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B Heym

Publications and source records attributed to B Heym.

32 records · Page 2Linked to original sources
PubMed1995

Mycobacterium tuberculosis is a natural mutant with an inactivated oxidative-stress regulatory gene: implications for sensitivity to isoniazid.

The systems participating in detoxification of reactive oxygen intermediates in Mycobacterium tuberculosis are believed to play a dual role in the biology of this highly adapted human pathogen: (i) they may contribute to the survival of this bacterium in the host; and (ii) alterations in the gene encoding catalase/peroxidase have been linked to this organism's resistance to the front-line antituberculosis drug isoniazid. These relationships prompted us to extend investigations of the oxidative-stress-response systems in M. tuberculosis by analysing the alkyl hydroperoxide reductase gene ahpC and its putative regulator oxyR. Surprisingly, the oxyR gene was found to be inactivated by multiple lesions in M. tuberculosis H37Rv. These alterations were observed in all M. tuberculosis strains tested, and in members of the M. tuberculosis complex: Mycobacterium bovis BCG, Mycobacterium africanum, and Mycobacterium microti. The corresponding region carrying these genes in Mycobacterium leprae, an organism not sensitive to isoniazid, has a complete oxyR gene divergently transcribed from ahpC. An increase in minimal inhibitory concentration for isoniazid was observed upon transformation of M. tuberculosis H37Rv with cosmids carrying the oxyR-ahpC region of M. leprae. In keeping with the observed inactivation of oxyR, transcriptional activity of the corresponding region in M. tuberculosis was an order of magnitude lower than that of the oxyR gene from M. leprae. While the loss of this putative regulator of oxidative-stress response in M. tuberculosis is paradoxical considering the fact that survival in host macrophages is regarded as a critical feature of this pathogen, it offers a partial explanation for the exquisite sensitivity of M. tuberculosis to isoniazid.

Amino Acid Sequence↗
PubMed1995

Missense mutations in the catalase-peroxidase gene, katG, are associated with isoniazid resistance in Mycobacterium tuberculosis.

The toxicity of the powerful anti-tuberculosis drug isoniazid (INH) is believed to be mediated by the haem-containing enzyme catalase-peroxidase, encoded by the katG gene of Mycobacterium tuberculosis. Compelling evidence for this was obtained by studying a panel of INH-resistant clinical isolates using a novel strategy based on the polymerase chain reaction and single-strand-conformation polymorphism analysis (PCR-SSCP) to detect mutations in katG. In most cases INH resistance was associated with missense mutations while in a small number of strains the gene had been completely, or partially, deleted. The missense mutations fell into two groups, the larger of which contained several independent mutations that affected the N-terminal peroxidase domain of the protein, resulting in the production of a catalase peroxidase with strongly reduced enzyme activity and increased heat liability. The effects of these substitutions could be interpreted by means of molecular modelling using the crystal structure of the related enzyme cytochrome c peroxidase from yeast as a template. The second group comprises a frequently occurring amino acid substitution and a single mutation that are both located in the C-terminal domain but do not noticeably alter either enzyme activity or heat stability.

Amino Acid Sequence↗
PubMed1994

Implications of multidrug resistance for the future of short-course chemotherapy of tuberculosis: a molecular study.

Tuberculosis-control programmes are compromised by the increased frequency of multidrug-resistant strains of Mycobacterium tuberculosis. We used the polymerase chain reaction (PCR) and single-strand conformation polymorphism (SSCP) analysis techniques to establish the molecular basis of resistance in 37 drug-resistant isolates of M tuberculosis, and correlated these findings with clinical and antibiotic-sensitivity data. Resistance to isoniazid was found in 36 strains, 16 of which were also resistant to ethionamide. Of the 36 isoniazid-resistant strains, 23 had mutations in the katG gene, and 5 of these also had mutations in the inhA gene. A further 5 strains had alterations in the inhA locus without the katG gene being mutated. Rifampicin resistance was less frequent (13 strains) and usually associated with isoniazid resistance (11 of 13 strains). Mutations in the rpoB gene were detected for all these rifampicin-resistant isolates. Mutations in the rpsL and rrs genes, associated with streptomycin resistance, were found in 13 of 25 and 2 of 25 streptomycin-resistant strains, respectively. The same chromosomal mutations, or combinations of mutations, were found in strains displaying single or multidrug resistance, from cases of both primary and secondary resistance, and from patients infected with human immunodeficiency virus. Thus, multidrug resistance is not due to a novel mechanism and tuberculosis chemotherapy is not subject to a new threat.

AIDS-Related Opportunistic Infections↗
PubMed1994

Use of cefotaxime or ceftazidime susceptibility tests for predicting susceptibility of Enterobacteriaceae and Pseudomonas aeruginosa.

To determine if susceptibility to aztreonam could be predicted from cefotaxime or ceftazidime disc diffusion testing, 919 Enterobacteriaceae and 187 Pseudomonas aeruginosa clinical strains were studied. The correlation coefficient between the diameters of inhibition zones was 0.9 for cefotaxime versus aztreonam and ceftazidime versus aztreonam comparisons in Enterobacteriaceae and 0.75 for ceftazidime versus aztreonam comparison in P. aeruginosa. For 99% of the Enterobacteriaceae, there was no risk in predicting susceptibility to aztreonam on the basis of cefotaxime or ceftazidime susceptibility tests. To minimize the risk of the remaining 1% of the strains being erroneously classified as susceptible to aztreonam, ceftoaxime should be tested in preference to ceftazidime, and the production of extended-spectrum beta-lactamases should be tested for using the cefotaxime-clavulanate disc synergy test. For P. aeruginosa strains, susceptibility to aztreonam could be accurately predicted from ceftazidime susceptibility tests for ticarcillin susceptible strains, but for ticarcillin resistant strains, susceptibility to aztreonam should be tested.

Aztreonam↗
PubMed1993

Characterization of the katG gene encoding a catalase-peroxidase required for the isoniazid susceptibility of Mycobacterium tuberculosis.

The isoniazid susceptibility of Mycobacterium tuberculosis is mediated by the product of the katG gene which encodes the heme-containing enzyme catalase-peroxidase. In this study, the chromosomal location of katG has been established and its nucleotide sequence has been determined so that the primary structure of catalase-peroxidase could be predicted. The M. tuberculosis enzyme is an 80,000-dalton protein containing several motifs characteristic of peroxidases and shows strong similarity to other bacterial catalase-peroxidases. Expression of the katG gene in M. tuberculosis, M. smegmatis, and Escherichia coli was demonstrated by Western blotting (immunoblotting). Homologous genes were detected in other mycobacteria, even those which are naturally insensitive to isoniazid.

Amino Acid Sequence↗
PubMed1992

The catalase-peroxidase gene and isoniazid resistance of Mycobacterium tuberculosis.

Tuberculosis is responsible for one in four of all avoidable adult deaths in developing countries. Increased frequency and accelerated fatality of the disease among individuals infected with human immunodeficiency virus has raised worldwide concern that control programmes may be inadequate, and the emergence of multidrug-resistant strains of Mycobacterium tuberculosis has resulted in several recent fatal outbreaks in the United States. Isonicotinic acid hydrazide (isoniazid, INH) forms the core of antituberculosis regimens; however, clinical isolates that are resistant to INH show reduced catalase activity and a relative lack of virulence in guinea-pigs. Here we use mycobacterial genetics to study the molecular basis of INH resistance. A single M. tuberculosis gene, katG, encoding both catalase and peroxidase, restored sensitivity to INH in a resistant mutant of Mycobacterium smegmatis, and conferred INH susceptibility in some strains of Escherichia coli. Deletion of katG from the chromosome was associated with INH resistance in two patient isolates of M. tuberculosis.

Amino Acid Sequence↗
PubMed1992

Isolation and characterization of isoniazid-resistant mutants of Mycobacterium smegmatis and M. aurum.

INH-resistant mutants of Mycobacterium aurum and M. smegmatis were isolated and characterized in an attempt to provide fresh insight into the activity of isoniazid (INH), a key antibiotic in the treatment of tuberculosis. In both cases, high levels of resistance were accompanied by slower growth rate, by loss of peroxidase and reduced catalase activities, although mycolic acid production was unaffected. A gene homologous to the katG gene of M. tuberculosis, encoding peroxidase-catalase, was detected in wild-type and INH-resistant strains and it appears that INH resistance may stem from the loss of its product.

Catalase↗
PubMed1987

[Microbiologic-immunologic laboratory diagnosis in suspected meningitis/encephalitis].

The diagnosis on the exclusion of infectious diseases of the central nervous system, especially of bacterial infections still is one of the most important issues in clinical microbiology. In bacterial meningitis, where lethal courses as well as severe sequelae are still frequent, there should be a rapid diagnosis not only with microscopy but also with Limulus test and antigen detection tests because a specific therapy should be initiated as soon as possible. But also viral infections caused by varicella or herpes virus are increasingly susceptible to chemotherapy. The indication for the examination of cerebrospinal fluid, the minimal volume for exhaustive laboratory tests and the possibilities of a stepwise diagnostic procedure are given with reference data from literature for the various techniques. In our experience the synopsis of laboratory results and clinical symptoms yielded in 75% of all cases the exclusion of an infectious etiology of the disease. In 17% a bacterial meningitis or the infection of a hydrocephalus shunt could be diagnosed. Viral infections could be proven in 4% either by antibody or by antigen detection. Only in 1% of all patients the clinical symptoms and the laboratory parameters remained unclear.

Antigens, Bacterial↗
PubMed1986

[Causative spectrum of bacteremia and sepsis: significance for therapy].

Nowadays, infection with septicemia still can be a life-threatening disease. We evaluated the therapeutic behavior of clinicians basing on our diagnostic experiences during the last years and data from continuous epidemiological analysis. Important statements resulted on therapy without knowledge of the pathogen. Our results allow us to calculate the probabilities of various kinds of pathogens as well as their resistance patterns, dependent on the ward. One third of our isolates were staphylococci, followed by about 15% E. coli. The portions of all the other pathogens, e.g. other gram-negative rods, streptococci or anaerobs, were 2% or less. The application of various classes of antibiotics has been rather constant in the years 1981-1984, the penicillins showing a slight increase while the cephalosporins decreased. However, our data proved the cephalosporins to be of marked better efficacy. This points out the importance of such evaluations, whose results must be given to the physicians.

Anti-Bacterial Agents↗
PubMed1986

[Blood culture: efficacy of the specimens for the analysis of bacteremia and sepsis].

The indication for examination of blood cultures is discussed. The evaluation of clinical information with respect to the underlying diseases demonstrated that in most cases a microbiological etiology was suspected. Mostly we obtained diagnosis like chill, septic shock or suspicion of nosocomial infection. In most cases the infection origin was related to the gastrointestinal tract or the genitourinary tract. The examination of different specimens yielded the blood culture bottle as the best medium for diagnosis of septicemia. The laboratory diagnostic procedure is briefly presented. The rate of positive results, the contamination rate and the interpretation are discussed.

Blood Specimen Collection↗