Quantification of Coxiella burnetii by polymerase chain reaction (PCR) and a colorimetric microtiter plate hybridization assay (CMHA)

Screening-level risk assessment of Coxiella burnetii (Q fever) transmission via aeration of drinking water

A screening-level risk assessment of Q fever transmission through drinking water produced from groundwater in the vicinity of infected goat barnyards that employed aeration of the water was performed. Quantitative data from scientific literature were collected and a Quantitative Microbial Risk Assessment approach was followed. An exposure model was developed to calculate the dose to which consumers of aerated groundwater are exposed through aerosols inhalation during showering. The exposure assessment and hazard characterization were integrated in a screening-level risk characterization using a dose-response model for inhalation to determine the risk of Q fever through tap water. A nominal range sensitivity analysis was performed. The estimated risk of disease was lower than 10(-4) per person per year (pppy), hence the risk of transmission of C. burnetii through inhalation of drinking water aerosols is very low. The sensitivity analysis shows that the most uncertain parameters are the aeration process, the transport of C. burnetii in bioaerosols via the air, the aerosolization of C. burnetii in the shower, and the air filtration efficiency. The risk was compared to direct airborne exposure of persons in the vicinity of infected goat farms; the relative risk of exposure through inhalation of drinking water aerosols was 0.002%.

Following the course of human leptospirosis: evidence of a critical threshold for the vital prognosis using a quantitative PCR assay

In order to follow the course of acute human leptospirosis, an ELISA microtiter plate hybridization method was developed for the quantitative determination of Leptospira spp. in biological samples after PCR. The biotin-labelled amplified product (331 bp from the rrs gene) was hybridized with a complementary capture probe covalently linked onto aminated polystyrene wells, and detected using a colorimetric reaction. The mean detection limit was 50 copies per 10 microl. In a prospective study of human leptospirosis cases, we obtained evidence that a density of 10(4) leptospires per ml of blood is a critical threshold for the vital prognosis of the patients. The practicability of the method makes it suitable for use in tropical areas for multicentric studies. Such studies could lead to a better knowledge of the natural history of the human disease. The method is also suitable for experimental evaluation of improved antibiotic treatments for leptospirosis.

Q fever

Q fever is a zoonosis with a worldwide distribution with the exception of New Zealand. The disease is caused by Coxiella burnetii, a strictly intracellular, gram-negative bacterium. Many species of mammals, birds, and ticks are reservoirs of C. burnetii in nature. C. burnetii infection is most often latent in animals, with persistent shedding of bacteria into the environment. However, in females intermittent high-level shedding occurs at the time of parturition, with millions of bacteria being released per gram of placenta. Humans are usually infected by contaminated aerosols from domestic animals, particularly after contact with parturient females and their birth products. Although often asymptomatic, Q fever may manifest in humans as an acute disease (mainly as a self-limited febrile illness, pneumonia, or hepatitis) or as a chronic disease (mainly endocarditis), especially in patients with previous valvulopathy and to a lesser extent in immunocompromised hosts and in pregnant women. Specific diagnosis of Q fever remains based upon serology. Immunoglobulin M (IgM) and IgG antiphase II antibodies are detected 2 to 3 weeks after infection with C. burnetii, whereas the presence of IgG antiphase I C. burnetii antibodies at titers of >/=1:800 by microimmunofluorescence is indicative of chronic Q fever. The tetracyclines are still considered the mainstay of antibiotic therapy of acute Q fever, whereas antibiotic combinations administered over prolonged periods are necessary to prevent relapses in Q fever endocarditis patients. Although the protective role of Q fever vaccination with whole-cell extracts has been established, the population which should be primarily vaccinated remains to be clearly identified. Vaccination should probably be considered in the population at high risk for Q fever endocarditis.

Nonculture Laboratory Methods for the Diagnosis of Infectious Endocarditis

Over the past few years new techniques have been developed to improve the diagnosis of infectious diseases. However, despite the various available culture systems, culture-negative endocarditis currently represents a challenge for physicians. In our laboratory, in an effort to reduce the rate of endocarditis of unknown etiology, we have used several recent histologic, serologic, and molecular tests. We review the latest technical developments for the diagnosis of infectious endocarditis, including those that we are currently using.

Quantitative method to determine mRNA levels by reverse transcriptase-polymerase chain reaction from leukocyte subsets purified by fluorescence-activated cell sorting: application to peripheral cannabinoid receptors

BACKGROUND

While cytometry is widely used in the detection of cell proteins, its application to quantitative evaluation remains problematic when target proteins or receptors are weakly expressed in cells. Reverse transcriptase-polymerase chain reaction (RT-PCR) is a technique whose sensitivity and specificity make it appropriate for analyzing nucleic acids and thus genes expressed in cells. Combining these two techniques, we developed a method to quantify the transcript expression of the peripheral cannabinoid receptor (CB2-r) in peripheral blood lymphocyte subpopulations and in tonsillar B-cell subpopulations.

METHODS

This strategy first involves quantitative RT-PCR performed kinetically, followed by enzyme detection of PCR products using an oligonucleotide probe sandwich-hybridization assay onto microplates.

RESULTS

B cells exhibit CB2-receptor mRNA levels 10 times higher than those of other lymphocyte subsets. Using this technique, we observed a modulation of CB2-r mRNA level following tonsillar B-cell differentiation. Lastly, this new technology was validated by comparing the mRNA levels of CB2-r with the expression of CB2-r proteins assayed by flow cytometry, using specific CB2-r antibody labelling.

CONCLUSIONS

This method allows precise measurement of the mRNA of CB2-r performed on cell numbers as low as 10(5) after sorting. Its performance, high accuracy, reproducibility, and reliability make it a valuable tool for assaying proteins weakly expressed in cells.

Quantitative PCR with colorimetric detection

We describe a quantitative polymerase chain reaction (PCR) technique with a colorimetric read-out, which enables quantitation of various sequences on a single microplate within one day. Using the quantitation of human IL10 and beta-actin transcripts, we show that this technique provides better reproducibility, as results are derived from a series of PCRs made with various amounts of standard. This also enables the control of the consistency of the data and elimination of some artifactual results.