Rapid Detection of Bacillus anthracis Bloodstream Infections by Use of a Novel Assay in the GeneXpert System

摘要

Bacillus anthracis, the causative pathogen of anthrax, is a tier 1 select agent, meaning that it has a great risk for deliberate misuse and a significant potential for causing mass casualties and other severe consequences (https://www.selectagents.gov/history.html) (1). Pulmonary or inhalational anthrax occurs when B. anthracis spores are inhaled into bronchioles and alveoli and then transported by macrophages to mediastinal lymph nodes, where the spores germinate. Pulmonary anthrax induces a hemorrhagic mediastinitis that can lead to bacteremia and meningitis. The mortality rate for untreated pulmonary anthrax is 50 to 90% (2, 3). The anthrax attacks of 2001, introduced by letters to unsuspecting individuals, resulted in 22 cases of anthrax, half of them pulmonary and the other half resulting in cutaneous infections. Five out of 11 victims with pulmonary disease died (3, 4). A recent anthrax outbreak in Siberia led to the hospitalization of approximately 100 suspected cases, including children, and killed a 12-year-old boy (5). Anthrax can progress quickly after exposure to spores, and rapid diagnosis and treatment are critical components of defense against anthrax exposure. However, with existing methodologies, it currently takes between 12 h and 5 days to detect B. anthracis in blood through blood culture, which is considered to be the gold standard (6, 7). Nucleic acid amplification (NAA) tests are potentially faster and more sensitive than pathogen detection using blood culture (8). However, most commercial assays for B. anthracis, including the GeneXpert BA-plex system (9), are made to test powders, surface contamination, or environmental contamination (9–13). Currently available NAA assays cannot rapidly detect B. anthracis from uncultured patient blood samples with sufficient sensitivity to detect early sepsis (8, 14). Furthermore, the majority of currently available anthrax detection technologies require manual DNA extraction steps that increase assay time and complexity. In contrast, the GeneXpert system detects pathogens using a simple plastic cartridge that integrates sample processing and target detection and requires few manual steps to perform (9, 15, 16). A GeneXpert-based test for B. anthracis spores has been used in the U.S. Post Office since 2004 (9, 17); however, to date, this technology has not been adapted to directly test human specimens for anthrax.