Joseph F. Petrosino Ph.D.
Functional Genomics of Biodefense and Emerging Infectious Disease Pathogens
- Assistant Professor
- Ph.D.
Baylor College of Medicine - Postdoc
Baylor College of Medicine - 713-798-7912
- jpetrosi@bcm.edu
Comparative Genomics of Francisella tularensis
The facultative intracellular pathogen, Francisella tularensis, is the causative agent of tularemia, and is among the most infectious pathogens known, both in terms of the number of zoonotic species it infects (>250), and the number of organisms needed to establish a potentially lethal infection (<10 by the airborne route). F. tularensis is a Category A biodefense agent because of its ability to cause incapacitating, potentially fatal, illness, its ability to spread via aerosolization, and for the potential burden it would have on the public health system in the event of an outbreak. There are four subspecies of Francisella tularensis: subspecies tularensis (Type A), subspecies holarctica (Type B), subspecies novicida, and subspecies mediasiatica. Type A, found exclusively in North America and Mexico, causes the most severe form of human disease, while Type B is less pathogenic in humans and is found throughout the northern hemisphere. Several decades ago, in the former Soviet Union, an attenuated live vaccine strain (LVS) was derived from repeated passage of a Type B strain. LVS offers protection against both Type A and Type B infection, but is not licensed for use in the U.S. because it’s immunogenicity in humans is poorly characterized, the mechanism of attenuation for this strain is unknown, and the strain kills mice with a LD50 of one bacterium when injected interperotineally.
Using state-of-the-art technologies and resources in the Baylor College of Medicine Human Genome Sequencing Center, we are determining the genomic sequences of multiple F. tularensis strains. Comparisons of Type A, Type B, LVS, and other Francisella sequences are highlighting genetic differences that will answer the following questions:
- Why are Type A Francisella strains more virulent than Type B strains?
- How are Francisella subspecies evolutionarily related?
- What makes Francisella so pathogenic in the absence of an obvious toxin?
- What genes mediate robust replication of Francisella in macrophages?
- What mutations attenuate LVS?
- What mutations are capable of rationally attenuating pathogenic strains?
Isogenic Francisella mutant strains will be constructed subsequently to test the roles of candidate alleles in strain attenuation and host specificity. These studies will reveal the pathogenicity mechanisms of one of the most virulent bacteria known and will further the development of improved attenuated vaccines and immunodiagnostics targeted against Francisella.
Functional Genomics of Francisella tularensis
Functional genomics approaches are being used to identify proteins important for F. tularensis recognition by the host immune response. With our collaborators, we are using the recombination-based, Gateway system (Invitrogen, Carlsbad, CA) to clone and express approximately 2000 open reading frames (ORFs) belonging to the Type A and Type B Francisella subspecies. This strategy permits the rapid conversion of the original plasmid clone set to other functional vectors containing various promoters or tag sequences. Through further collaboration with the BCM Vaccine Treatment and Evaluation Unit (VTEU) we are using this clone set, along with the shotgun library constructed to sequence the Francisella genome, to systematically identify F. tularensis proteins recognized by the human humoral and cell-mediated immune responses. Results from this work will further characterize the human response to LVS vaccination and will lead to the development of novel F. tularensis vaccines and immunodiagnostics.
The approaches outlined here are being adapted for additional functional genomics studies in other biodefense and emerging and infectious disease concerns to advance vaccine and diagnostic discovery in these organisms
Recent Publications (PubMed)