Mycobacterium tuberculosis from chronic murine infections that grows in liquid but not on solid medium.
BACKGROUND
Old, stationary cultures of Mycobacterium tuberculosis contain a majority of bacteria that can grow in broth cultures but cannot grow on solid medium plates. These may be in a non-replicating, dormant growth phase. We hypothesised that a similar population might be present in chronic, murine tuberculosis.


METHODS
Estimates of the numbers of viable M. tuberculosis, strain H37Rv, in the spleens and lungs of mice in a 7-day acute infection and in a 10-month chronic infection were made by conventional plate counts and, as broth counts, by noting presence or absence of growth in serial replicate dilutions in liquid medium.


RESULTS
Plate and broth counts in 6 mice gave similar mean values in the acute infection, 7 days after infection. However, the broth counts were much higher in 36 mice with a chronic infection at 10 months. Broth counts averaged 5.290 log10 cfu /organ from spleens and 5.523 log10 cfu/organ from lungs, while plate counts were 3.858 log10 cfu/organ from spleens and 3.662 log10 cfu/organ from lungs, indicating that the total bacterial population contained only 3.7% bacilli in spleens and 1.4% bacilli in lungs, capable of growth on plates.


CONCLUSIONS
The proportion growing on plates might be a measure of the "dormancy" of the bacilli equally applicable to cultural and animal models.
Dhillon
Jasvir
J
Department of Cellular and Molecular Medicine, St George's Hospital Medical School, London SW17 0RE, UK. jdhillon@sghms.ac.uk <jdhillon@sghms.ac.uk>
Lowrie
Douglas B
DB
Mitchison
Denis A
DA
D000208:Acute Disease; D000704:Analysis of Variance; D000818:Animals; D002908:Chronic Disease; D015169:Colony Count, Microbial; D003470:Culture Media / Q000145:classification*; D005260:Female; D008168:Lung / Q000382:microbiology; D051379:Mice; D008807:Mice, Inbred BALB C; D009169:Mycobacterium tuberculosis / Q000254:growth & development*; D013154:Spleen / Q000382:microbiology; D014376:Tuberculosis / Q000382:microbiology*
D003470:Culture Media