In vitro susceptibility of Coxiella burnetii to antibiotics, including several quinolones

Abstract

Antibiotic susceptibility testing of the rickettsial Q fever agent Coxiella burnetii was performed by using persistently infected L929 fibroblast cells. The efficacies of a variety of antibiotics with different metabolic targets were tested and compared. -The most effective antibiotics in bringing about the elimination of the parasite from infected cells included several quinolone compounds and rifampin. Of the' quinolone compounds tested, 'difloxacin (A-56619) was the most effective, followed by ciprofloxacin and oxolinic' acid. These three quinolones were apparently rickettsiacidal. After 48 h of exposure to micrQgram amounts of the compounds (ranging from 2 ,,g of difloxacin per ml to'5 jig of the other two antibiotics per ml), the number of intracellular parasites markedly declined; after' 10 days of treatment, very few intracellular rickettsiae were detected.Rifampin (1 ,Ig/ml) was also very effective in eliminating the parasites. Some of the 13 other antibiotics tested that were somewhat effective included chloramphemcol, doxycycline, and trimetloprim. The persistently infected L929 cells were found-to provide a convenient system for the relatively rapid determination of the susceptibility of C. burnetii to antibiotics.Chronic endocarditis and hepatosplenomegaly are occasionally associated with persistent and relapsing infection caused by the obligate intracellular procaryotic rickettsial agent of Q fever, Coxiella burnetii (8,12,18,19). Antibiotic treatment of chronic Q fever has not been consistently effective (8,13,18); in spite of treatment, the disease can continue or relapse, resulting in life-threatening endocarditis,'usually affecting the aortic and mitral valves (13,17,18). We have developed an in vitro model of persistent Q fever consisting of cell lines persistently infected with C. burnetii. These chronically infected cell lines include L929, J774, and P388D)1 (3,4). The persistently infected L929 cells have been maintained in continuous'culture for over 3 years without the addition of normal'cells; both the host cells and parasites divide, with C. burnetii proliferating within phagolysosomes (2). Recently, we discovered that heavily infected cells are capabl,e of division; those possessing one large parasite-containing vacuole give rise to both infected and uninfected daughter cells (15). This chronically infected model system was employed in this study for examining the efficacies of several antibiotics, including several DNA gyrase inhibitors (16) of the quinolone family. In this report we provide evidence that rifampin and several quinolones are effective in rapidly eliminating the parasite from chronically infected L929 cells. Unlike other host systems (embryonated eggs, guinea pigs) that have been used previously by other investigators (7, 9, 10, 17) to determine the' antibiotic susceptibility of C. burnetii, the system we describe is more convenient and precise and it allows one to obtain drug efficacy data in a relatively short time. Rocky Mountain Laboratory, Hamilton, Mont. The plaque...

Q fever endocarditis: A case report and review of the literature

“…In vitro studies, using chronically infected cell cultures (which better mimic the conditions of chronic Q fever), have shown doxycycline, chloramphenicol, rifampin and quinolones to be active against C burnetii (31,32). Whether these antibiotics are truly bactericidal or simply bacteriostatic depends on the cell culture model used.…”

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

“…Furthermore, the Nine Mile (NM; RSA 493) and Priscilla (PRS; Q177) isolates, implicated in acute and chronic disease syndromes, respectively, exhibit dramatically different susceptibilities to a variety of antibiotics, including doxycycline, rifampin, and several fluoroquinolones (31,32). These observations correlate with clinical success in treating acute Q fever and the poor antibiotic manageability of chronically diseased patients (29).…”

“…These drugs have been previously shown to possess differential efficacies against the NM, S Q217, and PRS isolates (30)(31)(32). The antibiotic susceptibilities of C. burnetii plasmid-transduced E. coli HB101 isolates were also determined for transductants treated with ciprofloxacin to eliminate plasmids (Table 1) Isolates were purified from L929 fibroblasts persistently infected for over 250 days and brought to equivalent concentrations in modified P-25 buffer (11).…”

“…All organisms were obtained in yolk sac homogenates and propagated within L929 mouse fibroblast cell cultures (21). Recent infections were initiated and maintained as described previously (32) Norfloxacin accumulation by purified C. burnetii isolates was also determined by spectrofluorometry with the methods of Chapman and Georgopapadakou (5). Purified C.…”

“…The drugs to which the three C. burnetii isolates studied (NM, S Q217, and PRS) exhibited differential susceptibilities (30)(31)(32)(33) have different targets and modes of action (19). It is therefore unlikely that drug-specific mutational alterations account for the differential susceptibilities of the isolates to doxycycline, rifampin, or the fluoroquinolones.…”