in immunocompromised/debilitated patients.

It is also associated with perinatal infections (maternal fever/neonatal sepsis +/- meningitis).

Usual Susceptibility Pattern

This organism is susceptible to penicillin and ampicillin (ampicillin tolerance has been reported). In serious infections, addition of TMP/SMX has been recommended.

Although it tests susceptible to meropenem, clinical failures have been documented.

This organism is resistant to cephalosporins and quinolones (moxifloxacin appears to have some activity but clinical efficacy has not been established).

Vancomycin is associated with poor clinical outcomes.

Linezolid exhibits bacteriostatic activity and has been used as salvage therapy.

Daptomycin is not recommended.

Prolonged therapy (3 weeks) is recommended.