When administered, the antibiotic becomes ion-trapped in the acidic lysosomes of white blood cells including macrophages resulting in a high intracellular concentration compared to the plasma during the dose period. Intracellular concentrations remain high after the dose period ends with a half-life of 68 hours . Murine macrophages J774A.1 are a well-studied in vitro model system for tularemia [19, 20] and were chosen as a model cell system to study Francisella infection and treatment by Az. The murine Birinapant cost macrophage cell line J774A.1 supports the intracellular
replication of F. tularensis LVS , F. novicida , and F. tularensis Schu S4 . For a model of the human system, human lung epithelial cells A549 were chosen. F. tularensis LVS has been previously shown to infect and replicate within A549 cells [22–24]. We hypothesized that the ability of Az to concentrate at high levels within the macrophages may result in effectiveness against
intracellular infections by Francisella species, even at extracellular Az levels lower than the MIC. The larval stage of Galleria (G.)mellonella, wax moth caterpillar, has been used as a model to study infections caused by some bacteria buy GSK1210151A including F. tularensis LVS . The larvae do not have an adaptive immune system, but have resistance to microbial infections via cellular and humoral defenses . The analysis of insect responses to pathogens can provide an accurate indication of the GSK2118436 mammalian response to that pathogen. Physical effects such as color change can be observed when the bacteria replicates and increases in the larvae . We used G. mellonella as an alternative to the mouse model of Francisella infection to test our hypothesis that Az treatment could prolong the survival of Francisella infected caterpillars. heptaminol Results Francisella’s sensitivity to Az It has been reported that European clinical strains of Type
B F. tularensis are resistant to Az . However, we observed that commonly used laboratory strains of Francisella are sensitive to Az. In vitro susceptibility testing of Az confirmed that F. tularensis LVS strain was not highly sensitive in vitro to this antibiotic, confirming that the Type B strains are relatively resistant to this antibiotic. Our study demonstrated that F. philomiragia, F. novicida and Type A F. tularensis tularensis, including both F. tularensis tularensis NIH B38 and F. tularensis Schu S4 strains, were susceptible to this drug in vitro and in vivo. Francisella strains were tested in a Kirby-Bauer disc inhibition assay for sensitivity to Az. F. novicida, F. philomiragia, and F. tularensis tularensis B38 were sensitive to 15 μg Az discs, whereas F. tularensis LVS was not sensitive to this concentration. F. novicida had a zone of inhibition of 28.7 ± 0.7 mm in diameter around the 6 mm Az disc, and F. philomiragia’s zone of inhibition was 21.7 ± 0.