The History of “Suicide PCR” and How it is Used Today

Suicide PCR got its unusual name because the primers were used only once. Raoult and colleagues first published the method in 2000, using it to identify Yersinia pestis in dental pulp from 14th-century plague burials in France.[1]

Since then, researchers have applied suicide PCR to other historical questions. For example, researchers used it to investigate a louse-borne typhus outbreak in Douai in 1710–1712 and to confirm findings in medieval coprolites.[2,3] It was also proposed as a diagnostic strategy for rickettsial infections from skin biopsies.[4]

While paleomicrobiology, the field it was invented for, has changed almost beyond recognition, we can still learn much from this technique’s history to help our research today.

Why Suicide PCR Was Invented

A single PCR reaction produces enormous numbers of sequence copies, but that also makes it prone to contamination. Unwanted amplicons get onto pipettes, benches, gloves, aerosols, reagent stocks, and they persist. If you then run a new reaction using primers that amplify that same sequence, a stray molecule from last month’s experiment is indistinguishable from a genuine hit.

For ancient DNA, this is catastrophic, because the authentic target sits at a vanishingly low copy number among potential contaminants. Host DNA, soil microbial DNA, DNA from post-mortem colonizers, and modern human DNA introduced during excavation, curation, and handling can all muddy the results. Just a handful of contaminating amplicons can easily outnumber the genuine template and dominate the reaction.

This is the problem suicide PCR was invented to solve. Here is how the methodology varies from other PCR techniques to reduce the effect of contamination:

• Each target-specific primer pair is used only once: This is where the technique gets its name. A primer pair that has generated a product has, by definition, put that amplicon into your laboratory. Retiring the pair permanently means it is never used again, so any stray copies of that amplicon cannot be re-amplified in a later assay, because nothing in that assay can prime off them. Genius!
• The target sequence should never previously have been amplified in that laboratory: Same logic, applied to the sequence rather than the oligos. If nobody has ever amplified this region on these benches, no reservoir of it is waiting to be picked up.
• Try multiple primer sets against the target in sequence until one yields a product of the expected size: Use each primer set once, then retire it.
• Sequence any product to confirm its identity: A band of the right size is not a result.
• No positive control: Yes, really! More on this below.

Why Positive Controls Were Deliberately Omitted in Suicide PCR

Omitting the positive control is a defining feature of suicide PCR. This is because running a positive control requires bringing the target sequence (as plasmid, genomic DNA, or a previous amplicon) into the laboratory and handling it alongside your sample. Exactly what this method is trying to avoid!

So in suicide PCR, a negative result is followed by a new primer pair rather than by troubleshooting against a known positive. That trade-off made sense in the specific context of detecting a pathogen that had probably never been in the building.

But in contemporary molecular diagnostics and most research PCR, appropriate positive and negative controls are expected, and an assay without them cannot distinguish “target absent” from “reaction failed.” So make sure you use appropriate controls in PCR – don’t think you can get away without them!

The Limitations of Suicide PCR

Suicide PCR might reduce the risk of in-lab amplicon carryover, but it does not eliminate false positives, and it cannot, because contamination has many other entry points:

• Contamination during excavation and handling, often years before the sample reaches you
• Environmental and modern DNA in the burial context or the lab
• Contaminated reagents, plasticware, or water
• Cross-contamination during extraction
• Nonspecific amplification of something that isn’t your target
• Misidentification at the sequence-interpretation stage, particularly with short reads from closely related organisms

Any of these can still produce a convincing false-positive in a suicide PCR reaction.

No PCR Can Confirm DNA Age

A genuinely ancient DNA molecule is like a torn scrap of paper. The tear marks along its edges are a “damage signature”, or the chemical wear that proves it’s old genetic material and not contamination.

But PCR doesn’t pick up those signatures. Instead, it reads the middle portion of the DNA and then prints thousands of clean, freshly made copies. So when you sequence the product, you’re reading brand-new DNA the polymerase made yesterday. The damage signature that proves the sample’s actual age is gone.

Sequencing the amplicon tells you what you amplified, but it cannot tell you how old the amplicon was. It could be a genuine 700-year-old molecule or a fresh contaminant your colleague brought in last week, and you won’t know the difference.

To see these damage signatures, you have to sequence the original molecules directly rather than amplifying a chosen region first. Modern sequencing-library workflows do this and, as a result, have largely replaced suicide PCR in modern paleomicrobiology.

How the Historical Workflow Looked

A modern ancient-DNA project has dedicated clean facilities with a directional workflow, extraction blanks and negative controls at every stage, and, critically, sequencing libraries built from the extract rather than single amplicons.

If you want to understand how the historical technique worked, we have included a simplified description of the original approach below:

1. Recovery of archaeological skeletal remains, typically teeth, from a documented burial context.
2. DNA extraction from dental pulp enclosed within the tooth. This relatively protected compartment would have contained circulating pathogens at the time of death. That made it attractive for blood-borne pathogens.
3. Run PCR with one fresh primer pair at a time, retiring each after use, with no positive control.
4. Continue through primer sets until a product of the expected size appears.
5. Sequence the product and compare against reference sequences to establish what was amplified.

Older accounts of this technique suggest suicide PCR amplicons are “generally small, around 300 bp”, but ancient DNA is usually fragmented well below this. Suicide PCR amplicons are typically under 150 bp, with median fragment lengths often under 75 bp and modes under 50 bp, depending on age, burial environment, and tissue.

That matters practically because PCR copies the stretch between two primers. For that to happen, both primer sites, plus everything in between, must sit on an unbroken DNA molecule. If your surviving DNA is 60 bases long and you’ve designed an assay to amplify a 300-base region, there is simply no intact molecule for the reaction to copy. You get nothing. So in suicide PCR, you must design short targets.

Why We Stopped Using Suicide PCR

Almost everything that made suicide PCR necessary is addressed today using a different technique, methodology, or philosophy. There are two key reasons that the technique fell out of favor:

New Sequencing Techniques Developed

Ancient pathogen research is now dominated by high-throughput sequencing. DNA is converted into sequencing libraries; targeted enrichment or hybridization capture pulls out pathogen sequences from an overwhelming host and environmental background; shotgun metagenomics allows screening without a prior hypothesis about the organism. And researchers have reconstructed whole ancient genomes of Y. pestis, Mycobacterium leprae, M. tuberculosis, Salmonella enterica, and others this way.

Clinical Diagnostics Matured

In 2004, Suicide PCR was proposed as a diagnostic approach for rickettsioses, where the organism is difficult to culture, and serology is effectively retrospective.[4] However, current rickettsial diagnosis rests on indirect immunofluorescence serology alongside real-time and multiplex PCR assays on blood, eschar swabs, or skin biopsy, with sequencing for species-level resolution. Those assays are validated, controlled, and repeatable, which is the opposite of a single-use, control-free design.

Furthermore, routine diagnostics now manage carryover contamination through uracil-DNA glycosylase carryover prevention, closed-tube real-time chemistries, physical separation of pre- and post-amplification areas, and no-template controls on every run. Those measures are compatible with running the same assay thousands of times, which is an essential requirement for a diagnostic test, and suicide PCR cannot offer them by design.

So Is Suicide PCR Still Relevant?

Suicide PCR remains scientifically interesting and is occasionally used as an extreme contamination-control strategy. It still appears in paleomicrobiology, but as one of several authentication criteria rather than as a standalone method. Where carryover is a genuinely exceptional concern in PCR, the method’s underlying logic is sound.

Today, the real value of suicide PCR is conceptual. It’s a clear case study in how a field confronted a contamination problem severe enough to cast doubt on its entire literature, and solved it by redesigning the experiment rather than by adding more precautions.

So when you’re next stuck, it’s worth taking a step back and seeing the situation with new eyes instead of adding more red tape to your workflow.

References

1. Drancourt M, Aboudharam G, Signoli M, Dutour O, Raoult D (1998). Detection of 400-year-old Yersinia pestis DNA in human dental pulp: an approach to the diagnosis of ancient septicemia. Proc Natl Acad Sci U S A 95(21):12637–12640.
2. Nguyen-Hieu T, Aboudharam G, Signoli M, Rigeade C, Drancourt M, Raoult D (2010). Evidence of a louse-borne outbreak involving typhus in Douai, 1710–1712 during the war of Spanish succession. PLoS One 5(10):e15405.
3. Appelt S, Fancello L, Le Bailly M, Raoult D, Drancourt M, Desnues C (2014). Viruses in a 14th-century coprolite. Appl Environ Microbiol 80(9):2648–2655. (Metagenomic sequencing characterised the viral and microbial content; suicide PCR was used to confirm selected findings, not to generate the community profile.)
4. Fournier PE, Raoult D (2004). Suicide PCR on skin biopsy specimens for diagnosis of rickettsioses. J Clin Microbiol 42(8):3428–3434.vv

Modern Methodology, Authentication and Diagnostic Resources

• Orlando L, Allaby R, Skoglund P, et al. (2021). Ancient DNA analysis. Nat Rev Methods Primers 1:14. doi:10.1038/s43586-020-00011-0
• Spyrou MA, Bos KI, Herbig A, Krause J (2019). Ancient pathogen genomics as an emerging tool for infectious disease research. Nat Rev Genet 20:323–340. doi:10.1038/s41576-019-0119-1
• Duchêne S, Ho SYW, Carmichael AG, Holmes EC, Poinar H (2020). The recovery, interpretation and use of ancient pathogen genomes. Curr Biol 30(19):R1215–R1231. doi:10.1016/j.cub.2020.08.081
• Key FM, Posth C, Krause J, Herbig A, Bos KI (2017). Mining metagenomic data sets for ancient DNA: recommended protocols for authentication. Trends Genet 33(8):508–520.
• Rohland N, Glocke I, Aximu-Petri A, Meyer M (2018). Extraction of highly degraded DNA from ancient bones, teeth and sediments for high-throughput sequencing. Nat Protoc 13:2447–2461. doi:10.1038/s41596-018-0050-5
• Drancourt M, Raoult D (2016). Paleomicrobiology data: authentication and interpretation. Microbiol Spectr 4(4). doi:10.1128/microbiolspec.PoH-0017-2015
• Mir YB, Manzoor T, Mushtaq D, Najar AH, Kawoosa F, Bhatia D, Qadri SM, Siraj F, Ahmad SM (2026). Diagnostic challenges in re-emerging rickettsioses: why current tools fall short. Clin Microbiol Rev 39(3):e00020-26. doi:10.1128/cmr.00020-26 — https://pubmed.ncbi.nlm.nih.gov/42390463/
• Stewart AG, Stewart AGA (2021). An update on the laboratory diagnosis of Rickettsia spp. infection. Pathogens 10(10):1319. doi:10.3390/pathogens10101319 — https://pubmed.ncbi.nlm.nih.gov/34684267/