Advancing the development of diagnostic tests and biomarkers for tuberculosis

High costs and limited returns on investment have hampered progress in developing new diagnostic tests and treatments for tuberculosis (TB). We need new biomarkers to develop assays that can rapidly, efficiently and reliably detect Mycobacterium tuberculosis infection and disease, identify drug resistance and expedite drug and vaccine development. This can only be accomplished through cross-disciplinary collaborations to facilitate access to human specimens. The Food and Drug Administration, Centers for Disease Control and Prevention, National Institutes of Health, the industry and academia experts came together in a June 2010 workshop to examine the field of TB diagnostic test development and biomarker discovery, identify areas of most urgent need and formulate strategies to address those needs.

Clinical relevance of chest pain during dobutamine stress echocardiography in women

BACKGROUND

Dobutamine stress echocardiography (DSE) is commonly used for diagnosis and management of patients with known or suspected coronary artery disease. Chest pain occurring during DSE potentially provides additional diagnostic accuracy. Our experience suggests that chest pain occurs frequently in women undergoing DSE.

HYPOTHESIS

It was the purpose of this study to determine the frequency with which chest pain occurs in women undergoing DSE and the relation to inducible ischemia or coronary artery stenosis.

METHODS

To determine the prevalence and clinical significance or chest pain during DSE, we reviewed the records of 154 consecutive women undergoing DSE in our laboratory. Of these, 59 patients (37.5%) also underwent coronary angiography. The presence or absence of chest pain was correlated with ECG changes, left ventricular wall motion abnormalities during DSE, and coronary stenosis by angiography.

RESULTS

Forty-one women (26%) developed chest pain during DSE. Patients experiencing chest pain were older (58.5 +/- 9.3 vs. 54.9 +/- 12.6; p = 0.05), and had lower resting heart rates (71 +/- 12.2 vs. 77.9 +/- 14.9; p = 0.008), but received similar maximum doses of dobutamine and reached comparable peak heart rates (131.1 +/- 17.4 vs. 133.5 +/- 21.7; p = NS). Patients with chest pain more commonly exhibited ST-segment depression > or = 1 mm during dobutamine infusion (13/41, 32%, vs. 17/113, 15%; p = 0.02), but chest pain showed no statistically significant correlation with abnormal DSE or with coronary stenosis.

CONCLUSIONS

In women undergoing DSE, chest pain occurs in 26% and does not appear to be related to inducible myocardial ischemia. Electrocardiographic changes occur more frequently in patients who experience chest pain, but are also often unrelated to inducible myocardial ischemia.

Helicobacter pylori-selective antibacterials based on inhibition of pyrimidine biosynthesis

We report the discovery of a class of pyrazole-based compounds that are potent inhibitors of the dihydroorotate dehydrogenase of Helicobacter pylori but that do not inhibit the cognate enzymes from Gram-positive bacteria or humans. In culture these compounds inhibit the growth of H. pylori selectively, showing no effect on other Gram-negative or Gram-positive bacteria or human cell lines. These compounds represent the first examples of H. pylori-specific antibacterial agents. Cellular activity within this structural class appears to be due to dihydroorotate dehydrogenase inhibition. Minor structural changes that abrogate in vitro inhibition of the enzyme likewise eliminate cellular activity. Furthermore, the minimum inhibitory concentrations of these compounds increase upon addition of orotate to the culture medium in a concentration-dependent manner, consistent with dihydroorotate dehydrogenase inhibition as the mechanism of cellular inhibition. The data presented here suggest that targeted inhibition of de novo pyrimidine biosynthesis may be a valuable mechanism for the development of antimicrobial agents selective for H. pylori.

Extracellular expression of native human anti-lysozyme fragments in Staphylococcus carnosus

Xylose-inducible vectors have been constructed for extracellular production of antibody fragments in Staphylococcus carnosus. The pre-pro sequence of S. hyicus lipase was taken as secretional signal sequence, and the S. xylosus Xyl repressor was used to confer xylose inducibility of transcription. Cleavage sites for the IgA protease were engineered between the pre-pro sequence and the antibody fragments to permit removal of the pro sequence. Extracellular expression of the light chain and the Fd fragment of a chimeric Fab fragment containing the variable regions of the anti-lysozyme antibody D1.3 was achieved with these vectors. The pro sequence could be removed from the expression product by IgA protease treatment. When the light chain and the Fd fragment were co-secreted as a protein fusion they accumulated in a structure capable of heterodimerization after IgA cleavage. This fusion contains the pre-pro sequence followed by the light chain, a second IgA site and the Fd fragment.

Using fusions with luxAB from Vibrio harveyi MAV to quantify induction and catabolite repression of the xyl operon in Staphylococcus carnosus TM300

The luxA,B genes from the Gram-negative marine bacterium Vibrio harveyi MAV were used in Staphylococcus carnosus TM300 as a reporter system for regulated expression of xylose utilization. The luciferase genes were fused to the xyl operon from Staphylococcus xylosus C2a. Expression of bioluminescence was induced through addition of xylose and repressed in the presence of glucose. A method to quantitate bioluminescence directly from the culture is described.

Regulation of Staphylococcus xylosus xylose utilization genes at the molecular level

We have investigated the regulation of the operon encoding xylose utilization in Staphylococcus xylosus C2a and Staphylococcus carnosus TM300. For in vivo studies, transcriptional fusions of the xylAB regulatory region to the lipase gene from Staphylococcus hyicus were constructed. Repression of lipase activity depended on a functional xylR gene and an xyl operator palindrome downstream of the promoter, while induction was obtained in the presence of xylose. Inactivation of either xylR or the xyl operator led to constitutive expression in the absence of xylose. Crude protein extracts from xylR+ staphylococci led to gel mobility shifts of the xyl regulatory DNA in the absence but not in the presence of xylose. A copper-phenanthroline footprint of the shifted band revealed protection of 28 phosphodiesters from cleavage in each strand of the xyl operator. Thus, the Xyl repressor covers the DNA over more than 2.5 helical turns. Glucose repression of the xyl operon occurs at the level of transcription and is independent of a functional xylR gene. A potential cis-active sequence element for glucose repression is discussed on the basis of sequence similarities to respective elements from bacilli.

Organization, promoter analysis and transcriptional regulation of the Staphylococcus xylosus xylose utilization operon

The Staphylococcus xylosus xyl genes were cloned in Staphylococcus carnosus by complementation to xylose utilization. Xylose isomerase assays under inducing (xylose present) and non-inducing (xylose absent) conditions indicated the presence of a regulated xylA gene on the recombinant plasmid. The nucleotide sequence (4520 bases) revealed three open reading frames with the same polarity. They were identified by sequence homologies as xylR, encoding the Xyl repressor, xylA, encoding xylose isomerase and xylB, encoding xylulokinase. Primer extension analyses indicated constitutive transcription of xylR and xylose-inducible transcription of xylA. Promoter consensus sequences were found upstream of both transcriptional start sites. A transcriptional terminator between xylR and xylA separates the different transcriptional units. Potential regulatory elements were identified by sequence analysis and suggest a repressor-operator mechanism for the regulation of xylAB expression.

Quantitative analysis of Tn10 Tet repressor binding to a complete set of tet operator mutants

A saturating oligonucleotide-directed mutagenesis of both tet operators in the tet regulatory sequence was performed yielding mutants with four identical base pair exchanges at equivalent positions in the four tet operator half sides. The mutants were cloned between bipolar lacZ and galK indicator genes on a multicopy plasmid allowing the quantitative analysis of their effects in vivo. In the absence of Tet repressor the mutations lead to considerably different expression levels of both genes. They are discussed with respect to the promoter consensus sequences. In particular, the -10 region of the in vivo active tetPR2 promoter is unambiguously defined by these results. In the presence of Tet repressor most of the mutants exhibit a lower affinity for that protein as determined quantitatively by their reduced expression levels. In general, tet operator recognition is most strongly affected by alterations of base pairs near the center of the palindromic sequence. The most important position is the third base pair, followed by base pairs two, four, five and six, the latter showing similar effects as base pair one. At each position, the four possible base pairs show different affinities for Tet repressor. They are discussed according to their exposure of H-bond donors and -acceptors in the major and minor grooves of the B-DNA. The results are in agreement with major groove contacts at positions two, three and five. At position four a low potential correlation of efficiencies with the H-bonding in the minor groove is found, while mutations at position six seem to influence repressor binding by other mechanisms.