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Hunfeld KP, Kraiczy P, Norris DE, Lohr B. The In Vitro Antimicrobial Susceptibility of Borrelia burgdorferi sensu lato: Shedding Light on the Known Unknowns. Pathogens 2023; 12:1204. [PMID: 37887720 PMCID: PMC10609913 DOI: 10.3390/pathogens12101204] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2023] [Revised: 09/08/2023] [Accepted: 09/12/2023] [Indexed: 10/28/2023] Open
Abstract
Human Lyme borreliosis (LB) represents a multisystem disorder that can progress in stages. The causative agents are transmitted by hard ticks of the Ixodes ricinus complex that have been infected with the spirochete Borrelia burgdorferi sensu lato. Today, LB is considered the most important human tick-borne illness in the Northern Hemisphere. The causative agent was identified and successfully isolated in 1982 and, shortly thereafter, antibiotic treatment was found to be safe and efficacious. Since then, various in vitro studies have been conducted in order to improve our knowledge of the activity of antimicrobial agents against B. burgdorferi s. l. The full spectrum of in vitro antibiotic susceptibility has still not been defined for some of the more recently developed compounds. Moreover, our current understanding of the in vitro interactions between B. burgdorferi s. l. and antimicrobial agents, and their possible mechanisms of resistance remains very limited and is largely based on in vitro susceptibility experiments on only a few isolates of Borrelia. Even less is known about the possible mechanisms of the in vitro persistence of spirochetes exposed to antimicrobial agents in the presence of human and animal cell lines. Only a relatively small number of laboratory studies and cell culture experiments have been conducted. This review summarizes what is and what is not known about the in vitro susceptibility of B. burgdorferi s. l. It aims to shed light on the known unknowns that continue to fuel current debates on possible treatment resistance and mechanisms of persistence of Lyme disease spirochetes in the presence of antimicrobial agents.
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Affiliation(s)
- Klaus-Peter Hunfeld
- Institute for Laboratory Medicine, Microbiology & Infection Control, Northwest Medical Centre, Academic Teaching Hospital, Medical Faculty, Goethe University Frankfurt, Steinbacher Hohl 2-26, D-60488 Frankfurt am Main, Germany;
- INSTAND e.V., Gesellschaft zur Förderung der Qualitätssicherung in medizinischen Laboratorien e.V., Ubierstraße 20, D-40223 Düsseldorf, Germany
| | - Peter Kraiczy
- Institute for Medical Microbiology & Infection Control, University Hospital Frankfurt, Goethe University Frankfurt, Paul-Ehrlich Str. 40, D-60596 Frankfurt am Main, Germany;
| | - Douglas E. Norris
- W. Harry Feinstone Department of Molecular Microbiology & Immunology, Bloomberg School of Public Health, Johns Hopkins University, 615 N Wolfe St, Baltimore, MD 21205, USA;
| | - Benedikt Lohr
- Institute for Laboratory Medicine, Microbiology & Infection Control, Northwest Medical Centre, Academic Teaching Hospital, Medical Faculty, Goethe University Frankfurt, Steinbacher Hohl 2-26, D-60488 Frankfurt am Main, Germany;
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Abstract
Lyme disease represents a growing public health threat. The controversial science and politics of Lyme disease have created barriers to reliable diagnosis and effective treatment of this protean illness. Two major clinical hurdles are the absence of a therapeutic end point in treating Borrelia burgdorferi, the spirochetal agent of Lyme disease, and the presence of tickborne coinfections with organisms such as Babesia, Anaplasma, Ehrlichia and Bartonella that may complicate the course of the disease. From a pathophysiologic standpoint, the affinity of Borrelia burgdorferi for multiple cell types and the presence of nonreplicating forms of the Lyme disease spirochete have contributed to persistent infection and failure of simple antibiotic regimens. Newer approaches to the treatment of Lyme disease should take into account its clinical complexity in coinfected patients and the possible need for prolonged combination therapy in patients with persistent symptoms of this potentially debilitating illness. The optimal antibiotic regimen for chronic Lyme disease remains to be determined.
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Affiliation(s)
- Raphael B Stricker
- California Pacific Medical Center , 450 Sutter Street, Suite 1504, San Francisco, CA 94108, USA.
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Knauer J, Krupka I, Fueldner C, Lehmann J, Straubinger RK. Evaluation of the preventive capacities of a topically applied azithromycin formulation against Lyme borreliosis in a murine model. J Antimicrob Chemother 2011; 66:2814-22. [PMID: 21921078 PMCID: PMC3215302 DOI: 10.1093/jac/dkr371] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Objectives Systemic antibiotic treatment of Lyme borreliosis is effective during the early stages of the infection, while chronic manifestations of the disease may remain refractory and difficult to treat. This study was carried out in order to evaluate the potential of topically applied azithromycin to eliminate the spirochaetal organisms in the skin of the freshly bitten host and thereby prevent Lyme borreliosis. Methods Laboratory mice were challenged with Borrelia burgdorferi sensu stricto by needle inoculation or via infected ticks as vectors. Then, an azithromycin-containing formulation was applied once daily to the sites of exposure for three consecutive days. In the case of needle inoculation, a 5% azithromycin formulation was applied starting 1 h, 3 days and 5 days after infection. In the case of tick exposure, 4%, 10% and 20% azithromycin formulations were applied, starting directly after the detachment of the engorged ticks. Subsequently, the infection status of the mice was determined. Results Concentrations of azithromycin in murine skin were >3800-fold higher than the published minimal inhibitory concentration for B. burgdorferi as soon as 3 h after the first application. After needle inoculation, spirochaetes were not detectable in all infected mice after treatment, if the first application started 1 h or even after 3 days post-infection. Furthermore, no borrelial organisms were detected after topical treatment when ticks were used for spirochaete inoculation. Conclusions Our data indicate that topical treatment with a formulation containing azithromycin is a promising approach to prevent Lyme borreliosis shortly after a tick bite.
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Affiliation(s)
- Jens Knauer
- Fraunhofer Institute for Cell Therapy and Immunology, Cell Technology/GLP, Leipzig, Germany
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In vitro susceptibility of Borrelia spielmanii to antimicrobial agents commonly used for treatment of Lyme disease. Antimicrob Agents Chemother 2008; 53:1281-4. [PMID: 19075048 DOI: 10.1128/aac.01247-08] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Ten isolates of the recently delineated genospecies Borrelia spielmanii were tested against antimicrobial agents used to treat Lyme disease and compared to eight isolates of the other three human-pathogenic borrelial genospecies. Despite some small but significant differences in four out of eight antibiotic agents, the susceptibility pattern of B. spielmanii mainly parallels that of the other known human-pathogenic members of the B. burgdorferi sensu lato complex.
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Hammerschlag MR, Sharma R. Use of cethromycin, a new ketolide, for treatment of community-acquired respiratory infections. Expert Opin Investig Drugs 2008; 17:387-400. [DOI: 10.1517/13543784.17.3.387] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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Lee J, Wormser GP. Pharmacodynamics of doxycycline for chemoprophylaxis of Lyme disease: preliminary findings and possible implications for other antimicrobials. Int J Antimicrob Agents 2008; 31:235-9. [PMID: 18226504 DOI: 10.1016/j.ijantimicag.2007.11.011] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2007] [Accepted: 11/27/2007] [Indexed: 11/17/2022]
Abstract
The purpose of this study was to begin to characterise the pharmacodynamic parameters of single-dose doxycycline for the prevention of Lyme disease following a tick bite. Based on limited data from published human and murine studies, it was found that there is a direct correlation between efficacy rate and the area under the time-concentration of free antibiotic curve divided by the minimum inhibitory concentration (fAUC/MIC) (R(2)=0.74, using Pearson correlation), but not the maximum concentration of free drug in serum divided by the MIC (fC(max)/MIC) or the time that the free drug concentration remains above the MIC (fT>MIC). To determine the possible implications of these findings for other antimicrobials, it was assumed that the pharmacodynamic properties of doxycycline would be pertinent to azithromycin, an antibiotic whose activity is known to correlate with AUC/MIC. By making such an extrapolation and using pharmacokinetic modelling with conservative assumptions on MIC values against Borrelia burgdorferi, it is hypothesised that a single 500 mg dose of azithromycin in humans should have comparable efficacy to doxycycline for the prevention of Lyme disease. Additional experimental studies are needed to clarify more precisely the pharmacodynamic properties of doxycycline and to validate the accuracy of this hypothesis.
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Affiliation(s)
- Jooyun Lee
- Division of Infectious Diseases, Department of Medicine, New York Medical College, Valhalla, NY 10595, USA.
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Hansmann Y. Le traitement des phases secondaires et tertiaires de la borréliose de Lyme. Med Mal Infect 2007; 37:479-86. [PMID: 17367972 DOI: 10.1016/j.medmal.2006.01.020] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2006] [Accepted: 01/15/2006] [Indexed: 12/21/2022]
Abstract
The treatment of secondary and tertiary Lyme borreliosis is difficult because of antibiotic lack of efficacy. This fact may be explained by several factors: the specific pathophysiology, involving not only the presence of bacteria, but also immunological reactions. There is no specific method of diagnosis resulting in difficulties for good indication of treatment and to evaluate treatment efficacy. The literature review shows that ceftriaxone and doxycycline are the two most efficient antibiotics in this indication. Even if the methodology of the published studies is not always convincing, these two antibiotics proved their efficacy in articular as well as in neurological forms of the disease. In the late stage of borreliosis, antibiotics are less efficient. Various treatment modalities with different dosage or duration of treatment cannot let us conclude on a convincing regimen.
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Affiliation(s)
- Y Hansmann
- Service des maladies infectieuses et tropicales, hôpitaux universitaires de Strasbourg, 1, place de l'Hôpital, BP 426, 67091 Strasbourg cedex, France.
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Stricker RB. Counterpoint: long-term antibiotic therapy improves persistent symptoms associated with lyme disease. Clin Infect Dis 2007; 45:149-57. [PMID: 17578772 DOI: 10.1086/518853] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2007] [Accepted: 02/21/2007] [Indexed: 11/03/2022] Open
Abstract
BACKGROUND Controversy exists regarding the diagnosis and treatment of Lyme disease. Patients with persistent symptoms after standard (2-4-week) antibiotic therapy for this tickborne illness have been denied further antibiotic treatment as a result of the perception that long-term infection with the Lyme spirochete, Borrelia burgdorferi, and associated tickborne pathogens is rare or nonexistent. METHODS I review the pathophysiology of B. burgdorferi infection and the peer-reviewed literature on diagnostic Lyme disease testing, standard treatment results, and coinfection with tickborne agents, such as Babesia, Anaplasma, Ehrlichia, and Bartonella species. I also examine uncontrolled and controlled trials of prolonged antibiotic therapy in patients with persistent symptoms of Lyme disease. RESULTS The complex "stealth" pathology of B. burgdorferi allows the spirochete to invade diverse tissues, elude the immune response, and establish long-term infection. Commercial testing for Lyme disease is highly specific but relatively insensitive, especially during the later stages of disease. Numerous studies have documented the failure of standard antibiotic therapy in patients with Lyme disease. Previous uncontrolled trials and recent placebo-controlled trials suggest that prolonged antibiotic therapy (duration, >4 weeks) may be beneficial for patients with persistent Lyme disease symptoms. Tickborne coinfections may increase the severity and duration of infection with B. burgdorferi. CONCLUSIONS Prolonged antibiotic therapy may be useful and justifiable in patients with persistent symptoms of Lyme disease and coinfection with tickborne agents.
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Rödel R, Freyer A, Bittner T, Schäfer V, Hunfeld KP. In vitro activities of faropenem, ertapenem, imipenem and meropenem against Borrelia burgdorferi s.l. Int J Antimicrob Agents 2007; 30:83-6. [PMID: 17512703 DOI: 10.1016/j.ijantimicag.2007.03.008] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2007] [Revised: 03/13/2007] [Accepted: 03/14/2007] [Indexed: 11/28/2022]
Abstract
Little is known about the in vitro activity of penems and carbapenems against the spirochete Borrelia burgdorferi. Here, faropenem, ertapenem, imipenem and meropenem as well as the third-generation cephalosporin ceftriaxone and tobramycin were tested in vitro against 11 isolates of the B. burgdorferi sensu lato complex. On a microg/mL basis, ertapenem was the most potent carbapenem (minimal inhibitory concentration (MIC) range: 0.015-0.125 microg/mL), with in vitro activity comparable with that of ceftriaxone against Borrelia. These findings are supported by the results of time-kill experiments in a Borrelia afzelii skin isolate, demonstrating a >3 log10 unit (99.9%) reduction of the inoculum after 96 h of exposure to either drug at a concentration of three log2 unit dilutions above the respective MIC.
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Affiliation(s)
- Rebecca Rödel
- Institute of Medical Microbiology & Infection Control, University Hospital of Frankfurt, Paul-Ehrlich Str. 40, D-60596 Frankfurt/Main, Germany
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Hunfeld KP, Brade V. Antimicrobial susceptibility of Borrelia burgdorferi sensu lato: what we know, what we don't know, and what we need to know. Wien Klin Wochenschr 2007; 118:659-68. [PMID: 17160604 DOI: 10.1007/s00508-006-0693-z] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Human Lyme borreliosis is a multisystem disorder that can progress in stages and is transmitted by ticks of the Ixodes ricinus complex infected with the spirochete Borrelia burgdorferi sensu lato. Today, Lyme borreliosis is regarded as the most important human tickborne illness in the northern hemisphere. Soon after the causative agent was correctly identified and successfully isolated in 1982, antibiotic treatment was shown to be effective and since then a variety of in vitro and in vivo studies have been performed to further characterize the activity of antimicrobial agents against B. burgdorferi s.l. Although many antimicrobial agents have been tested for their in vitro activity against borreliae, the full spectrum of antibiotic susceptibility in B. burgdorferi s.l. has not been defined for many compounds. Moreover, our current understanding of possible antimicrobial resistance mechanisms in B. burgdorferi s.l. is limited and is largely founded on in vitro experiments on relatively few borrelial isolates. This review will summarize what is and what is not known about antimicrobial resistance in B. burgdorferi s.l. and will discuss open questions that continue to fuel the current debate on treatment-resistant Lyme borreliosis.
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Affiliation(s)
- Klaus-Peter Hunfeld
- Institute of Medical Microbiology and Infection Control, University Hospital of Frankfurt, Frankfurt/Main, Germany.
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Wormser GP, Dattwyler RJ, Shapiro ED, Halperin JJ, Steere AC, Klempner MS, Krause PJ, Bakken JS, Strle F, Stanek G, Bockenstedt L, Fish D, Dumler JS, Nadelman RB. The clinical assessment, treatment, and prevention of lyme disease, human granulocytic anaplasmosis, and babesiosis: clinical practice guidelines by the Infectious Diseases Society of America. Clin Infect Dis 2006; 43:1089-134. [PMID: 17029130 DOI: 10.1086/508667] [Citation(s) in RCA: 1262] [Impact Index Per Article: 70.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2006] [Accepted: 08/21/2006] [Indexed: 12/19/2022] Open
Abstract
Evidence-based guidelines for the management of patients with Lyme disease, human granulocytic anaplasmosis (formerly known as human granulocytic ehrlichiosis), and babesiosis were prepared by an expert panel of the Infectious Diseases Society of America. These updated guidelines replace the previous treatment guidelines published in 2000 (Clin Infect Dis 2000; 31[Suppl 1]:1-14). The guidelines are intended for use by health care providers who care for patients who either have these infections or may be at risk for them. For each of these Ixodes tickborne infections, information is provided about prevention, epidemiology, clinical manifestations, diagnosis, and treatment. Tables list the doses and durations of antimicrobial therapy recommended for treatment and prevention of Lyme disease and provide a partial list of therapies to be avoided. A definition of post-Lyme disease syndrome is proposed.
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Affiliation(s)
- Gary P Wormser
- Division of Infectious Diseases, Department of Medicine, New York Medical College, Valhalla, NY 10595, USA.
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Hunfeld KP, Ruzić-Sabljić E, Norris DE, Kraiczy P, Strle F. Risk of culture-confirmed borrelial persistence in patients treated for erythema migrans and possible mechanisms of resistance. Int J Med Microbiol 2006; 296 Suppl 40:233-41. [PMID: 16530006 DOI: 10.1016/j.ijmm.2006.01.028] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
Erythema migrans (EM) develops at the site of the tick bite in 77-90% of Lyme borreliosis (LB) patients and is therefore a common manifestation of early disease. Clinical treatment failures have been reported in early LB cases for almost every suitable antimicrobial agent. The exact risk of resistance to antibiotic treatment in patients with EM, however, is not known and there are few published cases of culture-proven treatment failure. Moreover, currently available diagnostic techniques cannot reliably discriminate between possible reinfection, true endogenous relapse and co-infection with other tick-borne pathogens. These drawbacks together with the phenomenon of resistance to therapy in individual patients undoubtedly contribute to the inconsistencies surrounding the optimal treatment regimens for LB and are often misinterpreted and misused to support prolonged antibiotic treatment regimens. The question for the underlying mechanisms of possible antimicrobial resistance in Borrelia burgdorferi sensu lato remains unresolved but a better understanding of such genetic or phenotypic mechanisms would be helpful for the treatment of LB and other spirochetal diseases. Investigations on this issue, at best, should start with borrelial isolates cultured from patients before the start of antibiotic therapy and again after the conclusion of treatment. This task, however, remains challenging insofar, as culture is rarely successful under routine laboratory conditions after antimicrobial therapy. Here, we review recent clinical and experimental data on treatment resistance in EM patients suggesting that, although rare, borrelial persistence does occur at the site of the infectious lesion after antibiotic treatment. Borrelial persistence, however, is unlikely to result from acquired resistance against antimicrobial agents that were used for initial specific chemotherapy.
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Affiliation(s)
- Klaus-Peter Hunfeld
- Institute of Medical Microbiology, University Hospital of Frankfurt, Paul-Ehrlich Str. 40, D-60596 Frankfurt/Main, Germany.
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Stricker RB, Lautin A, Burrascano JJ. Lyme disease: the quest for magic bullets. Chemotherapy 2006; 52:53-9. [PMID: 16498239 DOI: 10.1159/000091726] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2004] [Accepted: 06/20/2005] [Indexed: 01/20/2023]
Abstract
Lyme disease represents a growing public health threat. Recent molecular and genetic studies have confirmed that Borrelia burgdorferi, the spirochetal agent of Lyme disease, is one of the most complex bacteria known to man. Affinity for multiple cell types and the presence of non-replicating forms of B. burgdorferi have contributed to persistent infection and failure of simple antibiotic regimens. The controversial clinical science of Lyme disease has impeded reliable diagnosis and effective treatment of this protean illness. Two major clinical hurdles are the absence of a therapeutic endpoint in treating Lyme disease and the presence of tick-borne coinfections that may complicate the course of the illness. New strategies for the diagnosis, treatment and prevention of Lyme disease are urgently needed.
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Hunfeld KP, Ruzic-Sabljic E, Norris DE, Kraiczy P, Strle F. In vitro susceptibility testing of Borrelia burgdorferi sensu lato isolates cultured from patients with erythema migrans before and after antimicrobial chemotherapy. Antimicrob Agents Chemother 2005; 49:1294-301. [PMID: 15793100 PMCID: PMC1068612 DOI: 10.1128/aac.49.4.1294-1301.2005] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Clinical treatment failures have been reported to occur in early Lyme borreliosis (LB) for many suitable antimicrobial agents. Investigations of possible resistance mechanisms of the Borrelia burgdorferi complex must analyze clinical isolates obtained from LB patients, despite their receiving antibiotic treatment. Here, borrelial isolates obtained from five patients with erythema migrans (EM) before the start of antibiotic therapy and again after the conclusion of treatment were investigated. The 10 isolates were characterized by restriction fragment length polymorphism analysis and plasmid profile analysis and subjected to susceptibility testing against a variety of antimicrobial agents including those used for initial chemotherapy. Four out of five patients were infected by the same genospecies (Borrelia afzelii, n = 3; Borrelia garinii, n = 1) at the site of the EM lesion before and after antimicrobial therapy. In one patient the genospecies of the initial isolate (B. afzelii) differed from that of the follow-up isolate (B. garinii). No significant changes in the in vitro susceptibilities became obvious for corresponding clinical isolates before the start and after the conclusion of antimicrobial therapy. This holds true for the antimicrobial agents used for specific chemotherapy of the patients, as well as for any of the additional agents tested in vitro. Our study substantiates borrelial persistence in some EM patients at the site of the infectious lesion despite antibiotic treatment over a reasonable time period. Borrelial persistence, however, was not caused by increasing MICs or minimal borreliacidal concentrations in these isolates. Therefore, resistance mechanisms other than acquired resistance to antimicrobial agents should be considered in patients with LB resistant to treatment.
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Affiliation(s)
- Klaus-Peter Hunfeld
- Institute of Medical Microbiology, University Hospital of Frankfurt, Paul-Ehrlich Str. 40, D-60596 Frankfurt/Main, Germany.
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Hunfeld KP, Bittner T, Rödel R, Brade V, Cinatl J. New real-time PCR-based method for in vitro susceptibility testing of Anaplasma phagocytophilum against antimicrobial agents. Int J Antimicrob Agents 2004; 23:563-71. [PMID: 15194126 DOI: 10.1016/j.ijantimicag.2004.02.019] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2003] [Accepted: 02/12/2004] [Indexed: 11/29/2022]
Abstract
Up to now, only a few isolates of Anaplasma phagocytophilum have been tested for their susceptibility against a small number of antimicrobial agents. In addition, as with other fastidious or intracellular bacteria, the test methods are laborious and neither minimal inhibitory concentration (MIC) definitions, nor the test conditions and the inocula are standardised to date. A new 16S-rDNA-based real-time PCR assay has been developed and used under standardised conditions to analyse the activity of seven antimicrobial agents against two A. phagocytophilum isolates. After 72 h incubation, MICs were determined by software-assisted calculation of bacterial growth in samples and controls from semi-quantitative PCR results. In our study, the rank order of potency on a mg/l basis for the antimicrobial agents with enhanced in vitro activity against A. phagocytophilum was moxifloxacin (MIC: < or = 0.03 mg/l) > doxycycline (MIC: < or = 0.125 mg/l) > ciprofloxacin (MIC: 0.125 mg/l). Gentamicin, ampicillin, azithromycin and cethromycin showed no activity against the isolates tested in this investigation. Our new 16S-rDNA-PCR-based microdilution test system was shown to be sensitive, reproducible and reliable. The assay is capable of testing larger numbers of isolates and antimicrobial agents under standardised and very precise test conditions and may therefore offer a competent technical solution of the difficulties known to be associated with in vitro testing of other bacterial pathogens that grow intracellularly, such as chlamydia or rickettsia.
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Affiliation(s)
- Klaus-Peter Hunfeld
- Institute of Medical Microbiology, University Hospital of Frankfurt, D-60596 Frankfurt/Main, Germany.
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