Evaluation of the Efficacy of Doxycycline, Ciprofloxacin, Levofloxacin, and Co-trimoxazole Using In Vitro and In Vivo Models of Q Fever.

Q fever, caused by the intracellular pathogen Coxiella burnetii, is traditionally treated using tetracycline antibiotics, such as doxycycline. Doxycycline is often poorly tolerated, and antibiotic-resistant strains have been isolated. In this study, we have evaluated a panel of antibiotics (doxycycline, ciprofloxacin, levofloxacin, and co-trimoxazole) against C. burnetii using in vitro methods (determination of MIC using liquid and solid media; efficacy assessment in a THP cell infection model) and in vivo methods (wax moth larvae and mouse models of infection). In addition, the schedule for antibiotic treatment has been evaluated, with therapy initiated at 24 h pre- or postchallenge. Both doxycycline and levofloxacin limited overt clinical signs during treatment in the AJ mouse model of aerosol infection, but further studies are required to investigate the possibility of disease relapse or incomplete bacterial clearance after the antibiotics are stopped. Levofloxacin was well tolerated and therefore warrants further investigation as an alternative to the current recommended treatment with doxycycline.

Use of axenic media to determine antibiotic efficacy against coxiella burnetii.

The traditional methods of measuring minimum inhibitory concentration (MIC) of antibiotics against Coxiella burnetii are time-consuming and technically difficult. The discovery of axenic media for C. burnetii culture provided an opportunity to determine the feasibility of using both broth dilution and an antimicrobial gradient method (Etest) as a convenient method of measuring MICs. The MICs for a range of antibiotics that have proven or potential use in the treatment of Q fever, namely doxycycline, ciprofloxacin, levofloxacin, moxifloxacin and co-trimoxazole, were measured. It was possible to measure MICs using both microdilution and Etest methods. MICs obtained were comparable to those from other methods. This study demonstrates the potential use of a relatively simple test to measure MIC in an organism that is difficult to culture.

Efficacy of liposome-encapsulated ciprofloxacin in a murine model of Q fever.

Encapsulation of antibiotics may improve treatment of intracellular infections by prolonging antibiotic release and improving antibiotic uptake into cells. In this study, liposome-encapsulated ciprofloxacin for inhalation (CFI) was evaluated as a postexposure therapeutic for the treatment of Coxiella burnetii, the causative agent of Q fever. Intranasal treatment of male A/Jola (A/J) mice with CFI (50 mg/kg of body weight) once daily for 7 days protected mice against weight loss and clinical signs following an aerosol challenge with C. burnetii. In comparison, mice treated twice daily with oral ciprofloxacin or doxycycline (50 mg/kg) or phosphate-buffered saline (PBS) lost 15 to 20% body weight and exhibited ruffled fur, arched backs, and dehydration. Mice were culled at day 14 postchallenge. The weights and bacterial burdens of organs were determined. Mice treated with CFI exhibited reduced splenomegaly and reduced bacterial numbers in the lungs and spleen compared to mice treated with oral ciprofloxacin or doxycycline. When a single dose of CFI was administered, it provided better protection against body weight loss than 7 days of treatment with oral doxycycline, the current antibiotic of choice to treat Q fever. These data suggest that CFI has potential as a superior antibiotic to treat Q fever.

Galleria mellonella as an alternative model of Coxiella burnetii infection.

Coxiella burnetii is a Gram-negative intracellular bacterium and is the causative agent of the zoonotic disease Q fever. Several rodent and non-human primate models of virulent phase I C. burnetii [Nine Mile (NM)I] have been developed, and have been used to determine the efficacy of antibiotics and vaccine candidates. However, there are several advantages to using insect models to study host-microbe interactions, such as reduced animal use, lowered cost and ease of manipulation in high containment. In addition, many laboratories use the avirulent phase II C. burnetii clone (NMII) to study cellular interactions and identify novel virulence determinants using genetic manipulation. We report that larvae of the greater wax moth, Galleria mellonella, were susceptible to infection with both C. burnetii NMI and NMII. Following subcutaneous infection, we report that intracellular bacteria were present within haemocytes and that larval death occurred in a dose-dependent manner. Additionally, we have used the model to characterize the role of the type 4 secretion system in C. burnetii NMII and to determine antibiotic efficacy in a non-mammalian model of disease.