Detection of multiple strains of Mycobacterium tuberculosis using MIRU-VNTR in patients with pulmonary tuberculosis in Kampala, Uganda

Abstract

BackgroundMany studies using DNA fingerprinting to differentiate Mycobacterium tuberculosis (MTB) strains reveal single strains in cultures, suggesting that most disease is caused by infection with a single strain. However, recent studies using molecular epidemiological tools that amplify multiple targets have demonstrated simultaneous infection with multiple strains of MTB. We aimed to determine the prevalence of MTB multiple strain infections in Kampala, and the impact of these infections on clinical presentation of tuberculosis (TB) and response to treatment.MethodsA total of 113 consecutive smear and culture positive patients who previously enrolled in a house-hold contact study were included in this study. To determine whether infection with multiple MTB strains has a clinical impact on the initial presentation of patients, retrospective patient data (baseline clinical, radiological and drug susceptibility profiles) was obtained. To determine presence of infections with multiple MTB strains, MIRU-VNTR (Mycobacterial Interspersed Repetitive Unit-Variable-Number Tandem Repeats) -PCR was performed on genomic DNA extracted from MTB cultures of smear positive sputum samples at baseline, second and fifth months.ResultsOf 113 patients, eight (7.1%) had infection with multiple MTB strains, coupled with a high rate of HIV infection (37.5% versus 12.6%, p = 0.049). The remaining patients (105) were infected with single MTB strains. The proportions of patients with MTB smear positive cultures after two and five months of treatment were similar. There was no difference between the two groups for other variables.ConclusionInfection with multiple MTB strains occurs among patients with first episode of pulmonary tuberculosis in Kampala, in a setting with high TB incidence. Infection with multiple MTB strains had little impact on the clinical course for individual patients. This is the first MIRU-VNTR-based study from in an East African country.

Mixed Infections and Rifampin Heteroresistance among Mycobacterium tuberculosis Clinical Isolates

“…Nationality was considered for the first time as a factor influencing the occurrence of mixed infections; however, it was not significantly associated with mixed infections in our study, an observation that is similar to that with many other previously reported factors (Table 3) (7,8,43). From our data, there was a trend Non-Beijing (2, 100) …”

“…Older people, who normally have a poorer immune response, and those with immunosuppressive conditions, such as HIV infection, were considered to be associated with mixed infections to a higher extent (8,44). The sensitivity of the Xpert MTB/ RIF assay for RIF resistance detection was reduced in the cases of mixed infections and in HIV-infected patients who may suffer mixed infections (4).…”

“…Currently, mycobacterial interspersed repetitive unit-variable-number tandem repeat (MIRU-VNTR)-based methods have been the most widely used to detect mixed infections (5). Mixed infections are defined by the presence of strains with different MIRU-VNTR patterns at two or more loci in the same sputum, lymph, or other sample while having clonal heterogeneity with a different MIRU-VNTR pattern at a single locus (7)(8)(9).…”

Systematic Survey of Clonal Complexity in Tuberculosis at a Populational Level and Detailed Characterization of the Isolates Involved

“…The number of studies on clonal complexity in M. tuberculosis infection has increased in recent years (8,10,18). However, some of these studies examine anecdotal cases (2) and others analyze this phenomenon only in specific M. tuberculosis lineages (35) or specific phenotypes (34).…”

“…However, some of these studies examine anecdotal cases (2) and others analyze this phenomenon only in specific M. tuberculosis lineages (35) or specific phenotypes (34). Those which follow population-based designs to determine the proportion of clonally complex TB cases are performed mainly in epidemiological contexts with a markedly high incidence of TB (8,10,29,30,35) and/or where the possibility of overexposure is more likely (28).…”