A study of the relationship between the resistance of Mycobacterium tuberculosis to isonicotinic acid hydrazide (isoniazid) and to thiophen-2-carboxylic acid hydrazide

A katG S315T or an ahpC promoter mutation mediate Mycobacterium tuberculosis resistance to 2-thiophen carboxylic acid hydrazide, an inhibitor resembling the anti-tubercular drugs Isoniazid and Ethionamide

Clinical isolates of Mycobacterium tuberculosis and Mycobacterium bovis are differentially susceptible to 2-Thiophen Hydrazide (TCH); however its mechanism of action or the reasons for that difference are unknown. We report herein that under our experimental conditions, TCH inhibits M. tuberculosis in solid but not in liquid medium, and that in spite of resembling Isoniazid and Ethionamide, it does not affect mycolic acid synthesis. To understand the mechanisms of action of TCH we isolated M. tuberculosis TCH resistant mutants which fell into two groups; one resistant to TCH and Isoniazid but not to Ethionamide or Triclosan, and the other resistant only to TCH with no, or marginal, cross resistance to Isoniazid. A S315T katG mutation conferred resistance to TCH while katG expression from a plasmid reduced M. tuberculosis MIC to this drug, suggesting a possible involvement of KatG in TCH activation. Whole genome sequencing of mutants from this second group revealed a single mutation in the alkylhydroperoxide reductase ahpC promoter locus in half of the mutants, while the remaining contained mutations in dispensable genes. This is the first report of the genetics underlying the action of TCH and of the involvement of ahpC as the sole basis for resistance to an anti-tubercular compound.

Mycobacterial species causing pulmonary tuberculosis at the korle bu teaching hospital, accra, ghana

SUMMARY OBJECTIVE

Characterize mycobacterial species causing pulmonary tuberculosis (PTB) at the Korle-Bu Teaching Hospital in Ghana.

DESIGN

Sputum smear positive samples, two (2) from 70 patients diagnosed as having tuberculosis, after they had consented, were collected from the Korle-Bu Teaching Hospital Chest Clinic between January and July 2003.

SETTING

Korle-Bu Teaching Hospital Chest Clinic, Accra.

RESULTS

Sixty-four mycobacterial isolates were obtained and confirmed as members of Mycobacterium tuberculosis complex by colonial morphology and conventional biochemical assays. Forty-seven (73%) were M. tuberculosis, the human strain, 2 (3%) M. bovis, the bovine strain, 13 (20%) M. africanum I (West Africa type), and 2 (3%) M. africanum II (East Africa type).

CONCLUSION

The results indicate that, there are various strains causing PTB at the Korle-Bu Teaching Hospital and of great concern is M. bovis, which mostly causes extra-PTB in humans but found to cause PTB in this study. This calls for the need to conduct a nationwide survey using both conventional and molecular techniques to characterize various mycobacterial species causing TB in Ghana. This will result in better understanding of the various strains circulating in the country and inform individual TB treatment regimen especially the inclusion or exclusion of pyrazinamide.

A single-step sequencing method for the identification of Mycobacterium tuberculosis complex species

BACKGROUND

The Mycobacterium tuberculosis complex (MTC) comprises closely related species responsible for strictly human and zoonotic tuberculosis. Accurate species determination is useful for the identification of outbreaks and epidemiological links. Mycobacterium africanum and Mycobacterium canettii are typically restricted to Africa and M. bovis is a re-emerging pathogen. Identification of these species is difficult and expensive.

METHODOLOGY/PRINCIPAL FINDINGS

The Exact Tandem Repeat D (ETR-D; alias Mycobacterial Interspersed Repetitive Unit 4) was sequenced in MTC species type strains and 110 clinical isolates, in parallel to reference polyphasic identification based on phenotype profiling and sequencing of pncA, oxyR, hsp65, gyrB genes and the major polymorphism tandem repeat. Inclusion of M. tuberculosis isolates in the expanding, antibiotic-resistant Beijing clone was determined by Rv0927c gene sequencing. The ETR-D (780-bp) sequence unambiguously identified MTC species type strain except M. pinnipedii and M. microti thanks to six single nucleotide polymorphisms, variable numbers (1-7 copies) of the tandem repeat and two deletions/insertions. The ETR-D sequencing agreed with phenotypic identification in 107/110 clinical isolates and with reference polyphasic molecular identification in all isolates, comprising 98 M. tuberculosis, 5 M. bovis BCG type, 5 M. canettii, and 2 M. africanum. For M. tuberculosis isolates, the ETR-D sequence was not significantly associated with the Beijing clone.

CONCLUSIONS/SIGNIFICANCE

ETR-D sequencing allowed accurate, single-step identification of the MTC at the species level. It circumvented the current expensive, time-consuming polyphasic approach. It could be used to depict epidemiology of zoonotic and human tuberculosis, especially in African countries where several MTC species are emerging.

Rapid and simple approach for identification of Mycobacterium tuberculosis complex isolates by PCR-based genomic deletion analysis

Although the virulences and host ranges differ among members of the Mycobacterium tuberculosis complex (TBC; M. tuberculosis, M. africanum, M. canettii, M. microti, M. bovis, and M. bovis BCG), commercially available molecular assays cannot differentiate these organisms because of the genetic identities of their 16S rRNA gene sequences. Comparative genomic analyses with the complete DNA sequence of M. tuberculosis H37Rv has provided information on regions of difference (RD 1 to RD 16) deleted in members of the TBC other than M. tuberculosis. To determine whether deletion analysis could accurately differentiate members of TBC, we used PCR to assess the presence or absence of specific regions of the genome in 88 well-characterized isolates of M. tuberculosis, M. africanum, M. microti, M. bovis, and M. bovis BCG. The identifications obtained by use of the specific deletion profiles correlated 100% with the original identifications for all TBC members except M. africanum, but further characterization resulted in profiles specific for all members. Although six RD regions were used in the analyses with the original 88 isolates, it was found that the use of RD 1, RD 9, and RD 10 was sufficient for initial screenings, followed by the use of RD 3, RD 5, and RD 11 if the results for any of the first three regions were negative. When 605 sequential clinical isolates were screened, 578 (96%) were identified as M. tuberculosis, 6 (1%) were identified as M. africanum, 8 (1%) were identified as M. bovis, and 13 (2%) were identified as M. bovis BCG. Since PCR-based assays can be implemented in most clinical mycobacteriology laboratories, this approach provides a rapid and simple means for the differentiation of members of TBC, especially M. bovis and M. tuberculosis, when it is important to distinguish between zoonotic sources (i.e., cattle and unpasteurized dairy products) and human sources of tuberculosis disease.

IS6110 restriction fragment length polymorphism typing of clinical isolates of Mycobacterium tuberculosis from patients with pulmonary tuberculosis in Madras, south India

SETTING

Madras, India.

OBJECTIVE

To explore the utility of a standardized IS6110/PvuII deoxyribonucleic acid (DNA) fingerprinting restriction fragment length polymorphism (RFLP) typing method for distinguishing between isolates of Mycobacterium tuberculosis, and to assess the potential for distinguishing between relapse versus reinfection rates.

DESIGN

To assess RFLP heterogeneity in the population, initial isolates, obtained from the sputum of tuberculous 98 patients in diagnosis and follow-up during short-course chemotherapy, were stored and compared. To assess the frequency of disparity between the RFLP type of the initial isolate and one obtained after successful completion of chemotherapy, either during relapse or as an isolated positive culture, 124 isolates comprising 62 such pairs were coded and compared both blind and after decoding.

RESULTS

Although a wide variety of DNA band patterns (fingerprints) was present, the isolates from 39 (40%) of the patients showed a single copy of IS6110. Only 15 pairs of coded initial and follow-up isolates could be identified as having the same band pattern when isolates with zero or single bands were excluded. Nevertheless, after decoding, in a retrospective analysis that included all isolates, those isolates that bacteriologically defined a patient's relapse more often showed RFLP type identity with the initial isolate (19 of 30 comparisons) than did isolates that were obtained as isolated positive cultures (3 of 32 comparisons) (X2 P < 0.001). Tests of sensitivity to chemotherapeutic drugs, catalase activity and resistance to thiophene-2-carboxylic acid hydrazide were of minimal value in discriminating between isolates.

CONCLUSIONS

Despite the high frequency of single- and zero-band isolates in this population, the discriminatory power of RFLP typing with IS6110 is sufficiently high to be useful for clinical and epidemiological studies.

A bacteriological survey of tuberculosis due to the human tubercle bacillus (Mycobacterium tuberculosis) in south-east England: 1984-91

The occurrence and nature of bacteriologically confirmed tuberculosis due to Mycobacterium tuberculosis in South-East England in the period 1984-91 is reported and compared with the results of a study for 1977-83. Registered new cases reached a low of 1028 in 1988 but increased to 1252 in 1991. This appeared to be due to a halt in the previous decline in new cases of European patients, a small increase in the number of Indian subcontinent (ISC) patients and an increase in patients from Africa. A total of 122 patients, mostly of European ethnic origin, were known to be HIV positive. As in the 1977-83 study, disease in the ISC group affected younger patients than in the European group, tubercle bacilli were more frequently isolated from a non-pulmonary site in the ISC group (45%) than in the European group (19%) and there was a higher incidence of the South Indian variant of M. tuberculosis in the former group (17%) than in the latter (9%). The overall incidence of drug resistance has not altered significantly since the 1977-83 study but 46 strains resistant to 3 or more drugs were isolated from 4099 ISC patients, compared with 3 of 4594 strains from European patients. Six of the 122 isolates from HIV positive patients were drug-resistant but none was multi-drug resistant. The slight rise in registered bacteriologically proven cases of tuberculosis, the presence of multi-drug resistant strains, the occurrence of HIV-related tuberculosis and reports of the emergence of multi-drug-resistant HIV-related tuberculosis in other countries strongly indicate the need for continued careful surveillance.

The nature of mycobacterial disease in south east England, 1977-84

The nature and incidence of bacteriologically confirmed mycobacterial disease in south east England over the eight year period 1977-84 has been determined by a study of cultures received by the PHLS Regional Centre for Tuberculosis Bacteriology at Dulwich. The number of cases of tuberculosis in the ethnic European population has shown a decline, more so among males than females, but there has not been a significant decline in cases among ethnic Asians. Most tuberculosis is due to the classical human tubercle bacillus but cases due to the Asian human type, the bovine type (M. bovis), and the African types (M. africanum) also occur. The number of cases of disease due to 'atypical' mycobacteria has doubled over the eight year period, and these now account for about 5% of bacteriologically diagnosed mycobacterial disease in this region. The continuing role of reference facilities for the surveillance of tuberculosis and the diagnosis and management of the growing numbers of other mycobacterial infections is stressed.

Subdivision of Mycobacterium tuberculosis for epidemiological purposes: a seven year study of the "Classical' and 'Asian' types of the human tubercle bacillus in South-East England

Human strains of Mycobacterium tuberculosis were divided into the 'Classical' and 'Asian' types according to their sensitivity to thiophen-2-carboxylic acid hydrazide. The isolation of these two types in South-East England was studied during a seven-year period (1977-1983). The 'Asian' type was more prevalent among ethnic Asian patients than among ethnic Europeans. Among Europeans there was a decline in the isolation rate of 'Classical' strains and a small but significant increase in 'Asian' strains during the study period, so that the proportion of the latter type in this group is increasing. The type of bacillus was unrelated to the site of isolation except that the incidence of lymphadenitis due to the 'Asian' type among European females was significantly higher than expected. In general, European patients tended to be older than Asian patients, and the differences in age distribution according to site of isolation and type of bacillus in each ethnic group were small. A notable exception occurred with European females infected with the 'Asian' type, whose age distribution was similar to the Asians. In view of the differences in behaviour of the two types of human tubercle bacilli in this country there is a need to continue a bacteriological surveillance and also to determine whether the nature of the host-pathogen interaction varies according to the type of bacillus.