In vitro activity of vancomycin against the spirochete Borrelia burgdorferi

The In Vitro Antimicrobial Susceptibility of Borrelia burgdorferi sensu lato: Shedding Light on the Known Unknowns

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.

Evaluation of the clinical relevance of vancomycin for the treatment of Lyme disease

Vancomycin is active in vitro and in vivo in mouse systems against Lyme disease borrelia; however, there are no published data on the efficacy of vancomycin in patients with Lyme disease and no convincing theoretical advantages of vancomycin over the currently used and highly effective orally administered antimicrobial agents, including doxycycline, amoxicillin and cefuroxime axetil. In addition, vancomycin may cause a wide variety of potentially serious adverse effects and requires the placement of an intravenous catheter. It is concluded that vancomycin is a much less attractive option for the treatment of patients with early Lyme disease (or any other manifestation of Lyme disease), compared with the antimicrobials currently being used. Based on available evidence, clinical studies to evaluate the safety and efficacy of vancomycin for Lyme disease cannot be recommended.

Vancomycin Reduces Cell Wall Stiffness and Slows Swim Speed of the Lyme Disease Bacterium

Borrelia burgdorferi, the spirochete that causes Lyme disease, is a tick-transmitted pathogen that requires motility to invade and colonize mammalian and tick hosts. These bacteria use a unique undulating flat-wave shape to penetrate and propel themselves through host tissues. Previous mathematical modeling has suggested that the morphology and motility of these spirochetes depends crucially on the flagellar/cell wall stiffness ratio. Here, we test this prediction using the antibiotic vancomycin to weaken the cell wall. We found that low to moderate doses of vancomycin (≤2.0 μg/mL for 24 h) produced small alterations in cell shape and that as the dose was increased, cell speed decreased. Vancomycin concentrations >1.0 μg/mL also inhibited cell growth and led to bleb formation on a fraction of the cells. To quantitatively assess how vancomycin affects cell stiffness, we used optical traps to bend unflagellated mutants of B. burgdorferi. We found that in the presence of vancomycin, cell wall stiffness gradually decreased over time, with a 40% reduction in the bending stiffness after 36 h. Under the same conditions, the swimming speed of wild-type B. burgdorferi slowed by ∼15%, with only marginal changes to cell morphology. Interestingly, our biophysical model for the swimming dynamics of B. burgdorferi suggested that cell speed should increase with decreasing cell stiffness. We show that this discrepancy can be resolved if the periplasmic volume decreases as the cell wall becomes softer. These results provide a testable hypothesis for how alterations of cell wall stiffness affect periplasmic volume regulation. Furthermore, since motility is crucial to the virulence of B. burgdorferi, the results suggest that sublethal doses of antibiotics could negatively impact spirochete survival by impeding their swim speed, thereby enabling their capture and elimination by phagocytes.

In Vitro Susceptibility of Isolates of Borrelia Burgdorferi S.L. to Antimicrobial Agents

In the present study, we investigate the in vitro antimicrobial activity of macrolides, β-lactams and tetracycline against Borrelia burgdorferi s.l. clinical and tick isolates. Minimal inhibitory concentrations (MICs) were determined in normal growth condition and after pre-exposure of the strains to sub-MIC of the founder of each drug family. All the classes of tested antibiotics showed good antibacterial activity against all the borreliae isolates and there were no significant susceptibility differences among clinical and tick isolates. After pre-exposure of the strains to sub-MIC of erythromycin, cefoxitin and tetracycline, we observed that some strains of B. burgdorferi s.l. showed higher MIC values to both the pre-exposed drug and drugs of the same family. The less susceptibility of borreliae, in the last growth condition in vitro, could be one of the justifications of clinical results indicating the limited efficacy of these antibiotics in treatment of B. burgdoferi infections.

Acetyl-Phosphate Is Not a Global Regulatory Bridge between Virulence and Central Metabolism in Borrelia burgdorferi

In B. burgdorferi, the Rrp2-RpoN-RpoS signaling cascade is a distinctive system that coordinates the expression of virulence factors required for successful transition between its arthropod vector and mammalian hosts. Rrp2 (BB0763), an RpoN specific response regulator, is essential to activate this regulatory pathway. Previous investigations have attempted to identify the phosphate donor of Rrp2, including the cognate histidine kinase, Hk2 (BB0764), non-cognate histidine kinases such as Hk1, CheA1, and CheA2, and small molecular weight P-donors such as carbamoyl-phosphate and acetyl-phosphate (AcP). In a report by Xu et al., exogenous sodium acetate led to increased expression of RpoS and OspC and it was hypothesized this effect was due to increased levels of AcP via the enzyme AckA (BB0622). Genome analyses identified only one pathway that could generate AcP in B. burgdorferi: the acetate/mevalonate pathway that synthesizes the lipid, undecaprenyl phosphate (C₅₅-P, lipid I), which is essential for cell wall biogenesis. To assess the role of AcP in Rrp2–dependent regulation of RpoS and OspC, we used a unique selection strategy to generate mutants that lacked ackA (bb0622: acetate to AcP) or pta (bb0589: AcP to acetyl-CoA). These mutants have an absolute requirement for mevalonate and demonstrate that ackA and pta are required for cell viability. When the ΔackA or Δpta mutant was exposed to conditions (i.e., increased temperature or cell density) that up-regulate the expression of RpoS and OspC, normal induction of those proteins was observed. In addition, adding 20mM acetate or 20mM benzoate to the growth media of B. burgdorferi strain B31 ΔackA induced the expression of RpoS and OspC. These data suggest that AcP (generated by AckA) is not directly involved in modulating the Rrp2-RpoN-RpoS regulatory pathway and that exogenous acetate or benzoate are triggering an acid stress response in B. burgdorferi.

Drug combinations against Borrelia burgdorferi persisters in vitro: eradication achieved by using daptomycin, cefoperazone and doxycycline

Although most Lyme disease patients can be cured with antibiotics doxycycline or amoxicillin using 2-4 week treatment durations, some patients suffer from persistent arthritis or post-treatment Lyme disease syndrome. Why these phenomena occur is unclear, but possibilities include host responses, antigenic debris, or B. burgdorferi organisms remaining despite antibiotic therapy. In vitro, B. burgdorferi developed increasing antibiotic tolerance as morphology changed from typical spirochetal form in log phase growth to variant round body and microcolony forms in stationary phase. B. burgdorferi appeared to have higher persister frequencies than E. coli as a control as measured by SYBR Green I/propidium iodide (PI) viability stain and microscope counting. To more effectively eradicate the different persister forms tolerant to doxycycline or amoxicillin, drug combinations were studied using previously identified drugs from an FDA-approved drug library with high activity against such persisters. Using a SYBR Green/PI viability assay, daptomycin-containing drug combinations were the most effective. Of studied drugs, daptomycin was the common element in the most active regimens when combined with doxycycline plus either beta-lactams (cefoperazone or carbenicillin) or an energy inhibitor (clofazimine). Daptomycin plus doxycycline and cefoperazone eradicated the most resistant microcolony form of B. burgdorferi persisters and did not yield viable spirochetes upon subculturing, suggesting durable killing that was not achieved by any other two or three drug combinations. These findings may have implications for improved treatment of Lyme disease, if persistent organisms or detritus are responsible for symptoms that do not resolve with conventional therapy. Further studies are needed to validate whether such combination antimicrobial approaches are useful in animal models and human infection.

A systematic review of Borrelia burgdorferi morphologic variants does not support a role in chronic Lyme disease

BACKGROUND

 Much of the controversy that surrounds Lyme disease pertains to whether it produces prolonged, treatment-refractory infection, usually referred to as chronic Lyme disease. Some have proposed that round morphologic variants of Borrelia burgdorferi, known variably as "cyst forms" and "L-forms," are responsible for the pathogenesis of chronic Lyme disease. We have undertaken a systematic review of the literature to determine if there is a documented role of these variants in Lyme disease pathogenesis or in syndromes compatible with chronic Lyme disease.

METHODS

 Two systematic literature searches were performed to identify studies in which round morphologic variants of B. burgdorferi have been described in situ in human specimens.

RESULTS

 Our primary literature search identified 6 studies that reported round morphologic variants of B. burgdorferi in specimens obtained from 32 total patients. No study described these forms in patients who had purely subjective symptom complexes (eg, fatigue or pain). No study investigated a causal relationship between morphologic variants and clinical disease or evaluated treatment of morphologic variants in vivo. Of 29 additional studies that described the morphology of B. burgdorferi from patients with Lyme disease, the organism was invariably described as having spirochetal morphology.

CONCLUSIONS

 In the context of the broader medical literature, it is not currently possible to ascribe a pathogenic role to morphologic variants of B. burgdorferi in either typical manifestations of Lyme disease or in other chronic disease states that are often labeled chronic Lyme disease. There is no clinical literature to justify specific treatment of B. burgdorferi morphologic variants.

Destruction of spirochete Borrelia burgdorferi round-body propagules (RBs) by the antibiotic tigecycline

Persistence of tissue spirochetes of Borrelia burgdorferi as helices and round bodies (RBs) explains many erythema-Lyme disease symptoms. Spirochete RBs (reproductive propagules also called coccoid bodies, globular bodies, spherical bodies, granules, cysts, L-forms, sphaeroplasts, or vesicles) are induced by environmental conditions unfavorable for growth. Viable, they grow, move and reversibly convert into motile helices. Reversible pleiomorphy was recorded in at least six spirochete genera (>12 species). Penicillin solution is one unfavorable condition that induces RBs. This antibiotic that inhibits bacterial cell wall synthesis cures neither the second "Great Imitator" (Lyme borreliosis) nor the first: syphilis. Molecular-microscopic techniques, in principle, can detect in animals (insects, ticks, and mammals, including patients) helices and RBs of live spirochetes. Genome sequences of B. burgdorferi and Treponema pallidum spirochetes show absence of >75% of genes in comparison with their free-living relatives. Irreversible integration of spirochetes at behavioral, metabolic, gene product and genetic levels into animal tissue has been documented. Irreversible integration of spirochetes may severely impair immunological response such that they persist undetected in tissue. We report in vitro inhibition and destruction of B. burgdorferi (helices, RBs = "cysts") by the antibiotic Tigecycline (TG; Wyeth), a glycylcycline protein-synthesis inhibitor (of both 30S and 70S ribosome subunits). Studies of the pleiomorphic life history stages in response to TG of both B. burgdorferi and Treponema pallidum in vivo and in vitro are strongly encouraged.

Daptomycin: The First Approved Lipopeptide Antimicrobial

OBJECTIVE

To review the literature concerning the first Food and Drug Administration-approved lipopeptide antimicrobial, daptomycin.

DATA SOURCES

A PUBMED search was conducted to identify pertinent English-language journal articles between 1985 and November 2003, and additional references were obtained from the bibliographies of these articles. Abstracts from the Interscience Conference on Antimicrobial Agents and Chemotherapy meetings from 1985 through 2003 also were reviewed.

STUDY SELECTION

All studies evaluating any aspect of daptomycin.

DATA SYNTHESIS

Daptomycin is a semisynthetic lipopeptide, the first such antimicrobial agent to reach the marketplace. Its mechanism of action differs from that of the related agent vancomycin in that much of its effect is not because of inhibition of peptidoglycan biosynthesis, but instead is a result of alterations in cell-membrane electrical charge and transport. It exhibits a broad spectrum of activity against gram-positive aerobes and anaerobes, including methicillin-, penicillin-, aminoglycoside-, and vancomycin-resistant strains. In subjects with normal renal function, the terminal disposition half-life is about 7 to 10 hours. It is principally eliminated as unchanged drug in the urine. Available clinical trial data demonstrate efficacy in complicated skin and skin-structure infections resulting from susceptible gram-positive pathogens, but not in pneumonia. The principal adverse event of concern, although rare, is myotoxicity, manifested by muscle pain and/or weakness and elevated serum creatine phosphokinase (CPK) concentrations. The approved dosage regimen is 4 mg/kg intravenously over 30 minutes once daily for 7 days to 14 days. Studies are underway evaluating doses of up to 8 mg/kg once daily.

CONCLUSIONS

Daptomycin, the first lipopeptide antimicrobial to be marketed, exhibits activity against multiresistant gram-positive pathogens, including linezolid- and quinupristindalfopristin-resistant strains. As such, it is a potentially valuable agent to treat infections resulting from such pathogens. To preserve its utility, it should not be used indiscriminately for infections resulting from pathogens sensitive to other antimicrobials. It is probably best used with restricted access and used only for multiresistant gram-positive pathogens where alternative agents cannot be employed. If used, careful monitoring for the signs and symptoms of myotoxicity, including obtaining weekly serum CPK levels, is mandatory. In addition, bacterial sensitivities to this agent should be prospectively monitored by national antimicrobial surveillance programs like SENTRY, TRUST, and LIBRA.

Antimicrobial susceptibility of Borrelia burgdorferi sensu lato: what we know, what we don't know, and what we need to know

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.

Role of Borrelia burgdorferi linear plasmid 25 in infection of Ixodes scapularis ticks

The tick-borne bacterium Borrelia burgdorferi has over 20 different circular and linear plasmids. Some B. burgdorferi plasmids are readily lost during in vitro culture or genetic manipulation. Linear plasmid 25, which is often lost in laboratory strains, is required for the infection of mice. Strains missing linear plasmid 25 (lp25(-)) are able to infect mice if the BBE22 gene on lp25 is provided on a shuttle vector. In this study, we examined the role of lp25 and BBE22 in tick infections. We tested the hypothesis that complementation with BBE22 in spirochetes lacking lp25 would restore the ability of spirochetes to infect ticks. A natural tick infection cycle was performed by feeding larvae on mice injected with the parental, lp25(-), or lp25(-) BBE22-complemented spirochete strains. In addition, larvae and nymphs were artificially infected with different strains to study tick infections independent of mouse infections. B. burgdorferi missing lp25 was significantly impaired in its ability to infect larval and nymphal ticks. When an lp25(-) strain was complemented with BBE22, the ability to infect ticks was partially restored. Complementation with BBE22 allowed spirochetes lacking lp25 to establish short-term infections in ticks, but in most cases the infection prevalence was lower than that of the wild-type strain. In addition, the number of infected ticks decreased over time, suggesting that another gene(s) on lp25 is required for long-term persistence in ticks and completion of a natural infection cycle.

In vitro activity of eight oral cephalosporins against Borrelia burgdorferi

Oral cephalosporins have not previously been extensively tested against larger numbers of Borrelia burgdorferi isolates derived from different clinical and geographical sources. This study investigated the in vitro activity of eight oral cephalosporins in addition to ceftriaxone and apramycin, against 17 isolates of the B. burgdorferi complex, including one B. valaisiana and one B. bissettii tick isolate. Minimal inhibitory concentrations and minimal borreliacidal concentrations providing 100% killing of the final inoculum were determined by a standardised methodology in Barbour-Stoenner-Kelly-medium after 72 h of incubation. The rank order of potency was ceftriaxone>cefuroxime-axetil>cefixime, cefdinir>cefpodoxime>cefaclor >ceftibuten, loracarbef>cefetamet-pivoxil, apramycin. Our study demonstrates the superior in vitro effectiveness of ceftriaxone with good to excellent activity with the oral agents cefuroxime-axetil, cefixime and cefdinir against B. burgdorferi under strictly standardised test conditions.

Standardised in vitro susceptibility testing of Borrelia burgdorferi against well-known and newly developed antimicrobial agents--possible implications for new therapeutic approaches to Lyme disease

Lyme disease represents a disorder of potentially chronic proportions, and relatively little is known about the in vivo pharmacodynamic interactions of antimicrobial agents with borreliae. So far, evidence-based drug regimens for the effective treatment of Lyme disease have not been definitively established. Moreover, therapeutic failures have been reported for almost every suitable antimicrobial agent currently available. Resistance to treatment and a protracted course of the disease, therefore, continue to pose problems for clinicians in the management of patients suffering from chronic Lyme disease. Further characterisation of the antibiotic susceptibility pattern and a better understanding of the interactions of B. burgdorferi with antimicrobial agents are urgently needed and continue to be crucial owing to considerable differences in the experimental conditions and test methods applied. The development of easily performed, new techniques for the sensitivity testing of B. burgdorferi provides the opportunity to study factors affecting the bacteriostatic and bactericidal action of recently introduced chemotherapeutic agents under more standardised conditions. For the first time, these studies provide direct evidence that, in addition to beta-lactams, macrolides, and tetracyclines which are recommended for stage-dependent treatment of Lyme borreliosis, other recently introduced substances, such as fluoroquinolones, everninomycins, and the ketolide family of antimicrobial agents, also show enhanced in vitro activity against borreliae. Some of these compounds, if effective in vivo as well, may prove to be useful agents in the treatment of certain manifestations of Lyme disease. As such, their potential role should be evaluated further by in vivo experiments and clinical trials. Finally, these antimicrobial agents may turn out to be very effective therapeutic alternatives on account of their oral availability, favourable pharmacodynamic profiles, and high tissue levels in cases where beta-lactames or tetracyclines cannot be administered without detrimental side-effects.

Genetics and regulation of chitobiose utilization in Borrelia burgdorferi

Borrelia burgdorferi spends a significant proportion of its life cycle within an ixodid tick, which has a cuticle containing chitin, a polymer of N-acetylglucosamine (GlcNAc). The B. burgdorferi celA, celB, and celC genes encode products homologous to transporters for cellobiose and chitobiose (the dimer subunit of chitin) in other bacteria, which could be useful for bacterial nutrient acquisition during growth within ticks. We found that chitobiose efficiently substituted for GlcNAc during bacterial growth in culture medium. We inactivated the celB gene, which encodes the putative membrane-spanning component of the transporter, and compared growth of the mutant in various media to that of its isogenic parent. The mutant was no longer able to utilize chitobiose, while neither the mutant nor the wild type can utilize cellobiose. We propose renaming the three genes chbA, chbB, and chbC, since they probably encode a chitobiose transporter. We also found that the chbC gene was regulated in response to growth temperature and during growth in medium lacking GlcNAc.

In vitro activities of fluoroquinolones against the spirochete Borrelia burgdorferi

Little is known to date about the in vitro activity of fluoroquinolones against Borrelia species. Our study aimed at determining the in vitro activities of 15 quinolones against nine isolates of the Borrelia burgdorferi sensu lato complex in addition to one Borrelia valaisiana and one Borrelia bissettii tick isolate. For the determination of MICs, a standardized colorimetric microdilution method was applied. Determination of minimal borreliacidal concentrations providing 100% killing of the final inoculum (MBCs) after 72 h and time-kill experiments were performed by conventional culture in Barbour-Stoenner-Kelly medium in combination with dark-field microscopy. The rank order of potency on a microgram-per-milliliter basis for the substances with in vitro activity against B. burgdorferi was gemifloxacin (MIC at which 90% of the isolates tested are inhibited [MIC(90)], 0.12 microg/ml) > sitafloxacin (MIC(90), 0.5 microg/ml), grepafloxacin (MIC(90), 0.5 microg/ml) > gatifloxacin (MIC(90), 1 microg/ml), sparfloxacin (MIC(90), 1 microg/ml), trovafloxacin (MIC(90), 1 microg/ml) > moxifloxacin (MIC(90), 2 microg/ml), ciprofloxacin (MIC(90), 2 microg/ml) > levofloxacin (MIC(90), 4 microg/ml) > ofloxacin (MIC(90), 8 microg/ml), norfloxacin (MIC(90), 8 microg/ml) > fleroxacin (MIC(90), >16 microg/ml), and pefloxacin (MIC(90), 32 microg/ml) > nalidixic acid (MIC(90), 256 microg/ml). After 72 h of exposure, gemifloxacin was borreliacidal (100% killing) against the isolates investigated at a median MBC of 4 microg/ml. In the other compounds tested, median MBCs were higher (> or =8 microg/ml). Results of electron microscopy and time-kill studies clearly support an in vitro activity of some fluoroquinolones against borreliae. Our study demonstrates for the first time the enhanced in vitro effectiveness of some of the recently introduced 4-quinolones against B. burgdorferi.

In vitro activity of mezlocillin, meropenem, aztreonam, vancomycin, teicoplanin, ribostamycin and fusidic acid against Borrelia burgdorferi

The in vitro susceptibility profile of Borrelia burgdorferi is not yet well defined for several antibiotics. Our study explored the in vitro susceptibility of B. burgdorferi to mezlocillin, meropenem, aztreonam, vancomycin, teicoplanin, ribostamycin and fusidic acid. Minimal inhibitory concentrations (MICs) and minimal borreliacidal concentrations (MBCs) were measured using a standardised colorimetric microdilution method and conventional subculture experiments. MIC values were lowest for mezlocillin (MIC(90), < or =0.06 mg/l) and meropenem (MIC(90), 0.33 mg/l). Vancomycin (MIC(90), 0.83 mg/l) was less effective in vitro. Borreliae proved to be resistant to aztreonam (MIC(90), >32 mg/l), teicoplanin (MIC(90), 6.6 mg/l), ribostamycin (MIC(90), 32 mg/l), and fusidic acid (MIC(90), >4 mg/l). The mean MBCs resulting in 100% killing of the final inoculum after 72 h of incubation were lowest for mezlocillin (MBC, 0.83 mg/l). This study gathered further data on the in vitro susceptibility patterns of the B. burgdorferi complex. The excellent in vitro effectiveness of acylamino-penicillin derivatives and their suitability for the therapy of Lyme disease is emphasised.

Borrelia burgdorferi periplasmic flagella have both skeletal and motility functions

Bacterial shape usually is dictated by the peptidoglycan layer of the cell wall. In this paper, we show that the morphology of the Lyme disease spirochete Borrelia burgdorferi is the result of a complex interaction between the cell cylinder and the internal periplasmic flagella. B. burgdorferi has a bundle of 7-11 helically shaped periplasmic flagella attached at each end of the cell cylinder and has a flat-wave cell morphology. Backward moving, propagating waves enable these bacteria to swim in both low viscosity media and highly viscous gel-like media. Using targeted mutagenesis, we inactivated the gene encoding the major periplasmic flagellar filament protein FlaB. The resulting flaB mutants not only were nonmotile, but were rod-shaped. Western blot analysis indicated that FlaB was no longer synthesized, and electron microscopy revealed that the mutants were completely deficient in periplasmic flagella. Wild-type cells poisoned with the protonophore carbonyl cyanide-m-chlorophenylhydrazone retained their flat-wave morphology, indicating that the periplasmic flagella do not need to be energized for the cell to maintain this shape. Our results indicate that the periplasmic flagella of B. burgdorferi have a skeletal function. These organelles dynamically interact with the rod-shaped cell cylinder to enable the cell to swim, and to confer in part its flat-wave morphology.

Development of an extrachromosomal cloning vector system for use in Borrelia burgdorferi

Molecular genetic analysis of Borrelia burgdorferi, the cause of Lyme disease, has been hampered by the absence of any means of efficient generation, identification, and complementation of chromosomal and plasmid null gene mutants. The similarity of borrelial G + C content to that of Gram-positive organisms suggested that a wide-host-range plasmid active in Gram-positive bacteria might also be recognized by borrelial DNA replication machinery. One such plasmid, pGK12, is able to propagate in both Gram-positive and Gram-negative bacteria and carries erythromycin and chloramphenicol resistance markers. pGK12 propagated extrachromosomally in B. burgdorferi B31 after electroporation but conferred only erythromycin resistance. pGK12 was used to express enhanced green fluorescent protein in B31 under the control of the flaB promoter. Escherichia coli transformed with pGK12 DNA extracted from B31 expressing only erythromycin resistance developed both erythromycin and chloramphenicol resistance, and plasmid DNA isolated from these transformed E. coli had a restriction pattern similar to the original pGK12. Our data indicate that the replicons of pGK12 can provide the basis to continue developing efficient genetic systems for B. burgdorferi together with the erythromycin resistance and reporter egfp genes.

In-vitro and in-vivo antibiotic susceptibilities of Lyme disease Borrelia isolated in China

The antibiotic susceptibilities of seven Borrelia burgdorferi sensu lato isolates from Ixodes persulcatus in China were examined by in-vitro microdilution minimum inhibition concentration (MIC) and macrodilution minimum bactericidal concentration (MBC) methods. All isolates tested were susceptible to amoxicillin, erythromycin, and minocycline. The MICs of these drugs for the Chinese isolates were 0.025-0.1 microg/ml, <0.012-0.05 microg/ml, and <0.012-0.05 microg/ml, respectively. The MBCs were 0.1-0.39 microg/ml, <0.012-0.2 microg/ml, and 0.025-0.39 microg/ml, respectively. The in-vivo antimicrobial susceptibilities of the Chinese Borrelia isolates to two test drugs, amoxicillin and minocycline, were evaluated using ddY mice. Mice were infected by subcutaneous inoculation into the right hind footpad. When infection was confirmed, the mice were treated by subcutaneous injection of the test drugs into the back. Amoxicillin and minocycline, which possessed high in-vitro activities against Lyme disease Borrelia, provided good protection against borreliosis in this animal model. Higher doses of these drugs resulted in elimination of the Lyme disease spirochete from all animals receiving this course of treatment. The 50% curative doses (CD50) of amoxicillin and minocycline were 8.7 mg/kg and 3.1 mg/kg, respectively. This suggested that amoxicillin and minocycline could be useful for the treatment of Chinese Borrelia infection.

In vitro activities of the everninomicin SCH 27899 and other newer antimicrobial agents against Borrelia burgdorferi

The in vitro activity of the everninomicin antibiotic SCH 27899 against 17 isolates of Borrelia spp. was investigated. MICs ranged from 0.06 to 0.5 microg/ml. Time-kill studies with the B31 strain of B. burgdorferi demonstrated >/=3-log10-unit killing after 72 h with concentrations representing four times the MIC. The in vitro activity of four other newer antimicrobial agents, meropenem, cefepime, quinupristin-dalfopristin, and linezolid, was also tested against the B31 strain. Meropenem was the most potent of the latter agents, with an MIC of 0.125 microg/ml.

An in vitro study of the susceptibility of mobile and cystic forms of Borrelia burgdorferi to metronidazole

The aim of this study was to examine the susceptibility of mobile and cystic forms of Borrelia burgdorferi to metronidazole. Because B. burgdorferi is a microaerobic bacterium like Helicobacter pylori, metronidazole (MZ) was chosen in the susceptibility test. For both microaerobic and aerobic incubation the normal mobile spirochetes were resistant to this antibiotic with an MBC > or = 512 microg/ml. Conversion of mobile spirochetes to cystic forms was not observed when they were incubated with MZ. When they were incubated under microaerobic conditions, the biologically active cystic forms had an MBC > or = 4 microg/ml, but the MBC was > or = 32 microg/ml with aerobic incubation at 37 degrees C. Staining with acridine orange (AO), dark field microscopy (DFM), and transmission electron microscopy (TEM) revealed that the contents of the cysts were degraded when the concentration of MZ was > or = MBC. Some cysts were also ruptured. When incubated with a sufficient concentration of MZ, core structures did not develop inside the cysts, and AO revealed less RNA in the cysts. Our observations may help efforts to treat resistant infections caused by B. burgdorferi with a combination of MZ and other antibiotics in order to eradicate both cystic and mobile forms of B. burgdorferi.

Characterization of the physiological requirements for the bactericidal effects of a monoclonal antibody to OspB of Borrelia burgdorferi by confocal microscopy

A confocal microscopy study was undertaken to characterize the bactericidal effects of the Fab fragments of CB2, an immunoglobulin G1kappa murine monoclonal antibody, to an epitope in the carboxy region of the outer surface protein B (OspB) of Borrelia burgdorferi. Simultaneous direct labeling of both fixed and live spirochetes with fluorochrome-labeled Fab-CB2 and 11G1, and an immunoglobulin Mkappa monoclonal antibody to OspA, showed that OspA and OspB seem to colocalize in dead spirochetes but do not appear to be physically associated when the organisms are alive. A polar bleb composed of a Fab-CB2-OspB complex, followed by incorporation of 11G1-OspA, precedes the formation of a spheroplast. The spheroplasts contain both OspA and OspB and are a terminal stage in the bactericidal process induced by Fab-CB2. Outer membrane destabilization by Fab-CB2, but not cell wall or cytoplasmic membrane alterations, was demonstrated experimentally by the sequential treatment of spirochetes with Fab-CB2 and monoclonal antibodies to flagellin and DnaK. The action of Fab-CB2 is epitope specific, as another monoclonal antibody to an epitope in the amino terminus of OspB was not bactericidal. The bactericidal effect of Fab-CB2 is not dependent on the induction of spirochetal proteases but is dependent on the presence of Ca2+ and Mg2+. Supplementation of Ca2(+)- and Mg2(+)-free medium with these cations restored the bactericidal effects of Fab-CB2. The mechanism by which a Fab fragment of an antibody destroys a bacterium directly may represent a novel form of antibody-organism interaction.

In vivo activities of ceftriaxone and vancomycin against Borrelia spp. in the mouse brain and other sites

Borrelia burgdorferi, the agent of Lyme disease, and B. turicatae, a neurotropic agent of relapsing fever, are susceptible to vancomycin in vitro, with an MIC of 0.5 microgram/ml. To determine the activity of vancomycin in vivo, particularly in the brain, we infected adult immunocompetent BALB/c and immunodeficient CB-17 scid mice with B. burgdorferi or B. turicatae. The mice were then treated with vancomycin, ceftriaxone as a positive control, or normal saline as a negative control. The effectiveness of treatment was assessed by cultures of blood and brain and other tissues. Ceftriaxone at a dose of 25 mg/kg of body weight administered every 12 h for 7 to 10 days eliminated cultivable B. burgdorferi or B. turicatae from all BALB/c or scid mice in the study. Vancomycin at 30 mg/kg administered every 12 h was effective in eliminating infection from immunodeficient mice if treatment was started within 3 days of the onset of infection. If treatment with vancomycin was delayed for 7 days or more, vancomycin failed to eradicate infection with B. burgdorferi or B. turicatae from immunodeficient mice. The failure of vancomycin in eradicating established infections in immunodeficient mice was associated with the persistence of viable spirochetes in the brain during antibiotic treatment.

In vitro antimicrobial susceptibility testing of Borrelia burgdorferi: influence of test conditions on minimal inhibitory concentration (MIC) values

A broth microdilution assay was performed to determine the minimal inhibitory concentrations (MICs) of 25 antimicrobial agents for two strains of Borrelia (B.) burgdorferi sensu lato and one strain of B. hermsii. The method comprised BSK II medium lacking gelatin and an incubation period of 72 hours. To investigate the influence of reading mode and density of inoculum on MIC values, microscopical as well as macroscopical MIC reading was performed using standardized final inocula of 10(6) and 10(7) borreliae/ml. Data were processed by two-way analysis of variance. In the microdilution assay, MIC values were significantly influenced either by the inoculum density or reading mode. However, using clearly defined criteria for macroscopical endpoint determination, MICs from macroscopical and microscopical reading were found to be in close agreement. B. burgdorferi sensu lato strains tested were highly susceptible to azithromycin, erythromycin, mezlocillin, piperacillin as well as ceftriaxone, with MICs ranging from < or = 0.016 to 0.125 microgram/ml. B. hermsii was highly susceptible to azithromycin and erythromycin. In comparison to B. hermsii, the beta-lactam antibiotics revealed a significantly higher activity and gentamicin, ofloxacin, and rifampin revealed a significantly lower activity against B. burgdorferi sensu lato strains. To further investigate interactions between BSK II medium, incubation time, and antibiotic efficacy, an agar diffusion bioassay was performed. Out of seven antibiotics tested, the activities of mezlocillin, penicillin G, and piperacillin were significantly influenced by BSK II medium and incubation period and showed a marked decrease of on average 84.0% within 72 hours of incubation.

Effects of penicillin, ceftriaxone, and doxycycline on morphology of Borrelia burgdorferi

Antibiotic therapy with penicillin, doxycycline, and ceftriaxone has proven to be effective for the treatment of Lyme borreliosis. In some patients, however, it was noticed that borreliae can survival in the tissues in spite of seemingly adequate therapy. For a better understanding of this phenomenon, we investigated the different modes of degeneration of Borrelia burgdorferi suspensions during a 96-h exposure to various antibiotics. By dark-field microscopy and ultrastructural investigations, increasing blebbing and the gradual formation of granular and cystic structures could be followed during the exposure time. Although antibiotic concentrations at the MIC at which 90% of organisms are inhibited after 72 h were 80% or even greater, motile organisms were still present after incubation with penicillin and doxycycline but not after incubation with ceftriaxone. By transmission electron microscopy, intact spirochetal parts, mostly situated in cysts, were seen up to 96 h after exposure with all three antibiotics tested. According to experiences from studies with other spirochetes it is suggested that encysted borreliae, granules, and the remaining blebs might be responsible for the ongoing antigenic stimulus leading to complaints of chronic Lyme borreliosis.

Ultrastructure of Borrelia burgdorferi after exposure to benzylpenicillin

The aim of this study was to investigate the morphological changes of Borrelia burgdorferi associated with penicillin treatment. An isolate of B. burgdorferi from an erythema migrans lesion was cultivated in BSK II medium and exposed to increasing concentrations (0.0625 mg/l-2 mg/l) of penicillin G for 5 days. The in vitro minimal inhibitory concentration (MIC) was determined to be 0.5 mg/l by broth dilution method. The morphological structures of untreated spirochetes, as well as their characteristic ultrastructural changes when exposed to penicillin, were observed by electron microscopy. The following alterations were discovered: (i) Numerous outer sheath blebs at a penicillin concentration of 0.0625 mg/l. (ii) A characteristic irregular waveform of the borrelial cells and complete loss of the outer sheath at a penicillin concentration of 0.125 mg/l. (iii) The presence of "spheroplasts" at the same concentration. (iv) Structural changes of the protoplasmic cylinder complex which showed an irregular pattern at a penicillin concentration of 0.125 mg/l. (v) Disruption of the protoplasmic cylinder complex into several parts at penicillin concentrations of 0.25 mg/l and 0.5 mg/l. (vi) Severe cytolysis at penicillin concentrations of 1 mg/l and 2 mg/l.

In vitro antibiotic susceptibilities of Borrelia isolates from erythema migrans lesion of Lyme disease patients in Japan

Antibiotic susceptibilities of twelve borrelial isolates from skin of patients with erythema migrans (EM) and ticks (Ixodes persulcatus and I. ovatus) in Japan were examined by in vitro microdilution MIC method and macrodilution MBC method. Nine EM isolates and 3 tick isolates were susceptible to amoxicillin, erythromycin, and minocycline. MICs for Japanese isolates were 0.038-0.30 microgram/ml, < 0.012 microgram/ml, and < 0.012-0.05 microgram/ml, respectively. MBCs were as follows: 0.038-0.88 microgram/ml, < 0.012-0.10 microgram/ml, and < 0.025-0.78 microgram/ml, respectively. These antibiotics could be recommended for treatment of patients in early stage of Lyme disease in Japan.

A bactericidal antibody to Borrelia burgdorferi is directed against a variable region of the OspB protein

Borrelia burgdorferi, an agent of Lyme disease, is killed by some monoclonal antibodies in the absence of complement or phagocytes. In the present study, the bactericidal action of monoclonal antibodies against B. burgdorferi and B. hermsii, a cause of relapsing fever, was further characterized. H6831, an antibody recognizing the OspB proteins of some B. burgdorferi strains, and H4825, an antibody specific for one serotype of B. hermsii, were purified, and Fab fragments of the antibodies were prepared. In time-kill studies, more than 99.9% of strain B31 B. burgdorferi cells were killed after 30 min of exposure to H6831 Fab fragments. The MBC of the Fab fragments was 10 micrograms/ml. Electron microscopy revealed that the bactericidal Fab fragments produced numerous blebs and cell lysis of the borrelias for which they were specific. To identify the epitope for H6831, the OspB sequences of H6831-susceptible and -resistant strains and mutants were determined. The deduced OspB proteins of all H6831-resistant strains and mutants differed from the strain B31 OspB at residue 253. Murine antisera raised against a 21-mer synthetic peptide representing the region around residue 253 were specific for strain B31 by Western blot (immunoblot) and growth inhibition assays. Furthermore, the antipeptide serum inhibited the binding of H6831 to whole borrelias. These findings indicated that the linear component of the bactericidal antibody's epitope was located at or near residue 253.