Garth D. Ehrlich

Garth D. Ehrlich, PhD, FAAAS, FAAM

Professor of Microbiology & Immunology; Professor of Otolaryngology-Head and Neck Surgery


Department: Microbiology & Immunology, Otolaryngology

Education

  • BA - Alfred University cum laude (1977)
  • PhD - Syracuse University (1987)
  • Postdoctoral Fellowship - SUNY Upstate Medical Center (1988)

Awards & Honors

  • American Academy of Microbiology (ASM), Distinguished Lecturer Roster (2023-2025)
  • American Academy of Microbiology (ASM), Elected Fellow (2022)
  • BioSpectrum 2020, University of Engineering and Management, Kolkata INDIA, Conference Chair (honorary)
  • NIH, NIDCD's Otitis Media Working Group Workshop, Invited Panel Member (2020)
  • American Association for the Advancement of Science (AAAS), Elected Fellow (2014)

Garth Ehrlich, PhD, FAAAS, FAAM is a professor of microbiology and immunology, and otolaryngology-head and neck surgery at Drexel University College of Medicine.

Administrative Overview

Dr. Ehrlich is the executive director of three Research Centers of Excellence in the Institute for Molecular Medicine and Infectious Diseases: the Center for Advanced Microbial Processing (CAMP), the Center for Genomic Sciences (CGS), and the Center for Surgical Infection and Bacterial Biofilm. He also serves as executive director of the Genomics Core Facility, which is a University-wide sequencing and bioinformatics service core. In response to the COVID-19 pandemic Dr. Ehrlich founded and currently serves as executive director of the Center for Molecular Diagnostics, and as section director, Molecular Pathology Section, Drexel Medicine Diagnostics (a CLIA/CAP certified high-complexity clinical diagnostics laboratory).

Editorial Roles

Dr. Ehrlich is editor-in-chief of Genetic Testing and Molecular Biomarker, a MaryAnn Liebert Publication. In addition, he is an associate editor of BMC Evolutionary Biology and the MDPI journal GENES.

Productivity Metrics

Dr. Ehrlich has a Google h-factor of 83, an i10-index of 227 and with nearly 28,000 citations of his published papers; he also has a ResearchGate h-factor of 78 with an RG Score of 51 and has had 6 papers cited by the Faculty of 1000.

UPCOMING INTERNATIONAL LYME AND ASSOCIATED DISEASES SOCIETY (ILADS) AND ALZHEIMER PATHOBIOME INITIATIVE (ALZPI) EVENTS

2024 Germany - ILADS

Make plans to join us in Germany next spring for the ILADS European Scientific Conference. April 19-21, 2024, Hotel Vier Jahreszeiten Starnberg, Germany

2024 AlzPI & IDSA Joint Conference

Microbes & Dementia: Bridging Silos to Accelerate Innovation, PCOM, Philadelphia PA, July 27, 2024

Research Interests

Use of large-scale comparative genomic technologies to explore the molecular pathogenesis of chronic infectious diseases and the human genetics of susceptibility and resistance to infection.

Research

Chronic Bacterial Pathogenesis

Dr. Ehrlich and his lab are interested in how chronic bacterial pathogens persist in the face of antimicrobial therapy, and the innate and adaptive host responses. To understand this complex phenomenon, Dr. Ehrlich promulgated the rubric of “bacterial plurality,” which embodies the concept that chronic pathogens display enormous heterogeneity at many levels including: phenotypic, metabolic and genotypic. The reasoning behind the development of this theoretical construct was to provide a paradigm that more accurately models chronic pathogenic processes enabling the development of rational therapies for these diseases that are recalcitrant to current medical management. It is our belief that the extant paradigms of bacterial pathogenesis passed down to us from Robert Koch and developed for acute epidemic infections, although powerful and useful for clonal planktonic infections, acted for decades as blinders toward our understanding of chronic infections.

As part of our studies of bacterial plurality, we have participated in the development of a new understanding of bacterial ecology, which includes the realization that bacteria have a developmental life cycle, can exist as solitary organisms or as part of a complex interacting multicellular community, and can phenotypically adapt to changing environmental conditions. Phenotypic heterogeneity is explained by the fact that nearly all bacteria can form biofilms or even more complex large-scale structures for protection, generation of reducing power and dispersal.  Metabolic heterogeneity results (in part) from the understanding of limiting nutrient fluxes into a biofilm.

Genotypic heterogeneity at the bacterial species level is a result of genomic plasticity embodied in Dr. Ehrlich’s distributed genome hypothesis (DGH), which he advanced in 2001. The DGH states that chronic bacterial pathogens utilize a survival strategy wherein a large set of genes are distributed among a population and are not found in all members of a species; thus there exists a supra-genome (pangenome) at the population level that is far greater in size than the genome of any one organism. The DGH includes the concept that energetic methods of horizontal gene transfer (HGT) are population-based virulence factors that evolved specifically to create diversity and drive strain evolution. Furthermore, the distribution of contingency genes among a population serves as a supra-virulence factor that provides for improved population survival through increased rates of horizontal gene transfer, which provides the engine for rapid adaptation to environmental conditions through the reassortment of genes among strains.

As part of the development of the field of comparative genomics and to test the DGH, our Research Centers of Excellence have been on the cutting edge of genomic technology development for nearly 20 years, beginning with the design and operationalization a fully automated robotic Sanger sequencing facility in the late 90s that covered everything from colony picking to cycle sequencing. Subsequently in 2003 we were chosen as academic partners and alpha testers by 454 LifeSciences to participate in the development of their revolutionary massively parallel long-read pyrosequencing technology (the first of the next-generation DNA sequencing technologies). We then received our beta test instrument from 454 in 2005. As part of the next big jump in technology, we became beta testers for Pacific Biosciences (PacBio) SMRT technology in 2011, and in 2017 we upgraded our facilities to include PacBio’s second-generation Sequel platform. In parallel with our development of sequencing technologies we have created, in-house, a suite of bioinformatic and mathematical modeling tools to analyze the genomic data generated in our laboratories. Most recently we have developed and applied machine learning algorithms to identify in an unbiased fashion distributed genes that are associated with specific traits.

Using these technologies and computational tools we have:

  1. Performed whole genome sequencing, assembly and annotation on over 4,000 bacterial strains
  2. Performed comparative genomics on these and many other sequenced bacterial strains to characterize the core, distributed and supra-genomes of dozens of bacterial species and to identify candidate genes associated with virulence and tissue tropisms.

The data from these studies have demonstrated that the DGH holds for all bacterial species examined, including pathogens and nonpathogens alike, and that the supra-genomes for the vast majority of bacterial species are several times the size of the species’ core genomes. Importantly the species examined cover Gram-negatives, Gram-positives, Gram-indeterminates, spirochetes, professional pathogens, opportunistic pathogens and free-living environmental and commensal organisms. We therefore feel comfortable stating that the DGH is broadly applicable across the entire spectrum of free-living bacteria and that bacterial diversity provides bacterial species as a whole—regardless of their individual environmental niches—with the ability to persist in the face of multifaceted environmental challenges.

More recently we have been expanding the concept of population-based virulence factors, which are phenomena that exist only at the population level and are thus not observable at the level of the individual bacterium. These include biofilm formation, caserna construction and other complex cellular organizations such as nanowires; bacterial communication systems such as quorum sensing and vesicle formation and disbursement; and horizontal gene transfer mechanisms. Collectively these systems imbue bacteria with a type of intelligence analogous to cellular automation.

An Infectious Etiological Component for Alzheimer’s Disease (AD)?

Dr. Ehrlich and his team have been at the forefront of the movement to determine if bacteria and other infectious agents can act as triggers in the development of AD. Dr. Ehrlich serves as a founding board member of the Alzheimer’s Pathobiome Initiative (AlzPI), a global consortium of researchers focused on developing improved diagnostics and therapeutics for AD and precursor syndromes. Towards this end they have developed a species-specific, trans-pan-domain molecular diagnostic that can quantitatively determine the microbial composition of any specimen for any cellular microbe including bacteria, fungi, and parasites. The application of this diagnostic has resulted in the recent publication of a high impact paper by Mone et al (2023).

Development of Anti-biofilm Drugs

Working in collaboration with colleagues in the Department of Microbiology and Immunology, Assistant Professor Donald (DJ) Hall, and Chemistry, Professor Frank Ji, Dr. Ehrlich is leading a team in the development of the first drugs rationally designed to treat biofilm infections. Bacterial biofilms are metabolically resistant to antibiotics. To overcome this resistance, which is triggered by the stringent response, Dr. Ehrlich’s team has developed a combination in silico-laboratory pipeline for the identification and testing of small molecules that act as competitive inhibitors of the RelA enzyme to be used with antibiotics for their “re-potention” against bacterial persister cells. Excitingly, our lead compound also profoundly inhibits virulence factor production by both major Gram-negative (Pseudomonas aeruginosa) and Gram-positive (MRSA USA 300) bacteria – thereby “defanging” these pathogens. This project has attracted preliminary funding from the Bill and Marion Cook Foundation and the Coulter-Drexel Translational Research Partnership Program.

Human Disease, Susceptibility and Performance Gene Mapping and Cloning

We are involved in a number of human gene identification projects with a recent emphasis on understanding the susceptibility and resistance to bacterial infection. Currently, we are working with Drs. Noam Cohen and Dani Reed, respectively at the University of Pennsylvania and the Monell Chemical Senses Institute, to understand the innate immune role of the genes that encode the bitter taste receptors (the bitterome). This project involves genotyping infection-defined cohorts of patients, and comparing their genetics with their sinonasal microbiomes, as well as functional studies of their ciliated epithelium in response to bacteria and their metabolic products. We are also continuing our long-standing interest in skeletal diseases, and have recently identified a family with a unique patellar tendon insertional defect that follows an autosomal dominant mode of inheritance. Additionally we are also exploring a program to identify genes associated with control of tuberculosis (TB), as there are many patients with latent TB who never develop clinical disease.

Our legacy human genetic projects have included mapping (M) and cloning (C) of genes for several skeletal and connective tissue diseases including Crouzon syndrome (M&C), Jackson-Weiss syndrome (M&C) ectrodactyly (M), and Dupuytrens’ contracture (M); as well as several, gastrointestinal/mobility diseases including hereditary pancreatitis (M&C), DAIA (M), and severe pediatric gastroesophageal reflux disease or GERD (M).

In the Media

See Dr. Ehrlich on Wikipedia.

See Dr. Ehrlich on Google Scholar.

“FactChecking RFK Jr.’s Other Health Claims During HHS Confirmation Hearings”
Factcheck.org (February 6, 2025)

“RFK Jr.'s insistence that the government ignores chronic disease is misguided”
NBC News, yahoo! News (February 1, 2025)

“Why the brain's microbiome could hold the key to curing Alzheimer's”
New Scientist (February 19, 2024)

Could a Breakdown in the Brain’s Networks Allow Infections to Contribute to Alzheimer’s Disease?
Drexel News (September 13, 2023)

“The International Lyme and Associated Diseases Society Brings Annual Scientific Conference to Boston”
PR Newswire (June 29, 2023)

Additional articles...

Publications

Editorial Roles

  • Editor-in-chief, Genetic Testing and Molecular Biomarkers, Mary Ann Liebert, Inc Publishers
  • Associate editor, BMC Ecology and Evolution, BMC Series Journals, Springer Nature Group
  • Associate editor, Frontiers in Microbiology
  • Associate editor, Frontiers in Genetics, Genetics of Common and Rare Diseases
  • Guest editor, Frontiers in Genetics (with Drs. Regie Santoz-Cortez [GEIC] & Allen Ryan); Human Genetics Section; Topic Title – Otitis Media Genomic and Middle-ear Microbiome
  • Editorial board, Microorganisms, MDPI
  • Editorial board, Journal of Clinical Medicine, MDPI
  • Editorial board, Genes, MDPI

See all Garth Ehrlich's publications in PubMed.

Recent Selected Publications

Classic Publications

Presentations

Keynote Speaking Engagements

Invited Speaking Engagements

Keynote Talks

Invited Talks