Mechanisms that may account for differential antibiotic susceptibilities among Coxiella burnetii isolates

Q fever

Q fever is an acute febrile illness first described in 1935 and now seen in many parts of the world. Human infection follows exposure to animals, especially domestic livestock. Recent outbreaks in metropolitan areas have implicated cats as the carrier of disease to humans. The etiologic agent, Coxiella burnetti, belongs to the family Rickettsiaceae, although it has distinct genetic characteristics and modes of transmission. Most recent attention has been focused on a number of large outbreaks of Q fever associated with medical research involving pregnant sheep. Although most infections are self-limited, some patients require prolonged treatment. Recent vaccines have had encouraging success in the prevention of disease in individuals at high risk of exposure.

Phagolysosomes of Coxiella burnetii-infected cell lines maintain an acidic pH during persistent infection

Coxiella burnetii, the agent of Q fever, is an obligate intracellular bacterium that multiples within vacuoles of phagolysosomal origin. Persistently infected cell lines were maintained in continuous culture for months. We studied the pH of the phagolysosomes by using two murine cell lines during early propagation of the bacteria and after establishment of persistent infection. Three strains of C. burnetii were studied because of the purported propensity of each strain to cause acute or chronic disease and to be resistant or susceptible to antibiotics. The pHs were calculated from fluorescence experiments with fluoresceinated dextran as a lysosomal probe. Phagolysosomal vacuoles maintained an acidic pH during a 36-day infection. Minimal variation of the pH occurred over the duration of the experiment with strains that caused either acute or chronic disease. Phagolysosomal pH remained stable for as long as 153 days with the Nine Mile phase II isolate. Thus, neither the course of C. burnetti infection nor the diversity of antibiotic susceptibility of the strains is related to variations in the phagolysosomal pH.

Monoclonal antibody based capture ELISA/ELIFA for detection of Coxiella burnetii in clinical specimens

A CAPTURE ELISA/ELIFA system based on monoclonal capture and biotinylated monoclonal detection antibody is described. The assay is fast, highly specific and detects a minimum dose of 2500 Coxiella (C.) burnetii particles. In contrast to the sophisticated and cumbersome isolation procedures, even non-specialized laboratories could use this assay system for investigating clinical samples of different origin for C. burnetii within a short period of time.