Infection of Vero cells with Coxiella burnetii phase II: relative intracellular bacterial load and distribution estimated by confocal laser scanning microscopy and morphometry

• Published in: Journal of microbiological methods 2001, Vol.43 (3), p.223-232
• Main Authors: Zamboni, Dario S, Mortara, Renato A, Rabinovitch, Michel
• Format: Article
• Language: English
• Subjects: Animals; Bacteriology; Biological and medical sciences; Cell Size; Cercopithecus aethiops; Confocal laser fluorescence microscopy; Coxiella burnetii - physiology; Coxiella burnetii phase II; Fluorescence; Fundamental and applied biological sciences. Psychology; Image Processing, Computer-Assisted; Intracellular infection; laser scanning microscopy; Microbiology; Microscopy, Confocal - methods; morphometry; Parasitophorous vacuoles; Pathogenicity, virulence, toxins, bacteriocins, pyrogens, host-bacteria relations, miscellaneous strains; Phagosomes; Q Fever - microbiology; Quantitative fluorescence; Vacuoles - microbiology; Vero Cells
• ISSN: 0167-7012; 1872-8359
• DOI: 10.1016/S0167-7012(00)00223-2

Coxiella burnetii, the agent of Q fever in man and of coxiellosis in other species, is an intracellular pathogen not yet grown axenically. Confocal laser fluorescence microscopy and morphometry were used to measure relative C. burnetii phase II loads and their intracellular distribution in aldehyde fixed and DAPI stained Vero cell monolayers. The fluorescence of single horizontal optical sections provided useful information on relative loads of bacteria in cells and vacuoles. The relative density of the bacteria in the vacuoles was inferred from ratios of fluorescence to vacuolar section areas. Relative bacterial loads, bacterial densities and section areas of large vacuoles increased exponentially between days 2 and 4 of the infection of γ-irradiated host cells, stabilized between days 4 and 6, and decreased thereafter. Estimated minimum doubling times were higher for the overall complement of the intracellular organisms (about 12 h) than for bacteria that were confined to larger vacuoles (about 10 h).