Endocarditis Due to Listeria monocytogenes in an Academic Teaching Hospital: Case Report

Abstract

Endocarditis is a rare but serious infection observed in about 8% of patients infected with Listeria monocytogenes. According to Antolin and others, there had been 68 case reports up to 2008. The reported mortality rate for this infection, which has ranged from 37% to 50%, has decreased appreciably in recent decades. Listeria monocytogenes is an aerobic, gram-positive coccobacillus. The organism may be isolated from soil, dust, animal feed, water, sewage, and the tissues or fluids of almost any type of animal. It is frequently found in raw and unprocessed food products such as meats, vegetables, and dairy and delicatessen products that are intended for consumption without further heating. Reported outbreaks of this organism have been associated with contaminated rice salad, coleslaw, soft cheese, hot dogs, shrimp, chocolate milk, and corn salad. In the summer of 2008, an outbreak of listeriosis associated with one company’s meat products occurred across 7 provinces in Canada; a total of 56 people were affected, and at least 21 people died. Although L monocytogenes is a transient colonizer in the human gastrointestinal tract, infection does not occur unless host factors promoting invasive disease are present or the amount of bacteria delivered to the intestinal tract is great enough to overwhelm local gastrointestinal barriers. This organism can produce severe sepsis, meningoencephalitis, focal infections in infants and adults, and death, as illustrated by the Canadian outbreak. Listeria monocytogenes penetrates into a wide range of host cells (phagocytes, epithelial cells, and parenchymal cells) through phagocytosis or induced phagocytosis. A cluster of virulence genes enables this pathogenic bacterium to evade the phagocytic vacuoles, and it resides and multiplies within the cytoplasm. Once the organisms reach the cytoplasm, the bacteria wrap themselves in a sheet of actin filaments derived from the host cell, forming a comet-like structure. In essence, the bacteria become hidden within the host’s cells, protected from the host’s humoral defence mechanisms and from anti biotics in the extracellular fluid. In this article, we describe a case of endocarditis caused by L monocytogenes and discuss the features of this disease in relation to effective antibiotic therapy.