Impact of Anesthesia Protocols on In Vivo Bioluminescent Bacteria Imaging Results.

Infectious murine models greatly benefit from optical imaging using bioluminescent bacteria to non-invasively and repeatedly follow in vivo bacterial infection. In this context, one of the most critical parameters is the bioluminescence sensitivity to reliably detect the smallest number of bacteria. Another critical point is the anesthetic approaches that have been demonstrated to impact the bioluminescence flux emission in studies with luciferase-transfected tumor cells. However, this impact has never been assessed on bacteria bioluminescent models. To this end, we investigated the effects of four anesthesia protocols on the bioluminescence flux in a central venous catheter murine model (SKH1-hr(hr) mice) infected by a bioluminescent S. aureus Xen36 strain. Bioluminescence imaging was performed on mice anesthetized by either ketamine/xylazine (with or without oxygen supplementation), or isoflurane carried with air or oxygen. Total flux emission was determined in vivo daily for 3 days and ex vivo at the end of the study together with a CFU counting of the biofilm in the catheter. Bioluminescence flux differences appear between the different anesthetic protocols. Using a ketamine/xylazine anesthesia (with air), bacteria detection was impossible since the bioluminescence signal remains in the background signal. Mice anesthetized with isoflurane and oxygen led to a signal significantly higher to the background all along the kinetics. The use of isoflurane in air presents a bioluminescence signal similar to the use of ketamine/xylazine with oxygen. These data highlight the importance of oxygen to improve bioluminescence flux by bacteria with isoflurane as well as with ketamine/xylazine anesthetics. As a conclusion, we recommend the use of isoflurane anesthetic with oxygen to increase the bioluminescence sensitivity in this kind of study.

Role of transferrin receptor from a Neisseria meningitidis tbpB isotype II strain in human transferrin binding and virulence.

Neisseria meningitidis acquires iron through the action of the transferrin (Tf) receptor, which is composed of the Tf-binding proteins A and B (TbpA and TbpB). Meningococci can be classified into isotype I and II strains depending on whether they harbor a type I or II form of TbpB. Both types of TbpB have been shown to differ in their genomic, biochemical, and antigenic properties. Here we present a comparative study of isogenic mutants deficient in either or both Tbps from the isotype I strain B16B6 and isotype II strain M982. We show that TbpA is essential in both strains for iron uptake and growth with iron-loaded human Tf as a sole iron source. No growth has also been observed for the TbpB- mutant of strain B16B6, as shown previously, whereas the growth of the analogous mutant in M982 was similar to that in the wild type. This indicates that TbpB in the latter strain plays a facilitating but not essential role in iron uptake, which has been observed previously in similar studies of other bacteria. These data are discussed in relation to the fact that isotype II strains represent more than 80% of serogroup B meningococcal strains. The contribution of both subunits in the bacterial virulence of strain M982 has been assessed in a murine model of bacteremia. Both the TbpB- TbpA- mutant and the TbpA- mutant are shown to be nonvirulent in mice, whereas the virulence of the TbpB- mutant is similar to that of the wild type.