Induced Prophages Detected from the Hemoculture: a Biomarker for Infection

Bacteriophages (phages), viruses that infect bacteria, are found in abundance not only in the environment but also in the human body. The use of phages for the diagnosis of melioidosis, a tropical infectious disease caused by , is emerging as a promising novel approach, but our understanding of conditions under which prophages can be induced remains limited. Here, we first demonstrated the isolation of phages from the hemocultures of melioidosis patients. The -positive hemoculture bottles were filtered to remove bacteria, and then phages were isolated and purified by spot and double agar overlay plaque assays. Forty blood samples (hemoculture-confirmed melioidosis) were tested, and phages were found in 30% of the samples. Transmission electron microscopy and genome analysis of the isolated phages, vB_HM387 and vB_HM795, showed that both phages are Myoviruses. These two phages were stable at a pH of 5-7 and temperatures of 25-37°C, suggesting their ability to survive in human blood. The genome sizes of vB_HM387 and vB_HM795 are 36.3 and 44.0 kb, respectively. A phylogenetic analysis indicated that vB_HM387 has homologs, but vB_HM795 is a novel Myovirus, suggesting the heterogeneity of phages in melioidosis patients. The key finding that phages could be isolated from the blood of melioidosis patients highlights the potential application of phage-based assays by detecting phages in blood as a pathogen-derived biomarker of infection.