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Biomedical subjects

S J Andersen

Publications and source records attributed to S J Andersen.

13 recordsLinked to original sources
PubMed2000

The stringent response of Mycobacterium tuberculosis is required for long-term survival.

The stringent response utilizes hyperphosphorylated guanine [(p)ppGpp] as a signaling molecule to control bacterial gene expression involved in long-term survival under starvation conditions. In gram-negative bacteria, (p)ppGpp is produced by the activity of the related RelA and SpoT proteins. Mycobacterium tuberculosis contains a single homolog of these proteins (Rel(Mtb)) and responds to nutrient starvation by producing (p)ppGpp. A rel(Mtb) knockout strain was constructed in a virulent strain of M. tuberculosis, H37Rv, by allelic replacement. The rel(Mtb) mutant displayed a significantly slower aerobic growth rate than the wild type in synthetic liquid media, whether rich or minimal. The growth rate of the wild type was equivalent to that of the mutant when citrate or phospholipid was employed as the sole carbon source. These two organisms also showed identical growth rates within a human macrophage-like cell line. These results suggest that the in vivo carbon source does not represent a stressful condition for the bacilli, since it appears to be utilized in a similar Rel(Mtb)-independent manner. In vitro growth in liquid media represents a condition that benefits from Rel(Mtb)-mediated adaptation. Long-term survival of the rel(Mtb) mutant during in vitro starvation or nutrient run out in normal media was significantly impaired compared to that in the wild type. In addition, the mutant was significantly less able to survive extended anaerobic incubation than the wild-type virulent organism. Thus, the Rel(Mtb) protein is required for long-term survival of pathogenic mycobacteria under starvation conditions.

Cell Line↗
PubMed2000

Prevalence and patterns of alternative medication use in a university hospital outpatient clinic serving rheumatology and geriatric patients.

A random sample of 176 patients seen at least once during 1997 in a University hospital outpatient clinic serving rheumatology and geriatric patients were surveyed in a telephone interview to determine the prevalence of, and reasons for taking, alternative medications. Interviews were conducted from November 1997-March 1998. The survey elicited information about patients' ability to provide self-care, demographics, work status, satisfaction with current disease management, types of alternative medications taken, sources of information about the products, where they obtained the products, and reasons for taking the products. Patients also were questioned as to their knowledge of safety of these products. Statistical comparisons were determined between patients who used alternative agents and those who did not. Prevalence of use was 66%. Most patients thought that the agents were safe and took them because they believed they have "added benefits."

Adult↗
PubMed1998

DNA repair in Mycobacterium tuberculosis. What have we learnt from the genome sequence?

The genome sequence of Mycobacterium tuberculosis was analysed by searching for homologues of genes known to be involved in the reversal or repair of DNA damage in Escherichia coli and related organisms. Genes necessary to perform nucleotide excision repair (NER), base excision repair (BER), recombination, and SOS repair and mutagenesis were identified. In particular, all of the genes known to be directly involved in the repair of oxidative and alkylative damage are present in M. tuberculosis. In contrast, we failed to identify homologues of genes involved in mismatch repair. This finding has potentially significant implications with respect to genome stability, strain variability at repeat loci and the emergence of chromosomally encoded drug resistance mutations.

DNA Damage↗
PubMed1997

SOS induction in mycobacteria: analysis of the DNA-binding activity of a LexA-like repressor and its role in DNA damage induction of the recA gene from Mycobacterium smegmatis.

The protein encoded by the lexA gene from Mycobacterium leprae was overproduced in Escherichia coli. The recombinant protein bound to the promoter regions of the M. leprae lexA, M. leprae recA and M. smegmatis recA genes at sites with the sequences 5'-GAACACATGTTT and 5'-GAACAGGTGTTC, which belong to the 'Cheo box' family of binding sites recognized by the SOS repressor from Bacillus subtilis. Gel mobility shift assays were used to confirm that proteins with the same site specificity of DNA binding are also present in Mycobacterium tuberculosis and M. smegmatis. Complex formation was impaired by mutagenic disruption of the dyad symmetry of the M. smegmatis recA Cheo box. LexA binding was also inhibited by preincubation of the M. smegmatis and M. tuberculosis extracts with anti-M. leprae LexA antibodies, suggesting that the mycobacterial LexA proteins are functionally conserved at the level of DNA binding. Finally, exposure of M. smegmatis to DNA-damaging agents resulted in induction of the M. smegmatis recA promoter with concomitant loss of DNA binding of LexA to its Cheo box, confirming that this organism possesses the key regulatory elements of a functional SOS induction system.

Bacterial Proteins↗
PubMed1997

Monooxygenase-like sequence of a Rhodococcus equi gene conferring increased resistance to rifampin by inactivating this antibiotic.

A DNA clone from Rhodococcus equi conferring low-level rifampin resistance through the ability to inactivate this antibiotic via its decomposition was identified. The iri (inactivation of rifampin) gene consisted of an open reading frame of 1,437 bp encoding a 479-amino-acid sequence strongly resembling those of monooxygenases acting upon phenolic compounds or involved in polyketide antibiotic synthesis. When expressed in Escherichia coli, the gene conferred resistance to a > 50-micrograms/ml concentration of the drug.

Amino Acid Sequence↗
PubMed1996

Construction by homologous recombination and phenotypic characterization of a DNA polymerase domain polA mutant of Mycobacterium smegmatis.

Gene replacement was achieved by homologous recombination in Mycobacterium smegmatis (Ms) using a cloned segment of the polA gene (encoding the DNA polymerase I) disrupted within the region encoding the C-terminal DNA polymerase domain by a kanamycin-resistance marker. The Ms polA755:aph mutant thus generated displayed a phenotype of hypersensitivity to DNA damage induced by UV irradiation and by hydrogen peroxide challenge.

Cloning, Molecular↗
PubMed1995

Taxonomy of Penicillium nalgiovense isolates from mould-fermented sausages.

A large number of Penicillium nalgiovense isolates from mould fermented sausages and the ex type culture were examined for characters of morphology, physiology and production of secondary metabolites. To separate biotypes within the P. nalgiovense species, the data obtained were evaluated using multivariate statistical methods. The macromorphological characters of the ex type culture and isolates from meat products appeared to be distinctive. The ex type culture is characterized by a brown reverse on both Czapek yeast extract and malt extract agar while the isolates from meat products have a yellow to orange reverse. Proteolytic and/or lipolytic activity was demonstrated by 75% of the examined cultures and all of them demonstrated ability to utilize lactate as sole carbon source. Growth on creatine sucrose agar was very inhibited and acid production was absent or very weak. TLC analysis showed production of three unknown secondary metabolites that constituted the characteristic profile. HPLC analysis showed production of only three known secondary metabolites; chrysogine (96%), nalgiolaxin and nalgiovensin (9%). The ex type culture produced nalgiolaxin and nalgiovensin but not chrysogine. The chemometric evaluation showed that P. nalgiovense isolates from meat products from a homogenous species, which can not be divided into biotypes. The only indication of grouping, beside a separation of the ex type culture, was related to the conidium colour (white, turquoise or grey green). The examined P. nalgiovense isolates showed some resemblance (morphologically and chemically) to P. chrysogenum.

Chromatography, High Pressure Liquid↗
PubMed1995

Rifampicin inactivation by Bacillus species.

The ability of strains of Bacillus, Staphylococcus, Pseudomonas, and Escherichia coli to inactivate rifampicin was tested. Most Bacillus strains were found to inactivate rifampicin. Two modes of inactivation were identified; one was phosphorylation and the other involved decolorization. Presence or absence of either mechanism appeared unrelated to the phylogenetic relatedness of strains. None of the other organisms could inactivate this antibiotic.

Bacillus↗
PubMed1994

Penicillin production by Penicillium nalgiovense.

A large number of Penicillium nalgiovense strains were found to be as good penicillin producers on optimal production media as strains of Penicillium chrysogenum. It is not known whether penicillin can be produced on fermented sausages, but selection for non-penicillin producing fermenting strains of P. nalgiovense is suggested.

Culture Media↗
PubMed1992

The relationship between the transfer factor obtained at rest, and arterial oxygen tension during exercise, in patients with miscellaneous pulmonary diseases.

Forty-one consecutive patients with the symptom 'exertional dyspnoea' were referred to the Department of Clinical Physiology for evaluation. Pulmonary fibrosis and chronic obstructive pulmonary disease were the most common diagnoses but other diagnoses were also represented. Some patients had no clinical diagnosis or radiological signs. All patients underwent exercise testing with sampling of arterial blood for blood gas analysis and pulmonary function testing including measurement of the transfer factor (carbon monoxide diffusing capacity) at rest. Independent of spirometric findings and diagnosis a significant correlation (r = 0.80, P < 0.001) was shown to exist between the transfer factor measured at rest and the arterial oxygen tension at maximal exercise level. We recommend measurement of the transfer factor as a screening test for exertional hypoxaemia and suggest that exercise blood gas analysis only seems necessary in patients with a transfer factor between 55% and 80% of the predicted value.

Adult↗
PubMed1991

Cloning of nocardioform DNA conferring the ability to inactivate rifampicin.

A novel mechanism of resistance to rifampicin has recently been reported in which this antibiotic is inactivated. Here we describe the cloning of DNA from a nocardiofrom strain conferring this ability to inactivate rifampicin. Cloning was on the basis of complementation, as an increased resistance to the antibiotic. The genetic information was on a 8.3-kb BglII fragment.

Cloning, Molecular↗
PubMed1990

Nocardioform arsenic resistance plasmids and construction of Rhodococcus cloning vectors.

One of a number of large nocardioform plasmids previously obtained by a primarily genetic approach was reduced in size to about approximately 11 kb. This smaller plasmid possessed determinants for resistance to sodium arsenate and sodium arsenite, as well as immunity to nocardiophage Q4. It was joined to an Escherichia coli-positive selection vector constructed by M. Zabeau and colleagues, which had the EcoR1 endonuclease gene placed under the control of the PR promoter of lambda as well as a bla determinant. The resulting shuttle vector of about 14.6 kb was maintained in E. coli and in several strains of Rhodococcus. The vector was efficient in cloning DNA without prior alkaline phosphatase treatment, as a result of the presence of the positive selection function. This function was not significantly expressed in Rhodococcus, and the presence of the nocardioform resistance determinants led to no increase in arsenate or arsenite resistance in E. coli. The presence of the bla gene resulted in an increase of about threefold in ampicillin resistance in Rhodococcus strains.

Arsenic↗