Finally, the heterogeneity of within-host M.tb populations can
also have implications for resistance diagnostics. Culture-based
drug susceptibility testing usually involves the examination of a
single isolate from a single sample from a given disease episode,
with the assumption that it is representative of a homogeneous
bacterial population, which might not be the case. Knowing the
existence and prevalence of the different subpopulations and their
corresponding drug susceptibilities could be useful for the
management of the patient. To obtain a measure of the
heterogeneity of the TB infection, several independent bacterial
isolates should to be examined from each patient sample.
Similarly, the heterogeneity of M.tb infections might also confound
molecular antibiotic resistance tests. For example, the GeneXpert
MTB/RIF (Cepheid, Sunnyvale, CA, USA) (which is becoming a
leading screening tool for TB) has an increased false-negative rate
for detecting RIF resistance in mixed M.tb complex infections,
failing to identify it when