Beijing family Mycobacterium tuberculosis strains differ in their intracellular growth in THP-1 macrophages.
METHODS
Previous studies have shown that isolates from cases in IS6110 restriction fragment length polymorphism (RFLP) clusters that have persisted over several years and are widely distributed grow significantly faster in macrophages than isolates from cases with unique RFLP patterns. As members of the Beijing family of Mycobacterium tuberculosis are widely distributed and have been responsible for several large outbreaks, it has been suggested that this genotype may have a selective advantage over other strains.


OBJECTIVE
To determine whether rapid growth in macrophages is a common characteristic of Beijing family strains.


METHODS
T-helper precursor-1 human macrophages were infected with various Beijing family strains, and intracellular growth and tumor necrosis factor alpha (TNF-alpha) secretion were assessed. Strains differed in their genotype, with IS6110 copy number ranging from 9 to 22.


RESULTS
Strains demonstrated a range of growth phenotypes over the 7-day infection period. Three grew significantly more slowly than the other strains, whereas the fastest growth was observed consistently with isolates of strain 210.


CONCLUSIONS
Rapid growth in macrophages is not a common characteristic of all Beijing strains. Few Beijing strains are as virulent as strain 210. The growth advantage is consistent with strain 210 having persisted many years in different locations and having caused many outbreaks.
Theus
S
S
Department of Pathology, University of Arkansas for Medical Sciences, Little Rock, Arkansas 72205, USA.
Eisenach
K
K
Fomukong
N
N
Silver
R F
RF
Cave
M D
MD
D015373:Bacterial Typing Techniques; D004269:DNA, Bacterial / Q000235:genetics*; D004196:Disease Outbreaks; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D008264:Macrophages / Q000378:metabolism / Q000382:microbiology* / Q000473:pathology; D009169:Mycobacterium tuberculosis / Q000235:genetics / Q000254:growth & development*; D011110:Polymorphism, Genetic; D017422:Sequence Analysis, DNA; D018417:Th1 Cells / Q000378:metabolism / Q000382:microbiology* / Q000473:pathology; D014376:Tuberculosis / Q000453:epidemiology / Q000382:microbiology / Q000473:pathology; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
D004269:DNA, Bacterial; D014409:Tumor Necrosis Factor-alpha