Listeria monocytogenes is a gram-positive, non–spore-forming aerobic rod

-Oral, transplacental and birth canal transmission can occur 

-Most common food sources include dairy, processed meats, hot dogs, soft cheeses and fruits 

-infections are common in pregnant women (esp in the third trimester), neonates, immunocompromised patients, and elderly patients 

-Fetal infection can result in either stillbirth or early death 

Symptoms & Signs 

Normal hosts: self-limited illness with fever, gastroenteritis 

Pregnant women: relatively mild, fever, chills, and aches 

Newborn infection: fever, diarrhea, respiratory distress, papular rash, hepatosplenomegaly, pneumonia, sepsis, meningitis  

In utero infection: sepsis, widespread abscesses and granulomas in multiple internal organs

Diagnosis 

Labs: elevated WBC with a predominance of polymorphonuclear neutrophils and monocytes 

Diagnosis of listeriosis is by culture of blood, cerebrospinal fluid (CSF), or focal lesions

Cultures show gram positive rods that exhibit characteristic tumbling motility

Chief pathologic feature in neonatal sepsis: miliary granulomatosis with microabscesses in liver, spleen, CNS, lung, and bowel

Treatment 

Antibiotics: ampicillin (drug of choice), gentamicin, trimethoprim-sulfamethoxazole

Listeria are uniformly resistant to all cephalosporins 

Prevention

At-risk patients (eg, pregnant women) should avoid unpasteurized milk products