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Rapid dissemination of Francisella tularensis and the effect of route of infection.

Ojeda SS, Wang ZJ, Mares CA, Chang TA, Li Q, Morris EG, Jerabek PA, Teale JM - BMC Microbiol. (2008)

Bottom Line: By 20 hours, there was significant tropism to the lung compared with other tissues.MicroPET images correlated with the biodistribution of isotope and bacterial burdens in analyzed tissues.Our findings suggest that Francisella has a differential tissue tropism depending on the route of entry and that the virulence of Francisella by the pulmonary route is associated with a rapid bacteremia and an early preferential tropism to the lung.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Microbiology and Immunology, University of Texas Health Science Center at San Antonio, San Antonio, TX 78229, USA. ojeda@uthscsa.edu

ABSTRACT

Background: Francisella tularensis subsp. tularensis is classified as a Category A bioweapon that is capable of establishing a lethal infection in humans upon inhalation of very few organisms. However, the virulence mechanisms of this organism are not well characterized. Francisella tularensis subsp. novicida, which is an equally virulent subspecies in mice, was used in concert with a microPET scanner to better understand its temporal dissemination in vivo upon intranasal infection and how such dissemination compares with other routes of infection. Adult mice were inoculated intranasally with F. tularensis subsp. novicida radiolabeled with 64Cu and imaged by microPET at 0.25, 2 and 20 hours post-infection.

Results: 64Cu labeled F. tularensis subsp. novicida administered intranasally or intratracheally were visualized in the respiratory tract and stomach at 0.25 hours post infection. By 20 hours, there was significant tropism to the lung compared with other tissues. In contrast, the images of radiolabeled F. tularensis subsp. novicida when administered intragastrically, intradermally, intraperitoneally and intravenouslly were more generally limited to the gastrointestinal system, site of inoculation, liver and spleen respectively. MicroPET images correlated with the biodistribution of isotope and bacterial burdens in analyzed tissues.

Conclusion: Our findings suggest that Francisella has a differential tissue tropism depending on the route of entry and that the virulence of Francisella by the pulmonary route is associated with a rapid bacteremia and an early preferential tropism to the lung. In addition, the use of the microPET device allowed us to identify the cecum as a novel site of colonization of Francisella tularensis subsp. novicida in mice.

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Biodistribution of 64Cu labeled bacteria. The distribution of 64Cu labeled F. tularensis subsp. novicida was compared to 64Cu labeled K. pneumoniae, 64Cu labeled E. coli and 64Cu labeled LVS in each tissue at 20 hrs pi. The data represent an average of 3 – 9 mice per infection and are given as %ID/g of tissue. The data obtained for each of the tissues sampled 20 hrs p.i from mice infected with F. tularensis subsp. novicida was compared statistically to the same tissue when inoculated with 64Cu labeled K. pneumoniae and E. coli at 20 hrs p.i by using a two tail Student's t-test [e.g. lung (i.n) to lung (i.g)]. * = p < 0.05, ** = p < 0.01 and *** = p < 0.005.
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Figure 5: Biodistribution of 64Cu labeled bacteria. The distribution of 64Cu labeled F. tularensis subsp. novicida was compared to 64Cu labeled K. pneumoniae, 64Cu labeled E. coli and 64Cu labeled LVS in each tissue at 20 hrs pi. The data represent an average of 3 – 9 mice per infection and are given as %ID/g of tissue. The data obtained for each of the tissues sampled 20 hrs p.i from mice infected with F. tularensis subsp. novicida was compared statistically to the same tissue when inoculated with 64Cu labeled K. pneumoniae and E. coli at 20 hrs p.i by using a two tail Student's t-test [e.g. lung (i.n) to lung (i.g)]. * = p < 0.05, ** = p < 0.01 and *** = p < 0.005.

Mentions: To test the potential effects of bacterial strains on dissemination, two different bacterial strains, E. coli and K. pneumoniae, were labeled with 64Cu-PTSM and administered i.n at the same dose of 2 × 109 CFU/20 μl used for F. tularensis subsp. novicida. By both microPET analysis (Fig. 1) and ex vivo isotope distribution at 20 h (Fig. 5), E. coli exhibited the highest percentage of radioisotope in the digestive tract and a barely detectable percentage in the lung that was significantly lower than in the case of F. tularensis subsp. novicida infected mice (p < 0.005) (Fig. 5). In the case of K. pneumoniae infection (Fig. 1), another pulmonary pathogen, a larger percentage of labeled bacteria remained in the nasal cavity and less in the lung compared with F. tularensis subsp. novicida at all time points tested. Furthermore, our biodistribution data showed that by 20 hrs p.i the %ID/g obtained in the lung for K. pneumoniae infected mice are significantly lower than for F. tularensis subsp. novicida infected mice (p < 0.005). In addition, spread of bacteria to the digestive tract appeared to be somewhat delayed compared with F. tularensis subsp. novicida. Interestingly, F. tularensis subsp. novicida shows a significantly higher tropism for cecum when compared to K. pneumoniae (p < 0.05) but not with E. coli (Fig. 5). We also labeled LVS with 64Cu, infected mice by the i.n route and imaged them by MicroPET (data not shown). The results were similar to those obtained with i.n inoculation of F. tularensis subsp. novicida showing higher levels in the lung and GI tract. The biodistribution data is shown in Fig. 5.


Rapid dissemination of Francisella tularensis and the effect of route of infection.

Ojeda SS, Wang ZJ, Mares CA, Chang TA, Li Q, Morris EG, Jerabek PA, Teale JM - BMC Microbiol. (2008)

Biodistribution of 64Cu labeled bacteria. The distribution of 64Cu labeled F. tularensis subsp. novicida was compared to 64Cu labeled K. pneumoniae, 64Cu labeled E. coli and 64Cu labeled LVS in each tissue at 20 hrs pi. The data represent an average of 3 – 9 mice per infection and are given as %ID/g of tissue. The data obtained for each of the tissues sampled 20 hrs p.i from mice infected with F. tularensis subsp. novicida was compared statistically to the same tissue when inoculated with 64Cu labeled K. pneumoniae and E. coli at 20 hrs p.i by using a two tail Student's t-test [e.g. lung (i.n) to lung (i.g)]. * = p < 0.05, ** = p < 0.01 and *** = p < 0.005.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC2651876&req=5

Figure 5: Biodistribution of 64Cu labeled bacteria. The distribution of 64Cu labeled F. tularensis subsp. novicida was compared to 64Cu labeled K. pneumoniae, 64Cu labeled E. coli and 64Cu labeled LVS in each tissue at 20 hrs pi. The data represent an average of 3 – 9 mice per infection and are given as %ID/g of tissue. The data obtained for each of the tissues sampled 20 hrs p.i from mice infected with F. tularensis subsp. novicida was compared statistically to the same tissue when inoculated with 64Cu labeled K. pneumoniae and E. coli at 20 hrs p.i by using a two tail Student's t-test [e.g. lung (i.n) to lung (i.g)]. * = p < 0.05, ** = p < 0.01 and *** = p < 0.005.
Mentions: To test the potential effects of bacterial strains on dissemination, two different bacterial strains, E. coli and K. pneumoniae, were labeled with 64Cu-PTSM and administered i.n at the same dose of 2 × 109 CFU/20 μl used for F. tularensis subsp. novicida. By both microPET analysis (Fig. 1) and ex vivo isotope distribution at 20 h (Fig. 5), E. coli exhibited the highest percentage of radioisotope in the digestive tract and a barely detectable percentage in the lung that was significantly lower than in the case of F. tularensis subsp. novicida infected mice (p < 0.005) (Fig. 5). In the case of K. pneumoniae infection (Fig. 1), another pulmonary pathogen, a larger percentage of labeled bacteria remained in the nasal cavity and less in the lung compared with F. tularensis subsp. novicida at all time points tested. Furthermore, our biodistribution data showed that by 20 hrs p.i the %ID/g obtained in the lung for K. pneumoniae infected mice are significantly lower than for F. tularensis subsp. novicida infected mice (p < 0.005). In addition, spread of bacteria to the digestive tract appeared to be somewhat delayed compared with F. tularensis subsp. novicida. Interestingly, F. tularensis subsp. novicida shows a significantly higher tropism for cecum when compared to K. pneumoniae (p < 0.05) but not with E. coli (Fig. 5). We also labeled LVS with 64Cu, infected mice by the i.n route and imaged them by MicroPET (data not shown). The results were similar to those obtained with i.n inoculation of F. tularensis subsp. novicida showing higher levels in the lung and GI tract. The biodistribution data is shown in Fig. 5.

Bottom Line: By 20 hours, there was significant tropism to the lung compared with other tissues.MicroPET images correlated with the biodistribution of isotope and bacterial burdens in analyzed tissues.Our findings suggest that Francisella has a differential tissue tropism depending on the route of entry and that the virulence of Francisella by the pulmonary route is associated with a rapid bacteremia and an early preferential tropism to the lung.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Microbiology and Immunology, University of Texas Health Science Center at San Antonio, San Antonio, TX 78229, USA. ojeda@uthscsa.edu

ABSTRACT

Background: Francisella tularensis subsp. tularensis is classified as a Category A bioweapon that is capable of establishing a lethal infection in humans upon inhalation of very few organisms. However, the virulence mechanisms of this organism are not well characterized. Francisella tularensis subsp. novicida, which is an equally virulent subspecies in mice, was used in concert with a microPET scanner to better understand its temporal dissemination in vivo upon intranasal infection and how such dissemination compares with other routes of infection. Adult mice were inoculated intranasally with F. tularensis subsp. novicida radiolabeled with 64Cu and imaged by microPET at 0.25, 2 and 20 hours post-infection.

Results: 64Cu labeled F. tularensis subsp. novicida administered intranasally or intratracheally were visualized in the respiratory tract and stomach at 0.25 hours post infection. By 20 hours, there was significant tropism to the lung compared with other tissues. In contrast, the images of radiolabeled F. tularensis subsp. novicida when administered intragastrically, intradermally, intraperitoneally and intravenouslly were more generally limited to the gastrointestinal system, site of inoculation, liver and spleen respectively. MicroPET images correlated with the biodistribution of isotope and bacterial burdens in analyzed tissues.

Conclusion: Our findings suggest that Francisella has a differential tissue tropism depending on the route of entry and that the virulence of Francisella by the pulmonary route is associated with a rapid bacteremia and an early preferential tropism to the lung. In addition, the use of the microPET device allowed us to identify the cecum as a novel site of colonization of Francisella tularensis subsp. novicida in mice.

Show MeSH
Related in: MedlinePlus