Abstract
BackgroundPatients with mixed-strain Mycobacterium tuberculosis infections may be at a high risk of poor treatment outcomes. However, the mechanisms through which mixed infections affect the clinical manifestations are not well recognized. Evidence suggests that failure to detect the pathogen diversity within the host can influence the clinical results. We aimed to investigate the effects of different genotypes in mixed infections and determine their relationship with heteroresistance in the treatment of Iranian tuberculosis patients. MethodsOne of the genotypes was identified in the culture and another genotype pattern in the mixed infection was predicted by comparing the pattern of MIRU-VNTR between the clinical specimens and their respective cultures in each patient. For all patients, the drug susceptibility testing was carried out on three single colonies from each clinical sample. The follow-up of patients was carried out during six months of treatment. ResultsBased on MIRU-VNTR profiles of clinical samples, we showed that 55.6% (25/45) of the Iranian patients included in the study had mixed infections. Patients with mixed infections had a higher rate of treatment failure, compared to others (P=0.03). By comparing clinical sample profiles to profiles obtained after culture, we were able to distinguish between major and hidden genotypes. Among hidden genotypes, Haarlem (L4.1.2) and Beijing (L2) were associated to treatment failure (6/8 patients). ConclusionsTo conclude, we propose a procedure using the MIRU-VNTR method to identify the different genotypes in mixed infections. The present findings suggest that genotypes with potentially higher pathogenicity may not be detected when performing experimental culture in patients with mixed infections.
Highlights
Tuberculosis (TB) is one of the world's leading causes of morbidity and mortality
According to direct 24-locus MIRU-VNTR genotyping, 55.6% (25/45) of randomly selected TB patients showed mixed infections based on clinical samples analysis
Among 45 TB patients, 13.3% (6/45) showed heteroresistance, all belonging to the mixed infections subset as detected by MIRU-VNTR
Summary
Tuberculosis (TB) is one of the world's leading causes of morbidity and mortality. Development of drug-resistant TB, including multidrug-resistant TB (MDR-TB), has been a serious global challenge in the management of this disease (Zumla et al, 2012). Evidence suggests that patients with Mycobacterium tuberculosis mixed infections may be at a high risk of treatment failure. Patients with mixed-strain Mycobacterium tuberculosis infections may be at a high risk of poor treatment outcomes. We aimed to investigate the effects of different genotypes in mixed infections and determine their relationship with heteroresistance in the treatment of Iranian tuberculosis patients. Methods: One of the genotypes was identified in the culture and another genotype pattern in the mixed infection was predicted by comparing the pattern of MIRU-VNTR between the clinical specimens and their respective cultures in each patient. Results: Based on MIRU-VNTR profiles of clinical samples, we showed that 55.6% (25/45) of the Iranian patients included in the study had mixed infections. The present findings suggest that genotypes with potentially higher pathogenicity may not be detected when performing experimental culture in patients with mixed infections.
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