• Small Gram-positive rod.
  • Isolated from environmental sources such as water, sewerage and foodstuffs.
  • Grows on routine media.
    • Micro labs may occasionally confuse as a contaminant, reporting organisms as diphtheroids.
  • Main human pathogen: Listeria monocytogenes.
    • Other: L. ivanovii (rare)
  • Ability to grow in wide range of temperatures 4–37°C likely accounts for hardiness and ability for refrigerated foods to cause infection.


  • Risk factors:
    • Age < 1 month and > 60 yrs
    • Pregnancy
    • Hematologic malignancy
    • AIDS
    • Organ transplant
    • Steroid treatment
  • Epidemics: foodborne outbreaks, most common with milk, soft cheese, smoked fish, hot dogs, turkey deli meats, cantaloupes, cucumbers.
  • Cause of meningitis, especially in compromised host (organ transplants, AIDS [CD4 < 200/mm3], cancer therapy, steroids, lymphoma) and persons >50yrs; relatively rare in AIDS.
  • Other susceptible hosts: infants (< 1 month), pregnant women, elderly (>60 yrs)
  • Dx:
    • Culture from normally sterile site (CSF, blood, etc).
    • Serology (listeriolysin O antibody): helpful in the investigation of foodborne outbreaks.




  • Principles: most common serious forms of infection with
  • Meningitis
  • Bacteremia: use meningitis options x 2wks.
  • Brain abscess, rhomboencephalitis or cerebritis: use meningitis options x 4-6wks.
  • Gastroenteritis: as stool not typically cultured for this organism, most often not diagnosed and usually no antibiotic treatment.

General Prevention Measures

  • Thoroughly cook animal source food.
  • Thoroughly wash raw vegetables.
  • Avoid unpasteurized milk and food from unpasteurized milk.
    • Also, smoked seafoods, meat spreads, pâtés, cold cuts, hot dogs
  • Wash hands, utensils and cutting boards used with uncooked food.
  • Keep ready-to-eat food cold.
  • Person-to-person transmission is not a risk (except pregnant woman to unborn infant)

Prevention: High Risk Persons

  • High-risk groups: pregnant women, CMI compromise (organ transplants, chronic steroids, infliximab or other TNF-antagonists, cancer chemotherapy, elderly.
    • Avoid soft cheeses: Mexican style, feta, brie, Camembert, blue cheese.
    • Leftover foods and ready-to-eat foods should served only steaming hot.
    • May wish to avoid food from delicatessen counters.
  • Pregnancy: for those known to have been exposed to Listeria, recommendations based largely on expert opinion (ACOG 2014[1]).
    • 13x higher risk for developing listeriosis than general population
    • Recommendations based on state of pregnant patient:
      • Asymptomatic: no testing or treatment. Instruct to report sx of fever, GI disease, etc. within next 2 months as at risk.
      • Mild symptoms, afebrile: no data to guide
        • Perform blood culture OR
        • Follow expectantly including fetal well-being--testing if symptoms worsen
        • Treatment: no clear consensus, either observe pending test results or begin empiric therapy (IV ampicillin)
      • Fever (T > 38.1°C /100.6°F with our without symptoms consistent with listeriosis
        • Perform simultaneous testing and treatment (IV ampicillin)
        • Test: blood, placental cultures (if delivery occurs)
  • TMP/SMX given to HIV infected patients to prevent PCP is thought to reduce Listeria risk.
  • Routine stool culture for assessment: not recommended as may be frequently seen with fecal carriage/shedding without causing illness.

Selected Drug Comments




The drug of choice by virtually all authorities in the field - based on in vitro data, animal models and a small clinical experience. The evidence that it is superior to penicillin is not convincing. The evidence that it is better than cephalosporins is very convincing. Ampicillin is allegedly bacteriostatic to Listeria and this is the reason many advocate the addition of an aminoglycoside.


Cephalosporins do not have activity against Listeria. This is important to remember in the empiric selection of drugs for pyogenic meningitis.


Ceftriaxone/cefotaxime. Cephalosporins do not have activity against Listeria. This is important to remember in the empiric selection of drugs for pyogenic meningitis.


Often added to ampicillin to achieve synergy. It is not clear that this is necessary.


Good in vitro activity, but very limited clinical experience and dangerous for monotherapy of any infection. OK to add.


TMP/SMX The preferred drug in patients who cannot take ampicillin. This combination has good in vitro activity and is bactericidal vs Listeria.


There are clinical successes; there are also patients who developed Listeria meningitis while receiving vancomycin.


  • Major risks: 1) compromised CMI (steroids, transplants, cancer chemo Rx); 2) third-trimester pregnancy; 3) occasional cases: age >50yrs, diabetes, ulcerative colitis, antacids, cirrhosis.
  • Mortality: meningitis 20%; endocarditis 50%; pregnant women 20% stillbirths.
  • Major source: ingestion unpasteurized milk, fresh cheeses (especially imported, soft, ripened), ice cream, raw vegetables, fermented raw sausages, raw/cooked poultry, raw meats, smoked fish, deli meats and hot dogs.
  • Think Listeria when: "diphtheroids" in CSF, meningitis in compromised host or >50 yrs, fever, third trimester, foodborne outbreak w/ negative cultures.

Basis for recommendation

  1. Committee on Obstetric Practice, American College of Obstetricians and Gynecologists: Committee Opinion No. 614: Management of pregnant women with presumptive exposure to Listeria monocytogenes. Obstet Gynecol 124:1241, 2014  [PMID:25411758]

    Comment: Recommendations regarding pregnant women who are exposed to Listeria. Presumptive testing and treatment recommended.

  2. Tunkel AR et al: Practice guidelines for the management of bacterial meningitis. Clin Infect Dis 39:1267, 2004  [PMID:15494903]

    Comment: IDSA Guidelines for meningitis: For L. monocytogenesmeningitis - preferred is Penicillin G or ampicillin (consider adding gentamicin ). Alternatives are TMP-SMX or meropenem . Doses: Amp - 12gm/d, gent 5mg/kg/d, TMP-SMX 10-20mg/kg (TMP)/d.

  3. Rados C: Preventing Listeria contamination in foods. FDA Consum 38:10, 2004 Jan-Feb  [PMID:15032197]

    Comment: Keep ready-to-eat food cold

  4. No authors listed; Medical Letter, May 14, 2013;pg 7.


  1. Fox EM, Wall PG, Fanning S: Control of Listeria species food safety at a poultry food production facility. Food Microbiol 51:81, 2015  [PMID:26187831]

    Comment: Pulsed-field gel electrophoresis was used to facilitate control of Listeria in a food production facility.

  2. Heiman KE et al: Multistate outbreak of listeriosis caused by imported cheese and evidence of cross-contamination of other cheeses, USA, 2012. Epidemiol Infect Jun 30  [PMID:26122394]

    Comment: Outbreak of listeriosis from contaminated cheese from multiple sources. Molecular analysis connected multiple cheese sources possibly due to cross-contamination.

  3. Girard D et al: Pregnancy-related listeriosis in France, 1984 to 2011, with a focus on 606 cases from 1999 to 2011. Euro Surveill 19:, 2014  [PMID:25306879]

    Comment: The review from France includes listerosis in 606 listeria infections. Outcome showed fetal loss in 27% and live-born neonatal listerosis in 58%, and premature birth in 14%.

  4. Bodro M, Paterson DL: Listeriosis in patients receiving biologic therapies. Eur J Clin Microbiol Infect Dis 32:1225, 2013  [PMID:23568606]

    Comment: Major risk was infliximab based on FDA records showing 266 cases of listeriosis in patients getting biologies. Mortality rates: 11-27%.
    Rating: Important

  5. Centers for Disease Control and Prevention (CDC): Vital signs: Listeria illnesses, deaths, and outbreaks--United States, 2009-2011. MMWR Morb Mortal Wkly Rep 62:448, 2013  [PMID:23739339]

    Comment: Review of reported listeria to the CDC for 2009-2011 (n=1,651) 14% pregnant, 74% had immunosuppression from malignancy or treatment. Soft cheese was the most common source.
    Rating: Important

  6. Goulet V et al: Incidence of listeriosis and related mortality among groups at risk of acquiring listeriosis. Clin Infect Dis 54:652, 2012  [PMID:22157172]

    Comment: The review was 1959 cases of listerosis in France from 2001-2008. Risk was >1000 fold with chronic lymphocytic leukemia; risk was 100-1000 fold with liver cancer, myeloma, acute leukemia, giant cell arteritis, organ transplantation and pregnancy.

  7. Charlier C et al: Listeria monocytogenes-associated joint and bone infections: a study of 43 consecutive cases. Clin Infect Dis 54:240, 2012  [PMID:22100574]

    Comment: Authors review 43 cases of L. monocytogenes bone and joint infections. The most common treatment was amoxicillin (80%) with aminoglycosides (48%) for a median of 15 weeks. Prosthetic joints accounted for 36 (84%) at a median of 9 years post insertion.

  8. Kupferschmidt K: Epidemiology. Outbreak detectives embrace the genome era. Science 333:1818, 2011  [PMID:21960605]

    Comment: Review of gene sequence during outbreak investigation.
    Rating: Important

  9. Clauss HE, Lorber B: Central nervous system infection with Listeria monocytogenes. Curr Infect Dis Rep 10:300, 2008  [PMID:18765103]

    Comment: Review highlights: Listeria is the major cause of bacterial meningitis in persons >50 yrs (20%), neonates (20%) and patients with defective cell mediated immunity but not AIDS. Ampicillin is the preferred drug. Prevention: Avoid unpasteurized milk and soft cheese, deli-style meats and poultry products.

  10. Cabedo L, Picart i Barrot L, Teixidó i Canelles A: Prevalence of Listeria monocytogenes and Salmonella in ready-to-eat food in Catalonia, Spain. J Food Prot 71:855, 2008  [PMID:18468047]

    Comment: Cultures of 1,379 ready-to-eat products showed Listeria in the following: frozen Atlantic bonito fish pies -- 20%, smoked salmon -- 8%, pork luncheon meat -- 11%, chicken croquettes -- 6%, cured, dried sausage -- 17% and cook turkey breast samples -- 20%.

  11. Varma JK et al: Listeria monocytogenes infection from foods prepared in a commercial establishment: a case-control study of potential sources of sporadic illness in the United States. Clin Infect Dis 44:521, 2007  [PMID:17243054]

    Comment: CDC review of non-outbreak cases in 249 patients. New food sources -- melons and hummus.
    Rating: Important

  12. Brouwer MC et al: Community-acquired Listeria monocytogenes meningitis in adults. Clin Infect Dis 43:1233, 2006  [PMID:17051485]

    Comment: Review of 30 cases of Listeria meningitis - all were immunocompromised or >50yrs. Gram stain of CSF was pos in 7/25 (28%), Mortality 5/30 (17%).
    Rating: Important

  13. Schlech WF et al: Does sporadic Listeria gastroenteritis exist? A 2-year population-based survey in Nova Scotia, Canada. Clin Infect Dis 41:778, 2005  [PMID:16107973]

    Comment: Review 7,775 stools submitted for culture - 17 yielded L. monocytogenes. PFGE showed no clusters. Cases tended to have pre-existing GI conditions. Recommendation is to not culture stool for Listeria.

  14. Ooi ST, Lorber B: Gastroenteritis due to Listeria monocytogenes. Clin Infect Dis 40:1327, 2005  [PMID:15825036]

    Comment: Review of 7 outbreaks of foodborne gastroenteritis due to L. monocytogenes . Symptoms occur 24 hrs after ingestion of large inoculum with fever, watery diarrhea, nausea, headache and arthralgias. Most cases clear within 2 days and don't require antibiotics; consider ampicillin or TMP-SMX in susceptible hosts.

  15. Van Kessel JS et al: Prevalence of Salmonellae, Listeria monocytogenes, and fecal coliforms in bulk tank milk on US dairies. J Dairy Sci 87:2822, 2004  [PMID:15375040]

    Comment: Analysis of 861 bulk tank milk from 21 states showed Listeria in 56 (6.5%); of these 93% were serotypes commonly found in human disease.

  16. Safdar A, Armstrong D: Antimicrobial activities against 84 Listeria monocytogenes isolates from patients with systemic listeriosis at a comprehensive cancer center (1955-1997). J Clin Microbiol 41:483, 2003  [PMID:12517901]

    Comment: Data were provided from Sloan-Kettering Hospital for 84 isolates. All were sensitive to cefazolin, rifampin, TMP-SMX, vancomycin, imipenem and ciprofloxacin; nearly all strains (>97%) were sensitive to penicillin, gentamicin, tetracycline and erythromycin. These results may be deceptive due to intracellular location. The best results in animal studies are penicillin & gentamicin. Cipro looks good in vitro but show no effect intracellularly.

  17. Siegman-Igra Y et al: Listeria monocytogenes infection in Israel and review of cases worldwide. Emerg Infect Dis 8:305, 2002  [PMID:11927029]

    Comment: Review of 161 cases and 1808 reported cases. Immunosuppressed 74%, CNS involved 47%, bacteremia 48%, focal disease 4%. Mortality was 36%.

  18. Lecuit M et al: A transgenic model for listeriosis: role of internalin in crossing the intestinal barrier. Science 292:1722, 2001  [PMID:11387478]

    Comment: The authors describe A NEW VIRULENCE FACTOR for L. monocytogenes - a surface protein that binds to E - cadherin of enterocytes which is a necessary step for translocation.

  19. American Medical Association et al: Diagnosis and management of foodborne illnesses: a primer for physicians. MMWR Recomm Rep 50:1, 2001  [PMID:11214980]

    Comment: L. monocytogenes GASTROENTERITIS - incubation period 9-48hrs (2-6wks for invasive disease). Sx are fever, myalgias, nausea & diarrhea. Pregnant women may have mild illness that leads to premature delivery or stillbirth; immunosuppressed pts may get bacteremia or meningitis. Dx - culture blood & CSF; stool not useful due to asymptomatic carriage. Serology to listeriolysin O useful in outbreak.
    Rating: Important

  20. Dalton CB et al: An outbreak of gastroenteritis and fever due to Listeria monocytogenes in milk. N Engl J Med 336:100, 1997  [PMID:8988887]

    Comment: Outbreak of L. monocytogenes as cause of FOODBORNE OUTBREAK among 60 attendees at a Holstein cow show ascribed to post-pasteurization contamination of chocolate milk. Attack rate was 75%; symptoms were diarrhea 79%, fever 72% and chills 65%. The median incubation period was 20hrs and median duration of diarrhea 42hrs. Contamination level was up to 3x10" bacteria/person.

  21. Armstrong RW, Fung PC: Brainstem encephalitis (rhombencephalitis) due to Listeria monocytogenes: case report and review. Clin Infect Dis 16:689, 1993  [PMID:8507761]

    Comment: This is a BRAINSTEM ENCEPHALITIS which is an unusual CNS complication of Listeria that occurs in previously healthy adults. It is analogous to "circling disease" in sheep. Clinical features are biphasic: fever, headache, nausea & vomiting, lasting several days and then cerebellar signs: cranial nerve deficits & hemiparesis. CSF shows increased protein & WBC; culture is positive in 50%. MRI shows rhomboencephalitis.

  22. Durand ML et al: Acute bacterial meningitis in adults. A review of 493 episodes. N Engl J Med 328:21, 1993  [PMID:8416268]

    Comment: This review showed L. monocytogenes accounted for 29 (11%) of 253 cases of community-acquired MENINGITIS and had a mortality rate of 21%.

  23. Kalstone C: Successful antepartum treatment of listeriosis. Am J Obstet Gynecol 164:57, 1991  [PMID:1986626]

    Comment: Infection in PREGNANCY usually occurs in 3rd trimester, 22% result in stillbirth, susceptibility presumed to be due to compromised CMI of pregnancy, maternal meningitis is rare & early therapy is often effective in protecting the infant.

  24. Gellin BG, Broome CV: Listeriosis. JAMA 261:1313, 1989  [PMID:2492614]

    Comment: Review includes aspects of this pathogen causing meningitis, encephalitis, brain abscess & endocarditis.

  25. Gallagher PG, Watanakunakorn C: Listeria monocytogenes endocarditis: a review of the literature 1950-1986. Scand J Infect Dis 20:359, 1988  [PMID:3057615]

    Comment: Listeria accounts for about 7% of ENDOCARDITIS cases in adults, usually in patients with pre-existing valve disease. The mortality rate in this review was 48%.

  26. Lorber B; Listeria monocytogenes; Chapter 195 IN: Principles & Practice of Infect Dis, Mandell G, Bennett J & Dolin R. 5th Ed, Churchill Livingston; pp. 2208;

    Comment: AMPICILLIN is regarded as the drug of choice according to: 1)Gellin BG, et al JAMA 1989;261:1313; 2)Neiman R & Lorber B, RID 1980;2:207; 3) Cherubin CE, et al, RID 1991;13:1108; 4)Laretter A, et al, NEJM 1971;285:598; 5)Scheld M, et al, RID 1983;5:S593. The author (B Lorber) considers penicillin to be equally effective. Not effective - chloroamphenicol, cephalosporins.

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Last updated: May 1, 2016


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