Sources and culture methods for the isolation and cultivation of Coxiella burnetii

Abstract

Coxiella burnetii, the bacterium responsible for Q fever, is a highly infectious, environmentally resilient, and aerosol-transmissible zoonotic pathogen. While molecular and serological assays are the primary tools for routine diagnosis, isolating viable C. burnetii remains crucial for comprehensive pathogen characterization, including whole-genome sequencing, phenotypic analysis, antimicrobial susceptibility testing, vaccine development, and diagnostic assay validation. This review examines the literature on two key factors for successful C. burnetii recovery: selecting an appropriate specimen source and choosing a compatible cultivation platform. Viable organisms can be recovered from human clinical specimens, such as acute-phase blood and tissues from focal chronic infections (e.g., cardiac valves), provided that bacterial burden and viability are maintained. Animal-derived specimens, especially reproductive tissues, placental material, fetal tissues, milk, urine, feces, and genital secretions, are vital sources for veterinary investigations and zoonotic risk assessment. However, contamination with other microorganisms often complicates recovery from these samples. Tick-derived and environmental samples can broaden epidemiological insights, but their interpretation requires caution, as Coxiella-like endosymbionts and low viable bacterial burdens may hinder culture recovery. Regarding culture platforms, mammalian cell culture, particularly shell vial-based systems, is the most widely applicable method for primary isolation. Embryonated chicken eggs and animal inoculation are still valuable for biological amplification or generating phase variants. Furthermore, host cell-free axenic media have revolutionized C. burnetii propagation, metabolic analysis, and genetic studies. Successful isolation hinges on several factors: specimen type, processing, storage conditions, bacterial viability, strain characteristics, and compatibility with the chosen culture system. Future advancements should incorporate viability-based molecular preselection, high-throughput image-based culture screening, optimized cell-line selection, axenic media with broader strain permissiveness, and standardized reporting of culture attempts. These improvements will expand available isolate collections and diversify studies on C. burnetii biology, epidemiology, and control.