Early detection of multidrug resistant (MDR) Mycobacterium tuberculosis in a single tube with in-house designed fluorescence resonance energy transfer (FRET) probes using real-time PCR.

Rapid and correct diagnosis is crucial for the management of multidrug resistance (MDR) in Mycobacterium tuberculosis (MTB). The present study aims at rapid diagnosis for identification of multidrug resistance tuberculosis (MDR-TB) using real-time PCR. FRET hybridization probes targeting most prominent four selected codons for rpoB526 and 531 and for katG314 and 315 genes were designed and evaluated on 143 clinical MTB isolates and paired sputa for rapid detection of MDR-TB. The results of real-time PCR were compared with gold standard L-J proportion method and further validated by DNA sequencing. Of the 143 MTB positive cultures, 85 and 58 isolates were found to be ‘MDR’ and ‘pan susceptible’, respectively by proportion L-J method. The sensitivity of real-time PCR for the detection of rifampicin (RIF) and isoniazid (INH) were 85.88 and 94.11%, respectively, and the specificity of method was found to be 98.27%. DNA sequencing of 31 MTB isolates having distinct melting temperature (Tm) as compared to the standard drug susceptible H37Rv strain showed 100% concordance with real-time PCR results. DNA sequencing revealed the mutations at Ser531Leu, His526Asp of rpoB gene and Ser315Thr, Thr314Pro of katG gene in RIF and INH resistance cases. This real-time PCR assay that targets limited number of loci in a selected range ensures direct and rapid detection of MDR-TB in Indian settings. However, future studies for revalidation as well as refinement are required to break the limitations of MDR-TB detection.

Chikungunya virus susceptibility & variation in populations of Aedes aegypti (Diptera: Culicidae) mosquito from India.

Background & objectives: Although having immense clinical relevance, yet only a few studies have been targeted to understand the chikungunya virus (CHIKV) susceptibility and growth in Aedes aegypti populations from India. This study was undertaken to investigate CHIKV susceptibility and growth kinetics in Ae. aegypti along with genetic heterogeneity of Ae. aegypti populations. Methods: Dose dependent CHIKV susceptibility and growth kinetic studies for three CHIKV strains reported from India were carried out in Ae. aegypti mosquito populations. The phenotypic variation and genetic heterogeneity in five Ae. aegypti populations were investigated using multivariate morphometrics and allozyme variation studies. Results: The dissemination and growth kinetics studies of the three CHIKV strains showed no selective advantage for a particular strain of CHIKV in Ae. aegypti. At 100 per cent infection rate, five geographic Ae. aegypti populations showed differences in dissemination to three CHIKV strains. Morphometric studies revealed phenotypic variation in all the studied populations. The allelic frequencies, F statistics, and Nei’s genetic identity values showed that genetic differences between the populations were small, but significant. Interpretation & conclusions: The results obtained in this study suggest that genetic background of the vector strongly influences the CHIKV susceptibility in Ae. aegypti.

Identification of environmental mycobacteria isolated from Agra, north India by conventional & molecular approaches.

Background & objectives: Several environmental mycobacteria have been shown to be important human pathogens linked to immunomodulation especially in relation to effect on vaccination. Hence identification of mycobacteria to the species level is not only relevant to patient management but also to understand epidemiology of mycobacterial diseases and effect on vaccination. We undertook this study to assess the usefulness of various conventional and molecular methods in identification of environmental mycobacterial species from Agra, north India. Methods: One hundred nineteen isolates of environmental mycobacteria were grown from 291 (116 soil and 175 water) samples. These isolates were identified by standard biochemical tests, and a simple, rapid and cost-effective in-house developed gene amplification restriction analysis targeting 16S-23S rRNA spacer and flanking region and 16S rRNA sequencing. Results: Biochemical tests could clearly identify only 68.1 per cent (81/119) of isolates to species level. An in-house developed gene amplification - restriction analysis method could confirm the identity of 102 of 119 (85.7%) isolates and the remaining 17 isolates (14.3%) were confirmed by 16S rRNA sequencing also. These 119 environmental mycobacterial isolates, included several potentially pathogenic species such as M. fortuitum, M. chelonae, M. avium, M. marinum, M. manitobense, M. kansasii and others belonged to nonpathogenic species, M. terrae, M. smegmatis and M. flavescens. M. chelonae was isolated from water samples only whereas M. fortuitum was isolated from both water as well as soil samples. Interpretation & conclusion: The in-house developed gene amplification restriction analysis method though failed to accurately identify 14.3 per cent of isolates, facilitated rapid differentiation of most of environmental mycobacteria including potential pathogens from this area and thus would have diagnostic potential in cases with NTM infections. This combination strategy using PCR-RFLP and 16S rRNA sequencing may be useful for characterization of mycobacteria from similar environmental settings from other parts of world.

Molecular typing of Mycobacterium tuberculosis isolates from different parts of India based on IS6110 element polymorphism using RFLP analysis.

BACKGROUND & OBJECTIVE: IS 6110 based typing remains the internationally accepted standard and continues to provide new insights into the epidemiology of Mycobacterium tuberculosis. The aim of the study was to characterize M. tuberculosis isolates obtained from different parts of India based on IS6110 element polymorphism using restriction fragment length polymorphism (RFLP) analysis. METHODS: RFLP was analyzed among 308 isolates of M. tuberculosis deposited in the Mycobacterial Repository Centre, Agra, from different parts of India. DNAs isolated from these strains were restricted with Pvu II, transferred on to nylon membrane and hybridized with a PCR amplified DIG-labeled 245 bp IS6110 probe. RESULTS: Based on the copy number, M. tuberculosis isolates were classified into four groups, (i) lacking IS6110 element; (ii) low copy number (1-2); (iii) intermediate copy number (3-5); and (iv) high copy number (6-19). Copy number higher than 19 however was not observed in any of the isolates studied. At the national level, 56 per cent of the isolates showed high copy number of IS6110, 13 per cent showed intermediate copy number, 20 per cent showed low copy number, whereas 11 per cent isolates lacked IS6110 element. At the regional level, there was not much difference in the RFLP profiles of isolates (IS6110 copy numbers/patterns) from different parts of the country. INTERPRETATION & CONCLUSION: IS6110 DNA based fingerprinting could be a potentially useful tool for investigating the epidemiology of tuberculosis in India.

Rapid identification of mycobacteria by gene amplification restriction analysis technique targeting 16S-23S ribosomal RNA internal transcribed spacer & flanking region.

BACKGROUND & OBJECTIVE: Conventional identification of a clinical isolate of mycobacteria primarily based on culture characteristics and biochemical tests needs several weeks and may remain inconclusive. This study was undertaken to develop a new rapid method to identify the mycobacterial isolates at species level by gene amplification restriction analysis using primers encoding 16S-23S rRNA internal transcribed spacer (ITS) region and flanking parts of the 16S as well as 23S rRNA gene. METHODS: This system is based on the amplification of approximately 1.8 kb fragment encoding 16S-23S rRNA spacer region and flanking parts of the 16S as well as 23S rRNA gene. This assay was applied on 13 reference strains and 480 clinical isolates of mycobacteria to validate the technique. Restriction was carried out with three restriction endonucleases Hha I, Hinf I and Rsa I. RESULTS: Distinct gene amplification restriction analysis patterns were obtained by restriction of amplicons with three distinct restriction endonucleases (Hha I, Hinf I and Rsa I) which could differentiate various mycobacterial species. INTERPRETATION & CONCLUSION: Restriction patterns with the enzymes used in this study could clearly distinguish Mycobacterium tuberculosis complex from other non chromogenic clinically important species M. avium and M. intracellulare. Results indicated this assay to be a simple, rapid and reproducible method to identify clinically relevant mycobacteria.

Applications of real-time PCR technology to mycobacterial research.

Real-time polymerase chain reaction (PCR) is being used worldwide for various research purposes. In this review we discuss the principles of real-time PCR, different methodologies and chemistries available and their applications in mycobacterial research. This technology allows for the direct detection of PCR product during the exponential phase of the reaction. Being a very powerful, accurate, rapid and sensitive method, this technique holds immense promise for detection of mycobacteria, differentiation of mycobacterial species, quantification of mycobacterial load and detection of drug resistance in mycobacterial infection.

Characterization of mycobacteria isolated from bovines by PRA-targetting hsp 65 gene region.

Bovine tuberculosis caused by the bacterium Mycobacterium bovis is a major infectious disease of animals and has zoonotic importance for humans. Even though the incidence is believed to be very low in India, human tuberculosis caused by M. bovis has been increasingly recognized in many other countries of the world. As differentiation of mycobacterial species take long time, a method for the rapid identification of mycobacteria isolated from bovine samples to the species level was used, which is based on polymerase chain reaction (PCR) of the gene encoding for the 65-kD protein followed by restriction analysis. The method involves restriction enzyme analysis of PCR products obtained with primers common to all mycobacteria and generate M. tuberculosis complex specific pattern. PRA was performed on 33 bovine isolates of which 90.9% (30/33) isolates were identified clearly as M. tuberculosis complex, M. fortuitum, M. phlei and M. smegmatis using restriction enzyme Hae III.