In vitro susceptibility of Rickettsia conorii to ciprofloxacin as determined by suppressing lethality in chicken embryos and by plaque assay

Epidemiology, Clinical Aspects, Laboratory Diagnosis and Treatment of Rickettsial Diseases in the Mediterranean Area During COVID-19 Pandemic: A Review of the Literature

The purpose of the present review is to give an update regarding the classification, epidemiology, clinical manifestation, diagnoses, and treatment of the Rickettsial diseases present in the Mediterranean area.

We performed a comprehensive search, through electronic databases (Pubmed – MEDLINE) and search engines (Google Scholar), of peer-reviewed publications (articles, reviews, and books).

The availability of new diagnostic tools, including Polymerase Chain Reaction and nucleotide sequencing has significantly modified the classification of intracellular bacteria, including the order Rickettsiales with more and more new Rickettsia species recognized as human pathogens. Furthermore, emerging Rickettsia species have been found in several countries and are often associated with unique clinical pictures that may challenge the physician in the early detection of the diseases.

Rickettsial infections include a wide spectrum of clinical presentations ranging from a benign to a potentially life treating disease that requires prompt recognition and proper management. Recently, due to the spread of SARS-CoV-2 infection, the differential diagnosis with COVID-19 is of crucial importance. The correct understanding of the clinical features, diagnostic tools, and proper treatment can assist clinicians in the management of Rickettsioses in the Mediterranean area.

Randomized Trial of Clarithromycin for Mediterranean Spotted Fever

The classic antibiotic treatment for Mediterranean spotted fever (MSF) is based on tetracyclines or chloramphenicol, but chloramphenicol's bone marrow toxicity makes tetracyclines the treatment of choice. However, it is convenient to have alternatives available for patients who are allergic to tetracyclines, pregnant women, and children <8 years old. We conducted a randomized clinical trial to compare clarithromycin with doxycycline or josamycin in the treatment of MSF. Forty patients were evaluated (23 male; mean age, 39.87 years); 13 patients were aged <14 years. Seventeen patients received clarithromycin, and 23 received doxycycline or josamycin. The interval between the onset of symptoms and the start of treatment was 4.04 ± 1.70 days in the clarithromycin group versus 4.11 ± 1.60 days in the doxycycline/josamycin group (P = not significant [NS]). Time to the disappearance of fever after treatment was 2.67 ± 1.55 days in the clarithromycin group versus 2.22 ± 1.35 days in the doxycycline/josamycin (P = NS). The symptoms had disappeared at 4.70 ± 2.25 days in the clarithromycin group versus at 4.75 ± 3.08 days in the doxycycline/josamycin (P = NS). There were no adverse reactions to treatment or relapses in either group. In conclusion, clarithromycin is a good alternative to doxycycline or josamycin in the treatment of MSF.

Current and past strategies for bacterial culture in clinical microbiology

A pure bacterial culture remains essential for the study of its virulence, its antibiotic susceptibility, and its genome sequence in order to facilitate the understanding and treatment of caused diseases. The first culture conditions empirically varied incubation time, nutrients, atmosphere, and temperature; culture was then gradually abandoned in favor of molecular methods. The rebirth of culture in clinical microbiology was prompted by microbiologists specializing in intracellular bacteria. The shell vial procedure allowed the culture of new species of Rickettsia. The design of axenic media for growing fastidious bacteria such as Tropheryma whipplei and Coxiella burnetii and the ability of amoebal coculture to discover new bacteria constituted major advances. Strong efforts associating optimized culture media, detection methods, and a microaerophilic atmosphere allowed a dramatic decrease of the time of Mycobacterium tuberculosis culture. The use of a new versatile medium allowed an extension of the repertoire of archaea. Finally, to optimize the culture of anaerobes in routine bacteriology laboratories, the addition of antioxidants in culture media under an aerobic atmosphere allowed the growth of strictly anaerobic species. Nevertheless, among usual bacterial pathogens, the development of axenic media for the culture of Treponema pallidum or Mycobacterium leprae remains an important challenge that the patience and innovations of cultivators will enable them to overcome.

Treatment of Rickettsia spp. infections: a review

Human rickettsioses caused by intracellular bacteria of the genus Rickettsia are distributed worldwide and are transmitted by arthropod vectors such as ticks, fleas, mites and lice. They have a wide range of manifestations from benign to life-threatening diseases. Mortality rates of up to 30% have been reported for some rickettsioses. Here, the authors will review in vitro and human studies of the various compounds that have been used for the treatment of Rickettsia spp. infections. The authors will also provide recommendations for the treatment of spotted fever and typhus group rickettsioses.

Inappropriateness of quinolone in scrub typhus treatment due to gyrA mutation in Orientia tsutsugamushi Boryong strain

The use of quinolone for treatment of rickettsial diseases remains controversial. Recent clinical studies suggest that quinolone is not as effective as others in patients with rickettsial diseases including scrub typhus, although the mechanism is not well understood. In this study, we evaluated the mutation in gyrA associated with quinolone resistance. We prospectively enrolled scrub typhus patients, collected blood samples and clinical data from October, 2010 to November, 2011. Among the 21 patients enrolled, one initially received ciprofloxacin for 3 days but was switched to doxycycline due to clinical deterioration. We obtained the gyrA gene of Orientia tsutsugamushi from 21 samples (20 Boryong strain, 1 Kato strain) and sequenced the quinolone resistance-determining region. All of 21 samples had the Ser83Leu mutation in the gyrA gene, which is known to be associated with quinolone resistance. This suggests that quinolones may be avoided for the treatment of serious scrub typhus.

Diagnosis and treatment of tick infestation and tick-borne diseases with cutaneous manifestations

Hard and soft ticks may be associated directly or indirectly with a number of dermatoses, both infectious and inflammatory in origin. Morbidity may occur as a result of tick bites, tick toxicosis, and even infestation. These arthropod vectors may transmit life-threatening protozoan, bacterial, rickettsial, and viral diseases with systemic and cutaneous findings. Additionally, ticks may transmit more than one pathogen with subsequent human coinfection. This article reviews the presentation of tick-borne illnesses and the medical management of these diseases. Among others, diseases such as ehrlichiosis, anaplasmosis, babesiosis, tularemia, borrelioses, tick-borne encephalitides, rickettsial spotted fevers, and tick typhus are discussed in this article. The recognition of skin manifestations associated with these diseases is paramount to early diagnosis and treatment initiation.

Genome Comparison Analysis of Molecular Mechanisms of Resistance to Antibiotics in the Rickettsia Genus

In this study we describe molecular mechanisms of resistance to several classes of antibiotics within drug targets by in silico genome comparisons for bacteria of the genus Rickettsia. Apart from the mutations in the rpoB gene in naturally rifampin-resistant Rickettsia species previously reported by our team, we found that typhus group (TG) rickettsiae had a triple amino acid difference in the highly conserved region of the L22 ribosomal protein as compared to the spotted fever group rickettsiae (SFG), which could explain the natural resistance of SFG rickettsia to erythromycin. We found also that the genome of R. conorii contains an aminoglycoside 3'-phosphotransferase. Finally, either folA gene (encoding dihydrofolate reductase) and/or folP gene (encoding dihydropteroate synthase) was missing in the genome of rickettsial strains explaining the natural resistance to cotrimoxazole. Finally, multiple genes encoding for pump efflux were found especially in the genome of R. conorii that could be involved in resistance to antibiotics. Five specific ORFs related to antibiotic resistance have been identified in the genome of R. felis including a streptomycin resistance protein homologue, a class C beta-lactamase, a class D beta-lactamase, a penicillin acylase homologue, and an ABC-type multidrug transporter system. For the first time, using this approach, an experimental beta-lactamase activity has been shown for this bacterium. We believe that whole genome sequence analysis may help to predict several phenotypic characters, in particular resistance to antibiotics for obligate intracellular bacteria.

Mediterranean spotted fever during pregnancy: case presentation and literature review

Mediterranean spotted fever (MSF) is caused by Rickettsia conorii, an obligate intracellular parasite of eukaryotic cells. Although, usually this disease has a benign course, a rapidly fatal outcome can occur even in young healthy adults. We describe a case of a 40-year-old Bedouin woman gravida 11, para 10, who was admitted at 36 weeks gestation with this rickettsial disease. During pregnancy, the treatment of choice for Mediterranean spotted fever is chloramphenicol, but it seems that Azithromycin could be another possible option.

In vitro susceptibilities of Bartonella and Rickettsia spp. to fluoroquinolone antibiotics as determined by immunofluorescent antibody analysis of infected Vero cell monolayers

The in vitro susceptibilities of Bartonella and Rickettsia spp. to different concentrations of ciprofloxacin, levofloxacin, ofloxacin and sparfloxacin in Vero cell cultures, were determined by enumeration of immunofluorescent-stained bacilli. After incubation in a CO(2)-enriched atmosphere, inocula were replaced and tested with media containing 12 different concentrations of each antibiotic in replicate for each species and the monolayers were re-incubated. Growth status was determined by evaluation of immunofluorescent staining bacilli. Effective inhibitory antibiotic dilution endpoints were determined by counting Bartonella- and Rickettsia-specific fluorescent foci across a range of antibiotic dilutions with an epi-fluorescent microscope, and were compared with an antibiotic-negative control. Based upon the use of C(max):MIC and AUC:MIC data, levofloxacin exhibited activity against Bartonella elizabethae and B. quintana.

In vitro susceptibilities of 27 rickettsiae to 13 antimicrobials

The MICs of 13 antibiotics (doxycycline, thiamphenicol, rifampin, amoxicillin, gentamicin, co-trimoxazole, ciprofloxacin, pefloxacin, ofloxacin, erythromycin, josamycin, clarithromycin, and pristinamycin) were determined for 27 available rickettsial species or strains. We used two in vitro cell culture methods described previously: the plaque assay and the microplaque colorimetric assay. Our results confirm the susceptibilities of rickettsiae to doxycycline, thiamphenicol, and fluoroquinolones. Beta-lactams, aminoglycosides, and cotrimoxazole were not active. Typhus group rickettsiae were susceptible to all macrolides tested, whereas the spotted fever group rickettsiae, R. bellii, and R. canada were more resistant, with josamycin, a safe alternative for the treatment of Mediterranean spotted fever, being the most effective compound. Strain Bar 29, R. massiliae, R. montana, R. aeschlimannii, and R. rhipicephali, which are members of the same phylogenetic subgroup, were more resistant to rifampin than the other rickettsiae tested. Heterogeneity in susceptibility to rifampin, which we report for the first time, may explain in vivo discrepancies in the effectiveness of this antibiotic for the treatment of rickettsial diseases. We hypothesize that rifampin resistance and erythromycin susceptibility may reflect a divergence during the evolution of rickettsiae.

Susceptibility of Rickettsia conorii, R. rickettsii, and Coxiella burnetii to PD 127,391, PD 131,628, pefloxacin, ofloxacin, and ciprofloxacin

Plaque formation and dye uptake assays were used to measure the MICs of PD 127,391 and PD 131,628 against Rickettsia species. The MICs of PD 127,391 were 0.25 microgram/ml for Rickettsia rickettsii and 0.125 to 0.25 microgram/ml for Rickettsia conorii. The MICs of PD 131,628 were 0.25 to 0.5 microgram/ml for R. rickettsii and 0.5 microgram/ml for R. conorii. As determined by the shell vial technique, 15 strains of Coxiella burnetii were susceptible to PD 127,391 and PD 131,628 (MIC, < or = 1 microgram/ml), while one strain of C. burnetii (MP10) was of intermediate susceptibility.

Evaluation of ciprofloxacin and doxycycline in the treatment of Mediterranean spotted fever

A comparison was made of the results obtained with ciprofloxacin (750 mg/12 h) and doxycycline (100 mg/12 h), both administered p.o. for one week, in 34 and 36 patients respectively with Mediterranean spotted fever. Apyrexia was achieved after 50.1 +/- 34.2 h (mean +/- SD) of antibiotic therapy in the group of patients treated with ciprofloxacin and in 55.2 +/- 23.3 h in the group treated with doxycycline (no significant statistical differences). Resolution of the remaining signs and symptoms of the disease was achieved faster with ciprofloxacin. Both therapeutic regimens were effective and safe. Although more expensive than doxycycline, ciprofloxacin is a bactericidal compound which is better tolerated and has a lower risk of toxicity and of development of resistance. It can be considered, together with doxycycline, as an antibiotic of first choice in the treatment of Mediterranean spotted fever.

Efficacy of chloramphenicol, enrofloxacin, and tetracycline for treatment of experimental Rocky Mountain spotted fever in dogs

Dogs were experimentally inoculated with Rickettsia rickettsii to characterize the comparative efficacies of chloramphenicol, enrofloxacin, and tetracycline for the treatment of Rocky Mountain spotted fever (RMSF). All three antibiotics were equally effective in abrogating the clinical, hematologic, and vascular indicators of rickettsial infection. Antibiotic treatment for 24 h was sufficient to decrease the rickettsemia to levels below detection by Vero cell culture. Early treatment with all three antibiotics resulted in a similar decrease in antibody titer, but acute and convalescent serum samples taken at appropriate times would have still facilitated an accurate diagnosis of RMSF in all but one dog, which did not seroconvert. We conclude that chloramphenicol, enrofloxacin, and tetracycline are equally efficacious for treating experimental canine RMSF.

Antibiotic treatment of rickettsiosis, recent advances and current concepts

The author reviews the recent advances in the treatment of Mediterranean Spotted Fever and Q fever. In mediterranean spotted fever (M.S.F.), in vitro and preliminary in vivo data support the place of quinolones and josamycin in the treatment of M.S.F. In children josamycin could become the first choice drug as well as in pregnant woman. In Q fever chronic disease should be treated using a combination of antibiotic (doxycycline + quinolones) for a minimum of 3 years.

In vitro susceptibilities of Coxiella burnetii, Rickettsia rickettsii, and Rickettsia conorii to the fluoroquinolone sparfloxacin

In vitro susceptibilities of Rickettsia rickettsii, Rickettsia conorii, and Coxiella burnetii to the new fluoroquinolone sparfloxacin (AT-4140; RP 64206) were determined. Plaque and dye uptake assays were used to measure the MICs against R. rickettsii and R. conorii. The susceptibilities of C. burnetii Nine Mile and Q 212 were determined in two acute-infection models and in two chronic-infection models. The MICs were 0.125 to 0.25 microgram/ml for R. rickettsii and 0.25 to 0.5 microgram/ml for R. conorii. Sparfloxacin (1 microgram/ml) cured cells recently infected with C. burnetii Nine Mile and Q 212 within 4 to 9 days and cured multiplying, persistently infected cells within 10 days. As previously described with other fluoroquinolones (D. Raoult, M. Drancourt, and G. Vestris, Antimicrob. Agents Chemother. 34:1512-1514, 1990), sparfloxacin failed to cure cells persistently infected with C. burnetii and blocked from dividing with cycloheximide. As determined by the dye uptake assay, no cellular toxicity was noted with sparfloxacin at up to 128 micrograms/ml. These results are consistent with those previously obtained with fluoroquinolones (D. Raoult, M. Yeaman, and O. Baca, Rev. Infect. Dis. 11[Suppl. 5]:S986, 1989), although sparfloxacin may be slightly more active.

A review of the antimicrobial activity of the fluoroquinolones

The evolution of the fluoroquinolones is described, and structure-activity relationships outlined. The in-vitro antimicrobial activities of ciprofloxacin, enoxacin, norfloxacin, ofloxacin and pefloxacin against a wide range of organisms are critically reviewed. In-vitro factors influencing fluoroquinolone activity are discussed. Reports of the acquisition of resistance to the fluoroquinolones are evaluated. Finally, possible future directions for this group of antibiotics are discussed.

Randomized trial of doxycycline versus josamycin for Mediterranean spotted fever

We undertook a randomized clinical trial comparing therapeutic efficacy of the 1-day doxycycline regimen with the 5-day josamycin regimen for Mediterranean spotted fever. All 59 patients recovered uneventfully, and results did not significantly differ between the two schedules. One-day doxycycline therapy is an effective, easy, and inexpensive treatment. Josamycin is a useful therapeutic alternative that may be particularly convenient for pregnant women and patients with a history of allergy to tetracyclines.

Ciprofloxacin treatment of murine typhus

A 31-year-old woman developed fever, severe headache, myalgia and rash 3 weeks after a visit to Cyprus where she experienced insect bites in her bed. Treatment with ciprofloxacin resulted in a remarkable and rapid effect. Endemic typhus was proved by serology.

Antibiotic susceptibility of rickettsia and treatment of rickettsioses

The author describes the in vitro data for antibiotic susceptibility of Rickettsia and Coxiella burnetti. Tetracyclines are still the first antibiotic choice in spotted fevers, typhus and Q fever. In spotted fever a shortened treatment is suggested and the place of macrolide antibiotics, such as Josamycin, in treating children may be evaluated. In Q fever, according to the new biological data, an association of tetracyclines and Rifampin or Quinolones is suggested.

In vitro susceptibilities of Rickettsia rickettsii and Rickettsia conorii to roxithromycin and pristinamycin

In vitro susceptibilities of Rickettsia rickettsii and Rickettsia conorii to roxithromycin, pristinamycin, and the pristinamycin compounds, P1 and P2, were determined by a dye uptake assay and a plaque assay. The MICs were 1 microgram/ml for roxithromycin, 2 micrograms/ml for pristinamycin, greater than 256 micrograms/ml for P1, and 2 micrograms/ml for P2. Compounds P1 and P2 did not share synergetic activity. The toxicity of each compound was determined by a dye uptake assay. Toxic concentrations were 128 micrograms/ml for roxithromycin, 32 micrograms/ml for pristinamycin, greater than 256 micrograms/ml for P1, and 32 micrograms/ml for P2. Roxithromycin and pristinamycin could be useful in the treatment of Rocky Mountain spotted fever and Mediterranean spotted fever.

Mediterranean spotted fever in Lombardy: an epidemiological, clinical and laboratory study of 76 cases in the years 1977-1986

This paper describes the epidemiological, clinical and laboratory features of 76 cases of Mediterranean spotted fever occurring during the years 1977-1986. The patients observed all lived in the Lombardy region of Italy, which is not located on the Mediterranean Basin. Our data show the highest prevalence of the disease, as reported by other authors, in southern regions of Italy, in the same years: 1979-1983. No differences were noted between age groups or sexes, and the late spring-summer seasonality was confirmed. The clinical signs and symptoms in our cases were those common to the disease. The microimmunofluorescence method was found to be more sensitive and specific than the Weil-Felix test for serological diagnosis. Finally, we showed that doxycycline and oxytetracycline both induce rapid remission of fever.

Fluoroquinolone antimicrobial agents

The fluoroquinolones, a new class of potent orally absorbed antimicrobial agents, are reviewed, considering structure, mechanisms of action and resistance, spectrum, variables affecting activity in vitro, pharmacokinetic properties, clinical efficacy, emergence of resistance, and tolerability. The primary bacterial target is the enzyme deoxyribonucleic acid gyrase. Bacterial resistance occurs by chromosomal mutations altering deoxyribonucleic acid gyrase and decreasing drug permeation. The drugs are bactericidal and potent in vitro against members of the family Enterobacteriaceae, Haemophilus spp., and Neisseria spp., have good activity against Pseudomonas aeruginosa and staphylococci, and (with several exceptions) are less potent against streptococci and have fair to poor activity against anaerobic species. Potency in vitro decreases in the presence of low pH, magnesium ions, or urine but is little affected by different media, increased inoculum, or serum. The effects of the drugs in combination with a beta-lactam or aminoglycoside are often additive, occasionally synergistic, and rarely antagonistic. The agents are orally absorbed, require at most twice-daily dosing, and achieve high concentrations in urine, feces, and kidney and good concentrations in lung, bone, prostate, and other tissues. The drugs are efficacious in treatment of a variety of bacterial infections, including uncomplicated and complicated urinary tract infections, bacterial gastroenteritis, and gonorrhea, and show promise for therapy of prostatitis, respiratory tract infections, osteomyelitis, and cutaneous infections, particularly when caused by aerobic gram-negative bacilli. Fluoroquinolones have also proved to be efficacious for prophylaxis against travelers' diarrhea and infection with gram-negative bacilli in neutropenic patients. The drugs are effective in eliminating carriage of Neisseria meningitidis. Patient tolerability appears acceptable, with gastrointestinal or central nervous system toxicities occurring most commonly, but only rarely necessitating discontinuance of therapy. In 17 of 18 prospective, randomized, double-blind comparisons with another agent or placebo, fluoroquinolones were tolerated as well as or better than the comparison regimen. Bacterial resistance has been uncommonly documented but occurs, most notably with P. aeruginosa and Staphylococcus aureus and occasionally other species for which the therapeutic ratio is less favorable. Fluoroquinolones offer an efficacious, well-tolerated, and cost-effective alternative to parenteral therapies of selected infections.

Randomized double-blind evaluation of ciprofloxacin and doxycycline for Mediterranean spotted fever

A study of 43 patients with Mediterranean spotted fever showed that a 2-day course of ciprofloxacin or a 2-day course of doxycycline may be an effective mode of therapy. All patients in both arms of the study were cured; however, doxycycline produced a more rapid defervescence.

Susceptibility of Coxiella burnetii to pefloxacin and ofloxacin in ovo and in persistently infected L929 cells

The relative lack of efficacy of the antibiotic treatment of chronic Q fever endocarditis justifies the further evaluation of the susceptibility of Coxiella burnetii to the modern quinolone antibiotics. We evaluated the efficacies of pefloxacin and ofloxacin in controlling the Nine Mile isolate of C. burnetii by using an embryonated egg assay and persistently infected L929 cells in culture. Pefloxacin was effective in controlling the intracellular parasite at a concentration of 50 micrograms per egg and 1 microgram/ml in cultures of infected cells. Ofloxacin was effective at a concentration of 25 micrograms per egg and 0.5 microgram/ml in infected-cell cultures. In light of the fact that the concentrations of antibiotics used fall within physiological ranges used in humans, ofloxacin and pefloxacin may be useful in the clinical management of chronic Q fever, for which, to date, results have been poor.

Imported rickettsial disease: clinical and epidemiologic features

PURPOSE AND METHODS

The rickettsioses continue to constitute major health problems in many parts of the world. With increasing international travel, recognition of rickettsial diseases by physicians is becoming more important. The clinical features of four cases of rickettsial disease imported into Canada over a five-year period are presented; two patients with tick typhus (Rickettsia conorii), one patient with scrub typhus (R. tsutsugamushi), and one patient with murine typhus (R. typhi). We also present the North American data over the past 10 years from the Centers for Disease Control (CDC) (Atlanta).

RESULTS

Since 1983 in the United States, three cases of imported scrub typhus, all after travel to India, were confirmed, as well as six cases of murine typhus after travel to southeast Asia. At the CDC, 67 imported cases of tick typhus have been confirmed by indirect fluorescent antibody test since 1976; most illnesses occurred after travel to Africa.

CONCLUSION

Rickettsial diseases are underrecognized by physicians, who should consider these diagnoses in travelers returning from endemic areas. Since effective treatment is available, prompt diagnosis and treatment are important. In all cases, specific serologic confirmation should be obtained.

The 4-quinolone antibiotics: past, present, and future

During the past 5 years the 4-quinolone antibiotics have progressed from relative obscurity to a highly visible and intensely studied class of compounds. The zeal for developing and marketing newer fluoroquinolones closely parallels that of the cephalosporins for the last 10 years. All of these newer agents appear to have similar mechanisms of action, but numerous derivatives of the basic 4-quinolone structure have been synthesized in an effort to enhance the antimicrobial spectrum and pharmacologic properties of these antibiotics.

In vitro evaluation of josamycin, spiramycin, and erythromycin against Rickettsia rickettsii and R. conorii

The antimicrobial activities of josamycin, erythromycin, and spiramycin against Rickettsia conorii and R. rickettsii were evaluated in two tests: a dye-uptake assay and a plaque assay. The MIC of josamycin was 1 microgram/ml for both species; the MICs of erythromycin and spiramycin were 4 to 8 and 16 to 32 micrograms/ml, respectively, for both species. Only josamycin may be of clinical use in treating spotted fever rickettsiosis. It may be useful in treating pregnant women and young children.

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

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 microgram amounts of the compounds (ranging from 2 micrograms of difloxacin per ml to 5 micrograms 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 microgram/ml) was also very effective in eliminating the parasites. Some of the 13 other antibiotics tested that were somewhat effective included chloramphenicol, doxycycline, and trimethoprim. 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.

Ciprofloxacin therapy for Mediterranean spotted fever

We report the treatment of five patients with Mediterranean spotted fever with the antimicrobial agent ciprofloxacin. The treatment was administered intravenously for 2 days and then perorally for 8 days. All five patients were cured. These preliminary data seem to correlate with the in vitro activity of ciprofloxacin against Rickettsia conorii.