Francisella tularensis is a pathogenic species of Gram-negative coccobacillus, an aerobic bacterium. It is nonspore-forming, nonmotile, and the causative agent of tularemia, the pneumonic form of which is often lethal without treatment.

1. FRANCISELLA TULARENSIS
Dr. Chinnamani Prasannakumar
Assistant Professor
PG & Research Department of Biotechnology and Microbiology
National College,
Karumandappam (Dindigul road)
Tiruchirappalli- 620001

2. • A PATHOGENIC SPECIES OF GRAM-NEGATIVE COCCOBACILLUS, AN AEROBIC BACTERIUM.
• NONSPORE-FORMING, NONMOTILE, AND THE CAUSATIVE AGENT OF TULAREMIA.
• IT IS A FASTIDIOUS, FACULTATIVE INTRACELLULAR BACTERIUM, WHICH REQUIRES CYSTEINE FOR
GROWTH.
• DUE TO ITS LOW INFECTIOUS DOSE, EASE OF SPREAD BY AEROSOL, AND HIGH VIRULENCE, F.
TULARENSIS IS CLASSIFIED AS A TIER 1 SELECT AGENT OF BIOTERRORISM.
• WHEN FOUND IN NATURE, FRANCISELLA TULARENSIS CAN SURVIVE FOR SEVERAL WEEKS AT
LOW TEMPERATURES IN ANIMAL CARCASSES, SOIL, AND WATER.
• IN THE LABORATORY, F. TULARENSIS APPEARS AS SMALL RODS (0.2 BY 0.2 MICROMETR), AND
IS GROWN BEST AT 35–37 °C.

3. • HISTORY: THIS SPECIES WAS DISCOVERED IN GROUND SQUIRRELS IN TULARE COUNTY,
CALIFORNIA.
• IN 1911; BACTERIUM TULARENSE WAS SOON ISOLATED BY GEORGE WALTER MCCOY (1876–
1952) OF THE US PLAGUE LAB IN SAN FRANCISCO AND REPORTED IN 1912.

4. PATHOGENESIS
• F. TULARENSIS HAS BEEN REPORTED IN INVERTEBRATES INCLUDING INSECTS AND TICKS, BIRDS,
AMPHIBIANS, REPTILES, FISH AND MAMMALS INCLUDING HUMANS
• DIRECT CONTACT WITH INFECTED ANIMALS OR CARCASSES IS ANOTHER SOURCE.
• IMPORTANT RESERVOIR HOSTS INCLUDE RABBITS, RODENTS, GALLIFORM BIRDS AND DEER.
• AEROSOLS CONTAINING THE BACTERIA MAY BE GENERATED BY DISTURBING CARCASSES DUE
TO BRUSH CUTTING OR LAWN MOWING; AS A RESULT, TULAREMIA HAS BEEN REFERRED TO AS
"LAWNMOWER DISEASE"

6. HUMAN INFECTION:
• PORTALS OF ENTRY ARE THROUGH BLOOD AND THE RESPIRATORY SYSTEM.
• THE MOST COMMON OCCURS VIA SKIN CONTACT, YIELDING AN ULCEROGLANDULAR FORM OF THE DISEASE.
• INHALATION OF BACTERIA, PARTICULARLY BIOVAR F. T. TULARENSIS, LEADS TO THE POTENTIALLY LETHAL PNEUMONIC
TULAREMIA.
• WHILE THE PULMONARY AND ULCEROGLANDULAR FORMS OF TULAREMIA ARE MORE COMMON, OTHER ROUTES OF
INOCULATION HAVE BEEN DESCRIBED AND INCLUDE
• OROPHARYNGEAL INFECTION DUE TO CONSUMPTION OF CONTAMINATED FOOD OR WATER, AND
• CONJUNCTIVAL INFECTION DUE TO INOCULATION AT THE EYE

8. LIFECYCLE
• F. TULARENSIS IS A FACULTATIVE INTRACELLULAR BACTERIUM THAT IS CAPABLE OF INFECTING MOST
CELL TYPES, BUT PRIMARILY INFECTS MACROPHAGES IN THE HOST ORGANISM.
• ENTRY INTO THE MACROPHAGE OCCURS BY PHAGOCYTOSIS AND THE BACTERIUM IS SEQUESTERED
FROM THE INTERIOR OF THE INFECTED CELL BY A PHAGOSOME.
• F. TULARENSIS THEN BREAKS OUT OF THIS PHAGOSOME INTO THE CYTOSOL AND RAPIDLY
PROLIFERATES.
• EVENTUALLY, THE INFECTED CELL UNDERGOES APOPTOSIS, AND THE PROGENY BACTERIA ARE
RELEASED IN A SINGLE "BURST" EVENT TO INITIATE NEW ROUNDS OF INFECTION.

10. VIRULENCE FACTORS
• F. TULARENSIS STRAINS PRODUCE DIFFERENT HEMOLYTIC AGENTS, WHICH MAY FACILITATE DEGRADATION OF THE
PHAGOSOME
• THE EXPRESSION OF A 23-KD PROTEIN KNOWN AS IGLC IS REQUIRED FOR F. TULARENSIS PHAGOSOMAL BREAKOUT
AND INTRACELLULAR REPLICATION
• MUTANT F. TULARENSIS CELLS DIE AND ARE DEGRADED BY THE MACROPHAGE
• F. TULARENSIS, IN VITRO, DOWNREGULATES THE IMMUNE RESPONSE OF INFECTED CELLS.
• UNHINDERED BY THE HOST IMMUNE SYSTEM BY BLOCKING THE WARNING SIGNALS FROM THE INFECTED CELLS.
• THIS DOWNMODULATION OF THE IMMUNE RESPONSE REQUIRES THE IGLC PROTEIN.

11. DIAGNOSIS, TREATMENT, AND PREVENTION
• DIAGNOSED BY CLINICIANS BASED ON SYMPTOMS AND PATIENT HISTORY, IMAGING, AND LABORATORY STUDIES.
• TULAREMIA IS TREATED WITH ANTIBIOTICS, SUCH AS AMINOGLYCOSIDES, TETRACYCLINES, OR FLUOROQUINOLONES.
• PREVENTIVE MEASURES INCLUDE PREVENTING BITES FROM TICKS, FLIES, AND MOSQUITOS;
• ENSURING WELL COOKED MEAT; REFRAINING FROM DRINKING UNTREATED WATER; USING INSECT REPELLENTS.
• DURING LABORATORY HANDLING OF F. TULARENSIS; MAKING SURE TO WEAR A GOWN, IMPERMEABLE GLOVES,
MASK, AND EYE PROTECTION; AND WHEN DRESSING GAME, MAKING SURE TO WEAR IMPERMEABLE GLOVES.
• ALSO, A LIVE ATTENUATED VACCINE IS AVAILABLE FOR INDIVIDUALS WHO ARE AT HIGH RISK FOR EXPOSURE SUCH AS
LABORATORY PERSONNEL.