Microbiology: small, fac anaerobic, non-sporulating,  gram pos; grows on blood agar, chracteristic tumbling motility at 25C; grows well at refrigerator temp; often misidentified as diphtheroids, strep, enterococci.  L monocytogenes is the only species pathogenic for humans. 


Epidemiology: Found in decaying vegetation, fecal flora of many mammals.  Isolated from stool of 5% healthy adults.  Recovered from raw veggies, raw milk, fish, poultry, and meats (including deli meats).  Annual infection rate 7.4/million.  Rates highest among infants <1, adults >60.  Pregnant women 27%,  70% non-perinatal have hematologic malig, HIV, organ trx, steroids.  Foodbourne outbreaks linked to coleslaw, milk, soft cheeses, turkey franks, alfalfa tablets. 


Clinical settings in which to suspect listeria:

1.   Neonatal sepsis or meningitis

2.   Meningitis or parenchymal brain infection in hematologic malig, AIDS, organ trx, steroids:  most common cause in these settings.

3.   Meningitis in adults >50y:  2nd most common cause.

4.   Simult infection of meninges and parenchyma

5.   Subcortical brain abcess

6.   Fever in pregnancy

7.      “Diphtheroids” on GS or bld, CSF cx. 

8.      Foodbourne outbreaks of gastroenteritis in which routine cxs are neg. 


Pathogenesis: Infection begins with ingestion.  Incubation period 11-70 days (mean 31).  Crosses mucosal barrier into bloodstream, disseminates with predilection for CNS and placenta.  Phagocytosed by endothelial cells, escapes phagosomes into cytoplasm (listeriolysin O), replicates, forms pseudopod-like projections in cell membrane (Act A) which are phagocytosed by other cells.  Iron is important virulence factor, infxn assoc w/ iron overload such as Hemochromatosis. 

Immunity: cell-mediated.  Antibodies do not confer resistance.  Non CD4/CD8 cells responsible for immunity. 





Clinical syndromes:

1.   In pregnancy- proliferates in placenta.  CNS spread rare.  Manifests as acute febrile illness with myalgias, arthralgias, headache, and backache.  Usually in 3rd trimester (corresponds with major decine in cell-mediated immunity at 26-30 wks.  22% result in stillbirth or neonatal death, premature labor common. 

2.   Neonatal infection- may occur in utero(granulomatosis infantiseptica), or intrapartum. 

3.   CNS infection- tropic for brain (brainstem in particular) and meninges.  5th most common cause of meningitis (H flu, S pneumo, N meningit, GBS), but highest assoc mortality.  Brain stem infxn: prodrome fever, HA, N/V f/b assym CN deficits, cerebellar signs, hemiparesis/hemisensory deficits. 

Unique clinical features of listeria meningitis:

a.          acute or subacute presentation

b.          nuchal rigidity in only 15-20%

c.          mvmt d/o common (ataxia, tremors, myoclonus) in 15-20%

d.          Sz 25%

e.          Fluctuating MS

f.          Bld cx + in 75%5)

g.          CSF: GS neg 40%, glucose level nml >60%, mononuclear cells predominate in 1/3.

4.      Endocarditis- prosthetic and native valves. 


Dx: standard microbiologic techniques. 


1.   Amp (200mg/kg Q4) + Gent (5mg/kg Q8)- 3wks for meningitis, 6wks for brain abcess, 4-6 wks for endocarditis, 2 wks for bacteremia

2.   Bactrim- best alternative single agent.

3.   PCN, Imipenim, Vanco probably OK. 

4.      Chloramphenicol, erythro, tetracycline, quinolones no good. 


Clinical Infectious Diseases 1997; 24: 1-11