Epidemiologic consequences of microvariation in Mycobacterium tuberculosis

Area of Science:

• Microbiology
• Immunology
• Epidemiology

Background:

• Genetic diversity in pathogens like Mycobacterium tuberculosis can significantly influence infection outcomes and disease spread.
• Studied five closely related M. tuberculosis strains responsible for extensive disease (n=862) in US-born patients.

Purpose of the Study:

• To investigate the impact of genetic variation on the virulence and host response of M. tuberculosis.
• To understand how genotypic differences translate into phenotypic changes affecting disease progression and epidemiology.

Main Methods:

• Selected representative M. tuberculosis isolates using population-based genotyping from New York City and New Jersey.
• Assessed bacterial growth in human monocytes and measured cytokine/chemokine responses.
• Determined host survival and pathology in guinea pig models of aerosolized M. tuberculosis infection.

Main Results:

• Genotyping confirmed all studied strains were closely related.
• Two distinct growth phenotypes were observed in infected human monocytes: slow (∼55 hr doubling) and fast (∼25 hr doubling).
• Faster-growing strains induced higher levels of TNF-α and IL-1β, caused accelerated mortality in guinea pigs (∼9 weeks vs. 24 weeks), and were associated with increased lung inflammation.

Conclusions:

• Natural genetic variations within closely related M. tuberculosis isolates lead to detectable phenotypic differences.
• These phenotypic changes, particularly growth rate, can alter the epidemiologic patterns of tuberculosis in human populations.