An IS6110-targeting fluorescent amplified fragment length polymorphism alternative to IS6110 restriction fragment length polymorphism analysis for Mycobacterium tuberculosis DNA fingerprinting

IS6110-5'3'FP: an automated typing approach for Mycobacterium tuberculosis complex strains simultaneously targeting and resolving IS6110 5' and 3' polymorphisms

OBJECTIVES

Fingerprinting of Mycobacterium tuberculosis complex strains based on the IS6110 insertion sequence would considerably gain in terms of discriminatory power and versatility if both 5' and 3' polymorphisms were simultaneously targeted, and if it benefited from automated capillary electrophoresis. In response to these requirements, we developed IS6110-5'3'FP (IS6110 5' and 3' fluorescent polymorphisms).

METHODS

IS6110-5'3'FP involves the construction of an M. tuberculosis genomic library in a plasmid vector using HincII endonuclease, which cuts within the IS6110 sequence. After amplification in Escherichia coli, the library is subjected to selective and simultaneous PCR amplification of IS6110 5' and 3' polymorphic fragments, using differentially labeled fluorescent primers. The resulting amplicons are then fractionated on a capillary sequencer and the signal peaks analyzed as digital data.

RESULTS

IS6110-5'3'FP consistently detected and resolved both 5' and 3' IS6110 polymorphic fragments (35% and 65%, respectively) with a high level of reproducibility. The method differentiated all M. tuberculosis strains, as did IS6110 restriction fragment length polymorphism (RFLP), the gold standard of IS6110-based typing. Strikingly, the potential of IS6110-5'3'FP to resolve more polymorphic fragments than IS6110 RFLP was demonstrated.

CONCLUSIONS

IS6110-5'3'FP demonstrated sufficient potential to be a promising automated alternative to IS6110 RFLP, amenable to high throughput analysis and inter-laboratory comparison.

[Utility of molecular biology in the microbiological diagnosis of mycobacterial infections]

Species within the Mycobacterium genus are of major medical interest, since, together with environmental and opportunistic species, there are two species (Mycobacterium tuberculosis and Mycobacterium leprae) that remain an important public health challenge. Despite efforts to control tuberculosis (TB), this disease remains one of the most prominent health problems worldwide. In the last few years, mycobacteriology has experienced major technological advances. Nevertheless, the early diagnosis of mycobacterial infection and, especially of TB, is still based on microscopic examination of properly stained samples. At present, this procedure is still the simplest, fastest and most cost-effective method for preliminary diagnostic guidance. Effective control of TB is based on rapid detection of M. tuberculosis, followed by immediate implementation of the appropriate antituberculosis therapy. Because of the emergence of multidrug resistant strains, the development of rapid diagnostic methods, both for identification of M. tuberculosis and susceptibility testing, has become a pressing need. The availability of molecular epidemiology methods that are easy to implement and standardized and that would allow identification of related cases is of key importance to identify epidemic outbreaks and control the spread of TB. Despite the evident progress in the molecular diagnosis of mycobacterial infections, the available techniques are still inadequate. In this review, we describe the state of the art of the main molecular techniques for direct detection of mycobacteria in clinical samples, their identification, detection of resistance to the most important antituberculosis agents, and molecular epidemiology. In each case, we describe the advantages and limitations of current techniques. In the near future, clinical mycobacteriology will probably evolve to the universal use of genetic techniques for direct diagnosis and detection of resistance. The molecular epidemiology of TB will be performed, in its various applications, by faster and more automated techniques than those currently available.

DNA restriction fragment length polymorphism analysis of Mycobacterium tuberculosis isolates from HIV-seropositive and HIV-seronegative patients in Kampala, Uganda

BACKGROUND

The identification and differentiation of strains of Mycobacterium tuberculosis by DNA fingerprinting has provided a better understanding of the epidemiology and tracing the transmission of tuberculosis. We set out to determine if there was a relationship between the risk of belonging to a group of tuberculosis patients with identical mycobacterial DNA fingerprint patterns and the HIV sero-status of the individuals in a high TB incidence peri-urban setting of Kampala, Uganda.

METHODS

One hundred eighty three isolates of Mycobacterium tuberculosis from 80 HIV seropositive and 103 HIV seronegative patients were fingerprinted by standard IS6110-RFLP. Using the BioNumerics software, strains were considered to be clustered if at least one other patient had an isolate with identical RFLP pattern.

RESULTS

One hundred and eighteen different fingerprint patterns were obtained from the 183 isolates. There were 34 clusters containing 54% (99/183) of the patients (average cluster size of 2.9), and a majority (96.2%) of the strains possessed a high copy number (> or = 5 copies) of the IS6110 element. When strains with <5 bands were excluded from the analysis, 50.3% (92/183) were clustered, and there was no difference in the level of diversity of DNA fingerprints observed in the two sero-groups (adjusted odds ratio [aOR] 0.85, 95%CI 0.46-1.56, P = 0.615), patients aged <40 years (aOR 0.53, 95%CI 0.25-1.12, P = 0.100), and sex (aOR 1.12, 95%CI 0.60-2.06, P = 0.715).

CONCLUSION

The sample showed evidence of a high prevalence of recent transmission with a high average cluster size, but infection with an isolate with a fingerprint found to be part of a cluster was not associated with any demographic or clinical characteristics, including HIV status.