The study, published in Frontiers in Cellular and Infection Microbiology, was conducted at Severance Hospital, a large tertiary teaching hospital affiliated with Yonsei University College of Medicine in Seoul. Between January 2024 and June 2025, the investigators enrolled 216 adult liver transplant recipients in a prospective diagnostic cohort. Twenty-three patients were later excluded because a cell-free DNA sample could not be obtained on either of the two scheduled sampling days, leaving 193 participants in the final analysis. Each recipient underwent plasma microbial cell-free DNA metagenomic next-generation sequencing, abbreviated mcfDNA mNGS, on postoperative days 7 and 14. The technique works by isolating the small fragments of DNA that microbes shed into the blood, sequencing them without any prior assumption about which organism might be present, and then matching the resulting reads against reference genomes to identify bacteria, viruses, and fungi at the species level.

The laboratory workflow behind the assay is technically demanding. Whole blood was collected in specialized tubes that stabilize cell-free DNA, then centrifuged twice to separate the plasma. Cell-free DNA was extracted with a magnetic reagent kit and quantified with a high-sensitivity fluorescence assay before libraries were prepared and sequenced on an Illumina NovaSeq 6000 system. The resulting reads were first aligned to the human genome to strip away host DNA; the unmapped remainder was then fed into Kraken2, a fast taxonomic classifier running against a custom database built from NCBI bacterial, viral, and fungal genomes. To make results comparable across samples sequenced at different depths, the team converted raw read counts into a normalized metric called reads per ten million, or RPTM, and applied a uniform positivity threshold of RPTM at or above 5. Known environmental and skin organisms such as Cutibacterium acnes were masked, and organisms appearing in high abundance only within specific processing batches were manually excluded as extraction or library-preparation contaminants.

Because fungal detection is particularly prone to database-driven false discoveries, the researchers built an unusual cross-validation layer into their pipeline. Every fungal call from Kraken2 was re-examined with two auxiliary classifiers: Kaiju, which matches translated protein sequences, and EukDetect, which aligns fungal marker genes. Supporting reads were then retrieved from the host-depleted sequencing files and mapped directly against a custom reference panel of 416 fungal genomes, with the human genome included as a decoy. A candidate fungal detection was considered confirmed only when at least ten reads with high mapping quality were distributed across at least three distinct one-kilobase windows. This adjudication process confirmed 92.9 percent of the primary pipeline’s fungal detections, but it also revealed a serious blind spot: the primary classifier achieved high precision for the fungi it called yet captured only a small fraction of the alignment-confirmed fungal detections in the cohort, missing organisms including Candida species, Nakaseomyces glabrata, and Aspergillus niger. All of the missed detections were recovered by Kaiju, and a consensus across multiple classifiers confirmed every detection when all three pipelines agreed.

The headline results concern agreement with conventional microbiology. Among the 193 recipients, mNGS returned positive results in 14.5 percent of patients on day 7 and 21.8 percent on day 14. When the sequencing results for bacterial pathogens were compared directly with blood cultures, concordance appeared modest: 35.0 percent on day 7 and just 14.3 percent on day 14. But that comparison understates the assay’s real performance. When the researchers widened the reference standard to include cultures from other clinically relevant specimens collected within 14 days, such as sputum, peritoneal drain fluid, and urine, overall concordance rose to 80.0 percent on day 7 and 71.4 percent on day 14, a level the authors describe as clinically acceptable. The low direct agreement with blood cultures likely reflects both the higher analytical sensitivity of sequencing and the fact that most patients were already receiving broad-spectrum empirical antibiotics, which suppress culture growth but leave microbial DNA fragments circulating in the plasma.

The sequencing assay also uncovered pathogens that routine testing missed entirely. Bacteria were detected exclusively by mNGS in 59.3 percent of cases on day 7 and 74.2 percent on day 14. Fungal pathogens appeared in five and four cases on the two sampling days, with Aspergillus species identified only by sequencing on day 7. Viral detections were especially revealing: nine viral pathogens were found on day 7 and seventeen on day 14, including cytomegalovirus, herpes simplex virus, varicella-zoster virus, and roseolovirus. Cytomegalovirus detections were confirmed by quantitative PCR, but the other viruses are not routinely tested after liver transplant, and prophylactic strategies for them vary widely across countries. A retrospective chart review found that most patients with these unexpected viral detections had mucocutaneous manifestations suggestive of active infection, even though no diagnostic testing had been ordered and many had not received antiviral treatment. The authors suggest that these infections may be under-recognized under immunosuppression, and that sequencing could serve as an adjunctive diagnostic tool, while cautioning that some detected viruses might represent bystanders rather than true pathogens.

Discordant cases, where blood culture was positive but sequencing was negative, received detailed scrutiny. Thirteen such cases were identified. Two, or 15.4 percent, were classified as contamination or colonization, involving skin flora such as coagulase-negative staphylococci isolated from only one bottle of a blood culture pair or from a catheter specimen alone. Five, or 38.5 percent, were interpreted as weak positives, meaning the organism was present in the sequencing data but below the predefined RPTM threshold. The remaining six, or 46.2 percent, were classified as not detected; four involved Candida species, one Enterococcus faecium, and one Achromobacter species, and several of these were identified only from catheter blood cultures rather than peripheral blood. The Candida findings align with the pipeline’s documented limited sensitivity for fungi, reinforcing the authors’ argument that a single taxonomic classifier is insufficient for fungal surveillance and that negative sequencing results cannot reliably exclude fungal infection.

Sequencing positivity also tracked closely with clinical severity and survival. On day 7, patients with positive mNGS results had significantly higher plasma cell-free DNA concentrations, higher total bilirubin, higher C-reactive protein levels, and more impaired pre-transplant liver function than those with negative results. Their 28-day mortality was 26.9 percent versus zero percent among mNGS-negative patients, and their 90-day mortality was 30.8 percent versus 3.9 percent. On day 14, the 90-day mortality rate remained significantly higher among mNGS-positive patients. Among the 160 patients sampled at both time points, 15 of the 22 who were positive on day 7 remained positive on day 14, and the same organism persisted in 86.7 percent of those cases, indicating good reproducibility of the assay. Persistent positivity was associated with higher Sequential Organ Failure Assessment scores and elevated bilirubin and C-reactive protein levels, suggesting that the sequencing results mirror the recipient’s evolving clinical status rather than floating free of it.

The authors are careful to frame the technique as an adjunct rather than a replacement. Because mNGS is hypothesis-free and highly sensitive, it can detect DNA from dead or dying organisms, complicating interpretation and potentially prompting unnecessary antimicrobial use. Testing is also expensive, and the positivity rate in this unselected cohort was low, which the researchers argue supports selective deployment in situations where the expected diagnostic benefit is high, such as clinically ambiguous cases or patients already on broad empirical therapy in whom sequencing might facilitate early antibiotic de-escalation. Notably, most mNGS-positive patients in the study were already receiving active antibiotics against the detected pathogens, which limited the potential for the assay to trigger unnecessary new treatment. The study has limitations: sequencing was performed regardless of clinical suspicion, so positivity rates might be higher in suspected-infection settings; the comparison with blood cultures may have been skewed by prior antibiotic exposure; and the retrospective elements prevented assessment of whether sequencing-guided treatment improved outcomes. Cost-effectiveness, turnaround time, and antimicrobial resistance gene detection were not evaluated, and the authors suggest that differentiated thresholds, such as RPTM at or above 3 for viruses and at or above 8 for bacteria and fungi, might better balance sensitivity and specificity. Whether sequencing-guided management can improve clinical outcomes after liver transplantation remains the central question for future studies, but the evidence here indicates that plasma microbial cell-free DNA sequencing agrees substantially with conventional microbiology when clinically relevant specimens are considered, and that it reveals pathogens, particularly viruses and antibiotic-suppressed bacteria, that routine diagnostics would otherwise leave undetected during the fragile early weeks after surgery.

Subject of Research: Plasma microbial cell-free DNA metagenomic sequencing for early infection detection after liver transplantation

Article Title: Plasma microbial cell-free DNA metagenomic sequencing for early detection of infection after liver transplantation: a prospective cohort study

Article References: Lee, Y., Min, E.-K., Park, Y. J., Kim, D.-G., Joo, D. J., Kim, M. S., Shin, S., Lee, S.-T., Lee, J. G., & Jeong, S. J. (2026). Plasma microbial cell-free DNA metagenomic sequencing for early detection of infection after liver transplantation: a prospective cohort study. Frontiers in Cellular and Infection Microbiology, 16, Article 1930701. https://doi.org/10.3389/fcimb.2026.1930701

Image Credits: AI Generated

DOI: 10.3389/fcimb.2026.1930701

Keywords: liver transplantation, metagenomic next-generation sequencing, microbial cell-free DNA, infection diagnosis, bloodstream infection, organ transplant recipients, opportunistic pathogens, diagnostic microbiology, viral detection, fungal surveillance, prospective cohort study, antibiotic de-escalation

The research, conducted by Agata Marchi, Marcus Wenne, Vi Varga and Johan Bengtsson-Palme at Chalmers University of Technology and collaborators in Gothenburg, Sweden, was motivated by a simple but powerful premise: if a gene contributes to survival or virulence inside a human host, then strains repeatedly recovered from clinical sources should carry that gene more often than strains sampled from natural environments. By comparing the protein-coding content of P. aeruginosa genomes from these two ecological contexts, the researchers could flag candidate host-adaptation genes for further study, including potential virulence factors that have never been experimentally characterized.

Technically, the approach centered on clustering homologous proteins across many strains. Genes that are shared among bacteria tend to encode core cellular functions, while genes that appear preferentially in one ecological niche are candidates for niche-specific adaptation. The team grouped proteins into clusters of orthologous sequences and then applied statistical tests to identify clusters significantly enriched with sequences derived from human clinical isolates. This enrichment analysis transforms a simple catalog of gene presence and absence into a hypothesis-generating map of host-associated genetic equipment, allowing the researchers to prioritize the small subset of protein families most likely to matter during infection.

The scale of the analysis makes the findings particularly striking. Out of all protein clusters identified across the compared genomes, approximately three percent showed statistically significant enrichment in sequences from human isolates. That may sound like a modest proportion, but in a bacterium with a genome of well over six thousand genes, three percent represents a substantial number of candidate loci. More importantly, the enriched clusters were not randomly distributed with respect to function. When the researchers characterized forty-five clusters with particularly strong enrichment of human-derived sequences, they found that the genes within them were primarily associated with host interaction and horizontal gene transfer—the two processes most plausibly linked to successful colonization of a new host and acquisition of adaptive traits.

The functional picture that emerged is coherent with what is known about how opportunistic pathogens evolve. Host interaction genes include factors that help bacteria adhere to epithelial surfaces, evade immune defenses, scavenge nutrients from host tissues, and withstand the stresses encountered inside the body. Horizontal gene transfer machinery, meanwhile, reflects the reality that P. aeruginosa frequently acquires new genetic material through mobile elements such as genomic islands, plasmids, and phages. The co-enrichment of these two functional categories suggests that adaptation to the human host is not merely a matter of fine-tuning existing genes, but also of importing ready-made solutions from the broader bacterial gene pool and retaining those that confer a selective advantage during infection.

Perhaps the most tantalizing result concerns the twelve of the forty-five selected clusters that consisted entirely of genes with unknown function. These proteins, sometimes described as part of the genomic dark matter of the species, carry no annotated role in current databases, yet their consistent association with human clinical isolates marks them as prime suspects in the search for novel virulence factors. The authors emphasize that these uncharacterized clusters represent promising targets for future experimental investigation. If even a handful of them turn out to encode previously unrecognized infection machinery, the study will have uncovered molecular mechanisms that no hypothesis-driven, single-gene approach could have predicted.

The value of the work lies not only in the specific candidates it identifies but also in the validation of the comparative strategy itself. Among the human-enriched clusters, the researchers found genes with established virulence-associated functions alongside the uncharacterized proteins. This dual outcome is critical: it demonstrates that the method reliably recovers known biology, which builds confidence that the unknown clusters are genuine leads rather than statistical noise. In other words, the approach simultaneously rediscovers what is already known and points toward what is not, a hallmark of a productive screening method in genomics.

There are broader implications for how scientists study bacterial pathogenicity. P. aeruginosa is far from the only opportunistic pathogen that straddles environmental and clinical worlds; many members of the ESKAPE group of drug-resistant bacteria, as well as numerous less famous species, share this dual lifestyle. The authors suggest that their comparative genomics framework may be broadly applicable to other opportunistic pathogens, offering a generalizable recipe for mining genomic databases for host-adaptation candidates. As the volume of publicly available bacterial genome sequences continues to grow exponentially, such database-driven approaches become increasingly powerful, since the statistical signal of enrichment strengthens with every additional strain sequenced.

The study also carries practical relevance for clinical microbiology and drug discovery. Hospital-acquired infections caused by P. aeruginosa are notoriously difficult to treat, and the World Health Organization has flagged carbapenem-resistant strains as a critical priority for new therapeutics. Understanding which genes enable the bacterium to establish infection in humans opens potential avenues for anti-virulence strategies that disarm the pathogen rather than kill it, approaches that may exert weaker selective pressure for resistance than conventional antibiotics. The candidate genes identified here, particularly the uncharacterized clusters, could in principle inform future diagnostic markers that distinguish highly virulent clinical strains from environmental relatives, or serve as screens for new drug targets.

Funded through the Data-Driven Life Science program of the Knut and Alice Wallenberg Foundation, the Swedish Research Council, and the Swedish Foundation for Strategic Research, the work exemplifies the growing role of large-scale computational biology in infectious disease research. By treating thousands of genome sequences as a natural experiment in host adaptation, the Gothenburg team has converted genomic dark matter into a concrete, testable shortlist of candidate genes. The next step belongs to the experimentalists: knocking out these genes in laboratory strains, testing their effects in infection models, and determining whether the twelve mystery clusters indeed conceal novel virulence factors. If they do, this comparative genomics hunt will have paid off handsomely, revealing how an environmental survivor becomes a human pathogen one hidden gene at a time.

Subject of Research: Comparative genomics of Pseudomonas aeruginosa to identify candidate host-adaptation and virulence genes

Article Title: On the hunt for candidate genes involved in host-adaptation in Pseudomonas aeruginosa using comparative genomics

Article References: Marchi, A., Wenne, M., Varga, V., & Bengtsson-Palme, J. (2026). On the hunt for candidate genes involved in host-adaptation in Pseudomonas aeruginosa using comparative genomics. BMC Genomics. https://doi.org/10.1186/s12864-026-13405-3

Image Credits: AI Generated

DOI: 10.1186/s12864-026-13405-3

Keywords: Pseudomonas aeruginosa, comparative genomics, virulence factors, host adaptation, genomic dark matter, opportunistic pathogens, horizontal gene transfer, bacterial pathogenicity, hospital-acquired infections, functional genomics, protein clusters, BMC Genomics

The review, conducted by Maryam Babar and Aymen Arain of the Edward Via College of Osteopathic Medicine and Nina Martins of Virginia Commonwealth University, synthesizes peer-reviewed literature identified through PubMed searches using terms such as cosmetic contamination, public testers, and pathogens in makeup. Rather than applying a formal systematic protocol, the authors took a narrative approach, examining studies of personal-use cosmetics, salon-shared products, preservative efficacy, and regulatory policy to build a comprehensive picture of what is, and is not, known about contamination in cosmetics that pass through many hands. Their central and most sobering finding is a gap in the evidence itself: no study to date has directly measured microbial loads or quantified infection risks from public makeup testers in retail settings.

What the surrounding literature does show is cause for concern. Studies of cosmetics in general use have repeatedly isolated opportunistic pathogens, including Staphylococcus aureus, Pseudomonas aeruginosa, Candida albicans, and various Bacillus species, from both personal and shared products. Alarmingly, contamination has been detected even in items that were still unopened, suggesting that manufacturing-stage contamination or compromised packaging can introduce microbes before a product ever reaches a consumer’s hands. Once products are in use, repeated contact with fingers, faces, and the environment introduces new organisms, and many formulations provide the water, nutrients, and neutral pH that microbial life requires.

The technical reasons why cosmetics can support microbial growth are well understood. Water-containing products such as creams, liquid foundations, and mascaras are particularly vulnerable, since moisture is the fundamental requirement for bacterial and fungal proliferation. Preservative systems are designed to suppress this growth, and regulatory frameworks in most jurisdictions require demonstrated preservative efficacy before a product can be marketed. However, preservatives are not infallible. Their effectiveness depends on concentration, formulation chemistry, and the size and frequency of the inoculum they face. A tester that is opened all day, handled by dozens or hundreds of people, and never sanitized may present a microbial challenge that overwhelms even a well-designed preservative system. Research on preservative systems has also shown that they can alter the skin microbiome itself, complicating the picture of how cosmetic formulations interact with the microorganisms that naturally colonize healthy skin.

The closest real-world proxy for retail testers comes from studies of communal cosmetic kits in beauty salons, and those findings are consistently troubling. Investigations of shared makeup kits in women’s beauty salons have documented high rates of bacterial and fungal contamination, with contamination levels notably higher in communal-use settings than in products used by a single owner. One study of salon cosmetics also assessed exposure to microbial metabolites, underscoring that the risks of shared products may extend beyond live organisms to the bioactive compounds they produce. In a salon, the shared kit is typically used by a limited and semi-stable population; a retail tester, by contrast, may be touched by an essentially unbounded stream of strangers, none of whom have any knowledge of the product’s handling history.

The clinical consequences of exposure to contaminated cosmetics range from trivial to serious. Opportunistic pathogens such as Pseudomonas aeruginosa can cause severe eye infections, including keratitis that threatens vision, particularly when contaminated products contact the eye area around mascaras, eyeliners, and eye shadow. Staphylococcus aureus can provoke skin and soft tissue infections and, in some cases, more invasive disease. Candida albicans poses particular risks to immunocompromised individuals. Perhaps most strikingly, a recent study found that makeup testers can act as reservoirs and transmission sources of antibiotic-resistant bacteria, meaning that a swipe of contaminated lip gloss could theoretically transfer organisms that are difficult to treat even when they do cause infection. For vulnerable users, including people with compromised immune systems, broken skin, chronic skin conditions, or recent cosmetic procedures, exposure to contaminated testers represents a heightened and largely unrecognized risk.

Despite this accumulating evidence of risk in adjacent settings, the review emphasizes that retail testers themselves exist in a regulatory vacuum. There are no mandated sanitation protocols for testers, no requirements to track how long a tester has been in use, no expiration tracking for opened demonstration products, and no microbial testing obligations. In contrast, finished cosmetics sold to consumers are subject to established safety and shelf-life regulations in Europe and internationally, including requirements for preservative efficacy and period-after-opening labeling. A tester on a store counter, which may be exposed to more microbial pressure than any personal product ever will be, is exempt from all of these protections. The authors argue that this asymmetry is difficult to justify from a public health standpoint and that testers may serve as unrecognized vectors for microbial transmission and infection.

The methodological gap the review identifies is as important as the contamination findings themselves. Because no studies have directly sampled testers in real retail environments, the actual magnitude of the risk remains unknown. Microbial loads on testers could range from negligible to dangerous, and without direct measurement, neither regulators nor retailers can make evidence-based decisions. The authors call for research to evaluate the safety of these products in real-world settings, including surveys of contamination across product types, store formats, and climates, as well as studies quantifying the transfer of microbes from tester to skin. Such data would provide the foundation for establishing evidence-based hygiene protocols, whether that means scheduled sanitization, single-use applicators, sealed sampling systems, automatic replacement intervals, or the retirement of open testers altogether.

In the meantime, the review has practical implications for consumers and retailers alike. Shoppers with cuts, active skin infections, recent procedures, or weakened immune systems would be prudent to avoid shared testers entirely, particularly around the eye and lip areas where the infection risk is highest. Retailers and cosmetics companies, for their part, could adopt sanitation and replacement practices voluntarily, and the authors argue that recognizing the clinical relevance of tester contamination is essential for guiding future policy, public health measures, and consumer education in cosmetic safety. As the beauty industry continues to grow and as awareness of microbiome science reshapes how consumers think about the products they put on their skin, the humble makeup tester, sitting open on a brightly lit counter, may come to be seen less as a harmless indulgence and more as an unexamined interface between hundreds of strangers’ microbiomes and every new customer who stops to try a shade.

It is worth noting the nature of the evidence base itself. As a narrative review, the article does not pool data or grade studies systematically, and the authors acknowledge that no formal inclusion or exclusion criteria were applied. This means the conclusions should be read as a synthesis of available literature rather than a quantitative risk assessment, which makes their call for direct sampling studies all the more pointed. The review also received no external funding, and the authors declared no conflicts of interest.

The cited literature adds several instructive details. Quality investigations of commonly used topical cosmetic preparations have documented contamination in products beyond makeup, suggesting the problem spans cosmetic categories. Work on preservative systems in full formulations has examined their in-vivo effects on the skin microbiome, while separate research has tested how chemical preservatives affect resident flora isolated from healthy facial skin, indicating that formulation choices shape not only microbial survival in the product but also the ecology of the skin it contacts. Even unusual organisms have surfaced: Vibrio metschnikovii has been isolated from cosmetic products and proposed as a potential cause of skin infection, illustrating that the range of contaminants is not limited to the familiar staphylococcal and pseudomonal species.

The timeline of the underlying research is also relevant. Much of the foundational work on in-use cosmetic contamination dates back well over a decade, while studies of salon-shared kits and antibiotic-resistant organisms on testers are more recent, suggesting growing but still fragmented attention to the issue. The review went through revision in August 2026 and was published in September 2026 in volume 318 of the journal, arriving at a moment when consumer interest in microbiome-aware cosmetics is rising even as the hygiene of the products consumers actually touch in stores remains unmeasured.

Subject of Research: Microbial contamination of shared makeup testers in retail environments and its public health implications.

Article Title: Beauty or biohazard? Microbial contamination in shared makeup testers and public health implications: a narrative review

Article References: Babar, M., Arain, A., & Martins, N. (2026). Beauty or biohazard? Microbial contamination in shared makeup testers and public health implications: a narrative review. Archives of Dermatological Research, 318(1), Article 404. https://doi.org/10.1007/s00403-026-04928-6

Image Credits: AI Generated

DOI: 10.1007/s00403-026-04928-6

Keywords: cosmetic contamination, makeup testers, microbial safety, opportunistic pathogens, public health, skin microbiome, hygiene practices, antibiotic-resistant bacteria, beauty salons, preservative efficacy, Staphylococcus aureus, Pseudomonas aeruginosa