A new in vivo model to test anti-tuberculosis drugs using fluorescence imaging.
OBJECTIVE
The current method for testing new drugs against tuberculosis in vivo is the enumeration of bacteria in organs by cfu assay. Owing to the slow growth rate of Mycobacterium tuberculosis (Mtb), these assays can take months to complete. Our aim was to develop a more efficient, fluorescence-based imaging assay to test new antibiotics in a mouse model using Mtb reporter strains.


METHODS
A commercial IVIS Kinetic® system and a custom-built laser scanning system with fluorescence molecular tomography (FMT) capability were used to detect fluorescent Mtb in living mice and lungs ex vivo. The resulting images were analysed and the fluorescence was correlated with data from cfu assays.


RESULTS
We have shown that fluorescent Mtb can be visualized in the lungs of living mice at a detection limit of ∼8 × 10⁷ cfu/lung, whilst in lungs ex vivo a detection limit of ∼2 × 10⁵ cfu/lung was found. These numbers were comparable between the two imaging systems. Ex vivo lung fluorescence correlated to numbers of bacteria in tissue, and the effect of treatment of mice with the antibiotic moxifloxacin could be visualized and quantified after only 9 days through fluorescence measurements, and was confirmed by cfu assays.


CONCLUSIONS
We have developed a new and efficient method for anti-tuberculosis drug testing in vivo, based on fluorescent Mtb reporter strains. Using this method instead of, or together with, cfu assays will reduce the time required to assess the preclinical efficacy of new drugs in animal models and enhance the progress of these candidates into clinical trials against human tuberculosis.
Immunology and Infection Department, Faculty of Infectious and Tropical Diseases,  London School of Hygiene and Tropical Medicine, Keppel St., London WC1E 7HT,  UK.
Andrea
A
Zelmer
Paul
P
Carroll
Nuria
N
Andreu
Kristine
K
Hagens
Jacqueline
J
Mahlo
Natalja
N
Redinger
Brian D
BD
Robertson
Siouxsie
S
Wiles
Theresa H
TH
Ward
Tanya
T
Parish
Jorge
J
Ripoll
Gregory J
GJ
Bancroft
Ulrich E
UE
Schaible
D000818:Animals; D000995:Antitubercular Agents / Q000008:administration & dosage*; D004195:Disease Models, Animal; D005453:Fluorescence; D017930:Genes, Reporter; D007091:Image Processing, Computer-Assisted; D008164:Luminescent Proteins / Q000032:analysis* / Q000235:genetics; D008168:Lung / Q000382:microbiology; D051379:Mice; D016513:Mice, SCID; D008826:Microbial Sensitivity Tests / Q000379:methods; D009169:Mycobacterium tuberculosis / Q000187:drug effects*; D012680:Sensitivity and Specificity; D013194:Staining and Labeling / Q000379:methods*; D013997:Time Factors; D016896:Treatment Outcome; D014376:Tuberculosis / Q000188:drug therapy*; D051598:Whole Body Imaging / Q000379:methods
D000995:Antitubercular Agents; D008164:Luminescent Proteins