Listeria monocytogenes

Question 1

What are the bacteriological features of Listeria (Listeria monocytogenes)?

Answer 1

• Gram positive bacillus, non-sporing, aerobe/facultative anaerobe
• Exhibits characteristic tumbling motility @ 25oC
• Isolated from soil/water/vegetation, faeces of infected mammals, birds etc.
• Grows in wide range of temperatures (2-37oC) (=can grow in refrigerated foods)
• Infection incidence peaks in warmer months

Question 2

What are the transmission routes of Listeria monocytogenes?

Answer 2

• May be transmitted by animal contact, drinking contaminated milk, eating certain soft cheeses, pate etc.
• Local epidemics have been associated with consumption of contaminated milk, soft cheese, undercooked meat, unwashed vegetables etc.
• Vertical transmission from mother to foetus

Question 3

What is the pathogenesis of Listeria monocytogenes?

Answer 3

• After ingestion L monocytogenes may cross the mucosal barrier & disseminate
• Listeria can survive and multiply within macrophages
• Can spread from cell to cell without exposing itself to extracellular environment
• Need a T cell response to activate infected cells and produce intracellular killing.

Question 4

What is the clinical presentation of Listeriosis?

Answer 4

• Most infections asymptomatic or cause a mild influenza-like illness/ diarrhoea in healthy adults

1. Occupational exposure (farmers, vets)
2. Opportunistic pathogen, affects “at risk” groups
   – Pregnant women,
   – Neonates,
   – Immunosuppression

Question 5

What is the occupational exposure of Listeriosis?

Answer 5

– Farmers, vets, butchers
– Influenza-like illness / gastroenteritis
– Diarrhoea, fever, chills, headache

Question 6

What is the opportunistic infection of Listeriosis?

Answer 6

Pregnancy:    Clinical presentation
•	This may be divided into stages
•	Perinatal listeriosis:
–	“Influenza-like illness” – usually 3rd trimester. Fever, myalgia, backache, headaches, arthralgias
–	Perinatal infection may result in 
•	Miscarriage or intrauterine death
•	Premature labour and infected infant
•	Neonatal listeriosis

Question 7

What is the early onset neonatal Listeria infection?

Answer 7

• In the first 2 days of life
– Organism probably acquired in-utero (ascending infection)
– Bloodstream infection +/- pneumonia or cardiopulmonary distress, hepatosplenomegaly, abscesses, CNS involvement
– High Mortality (40 to 50%)

Question 8

What is the late onset neonatal Listeria infection?

Answer 8

• > 2 days (typically >5 days) old
– Organism may be acquired during birth from the maternal genital tract
– More common than early onset infection
– Meningitis or meningoencephalitis are more common than bloodstream infection
– Mortality ~ 12%

Question 9

What are other at-risk groups of Listeriosis?

Answer 9

Immunocompromised patients:
•	Immunosuppressive therapy
–	(e.g., transplant recipient)
•	Lymphoma
•	Splenectomy
•	May present with:
Pneumonia       Meningoencephalitis

Question 10

What is the diagnosis of Listeriosis?

Answer 10

•	Mother:	
–	Blood cultures, urine/stool 
–	High vaginal swab/placenta
•	Neonate:	
–	Blood culture
–	CSF, meconium
•	Adults:
–	Blood culture/ CSF

Question 11

What is the treatment of Listeriosis?

Answer 11

• High dose ampicillin/ amoxicillin with an aminoglycoside e.g., gentamicin (for synergy)
• Resistant to cephalosporins

Question 12

What are the methods of prevention of Listeriosis?

Answer 12

• People at high-risk should avoid raw/partially cooked foods of animal origin, pate, soft cheeses, unwashed vegetables