Published by Zhuhai Biori Biotechnology Co., Ltd.
Introduction: A Contamination Risk Long Overlooked
Spiroplasma bacteria are wall-less organisms of the class Mollicutes: close relatives of mycoplasma, but distinct in morphology, host range and growth requirements [6]. Insect cell processing carries an inherent risk of Spiroplasma introduction, because the cell line itself can be a carrier, and because the organism survives the antibiotic and filtration steps that clear most bacterial contamination [7]. A qPCR assay with a fluorescent probe answers the operational question — is Spiroplasma DNA present in this cell bank, raw material or harvest? — in about 1.5 hours, and meets the testing expectations now set by the Chinese Pharmacopoeia, USP <63> and Ph. Eur. 2.6.7 [1–3].
Key takeaways
- Spiroplasma is a wall-less Mollicute, not a mycoplasma, but contamination control handles the two together.
- Sf9, Sf21, High Five and S2 lines, and anything made in a baculovirus expression system, carry the highest intrinsic risk.
- Mycoplasma culture at 36 ± 1 °C and generic mycoplasma qPCR kits do not cover Spiroplasma; ChP 2025, USP <63> and Ph. Eur. 2.6.7 now expect a Spiroplasma-specific test.
Three biological features make Spiroplasma hard to control. It has no cell wall, so β-lactam antibiotics such as penicillin have no target. At 0.1–0.2 μm it passes 0.45 μm sterilising filters, so filtration is no barrier. And its natural hosts are plants and insects, so the cell substrate itself — not only the environment — is a credible route of entry [6,7].
What Is Spiroplasma and How Does It Differ from Mycoplasma?
Spiroplasma bacteria sit in the class Mollicutes, next to mycoplasma, but the genera diverge in ways that decide how a process is monitored. Contamination arrives by three routes: endogenous carriage by the insect cell line, raw materials of plant origin such as hydrolysates, and contamination carried between areas of the facility. Products built on insect cell and baculovirus expression systems (recombinant proteins, virus-like particle vaccines and AAV vectors made in Sf9 cells) are the highest risk category. Once inside a culture, Spiroplasma suppresses proliferation and perturbs metabolism, compromising yield and product safety [6,7].
The difference between mycoplasma and spiroplasma, at a glance
- Morphology and motility — Spiroplasma cells are helical and motile, driven by a contractile cytoskeleton that produces a corkscrew motion; mycoplasmas are pleomorphic and mostly non-motile. Neither has a cell wall.
- Host range — Spiroplasma is associated with plants and arthropods, including the lepidopteran and dipteran species behind Sf9, High Five and S2; mycoplasmas chiefly parasitise mammals, birds and reptiles.
- Growth temperature — many Spiroplasma species grow best near 30–32 °C, close to insect cell conditions, while compendial mycoplasma culture targets 35–38 °C [2,3]; a test held at 36 ± 1 °C can miss Spiroplasma.
- Filterability — both genera pass 0.45 μm and even 0.2 μm membranes.
- Reference strains — USP <63> names S. citri ATCC 29747 and S. melliferum ATCC 29416 for insect cell testing [2]; Ph. Eur. 2.6.7 asks for S. citri or another suitable Spiroplasma species in nucleic acid method validation [3].
Insect Cell Culture Systems: Where the Risk Is Highest
Insect cell lines are over-represented in contamination events for structural reasons: the cells come from species that carry spiroplasmas in nature, they are grown at temperatures where those organisms thrive, and a run can last for weeks.
- Sf9 and Sf21 (Spodoptera frugiperda) — the workhorses of baculovirus expression and AAV vector production; lepidopteran lines are the group for which compendial texts require a Spiroplasma control [2].
- High Five (Trichoplusia ni) — used where secreted protein yield matters; another lepidopteran substrate with insect-associated spiroplasmas in its background.
- S2 (Drosophila melanogaster) — a stable-expression platform whose host carries heritable Spiroplasma endosymbionts, transmitted vertically and not cleared by antibiotics [6].
- Baculovirus expression products — VLP vaccines, recombinant proteins and AAV vectors; test the virus seed and the unprocessed harvest, not only the cell bank.
The testing points are the MCB and WCB, the virus seed, the unprocessed harvest and the end-of-production cells (EOPC). Because Spiroplasma passes vertically through an insect colony, one negative cell bank does not prove absence later; re-testing at LIVCA and EOPC keeps the conclusion valid [1,2].
How to Test for Spiroplasma: Culture vs qPCR
Two method families are in routine use, and they answer different questions. Compendial culture is sensitive and cheap per sample but slow for Spiroplasma; nucleic acid testing answers the same day but must be validated against the compendial method for the matrix [1–3].
- Culture, agar and broth — specialist mollicute media (SP-4 or M1D) and, for Spiroplasma, incubation near 30–32 °C rather than 36 ± 1 °C; subculture and microscopic reading take two to four weeks [2,3].
- Indicator cell culture — sample inoculated onto a permissive line, incubated, then stained with a DNA fluorochrome; recovers non-cultivable mollicutes, adds about a week.
- qPCR with a fluorescent probe — extracted DNA is amplified with Spiroplasma-specific primers and probe; about 1.5 hours, covers non-viable organisms, but qualitative and matrix-dependent.
Most laboratories ask whether an existing mycoplasma qPCR testing kit will do. Usually not: those kits target conserved mycoplasma sequences and are validated with M. orale, M. pneumoniae and A. laidlawii, so Spiroplasma falls outside their validation and any cross-reactivity is incidental. An assay for insect cell processes should carry a Spiroplasma-specific target and be validated with S. citri or S. melliferum. Where both genera are in scope, BP-QN22 covers mycoplasma and BP-QN299 covers Spiroplasma, from the same extract.
For the mycoplasma side of the same workflow, see our guide to mycoplasma qPCR testing.
Whichever route is chosen, the validation package is the deliverable: a Spiroplasma strain in the panel, a matrix matching the product, and a documented LOD at or below 10 CFU/mL to match compendial sensitivity [3].
Regulatory Expectations: China, the United States and the EU
China: the 2025 Pharmacopoeia adds Spiroplasma testing
General Chapter 0234 of the 2025 Chinese Pharmacopoeia, Preparation and Quality Control of Animal Cell Substrates for the Production of Biological Products (Volume III), is the most consequential update for insect cell users. Where the production cells are insect cells, or plant-derived materials are used during culture, a Spiroplasma test shall be performed, and the method — culture or nucleic acid — must detect the genera Mesoplasma and Entomoplasma [1]. The requirement is conditional and risk-based, not a blanket mandate: a CHO or HEK293 process without plant-derived raw materials can justify its strategy by risk assessment. Samples are culture supernatant and/or cell suspension [1].
United States: USP <63> and FDA expectations
USP <63> Mycoplasma Tests, official since USP 33–NF 28 on 1 October 2010, is the compendial basis in the United States [2,4]; cell substrate expectations are set out in FDA’s 2010 guidance on characterisation and qualification of cell substrates [4]. The chapter is risk-oriented: a Spiroplasma control is required only when insect cell lines are tested.
When insect cell lines are tested, USP <63> requires a Spiroplasma control in addition to the two mycoplasma controls, naming Spiroplasma citri ATCC 29747, Spiroplasma melliferum ATCC 29416 or equivalent strains, and notes that these organisms are more fastidious and need the lower incubation temperatures used for insect cells [2]. A commercial strain used as a control must be qualified against the reference strain.
Europe: Ph. Eur. 2.6.7 and EMA expectations
The European framework rests on Ph. Eur. 2.6.7 Mycoplasmas — revised in Ph. Eur. 12.2 and effective 1 April 2026 — with EMA quality guidance for biotechnological products [3].
The revision changes the scope. 2.6.7 now covers the whole class Mollicutes — mycoplasma, ureaplasma, acholeplasma and spiroplasma — and states a limitation: its culture and indicator cell culture methods suit organisms growing optimally at 35–38 °C and are not adequate for insect or plant cell lines [3]. For an insect cell process the workable route is a validated nucleic acid method, and the chapter asks for a Spiroplasma strain (S. citri or another suitable species) in the validation panel.
Comparison of the three regulatory systems
| Comparison Item | Chinese Pharmacopoeia (2025 Edition) | US FDA / USP | EP / EMA |
|---|---|---|---|
| Primary Reference | Vol. III, General Chapter 0234 | USP <63> | EP 2.6.7 |
| Year of Initial Inclusion | 2025 | 2010 (USP 33–NF 28) | 2006; Mollicutes scope added 2026 |
| Trigger for Mandatory Testing | Insect cells, or plant-derived materials used in culture (conditional) | Insect cell lines (Spiroplasma control required); raw materials of plant origin | Insect or plant cell lines; validated nucleic acid method expected |
| Test Matrices | MCB, WCB, LIVCA, EOPC; culture supernatant and/or cell suspension | Raw materials, cell banks, harvest fluids | Cell banks, samples taken during processing, final products |
| Positive Control Specification | Not specified; method must cover Mesoplasma and Entomoplasma | S. citri ATCC 29747 or S. melliferum ATCC 29416, insect cell testing only | S. citri or another suitable Spiroplasma sp. for nucleic acid method validation |
| Exemption Scenarios | Not required where no insect cells and no plant-derived materials are used | — | Not applicable to insect cell processes; a validated nucleic acid method is expected instead |
Product Features: The BP-QN299 Spiroplasma qPCR Assay
The Spiroplasma DNA Detection Kit (qPCR) from BIORI, combined with the magnetic bead nucleic acid extraction kit, delivers these performance characteristics:
Catalogue number: BP-QN299-50 (50 reactions per kit).
| Intended Use | Qualitative detection of Spiroplasma DNA in raw materials, cell banks, virus seeds, harvest fluids and therapeutic cells. |
|---|---|
| High Sensitivity | Limit of detection (LOD): 10 CFU/mL (Spiroplasma citri, 24/24 replicates detected; BIORI internal data, BP-QN299) |
| Broad Coverage | In silico prediction against the NCBI database: more than 40 Spiroplasma species covered; species list on request. |
| Excellent Specificity | No reactivity against 14 materials, including mycoplasma species, engineered bacteria and Sf9 / High Five cell DNA (BIORI internal data) |
| Precision | Intermediate precision CV ≤ 5% (BIORI internal data) |
| Ease of use | PCR reagents supplied in a single tube; purified nucleic acid can be added directly without preparing multiple components |
| Rapid Turnaround | Approximately 1.5 hours from sample extraction to final readout |
Related Products
Mycoplasma DNA Detection Kit (qPCR)
Biopharma Quality Control Product Selection — choosing the right extraction and detection format for your process
Scope and Limitations
BP-QN299 is qualitative: it reports the presence or absence of Spiroplasma DNA, and does not quantify bioburden or identify species. Coverage of more than 40 species is a computational prediction, not empirical detection of each species, and a negative result is only as good as the matrices in which suitability was verified. Each laboratory should confirm performance for the Spiroplasma species and sample types used in its own process [1,2].
References
- Chinese Pharmacopoeia 2025, Volume III, General Chapter 0234: Preparation and Quality Control of Animal Cell Substrates for the Production of Biological Products. Beijing, 2025.
- USP NF. General Chapter <63> Mycoplasma Tests. United States Pharmacopeial Convention. Official 1 October 2010 (USP 33–NF 28); current revision USP–NF 2026.
- European Pharmacopoeia 12.2, General Chapter 2.6.7 Mycoplasmas. EDQM. Revised text, effective 1 April 2026.
- US Food and Drug Administration. Characterization and Qualification of Cell Substrates and Other Biological Materials Used in the Production of Viral Vaccines. Guidance for Industry, 2010.
- ICH Q5A(R2): Viral Safety Evaluation of Biotechnology Products Derived from Cell Lines of Human or Animal Origin. 2023.
- Regassa LB, Gasparich GE. Spiroplasmas: evolutionary relationships and biodiversity. Frontiers in Bioscience, 2006;11:2983–3002.
- Gasparich GE. Spiroplasmas and phytoplasmas: microbes associated with plant hosts. Biologicals, 2010;38(2):193–203.
FAQ
Does validation with S. citri cover every Spiroplasma species?
No. Spiroplasma citri (ATCC 29747) is the positive control strain referenced by USP <63> for Spiroplasma assay validation; success with it shows that the system detects this model species, not every Spiroplasma. The assay is predicted by in silico analysis to cover more than 40 species against the NCBI database, and the species list is given on the Spiroplasma DNA Detection Kit (qPCR) product page. End users should verify suitability for the Spiroplasma species expected in their own matrices.
Can penicillin clear a contaminant that has no cell wall?
No. Spiroplasma, like mycoplasma, is a Mollicute without a cell wall. Penicillin and related antibiotics act on cell wall synthesis, so these organisms are intrinsically resistant. Adding penicillin to insect cell culture will not eliminate Spiroplasma or mycoplasma; routine monitoring has to rely on nucleic acid testing.
Does a negative Spiroplasma result also rule out viral contamination?
No. This kit is for qualitative detection of Spiroplasma DNA; a negative result means only that no detectable Spiroplasma nucleic acid was present in the sample. It says nothing about adventitious viruses, which need separate assays specific to each virus, under ICH Q5A(R2) [5].
What is the difference between mycoplasma and spiroplasma?
Both are wall-less Mollicutes, but they differ in shape and motility, in host range — plants and insects versus mammals and birds — and in growth temperature, many Spiroplasma species preferring 30–32 °C rather than 35–38 °C [2,3,6].
Do standard mycoplasma qPCR kits detect Spiroplasma?
Not by design. Mycoplasma kits are validated with mycoplasma species, and Spiroplasma sits outside that validation; incidental cross-reactivity is no substitute for a Spiroplasma-specific assay such as BP-QN299.
