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

Clinical, epidemiological, and laboratory features of Rickettsia africae infection, African tick-bite fever: A systematic review

African tick-bite fever (ATBF), caused by Rickettsia africae, is the main tick-borne rickettsiosis and the second most frequent cause of fever after malaria in travelers returning from sub-Saharan Africa. General descriptions on ATBF were made in the first two decades after recognized as a new infectious entity, and since then, many authors have contributed to the knowledge of the disease by reporting clinical cases in scientific literature. We developed a systematic review that evaluated all available evidence in the literature regarding clinical, epidemiological, and laboratory features of confirmed R. africae rickettsiosis cases. We followed the recommendations made by the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guide. A total of 48 scientific publications (108 confirmed cases) were analyzed in order to extract data for developing this review. Overall, our results show that R. africae rickettsiosis is more frequent in males in the age group of 18-64 years, more than 80% of the cases occurred in European travelers, South Africa was the country where most infections were acquired, and almost 40% of cases occurred in clusters. Clinically, more than 80% of the cases had fever and eschar (55% developed multiple eschars), rash was present in less than the half of cases, and lymphangitis was not a common sign (11%). Headache, myalgia and regional lymphadenopathy were predominant nonspecific clinical manifestation (mean of 60%, 49% and 51%, respectively). Our results show that at least 70% of R. africae cases had altered laboratory parameters, most often showing an increase in transaminases and C-reactive protein. Tetracycline-class antibiotics, as monotherapy, were used in most (>90%) of the patients. Overall, only 4% of cases had complications, 12% required hospitalization, and there was a 100% rate of clinical recovery.

Treatment of Tick-Borne Diseases

OBJECTIVE:

To review the data regarding the pharmacotherapy of Lyme disease, Rocky Mountain spotted fever (RMSF), and the human ehrlichioses.

DATA SOURCES:

English-language literature was identified via MEDLINE (1966–January 2002) using the keywords Lyme disease, Rocky Mountain spotted fever, and ehrlichiosis. Textbooks and other pertinent resources were also reviewed.

STUDY SELECTION AND DATA EXTRACTION:

All articles identified through the data sources above were evaluated and reviewed if pertinent to the objective.

DATA SYNTHESIS:

Tick-borne diseases are the most common vector-transmitted diseases in North America. Each disease causes significant morbidity and, in the case of RMSF, mortality if patients go untreated. If the disease syndromes are recognized early and treatment is initiated, complications are greatly reduced. Doxycycline is active against each of the causative organisms, simplifying empiric treatment.

CONCLUSIONS:

Effective pharmacotherapy exists to treat each of these diseases, assuming diagnosis is made quickly. The β-lactam and tetracycline antibiotics appear to be the most effective therapy for Lyme disease. The tetracyclines, but not the β-lactams, are effective for RMSF and the human ehrlichioses. Since Borrelia burgdorferi and the human granulocytic ehrlichiosis agent are becoming more common coinfecting pathogens, tetracycline or doxycycline should be considered the drugs of choice for patients from endemic areas where exposure to both pathogens may have occurred. Doxycycline is the preferred agent because of decreased frequency of administration and adverse effects.

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.

Pristinamycin for Rickettsia africae infection

African tick bite fever is caused by Rickettsia africae. The number of reported cases in international travelers has significantly increased recently. The gold standard treatment is doxycycline. Here, we present a case of R africae infection associated with quick complete resolution following the initiation of pristinamycin therapy.

Clarithromycin versus azithromycin in the treatment of Mediterranean spotted fever in children: a randomized controlled trial

We conducted an open-label randomized controlled trial to compare the efficacy and safety of clarithromycin (15/mg/kg/day in 2 divided doses for 7 days) with those of azithromycin (10 mg/kg/day in 1 dose for 3 days) in the treatment of children with Mediterranean spotted fever. Until now, there has not been a gold-standard therapy for this rickettsial disease in children. Eighty-seven children were randomized to receive 1 of the 2 drugs. The mean time to defervescence (+/- standard deviation) was 46.2+/-36.4 h in the clarithromycin group and 39.3+/-31.3 h in the azithromycin group. These differences were not statistically significant and both drugs were equally well-tolerated. Clarithromycin and azithromycin could be acceptable therapeutic alternatives to chloramphenicol and tetracyclines for children aged < or =8 years with Mediterranean spotted fever. Azithromycin, because it has a long half-life, offers the advantages of administration in a single daily dose and a shorter duration of therapy, which could increase compliance in children.

In vitro susceptibilities of Bartonella henselae, B. quintana, B. elizabethae, Rickettsia rickettsii, R. conorii, R. akari, and R. prowazekii to macrolide antibiotics as determined by immunofluorescent-antibody analysis of infected Vero cell monolayers

The in vitro susceptibilities of Bartonella (Rochalimaea) henselae, B. quintana, B. elizabethae, Rickettsia akari, R. conorii, R. prowazekii, and R. rickettsii to different concentrations of azithromycin, clarithromycin, dirithromycin, erythromycin, and roxithromycin in Vero cell cultures were evaluated. Bartonella and Rickettsia spp. were allowed to initiate infection of the antibiotic-free Vero cell monolayers, which were maintained in 16-chamber microscope slides in the absence of antibiotics at 32 degrees C in a CO2-enriched atmosphere. The monolayers were then incubated for 3 h to allow for initial host cell intracellular penetration by infecting species. After inoculation, inocula were replaced and tested with media containing 12 different concentrations of each antibiotic in replicate (10 wells of each antibiotic dilution) for each species, and the monolayers were reincubated. Tetracycline served as the control. Growth status of Bartonella spp. and Rickettsia spp. was determined by evaluation of immunofluorescent staining bacilli. Five days later, when antibiotic-free, control-infected cell monolayers demonstrated significant fluorescence, media were removed for all cell monolayers, the monolayers were fixed, and all specimens were stained with standard indirect immunofluorescent antibody reagents. Fluorescent foci were enumerated by counting such foci on random fields visualized with an epifluorescence microscope. The extent of antibiotic-induced focus inhibition was recorded for each dilution of antibiotic and compared with that of an antibiotic-negative control. Effective antibiotic dilution endpoints for inhibition of Bartonella and Rickettsia proliferation, as judged by absence of increase of significant fluorescence (as compared with no-growth controls), were enumerated by determining the number of cell culture chambers at various antibiotic dilutions that were negative or positive for significant Bartonella- or Rickettsia-specific fluorescence. All of the macrolide agents tested were readily active against all three Bartonella organisms, and azithromycin, clarithromycin, and roxithromycin may have potential in the treatment of Rickettsia infections. Animal model-based clinical trials are warranted to define the specific treatment role of the newer macrolide antibiotics.

Optimum treatment of intracellular infection

The intracellular location of some micro-organisms has been early recognised as a critical point to explain failure of antibiotic therapy to eradicate such pathogens from infected hosts. Most often parasites invade 'professional' phagocytic cells, including neutrophils, monocytes and macrophages, by resisting the intracellular bactericidal phagolysosomal pathway. Alternatively, they may invade 'non-professional' phagocytic cells (cells with fewer phagocytic and bactericidal abilities) such as endothelial cells, or even cells without lysosomes such as erythrocytes. The intracellular activity of an antibiotic depends on several factors including its ability to reach the eukaryotic cell membrane, its subcellular localisation as compared to that of the parasite, the possibility that the intracellular milieu may partially inactivate its activity, and the susceptibility of the intracellular form of the parasite. In vitro and animal models have been developed to investigate antibiotic activity against intracellular pathogens. However, it should be emphasised that only data obtained from patients give reliable information to define the optimum antibiotic regimen.

In vitro susceptibilities of spotted fever group rickettsiae and Coxiella burnetti to clarithromycin

The in vitro bacteriostatic activity of clarithromycin, a new macrolide derivative, against Rickettsia rickettsii, Rickettsia conorii, and "Rickettsia israeli" was determined by the plaque assay and the dye uptake assay. Both bacteriostatic and bactericidal activities of clarithromycin against the Nine Mile, Q212, Priscilla, and ME9 strains of Coxiella burnetti were evaluated by using three cell culture systems. Clarithromycin showed improved antibacterial activity compared with that of erythromycin. A bacteriostatic activity was obtained at concentrations below the reported maximum concentration of clarithromycin in human serum (about 4 micrograms/ml) for all tested rickettsiae. MICs ranged from 1 to 2 micrograms/ml for the three Rickettsia species and from 1 to 4 micrograms/ml for the C. burnetti strains. No bactericidal activity against C. burnetti was obtained when clarithromycin was used at 4 micrograms/ml.

Identification of the satA gene encoding a streptogramin A acetyltransferase in Enterococcus faecium BM4145

Enterococcus faecium BM4145, a clinical isolate from urine, was resistant to streptogramin group A antibiotics by inactivation. The strain harbored a plasmid containing a gene, satA, responsible for this resistance; this gene was cloned and sequenced. It encoded SatA, a protein deduced to be 23,634 Da in mass and homologous with a new family of chloramphenicol acetyltransferases described in Agrobacterium tumefaciens, Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus. The similarity of SatA to other acetyltransferases, LacA (thiogalactoside acetyltransferase) and CysE (serine acetyltransferase) from E. coli, and to two putative acetyltransferases, NodL from Rhizobium leguminosarum and Urf1 from E. coli, was also observed in a region considered to be the enzyme's active site. Acetylation experiments indicated that acetyl coenzyme A was necessary for SatA activity and that a single acetylated derivative of pristinamycin IIA was produced. Other members of the streptogramin A group such as virginiamycin M and RP54476 were also substrates for the enzyme. We conclude that resistance to the streptogramin A group of antibiotics in E. faecium BM4145 is due to acetylation by an enzyme related to the novel chloramphenicol acetyltransferase family.

Semi-synthetic derivatives of erythromycin

Semi-synthetic derivatives of erythromycin have played an important role in antimicrobial chemotherapy. First generation derivatives such as 2'-esters and acid-addition salts significantly improved the chemical stability and oral bioavailability of erythromycin. A second generation of erythronolide-modified derivatives: roxithromycin, clarithromycin, azithromycin, dirithromycin and flurithromycin, have been synthesized and have exhibited significant improvements in pharmacokinetic and/or microbiological features. In addition, erythromycin itself has expanded its utility as an effective antibiotic against a variety of newly emerged pathogens. As a result of these developments, macrolide antibiotics have enjoyed a resurgence in clinical interest and use during the past half-dozen years, and semi-synthetic derivatives of erythromycin should continue to be important contributors to this macrolide renaissance. Despite these recent successes, other useful niches for macrolide antibiotics will remain unfilled. Consequently, the search for new semi-synthetic derivatives of erythromycin possessing even better antimicrobial properties should be pursued.

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 activity of RP 59500, a semisynthetic injectable pristinamycin, against staphylococci, streptococci, and enterococci

The in vitro activity of RP 59500, a semisynthetic pristinamycin, was compared with the activities of vancomycin, oxacillin, ampicillin, gentamicin, ciprofloxacin, and rifampin against five Staphylococcus species, five Streptococcus species, and four Enterococcus species. For staphylococci, MICs were 0.13 to 1 microgram/ml and the MICs for 90% of the strains tested (MIC90s) were 0.13 to 0.5 microgram/ml; there were no differences between oxacillin-susceptible and -resistant strains. For streptococci, MICs were 0.03 to 4 micrograms/ml and MIC90s were 0.25 to 2 micrograms/ml; viridans group streptococci were the least susceptible streptococci. For enterococci, MICs were 0.25 to 32 micrograms/ml and MIC90s were 2 to 4 micrograms/ml; Enterococcus faecalis was the least susceptible. Vancomycin was the only comparative drug with consistent activity against all species of gram-positive cocci. With RP 59500, raising the inoculum 100-fold, lowering the pH of cation-adjusted Mueller-Hinton broth to 5.5, or omitting cation supplementation had little effect on MICs, but 50% serum increased MICs 2 to 4 dilution steps. The differences between MBCs and MICs were greater for staphylococci and enterococci than for streptococci. Time-kill studies with 24 strains indicated that RP 59500 concentrations 2-, 4-, and 16-fold greater than the MICs usually killed bacteria of each species at similar rates; reductions in CFU per milliliter were less than those observed with oxacillin or vancomycin against staphylococci and less than those observed with ampicillin against enterococci. RP 59500 antagonized the bactericidal activities of oxacillin and gentamicin against Staphylococcus aureus ATCC 29213 and that of ampicillin against E. faecalis ATCC 29212. Against the latter, combination with gentamicin was indifferent. RP 59500 has a broad spectrum of in vitro activity against gram-positive cocci; combining it with other drugs is not advantageous.

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.