Isolated hair bacteria reveal different isolation possibilities under various conditions

Microorganisms are assumed to inhabit various environments and organisms, including the human body. The presence of more than 700 bacterial species on scalp hair has been reported through rRNA gene amplicon analysis. However, the biological properties of bacteria on the scalp hair (hair bacteria) and their functions are poorly understood as few hair bacteria have been isolated from hair in previous studies. This study aimed to isolate hair bacteria using standard media under 24 different conditions (including medium components, component concentrations, gelling agents, and atmospheric environments). Furthermore, we evaluated the possibility of isolating strains under these isolation conditions and examined the carbon metabolic ability of several predominantly isolated strains. A total of 63 bacterial species belonging to 27 genera were isolated from hair under 24 isolation conditions. The predominant bacterial species isolated from human hair in this study showed different carbon metabolic capabilities than those of the reference strains. In addition, isolation possibility was newly proposed to systematically evaluate the number of isolation conditions that could cultivate a bacterial species. Based on isolation possibility, the isolates were categorized into groups with a high number of isolation conditions (e.g., ≥25%; such as Staphylococcus) and those with a low number (e.g., ≤25%; such as Brachybacterium). These findings indicate the existence of easily isolated microorganisms and difficultly isolated microorganism from human hair.