Francisella tularensis is the causative agent of the acute disease tularemia. Due to its extreme infectivity and ability to cause disease upon inhalation, F. tularensis has been classified as a biothreat agent. Two subspecies of F. tularensis, tularensis and holarctica, are responsible for tularemia in humans. In comparison, the closely related species F. novicida very rarely causes human illness and cases that do occur are associated with patients who are immune compromised or have other underlying health problems. Virulence between F. tularensis and F. novicida also differs in laboratory animals. Despite this varying capacity to cause disease, the two species share ~97% nucleotide identity, with F. novicida commonly used as a laboratory surrogate for F. tularensis. As the F. novicida U112 strain is exempt from U.S. select agent regulations, research studies can be carried out in non-registered laboratories lacking specialized containment facilities required for work with virulent F. tularensis strains. This review is designed to highlight phenotypic (clinical, ecological, virulence, and pathogenic) and genomic differences between F. tularensis and F. novicida that warrant maintaining F. novicida and F. tularensis as separate species. Standardized nomenclature for F. novicida is critical for accurate interpretation of experimental results, limiting clinical confusion between F. novicida and F. tularensis and ensuring treatment efficacy studies utilize virulent F. tularensis strains.
Keywords: tularemia, Francisella tularensis, Francisella novicida, intracellular pathogen, virulence
Citation: Kingry LC and Petersen JM (2014) Comparative review of Francisella tularensis and Francisella novicida. Front. Cell. Infect. Microbiol. 4:35. doi: 10.3389/fcimb.2014.00035
Received: 12 December 2013; Accepted: 22 February 2014;
Published online: 13 March 2014.
Edited by:Max Maurin, Université Aix-Marseille II, France
Reviewed by:Andrey P. Anisimov, State Research Center for Applied Microbiology and Biotechnology, Russia
Copyright © 2014 Kingry and Petersen. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: Jeannine M. Petersen, Division of Vector-Borne Disease, Bacterial Diseases Branch, Centers for Disease Control and Prevention, 3150 Rampart Road, Fort Collins, CO 80523, USA e-mail: email@example.com