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Clinical Laboratories and Pathology Groups

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Might Bacteria be Used to Identify Cancer Cells? Some Researchers Using Synthetic Biology and Genetic Engineering Techniques Say ‘Yes’

Cellular healthcare is an approach that goes beyond clinical laboratory testing to identify the location of specific cancer cells and aid in treatment decisions

Advances in synthetic biology and genetic engineering are leading to development of bacterial biosensors that could eventually aid pathologists and clinical laboratories in diagnosis of many types of cancers.

One recent example comes from researchers at the University of California San Diego (UCSD) who worked with colleagues in Australia to engineer bacteria that work as “capture agents” and bind to tumorous material.

The resulting “bacterial biosensors” go on a “sort of molecular manhunt” to find and capture tumor DNA with mutations in the Kirsten Rat Sarcoma virus (KRAS) gene, according to an article published by the National Cancer Institute (NCI) titled, “Could Bacteria Help Find Cancer?

The KRAS gene is associated with colorectal cancer. The researchers named their development the Cellular Assay for Targeted CRISPR-discriminated Horizontal gene transfer (CATCH). 

CATCH successfully detected cancer in the colons of mice. The researchers believe it could be used to diagnose cancers, as well as infections and other diseases, in humans as well, according to a UCSD news release.

The researchers published their proof-of-concept findings in the journal Science titled, “Engineered Bacteria Detect Tumor DNA.”

Daniel Worthley, PhD

“If bacteria can take up DNA, and cancer is defined genetically by a change in its DNA, then, theoretically, bacteria could be engineered to detect cancer,” gastroenterologist Daniel Worthley, PhD, a cancer researcher at Colonoscopy Clinic in Brisbane, Australia, told MedicalResearch.com. This research could eventually provide clinical laboratories and anatomic pathologists with new tools to use in diagnosing certain types of cancer. (Photo copyright: Colonoscopy Clinic.)

Tapping Bacteria’s Natural Competence

In their Science paper, the researchers acknowledged other synthetic biology achievements in cellular biosensors aimed at human disease. But they noted that more can be done by leveraging the “natural competence” skill of bacteria. 

“Biosensors have not yet been engineered to detect specific extracellular DNA sequences and mutations. Here, we engineered naturally competent Acinetobacter baylyi (A. baylyi) to detect donor DNA from the genomes of colorectal cancer cells, organoids, and tumors,” they wrote.

“Many bacteria can take up DNA from their environment, a skill known as natural competence,” said Rob Cooper, PhD, co-first author of the study and a scientist at US San Diego’s Synthetic Biology Institute, in the news release. A. baylyi is a type of bacteria renowned for success in doing just that, the NCI article pointed out. 

CRISPR Aids CATCH Development

Inside Precision Medicine shared these steps toward creation of the CATCH technique:

  • Researchers engineered bacteria using CRISPR.
  • This enabled them to explore “free-floating DNA sequences on a genomic level.”
  • Those sequences were compared to “known cancer DNA sequences.”
  • A. baylyi (genetically modified) was tested on its ability to detect “mutated and healthy KRAS DNA.”
  • Only bacteria that had “taken up mutated copies of KRAS … would survive treatment with a specific drug.”

“It was incredible when I saw the bacteria that had taken up the tumor DNA under the microscope. The mice with tumors grew green bacterial colonies that had acquired the ability to be grown on antibiotic plates,” said Josephine Wright, PhD, Senior Research Fellow, Gut Cancer Group, South Australian Health and Medical Research Institute (SAHMRI), in the news release. 

Detecting DNA from Cancer Cells In Vitro and in Mice

Findings in vitro and in mice include the following:

  • The engineered bacteria enabled detection of DNA with KRAS G12D from colorectal cancer cells made in the lab, NCI reported.
  • When mice were injected with colorectal cancer cells, the researchers’ technology found tumor DNA, Engadget reported.

The study adds to existing knowledge of horizontal gene transfer from bacteria to bacteria, according to UCSD.

“We observed horizontal gene transfer from the tumor to the sensor bacteria in our mouse model of colorectal cancer. This cellular assay for targeted, CRISPR-discriminated horizontal gene transfer (CATCH) enables the biodetection of specific cell-free DNA,” the authors wrote in Science.

“Colorectal cancer seemed a logical proof of concept as the colorectal lumen is full of microbes and, in the setting of cancer, full of tumor DNA,” gastroenterologist Daniel Worthley, PhD, a cancer researcher at Colonoscopy Clinic in Brisbane, Australia, told MedicalResearch.com.

Finding More Cancers and Treatment

More research is needed before CATCH is used in clinical settings. The scientists are reportedly planning on adapting CATCH to multiple bacteria that can locate other cancers and infections.

“The most exciting aspect of cellular healthcare … is not in the mere detection of disease. A laboratory can do that,” wrote Worthley in The Conversation. “But what a laboratory cannot do is pair the detection of disease (a diagnosis) with the cells actually responding to the disease [and] with appropriate treatment.

“This means biosensors can be programmed so that a disease signal—in this case, a specific sequence of cell-free DNA—could trigger a specific biological therapy, directly at the spot where the disease is detected in real time,” he added.

Clinical laboratory scientists, pathologists, and microbiologists may want to stay abreast of how the team adapts CATCH, and how bacterial biosensors in general continue to develop to aid diagnosis of diseases and improve ways to target treatment.

—Donna Marie Pocius

Related Information:

Could Bacteria Help Find Cancer?

Researchers Engineer Bacteria That Can Detect Tumor DNA

Engineered Bacteria Can Act as Biosensors to Detect Cancer DNA

Engineered Bacteria Detect Tumor DNA

Engineered Bacteria Can Detect Tumor DNA

Scientists Genetically Engineer Bacteria to Detect Cancer Cells

Genetically Engineered Bacteria Can Detect Cancer Cells in a World-First Experiment

Protein Catalyzed Capture Agents

All of Us Genomic Research Program Hits Milestone of 250,000 Whole Genome Sequences

Expanded genomic dataset includes a wider racial diversity which may lead to improved diagnostics and clinical laboratory tests

Human genomic research has taken another important step forward. The National Institutes of Health’s All of Us research program has reached a milestone of 250,000 collected whole genome sequences. This accomplishment could escalate research and development of new diagnostics and therapeutic biomarkers for clinical laboratory tests and prescription drugs.

The wide-reaching program aimed at gathering diverse genomic data is giving scientists access to the nearly quarter million whole genome sequences—as well as genotyping arrays, long-read genome sequences, and more—to aid precision medicine studies, the National Institutes of Health (NIH) announced in a news release.

The NIH’s All of Us program “has significantly expanded its data to now include nearly a quarter million whole genome sequences for broad research use. About 45% of the data was donated by people who self-identify with a racial or ethnic group that has been historically underrepresented in medical research,” the news release noted.

Detailed information on this and future data releases is available at the NIH’s All of us Data Roadmap.

Andrea Ramirez, MD

“For years, the lack of diversity in genomic datasets has limited our understanding of human health,” said Andrea Ramirez, MD, Chief Data Officer, All of Us Research Program, in the news release. Clinical laboratories performing genetic testing may look forward to new biomarkers and diagnostics due to the NIH’s newly expanded gene sequencing data set. (Photo copyright: Vanderbilt University.)

Diverse Genomic Data is NIH’s Goal

NIH launched the All of Us genomic sequencing program in 2018. Its aim is to involve more than one million people from across the country and reflect national diversity in its database.

So far, the program has grown to include 413,450 individuals, with 45% of participants self-identifying “with a racial or ethnic group that has been historically under-represented in medical research,” NIH said.

“By engaging participants from diverse backgrounds and sharing a more complete picture of their lives—through genomic, lifestyle, clinical, and social environmental data—All of Us enables researchers to begin to better pinpoint the drivers of disease,” said Andrea Ramirez, MD, Chief Data Officer of the All of Us research program, in the news release.

More than 5,000 researchers are currently registered to use NIH’s All of Us genomic database. The vast resource contains the following data:

  • 245,350 whole genome sequences, which includes “variation at more than one billion locations, about one-third of the entire human genome.”
  • 1,000 long-read genome sequences to enable “a more complete understanding of the human genome.”
  • 413,350 survey responses.
  • 337,500 physical measurements.
  • 312,900 genotyping arrays.
  • 287,000 electronic health records.
  • 15,600 Fitbit records (data on sleep, activity, step count, heart rate).

The research could lead to:

  • Better understanding of genetic risk factors for disease.
  • Development of predictive markers for disease risk.
  • Analysis of drugs effectiveness in different patients.

Data Shared with Participants

Participants in the All of Us program, are also receiving personalized health data based on their genetic sequences, which Dark Daily previously covered.

In “US National Institutes of Health All-of-Us Research Program Delivering Genetic Test Results and Personalized Disease Risk Assessments to 155,000 Study Participants,” we reported how the NIH had “begun returning personalized health-related DNA results” to more than 155,000 study participants. In addition, participants who requested their results will receive genetic reports that detail whether they “have an increased risk for specific health conditions and how their body might process certain medications.”

“Through a partnership with participants, researchers, and diverse communities across the country, we are seeing incredible progress towards powering scientific discoveries that can lead to a healthier future for all of us,” said Josh Denny, MD, Chief Executive Officer, All of Us Research Program, in the news release.

Cloud-based Tool Aids Access to Data

The All of Us program makes a cloud-based platform—called Researcher Workbench—available to scientists for the study of genetic variation and other issues, Inside Precision Medicine explained.

“[Researchers] can get access to the tools and the data they need to conduct a project with our resources in as little as two hours once their institutional data use agreement is signed,” said Fornessa Randal, Executive Director, Center for Asian Health Equity, University of Chicago, in a YouTube video about Researcher Workbench.

A paper published in Annual Review of Biomedical Data Science titled, “The All of Us Data and Research Center: Creating a Secure, Scalable, and Sustainable Ecosystem for Biomedical Research,” noted that  the diseases most often being studied by researchers using All of Us data include:

Database’s Growth Good for Precise Diagnostics

For diagnostics professionals, the growth of available whole human genome sequences as well as access to participants in the All of Us program is noteworthy.

Also impressive is the better representation of diversity. Such information could result in medical laboratories having an expanded role in precision medicine.  

—Donna Marie Pocius

Related Information:

All of Us Research Program Makes Nearly 250,000 Whole Genome Sequences Available to Advance Precision Medicine

US National Institutes of Health All of Us Research Program Delivering Genetic Test Results and Personalized Disease Risk Assessments to 155,000 Study Participants

All of Us Research Hub

All of Us Researcher Workbench

All of Us Program Expands Whole Genome Data Available to Researchers

All of Us Releases Almost 250,000 Genomes

All of Us Data and Research Center Creating a Secure, Scalable, and Sustainable Ecosystem for Biomedical Research

Mapping Out the Human Genome

Northwestern University Study Shares News Insights into Aging Guided by Transcriptome, Gene Length Imbalance

Findings could lead to deeper understanding of why we age, and to medical laboratory tests and treatments to slow or even reverse aging

Can humans control aging by keeping their genes long and balanced? Researchers at Northwestern University in Evanston, Illinois, believe it may be possible. They have unveiled a “previously unknown mechanism” behind aging that could lead to medical interventions to slow or even reverse aging, according to a Northwestern news release.

Should additional studies validate these early findings, this line of testing may become a new service clinical laboratories could offer to referring physicians and patients. It would expand the test menu with assays that deliver value in diagnosing the aging state of a patient, and which identify the parts of the transcriptome that are undergoing the most alterations that reduce lifespan.

It may also provide insights into how treatments and therapies could be implemented by physicians to address aging.

The Northwestern University scientists published their findings in the journal Nature Aging title, “Aging Is Associated with a Systemic Length-Associated Transcriptome Imbalance.”

“I find it very elegant that a single, relatively concise principle seems to account for nearly all of the changes in activity of genes that happen in animals as they change,” Thomas Stoeger, PhD, postdoctoral scholar in the Amaral Lab who led the study, told GEN. Clinical laboratories involved in omics research may soon have new anti-aging diagnostic tests to perform. (Photo copyright: Amaral Lab.)

Possible ‘New Instrument’ for Biological Testing

Researchers found clues to aging in the length of genes. A gene transcript length reveals “molecular-level changes” during aging: longer genes relate to longer lifespans and shorter genes suggest shorter lives, GEN summarized.

The phenomenon the researchers uncovered—which they dubbed transcriptome imbalance—was “near universal” in the tissues they analyzed (blood, muscle, bone, and organs) from both humans and animals, Northwestern said. 

According to the National Human Genome Research Institute fact sheet, a transcriptome is “a collection of all the gene readouts (aka, transcript) present in a cell” shedding light on gene activity or expression.

The Northwestern study suggests “systems-level” changes are responsible for aging—a different view than traditional biology’s approach to analyzing the effects of single genes.

“We have been primarily focusing on a small number of genes, thinking that a few genes would explain disease,” said Luis Amaral, PhD, Senior Author of the Study and Professor of Chemical and Biological Engineering at Northwestern, in the news release.

“So, maybe we were not focused on the right thing before. Now that we have this new understanding, it’s like having a new instrument. It’s like Galileo with a telescope, looking at space. Looking at gene activity through this new lens will enable us to see biological phenomena differently,” Amaral added.

In their Nature Aging paper, Amaral and his colleagues wrote, “We hypothesize that aging is associated with a phenomenon that affects the transcriptome in a subtle but global manner that goes unnoticed when focusing on the changes in expression of individual genes.

“We show that transcript length alone explains most transcriptional changes observed with aging in mice and humans,” they continued.

Researchers Turn to AI, RNA Sequencing

According to their published study, the Northwestern University scientists used large datasets, artificial intelligence (AI), and RNA (ribonucleic acid) sequencing in their analysis of tissue derived from:

  • Humans (men and women), age 30 to 49, 50 to 69, and 70 years and older. 
  • Mice, age four months to 24 months.
  • Rats, age six to 24 months.
  • Killifish, age five weeks to 39 weeks.

Scientific American reported the following study findings:

  • In tissues studied, older animals’ long transcripts were not as “abundant” as short transcripts, creating “imbalance.”
  • “Imbalance” likely prohibited the researchers’ discovery of a “specific set of genes” changing.
  • As animals aged, shorter genes “appeared to become more active” than longer genes.
  • In humans, the top 5% of genes with the shortest transcripts “included many linked to shorter life spans such as those involved in maintaining the length of telomeres.”
  • Conversely, the researchers’ review of the leading 5% of genes in humans with the longest transcripts found an association with long lives.
  • Antiaging drugs—rapamycin (aka, sirolimus) and resveratrol—were linked to an increase in long-gene transcripts.

“The changes in the activity of genes are very, very small, and these small changes involve thousands of genes. We found this change was consistent across different tissues and in different animals. We found it almost everywhere,” Thomas Stoeger, PhD, postdoctoral scholar in the Amaral Lab who led the study, told GEN.

In their paper, the Northwestern scientists noted implications for creation of healthcare interventions.

“We believe that understanding the direction of causality between other age-dependent cellular and transcriptomic changes and length-associated transcriptome imbalance could open novel research directions for antiaging interventions,” they wrote.

Other ‘Omics’ Studies

Dark Daily has previously reported on transcriptomics studies, along with research into the other “omics,” including metabolomics, proteomics, and genomics.

In “Spatial Transcriptomics Provide a New and Innovative Way to Analyze Tissue Biology, May Have Value in Surgical Pathology,” we explored how newly combined digital pathology, artificial intelligence (AI), and omics technologies are providing anatomic pathologists and medical laboratory scientists with powerful diagnostic tools.

In “Swiss Researchers Develop a Multi-omic Tumor Profiler to Inform Clinical Decision Support and Guide Precision Medicine Therapy for Cancer Patients,” we looked at how new biomarkers for cancer therapies derived from the research could usher in superior clinical laboratory diagnostics that identify a patient’s suitability for personalized drug therapies and treatments.

And in “Human Salivary Proteome Wiki Developed at University of Buffalo May Provide Biomarkers for New Diagnostic Tools and Medical Laboratory Tests,” we covered how proteins in human saliva make up its proteome and may be the key to new, precision medicine diagnostics that would give clinical pathologists new capabilities to identify disease.

Fountain of Youth

While more research is needed to validate its findings, the Northwestern study is compelling as it addresses a new area of transcriptome knowledge. This is another example of researchers cracking open human and animal genomes and gaining new insights into the processes supporting life.

For clinical laboratories and pathologists, diagnostic testing to reverse aging and guide the effectiveness of therapies may one day be possible—kind of like science’s take on the mythical Fountain of Youth.  

—Donna Marie Pocius

Related Information:

Aging Is Driven by Unbalanced Genes

Aging Linked to Gene Length Imbalance and Shift Towards Shorter Genes

NIH: Transcriptome Fact Sheet

Aging Is Associated with a Systemic Length-Associated Transcriptome Imbalance

Aging Is Linked to More Activity in Short Genes than in Long Genes

Spatial Transcriptomics Provide a New and Innovative Way to Analyze Tissue Biology, May Have Value in Surgical Pathology

Swiss Researchers Develop a Multi-omic Tumor Profiler to Inform Clinical Decision Support and Guide Precision Medicine Therapy for Cancer Patients

Human Salivary Proteome Wiki Developed at University of Buffalo May Provide Biomarkers for New Diagnostic Tools and Medical Laboratory Tests

Scientists Revive and Characterize 13 Ancient “Zombie” Viruses Isolated from Siberian Permafrost

Viruses are between 27,000 to 48,500 years old and not dangerous, but researchers say thawing permafrost may one day release pathogens capable of infecting humans

Last fall, European researchers working with virologists and genetic scientists at the Aix-Marseille University in France reported having revived and characterized 13 previously unknown “zombie” viruses isolated from Siberian permafrost samples, including one that was almost 50,000 years old. This will be of particular interest to microbiologists and clinical laboratory managers since these organisms are new to science and may be precursors to infectious agents active in the world today.

The work of the European scientists demonstrates how advancements in genome sequencing and analysis of DNA data are becoming, faster, less expensive, and more precise. That’s good because the researchers warned that, should the permafrost continue to thaw, other previously dormant viruses could be released, posing potential risks for public health.

The scientists published their findings in the open-access journal Viruses titled, “An Update on Eukaryotic Viruses Revived from Ancient Permafrost.”

The pathogens isolated by the researchers are so-called “giant viruses” that infect Acanthamoeba, a commonly found genus of amoeba, and thus are not likely to pose an immediate health threat, the researchers wrote.

However, the scientists expressed concern. “We believe our results with Acanthamoeba-infecting viruses can be extrapolated to many other DNA viruses capable of infecting humans or animals. It is thus likely that ancient permafrost … will release these unknown viruses upon thawing,” they stated in their Viruses paper.

It’s unknown how long the viruses “could be infectious once exposed to outdoor conditions (UV light, oxygen, heat), and how likely they will be to encounter and infect a suitable host in the interval,” they added. However, “the risk is bound to increase in the context of global warming, in which permafrost thawing will keep accelerating, and more people will populate the Arctic in the wake of industrial ventures.”

Paulo Verardi, PhD

“In nature we have a big natural freezer, which is the Siberian permafrost,” virologist Paulo Verardi, PhD (above), head of the Department of Pathobiology and Veterinary Science at the University of Connecticut, told The Washington Post. “And that can be a little bit concerning.” However, “if you do the risk assessment, this is very low. We have many more things to worry about right now.” Nevertheless, clinical laboratories may want to remain vigilant. (Photo copyright: University of Connecticut.)

Extremely Old, Very Large Viruses

The newly discovered viruses were found in seven different permafrost samples. Radiocarbon dating determined that they had been dormant for 27,000 to 48,500 years. But viruses contained in permafrost could be even older, the researchers wrote, as the time limit is “solely dictated by the validity range of radiocarbon dating.”

In their Viruses paper, the researchers noted that most of the 13 viruses are “at a preliminary stage of characterization,” and others have been isolated in the research laboratory “but not yet published, pending their complete genome assembly, annotation, or detailed analysis.”

“Every time we look, we will find a virus,” study co-author Jean-Michel Claverie, PhD, told The Washington Post. “It’s a done deal. We know that every time we’re going to look for viruses—infectious viruses in permafrost—we are going to find some.”

Claverie is a professor emeritus of genomics and bioinformatics in the School of Medicine at Aix-Marseille Université in Marseille, France. He leads a university laboratory known for its work in “paleovirology,” and in 2003, discovered the first known giant virus, dubbed Mimivirus. The research team included scientists from Germany and Russia.

According to CNN, unlike regular viruses that generally require an electron microscope to be viewed, giant viruses can be seen under a standard light (optical) microscope. Claverie’s laboratory previously isolated giant viruses from permafrost in 2014 and 2015.

Protecting Against Accidental Infection

To demonstrate the infectious potential of the viruses, the researchers inserted the microbes into cultured amoeba cells, which the researchers describes as “virus bait,” The Washington Post reported. One advantage of using Acanthamoeba cultures is to maintain “biological security,” the researchers wrote in their paper.

“We are using [the amoeba’s] billion years of evolutionary distance with human and other mammals as the best possible protection against an accidental infection of laboratory workers or the spread of a dreadful virus once infecting Pleistocene mammals to their contemporary relatives,” the paper noted. “The biohazard associated with reviving prehistorical amoeba-infecting viruses is thus totally negligible compared to the search for ‘paleoviruses’ directly from permafrost-preserved remains of mammoths, woolly rhinoceros, or prehistoric horses.”

The paper cites earlier research noting the presence of bacteria in ancient permafrost samples, “a significant proportion of which are thought to be alive.” These include relatives of contemporary pathogens such as:

How Dangerous are Ancient Viruses?

“We can reasonably hope that an epidemic caused by a revived prehistoric pathogenic bacterium could be quickly controlled by the modern antibiotics at our disposal,” the researchers wrote, but “the situation would be much more disastrous in the case of plant, animal, or human diseases caused by the revival of an ancient unknown virus.”

However, according to The Washington Post, “Virologists who were not involved in the research said the specter of future pandemics being unleashed from the Siberian steppe ranks low on the list of current public health threats. Most new—or ancient—viruses are not dangerous, and the ones that survive the deep freeze for thousands of years tend not to be in the category of coronaviruses and other highly infectious viruses that lead to pandemics.”

Cornell University virologist Colin Parrish, PhD, President of the American Society for Virology, told The Washington Post that an ancient virus “seems like a low risk compared to the large numbers of viruses that are circulating among vertebrates around the world, and that have proven to be real threats in the past, and where similar events could happen in the future, as we still lack a framework for recognizing those ahead of time.”

Anthony Fauci, MD, former Director of the National Institute of Allergy and Infectious Diseases (NIAID), responded to an earlier study from Claverie’s lab by outlining all the unlikely events that would have to transpire for one of these viruses to cause a pandemic. “The permafrost virus must be able to infect humans, it must then [cause disease], and it must be able to spread efficiently from human to human,” he told The Washington Post in 2015. “This can happen, but it is very unlikely.”

Thus, clinical laboratories probably won’t see new diagnostic testing to identify ancient viruses anytime soon. But it’s always best to remain vigilant.

Stephen Beale

Related Information:

Scientists Have Revived a ‘Zombie’ Virus That Spent 48,500 Years Frozen in Permafrost

‘Zombie’ Viruses Are Thawing in Melting Permafrost Because of Climate Change

Ancient Dormant Viruses Found in Permafrost, Once Revived, Can Infect Amoeba

Scientists Revive 48,500-Year-Old ‘Zombie Virus’ Buried in Ice

Scientists Revived Ancient ‘Zombie Viruses’ Frozen for Eons in Siberia

Scientists Warn Long-Frozen ‘Zombie Virus’ Is ‘Public Health Threat’ Amid Thaw

Scientists Did Not Release a Zombie Plague by Reviving a Dormant Virus, but Their Warning of a Potential Public Health Crisis Is Legitimate

University of Washington Researchers Use Genomic Analysis to Track Shigella Infections as Decreased Cost of Gene Sequencing Aids Public Health Research

Another study in the United Kingdom that also used genomic analysis to understand drug-resistant Shigella produced findings that may be useful for microbiologists and medical laboratory scientists

From the onset of an infectious disease outbreak, public health officials, microbiologists, and clinical laboratory managers find it valuable to trace the origin of the spread back to the “index case” or “patient zero”—the first documented patient in the disease epidemic. Given the decreased cost of genomic analysis and improved accuracy of gene sequencing, infectious disease researchers are finding that task easier and faster than ever.

One recent example is a genomic study conducted at University of Washington (UW) in Seattle that enabled researchers to “retrace” the origin and spread of a “multidrug-resistant Shigellosis outbreak” from 2017 to 2022. “The aim of the study was to better understand the community transmission of Shigella and spread of antimicrobial resistance in our population, and to treat these multi-drug resistant infections more effectively,” the UW scientists stated in a new release.

Shigellosis (aka, bacillary dysentery) is a highly contagious disease of the intestines that can lead to hospitalization. Symptoms include fever, stomach cramps, diarrhea, dysentery, and dehydration.

“Additional analysis of the gut pathogen and its transmission patterns helped direct approaches to testing, treatment, and public health responses,” the UW news release states.

Usually prevalent in countries with public health and sanitation limitations, the “opportunistic” Shigella pathogen is now being seen in high-income countries as well, UW reported.

The researchers published their findings in Lancet Infectious Diseases, titled, “Genomic Reconstruction and Directed Interventions in a Multidrug-Resistant Shigellosis Outbreak in Seattle, WA, USA: A Genomic Surveillance Study.”

Ferric Fang, MD

“You can’t really expect an infectious disease to remain confined to a specific at-risk population. [Shigella infections are] very much an emerging threat and something where our public health tools and therapeutic tools have significant limitations,” infectious disease specialist Ferric Fang, MD (above) told CIDRAP News. Fang is a UW professor of Microbiology and Clinical Laboratory Medicine and a corresponding author of the UW study. (Photo copyright: University of Washington.)

Why are Shigella Cases Increasing?

The US Centers for Disease Control and Prevention (CDC) records more than 450,000 shigellosis infections each year in the US. The most common species in the US, according to CDC statistics, is Shigellaa sonnei.

Other members of the genus include:

Generally, Shigella infects children, travelers, and men who have sex with men (MSM), the CDC noted.

The UW researchers were motivated to study Shigella when they noticed an uptick in drug-resistant shigellosis cases in Seattle’s homeless population in 2020 at the beginning of the COVID-19 pandemic, Center for Infectious Disease Research and Policy News (CIDRAP News) reported.

“Especially during the pandemic, a lot of public facilities were closed that homeless people were used to using,” infectious disease specialist Ferric Fang, MD, told CIDRAP News. Fang is Professor of Microbiology and Laboratory Medicine at University of Washington and corresponding author of the UW study.

The researchers studied 171 cases of Shigella identified from 2017 to 2022 by clinical laboratories at Harborview Medical Center and UW Medical Center in Seattle. According to CIDRAP News, the UW researchers found that:

  • 46% were men who have sex with men (MSM).
  • 51% were people experiencing homelessness (PEH).
  • Fifty-six patients were admitted to the hospital, with eight to an intensive care unit.
  • 51% of isolates were multi-drug resistant (MDR).

Whole-Genome Sequencing Reveals Origin

The UW scientists characterized the stool samples of Shigella isolates by species identification, phenotypic susceptibility testing, and whole-genome sequencing, according to their Lancet Infectious Diseases paper. The paper also noted that 143 patients received antimicrobial therapy, and 70% of them benefited from the treatment for the Shigella infection.

Whole-genome sequencing revealed that two strains of Shigella (S. flexneri and S. sonnei) appeared first in Seattle’s MSM population before infecting the PEM population.

The genomic analysis found the outbreak of drug-resistant Shigella had international links as well, according to CIDRAP News:

  • One S. flexneri isolate was associated with a multi-drug resistant (MDR) strain from China, and
  • S. sonnei isolates resembled a strain characteristic of a current outbreak of MDR Shigella in England.

“The most prevalent lineage in Seattle was probably introduced to Washington State via international travel, with subsequent domestic transmission between at-risk groups,” the researchers wrote.

“Genomic analysis elucidated not only outbreak origin, but directed optimal approaches to testing, treatment, and public health response. Rapid diagnostics combined with detailed knowledge of local epidemiology can enable high rates of appropriate empirical therapy even in multidrug-resistant infection,” they continued.

UK Shigella Study Also Uses Genomics

Another study based in the United Kingdom (UK) used genomic analysis to investigate a Shigella outbreak as well.

Motivated by a UK Health Security Agency report of an increase in drug-resistance to common strains since 2021, the UK researchers studied Shigella cases from September 2015 to June 2022.

According to a paper they published in Lancet Infectious Diseases, the UK researchers “reported an increase in cases of sexually transmitted S. flexneri harboring blaCTX-M-27 (an antibiotic-resistant gene) in England, which is known to confer resistance to third-generation cephalosporins (antibiotics),” the researchers wrote.

Their analysis of plasmids (DNA with genes having antibiotic resistance) revealed a link in two drug-resistant Shigella strains at the same time, CIDRAP News explained.

“Our study reveals a worsening outlook regarding antimicrobial-resistant Shigella strains among MSM and highlights the value of continued integration of genomic analysis into surveillance and research,” the UK-based scientists wrote.

Current challenges associated with Shigella, especially as it evades treatment, may continue to demand attention from microbiologists, clinical laboratory scientists, and infectious disease specialists. Fortunately, use of genomic analysis—due to its ongoing improvements that have lowered cost and improved accuracy—has made it possible for public health researchers to better track the origins of disease outbreak and spread.    

Donna Marie Pocius

Related Information:

Genomic Reconstruction and Directed Interventions in a Multidrug-Resistant Shigellosis Outbreak in Seattle, Washington, USA: a Genomic Surveillance Study.

Genomics Aids Study of Seattle 2017-22 Shigella Outbreak

Q/A: Shigella—Shigellosis

A Spotlight on Growing Threat of Drug-Resistant Shigella

Emergence of Extensively Drug-Resistant and Multidrug-Resistant Shigella flexneri serotype 2a Associated with Sexual Transmission Among Gay, Bisexual, and Other Men Who Have Sex with Men, in England: A Descriptive Epidemiological Study

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