What is the microbiology of liver abscess?

Identify risk factors and mechanism of infection



A 29-year-old woman with chronic urticaria, previously on omalizumab, presented with 2 weeks of abdominal pain and fever. She had traveled to Nicaragua within the past 10 months. CT showed a 6 x 5 cm liver abscess. Entamoeba histolytica was detected by stool polymerase chain reaction, and E. histolytica antibody was positive. The abscess was drained, and she completed a 10-day course of metronidazole followed by a 7-day course of paromomycin.

Brief overview

Bacterial, parasitic, and fungal organisms can cause liver abscess. Worldwide, bacteria are the most common cause of liver abscess. Infection is usually polymicrobial, though Klebsiella and the Streptococcus milleri group are the most common organisms identified.

Entamoeba histolytica is the most frequent cause of amoebic liver abscess and should be strongly considered in a returning traveler, visitor from another country, or those on monoclonal antibody therapy directed against IgE such as omalizumab. Candida species are the most common fungal etiology; an example being hepatosplenic candidiasis in hematologic malignancies.

This iodine-stained photomicrograph reveals the presence of an Entamoeba histolytica amoebic parasitic cyst. CDC/ Dr. Mae Melvin

This iodine-stained photomicrograph reveals the presence of an Entamoeba histolytica amoebic parasitic cyst.

Liver abscesses not only cause local symptoms but can cause sepsis and can rupture into the pleural and peritoneal space. The aim of treatment is to control the local response, prevent rupture, and eradicate the pathogen.

Overview of the data

Pyogenic liver abscess. A variety of bacteria have been isolated from pyogenic liver abscesses (PLA) because of differences in mechanism of infection (such as biliary tract interventions, postoperative complications, and hematogenous spread), immunocompromised states, and geographical variation. The literature is not robust for pyogenic liver abscesses, and the microbiology isolated via epidemiologic studies are confounded by the mechanism of infection and thus difficult to generalize.

Initially, the Enterobacteriaceae including Klebsiella pneumoniae and Escherichia coli were the most common cause of PLA in the United States. The emergence of improved culturing techniques, which has improved the yield of facultative anaerobes such as the Streptococcus milleri (also known as Streptococcus anginosus) group, has led to an increased incidence and wider assortment of bacteria, with a more recent study of 38 patients in the Cleveland Clinic system showing that about half of the PLA were polymicrobial with the predominant organism when monomicrobial being of the Strep milleri group in 9/22 patients (Chemaly et al.).

Biliary tract disease, whether from choledocholithiasis, stricture, or malignant obstruction is the most common etiology of PLA. Much of the PLA-focused literature is from Asia, where Klebsiella is more commonly a cause of liver abscess. In a study of 248 Taiwanese patients with PLA, Klebsiella was responsible for 69% of PLA (Yang et al.). In a study of 79 patients hospitalized in New York, Klebsiella was the most common bacteria isolated, although more than half of the patients studied were Asian, and Klebsiella was more common among Asian patients than the other groups studied. An 8-year analysis of patients admitted to a University Hospital in Taiwan with cryptogenic PLA showed that the etiology was Klebsiella in 46/52 patients (Chen et al.). Most patients with Klebsiella liver abscess have documented bacteremia.


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