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* These authors contributed equally
In vitro culture is a direct detection method for the presence of living bacteria. This protocol describes methods for the culture of diverse Borrelia spirochetes, including those of the Borrelia burgdorferi sensu lato complex, relapsing fever Borrelia species, and Borrelia miyamotoi. These species are fastidious and slow growing but can be cultured.
The Borrelia consists of three groups of species, those of the Lyme borreliosis (LB) group, also known as B. burgdorferi sensu lato (s.l.) and recently reclassified into Borreliella, the relapsing fever (RF) group Borrelia, and a third reptile-associated group of spirochetes. Culture-based methods remain the gold standard for the laboratory detection of bacterial infections for both research and clinical work, as the culture of pathogens from bodily fluids or tissues directly detects replicating pathogens and provides source material for research. Borrelia and Borreliella spirochetes are fastidious and slow growing, and thus are not commonly cultured for clinical purposes; however, culture is necessary for research. This protocol demonstrates the methodology and recipes required to successfully culture LB and RF spirochetes, including all recognized species from B. burgdorferi s.l. complex including B. afzelii, B. americana, B. andersonii, B. bavariensis, B. bissettii/bissettiae, B. burgdorferi sensu stricto (s.s.), B. californiensis, B. carolinensis, B. chilensis, B. finlandensis, B. garinii, B. japonica, B. kurtenbachii, B. lanei, B. lusitaniae, B. maritima, B. mayonii, B. spielmanii, B. tanukii, B. turdi, B. sinica, B. valaisiana, B. yangtzensis, and RFspirochetes, B. anserina, B. coriaceae, B. crocidurae, B. duttonii, B. hermsii, B. hispanica, B. persica, B. recurrentis, and B. miyamotoi. The basic medium for growing LB and RF spirochetes is the Barbour-Stoenner-Kelly (BSK-II or BSK-H) medium, which reliably supports the growth of spirochetes in established cultures. To be able to grow newly isolated Borrelia isolates from tick- or host-derived samples where the initial spirochete number is low in the inoculum, modified Kelly-Pettenkofer (MKP) medium is preferred. This medium also supports the growth of B. miyamotoi. The success of the cultivation of RF spirochetes also depends critically on the quality of ingredients.
Borrelia is a genus of spirochete bacteria that encompasses three major clades: the Lyme borreliosis (LB) group, the relapsing fever (RF) group, and a less well-characterized group seemingly restricted to reptiles. Borrelia taxonomy is in flux with the advent of molecular methodologies that allow genome and proteome comparisons, as is true of most other taxonomic groups1,2,3,4,5,6,7. The LB group (also called the Lyme disease group) has traditionally been termed Borrelia burgdorferi sensu lato after its best-characterized member Borrelia burgdorferi sensu stricto. This paper uses the currently most widely used terminology: the LB, the RF, and the reptile-associated group, and describes the culture protocols for the LB and the RF groups.
As would be expected for a member of the family Spirochaetaceae, Borrelia can adopt the distinctively long and thin spiral shape, typically 20-30 µm long and 0.2-0.3 µm wide. However, Borrelia cells are highly pleomorphic and can adopt many other shapes in both culture and in vivo1,8 as a result of their complex cellular and genetic structure. In its spirochetal form, the planar sine wave morphology results from its axial endoflagella rotating in the periplasmic space between the inner and outer membranes. This structure enables the cells to be highly motile, with the outer membrane containing proteins that enable the cell to interact with host tissues9,10. The expression of the outer membrane proteins is tightly regulated and affect not only host tissue invasion but also interaction with the host immune system11. This complex gene expression allows the Borrelia cells to shuttle between the very different environments of vertebrate hosts and invertebrate vectors. The genome of Borrelia is unusual among prokaryotes, consisting of a linear rather than a circular chromosome. In addition to the linear chromosome, Borrelia species contain 7-21 plasmids, some linear and some circular. The plasmids harbor the majority of genes required for host adaptation and virulence, and the circular plasmids derived from prophages are thought to be responsible for the majority of horizontal gene flow between spirochetal cells12,13. Consistent with a role in host adaptation, some, possibly many or all, members of the Lyme borreliosis group lose plasmids in culture14. The best studied "lab adapted" strain of B. burgdorferi, B31, has only seven of the nine plasmids found in wild isolates of this species15. Similarly, B. garinii loses plasmids in culture16. Some studies have shown that RF species and B. miyamotoi retain plasmids when cultured14,17, but recent work demonstrates altered plasmids and infectivity with long-term in vitro cultivation18.
Culture-based methods remain the gold standard for the laboratory detection of bacterial infections, for both research and clinical work14,17. The culture of pathogens from bodily fluids or tissues directly detects replicating pathogens and provides source material for research14,17. This protocol demonstrates the methodology and recipes required to successfully culture the spirochetes of the LB group as well as RF Borrelia and B. miyamotoi. The basic medium for growing Borrelia spirochetes is the Barbour-Stoenner-Kelly medium (BSK-II or the commercially available BSK-H), with or without antibiotics to reduce the growth of contaminating prokaryotes. This medium was adapted from a medium originally used to support RF Borrelia19, further modified by Stoenner20 and then by Barbour21. Many modifications have since been developed, each having effects on bacterial physiology that can affect growth, infectivity, and pathogenicity22. This medium reliably supports the growth of spirochetes in established cultures and has been used to isolate spirochetes from tick, mammal, and clinical samples23. The more recently developed variation, modified Kelly-Pettenkofer (MKP) medium, can provide better isolation success, morphology, and motility when isolating new Borrelia isolates from environmental samples, when the number of spirochetes present in the sample available to seed the culture is low23,24. In all cases, the success of cultivation is critically dependent on the freshly prepared medium and the use of appropriate ingredients; not all commercial ingredients produce high-quality medium. Inoculated cultures can be conveniently incubated without shaking in a conventional 32-34 °C incubator in the presence of a small amount of residual ambient oxygen. Borrelia spirochetes are anaerobes but are exposed in nature to fluctuations in oxygen and carbon dioxide concentrations and respond with changes in gene expression26,27,28,29. Thus, gene expression, growth, and other metabolic studies should control for oxygen and carbon dioxide levels with the use of an oxygen-controlled incubator or anaerobic chamber. In culture, cultures are checked weekly, or more often, for the presence of spirochetes with either darkfield microscopy or phase contrast microscopy. Culture smears can be stained with either silver stains, immunohistochemistry, or through the use of fluorescently tagged strains29,30. PCR followed by DNA sequencing is a sensitive and specific method to detect and genetically identify or confirm the Borrelia species30,31,32,33.
Many minor variations on BSK-II exist, and some are commercially available. The protocol described here in section 1 has been adapted from Barbour (1984)21. Liquid MKP medium is a more recently developed medium and is described in section 2. It is prepared according to a previously reported protocol33,34, which, similarly to BSK medium, consists of two steps: preparation of basic medium and preparation of complete medium. Borrelia culture medium can be prepared with or without antibiotics, as described in section 3; the antibiotics act to reduce contaminating bacteria introduced when inoculating with clinical or environmental samples, as described in section 4; if inoculating with pure Borrelia sp. culture, antibiotics may not be needed. Making long-term Borrelia stocks is often important, and a protocol for doing so is described in section 5. Section 6 describes using these media to isolate pure Borrelia sensu lato clones from clinical or environmental samples. There are a number of approaches possible36; below is one found to be effective. The plating medium used in this protocol is a modification of BSK-II plating medium37 and MKP medium34 (with rabbit serum increased to 10%38).
All studies involving samples obtained from human subject were approved by the Institutional Review Board of the relevant University and/or medical facility, and written informed consent was obtained from participants before the samples were collected. All studies involving samples obtained from animals were approved and conducted under the guidelines of the Institutional Animal Ethics Committee. Where relevant, approvals have been obtained for environmental sampling.
NOTE: The success of culture is critically dependent on the quality of ingredients. Commercial BSK medium is available and robustly supports the growth of lab-adapted pure B. burgdorferi and related species where high dose inoculum can be used to seed the culture. For isolates of strains from primary biological material, freshly prepared medium is preferred and often necessary.
Borrelia sp. are known or suspected pathogens, and unscreened human or animal tissues can also be a biohazard. Handling of potentially infectious material requires personal protective equipment and sterile technique for investigator safety. Additionally, the medium is so nutrient-rich that the culture is easily contaminated. Biosafety level 2 containment is generally required for this work and all work with Borrelia sp. or samples should be conducted in a biological safety cabinet.
1. Instructions for making BSK-II medium
Constituents | Amount (/L) |
BSA fraction V | 50 g |
CMRL-1066 (10x) | 100 mL |
Neopeptone | 5 g |
Hepes | 6 g |
Citric acid trisodium salt dihydrate | 0.7 g |
Glucose | 5 g |
TC Yeastolate | 2 g |
Pyruvic acid (Na salt) | 0.8 g |
N-acetyl-D-glucoseamine | 0.4 g |
Sodium bicarbonate | 2.2 g |
Water (high purity) | 900 mL |
Table 1: Composition of 1 L of BSK-II medium.
Source | Suitability |
Serva GmbH, Heidelberg, Germany | Yes |
Proliant Biologicals, Boone IA, USA | Yes |
Sigma (Millipore-Sigma & Sigma- Aldrich), St. Louis, MO, United States | No |
Table 2: Sources of BSA and suitability for BSK-II medium.
2. Instructions for making MKP
Constituents | Amount (/L) |
CMRL-1066 (10x without glutamine) | 100 mL (if liquid)/9.7 g/L if powder |
Neopeptone | 3 g |
Hepes | 6 g |
Citric acid | 0.7 g |
Glucose | 3 g |
Pyruvic acid | 0.8 g |
N-acetylglucoseamine | 0.4 g |
Sodium bicarbonate | 2 g |
Table 3: Composition of 1 L of basic MKP (Modified Kelly-Pettenkofer) medium.
Constituents | Amount (mL) |
Basic medium | 500 |
7% gelatin (in H2O) (freshly autoclaved but not hot) | 100 |
Rabbit serum | 36 |
35% BSA | 17.5 |
Table 4: Composition of MKP (Modified Kelly-Pettenkofer) complete medium.
3. Culture of Borrelia, with or without antibiotics
4. Long-term storage of Borrelia cultures
5. Isolation of spirochetes from environmental or clinical sources
NOTE: If isolating material from human, animal, or environmental sources, research ethics, animal care, or ecological certification, as appropriate, must be obtained.
6. Isolation of monoclonal populations of B. burgdorferi sensu lato spirochetes and B. miyamotoi from liquid cultures by cultivation on solid media
Borrelia culture media BSK and MKP, and variants, are rich culture media with ingredients that need to be prepared and sterilized sequentially. When correctly prepared, BSK medium should be red-orange and clear (Figure 1). Turbidity and precipitation that persist after warming indicate problematic ingredients, medium production, or contamination; such medium is best discarded. If gelatin is added to BSK and with MKP, the medium will be gelatinous when refrigerated; upon warming, it ...
The laboratory culture of bacteria is the springboard for research. The profound advantage conferred by the ability to culture is exemplified by the struggle, over more than a century culminating only recently in success, to culture Treponema pallidum, the spirochete that is the etiological agent of syphilis44. Borrelia spirochetes are also challenging to culture, but culture is possible23,24,...
No conflicts of interest were declared.
This work was partially supported by the Natural Science and Engineering Research Council of Canada and the Canadian Lyme disease Foundation (AB and VL), the Swedish Research Council (SB, M-LF and IN), TAČR GAMA 2 project - "Support of application potential verification 2.0 at the Biology Centre CAS" (TP01010022) (MG and NR), and by a grant from Ministry of Health of the Czech Republic NV19-05-00191 (MG and NR). We thank S. Vranjes (2021, Rudenko lab) for the image in Figure 4 and J. Thomas-Ebbett (2021, Lloyd lab) for the images in Figure 5. We thank all researchers who have contributed to the field and apologize to those whose work we were not able to cite due to space limitations.
Name | Company | Catalog Number | Comments |
1.7 mL tubes | VWR | 87003-294 | Standard item - any supplier will do |
0.2 µm Sterile syringe filter | VWR | 28145-501 | Standard item - any supplier will do |
10 µL barrier pipette tip | Neptune | BT10XLS3 | Standard item - any supplier will do |
10 mL Serological pipettes | Celltreat | 229011B | Standard item - any supplier will do |
1000 µL barrier pipette tip | Neptune | BT1000.96 | Standard item - any supplier will do |
15 mL tube | Celltreat | 188261 | Standard item - any supplier will do |
20 µL barrier pipette tip | Neptune | BT20 | Standard item - any supplier will do |
20 mL Sterile syringe | BD | 309661 | Standard item - any supplier will do |
200 µL barrier pipette tip | Neptune | BT200 | Standard item - any supplier will do |
25 mL Screw Cap Culture Tubes | Fisher Scientific | 14-933C | Standard item - any supplier will do |
25 mL Serological pipettes | Celltreat | 229025B | Standard item - any supplier will do |
3 mL Sterile syringe | BD | 309657 | Standard item - any supplier will do |
35% BSA | Sigma | A-7409 | Source is important - see note |
5 mL Serological pipettes | Celltreat | 229006B | Standard item - any supplier will do |
50 mL tube | Celltreat | 229421 | Standard item - any supplier will do |
6.5 ml MKP glass tubes | Schott | Schott Nr. 26 135 115 | Standard item - any supplier will do |
Amikacine | Sigma | PHR1654 | Standard item - any supplier will do |
Amphotericin B | Sigma | A9528-100MG | Standard item - any supplier will do |
Bactrim/rimethoprim/sulfamethoxazole | Sigma | PHR1126-1G | Standard item - any supplier will do |
BBL Brucella broth | BD | 211088 | Standard item - any supplier will do |
Biosafety Cabinet | Labconco | 302419100 | Standard item - any supplier will do |
Blood collection tubes (yellow top - ACD) | Fisher Scientific | BD Vacutainer Glass Blood Collection Tubes with Acid Citrate Dextrose (ACD) | Standard item - any supplier will do |
BSK-H Medium [w 6% Rabbit serum] | Darlynn biologicals | BB83-500 | Standard item - any supplier will do |
centrifuge | Eppendorf | model 5430 | Standard item - any supplier will do |
Citric acid TrisodiumSaltDihydrate | Sigma | C-8532 100 g | Standard item - any supplier will do |
CMRL | Gibco BRL | 21540 500 mL | Standard item - any supplier will do |
CMRL-1066 | Gibco | 21-510-018 | Standard item - any supplier will do |
Cryogenic Tubes (Nalgene) | Fisher Scientific | 5000-0020 | Standard item - any supplier will do |
Deep Petri with stacking ring 100 mm × 25 mm | Sigma | P7741 | Standard item - any supplier will do |
Digital Incubator | VWR | model 1545 | Standard item - any supplier will do |
DMSO | ThermoFisher | D12345 | Standard item - any supplier will do |
Filters for filter sterilization | Millipore 0.22μm GPExpressPLUS Membrane | SCGPU05RE | Standard item - any supplier will do |
Gelatin | Difco BD | 214340 500 g | Standard item - any supplier will do |
Glass Culture Tubes | Fisher Scientific | 99449-20 | Standard item - any supplier will do |
Glucose | Sigma | G-7021 1 kg | Standard item - any supplier will do |
Glycerol | Sigma | G5516 | Standard item - any supplier will do |
Hemafuge (Hematocrit & Immuno hematology centrifuge ) | Labwissen | Model 3220 | Standard item - any supplier will do |
HEPES | Sigma | H-3784 100 g | Standard item - any supplier will do |
N-acetylglucoseamine | Sigma | A-3286 25 g | Standard item - any supplier will do |
Neopeptone | Difco BD | 211681 500 g | Standard item - any supplier will do |
Neubauer Hematocytometer | Sigma | Z359629 | Standard item - any supplier will do |
Phase contrast microscope | Leitz | Standard item - any supplier will do | |
Phosphomycin | Sigma | P5396-1G | Standard item - any supplier will do |
Phosphomycine | Sigma | P5396 | Standard item - any supplier will do |
Pipetboy | Integra | Standard item - any supplier will do | |
Precision Standard Balance | OHAUS | model TS200S | Standard item - any supplier will do |
Pyruvic acid (Na salt) | Sigma | P-8574 25 g | Standard item - any supplier will do |
Rabbit Serum | Gibco | 16-120-032 | Source is important |
Rabbit Serum | Sigma | R-4505 100 mL | Source is important |
Rifampicin | Sigma | R3501-1G | Standard item - any supplier will do |
Sodium bicarbonate | Sigma | S-5761 500 g | Standard item - any supplier will do |
Sufametaxazole | Sigma | PHR1126 | Standard item - any supplier will do |
TC Yeastolate | Difco BD | 255752 100 g | Standard item - any supplier will do |
Transfer Pipettes | VWR | 470225-044 | Standard item - any supplier will do |
Trimethoprim | Sigma | PHR1056 | Standard item - any supplier will do |
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