Culture confirmation of cytomegalovirus and herpes simplex virus by direct enzyme-labeled DNA probes and in situ hybridization

Sensitive and Specific Detection of Mycoplasma species by Consensus Polymerase Chain Reaction and Dot Blot Hybridization

Mycoplasmas are highly fastidious bacteria, difficult to culture and slow growing. Many species of mycoplasmas are important pathogens that cause respiratory infection in laboratory animals and that are known to affect experimental results obtained with contaminated animals. The aim of the present study was to develop a sensitive and specific assay for the detection of mycoplasma species. To this end, we developed a polymerase chain reaction and dot blot hybridization assay (PCR/DBH) for detecting mycoplasma DNA and evaluated it for its sensitivity and specificity. Mycoplasma consensus primer pairs were used for the amplification of target DNA. When PCR product was visually detected, the limit of detection of the PCR test was 10² pg of mycoplasma purified DNA. For DBH, the amplified DNA was labeled by incorporation of digoxigenin (DIG). This DIG-labeled probe was capable of detecting 10⁴ pg of purified mycoplasma DNA by DBH. PCR/DBH was more sensitive than PCR or DBH alone and was also very specific. Our PCR/DBH assay can be applied efficiently to confirm the presence of mycoplasma species on clinical samples and to differentiate between mycoplasma species infection and other bacterial infections.

Non-radioactive digoxigenin DNA labeling and immunologic detection of HSV PCR products

BACKGROUND

Herpes simplex virus (HSV) is a common cause of human skin and mucous membrane infections, and also causes sporadic meningoencephalitis. As a new method for rapid HSV diagnostics, polymerase chain reaction (PCR) has been introduced in clinical laboratories. Radioactive labeling of DNA probes has become a common practice in experimental laboratories. To avoid radioactive labeling of HSV oligonucleotide probes or PCR products, non-radioactive compounds, which are easily detected by enzyme or immunoassay techniques, are introduced.

OBJECTIVES

The aim of our study was (1) to introduce non-radioactive labeling of HSV DNA probe by digoxigenin-labeled dUTP; (2) to establish a rapid and reliable laboratory method for rapid HSV diagnostics; (3) to compare the PCR method with the standard virology techniques, such as cell culture virus isolation and HSV direct fluorescent antibody test (DFA).

STUDY DESIGN

We have tested the efficiency of PCR method and non-radioactive labeling of HSV DNA probe for detection of HSV from 30 clinical specimens (skin and mucous membrane swabs). HSV was detected in the specimens by standard virology techniques and PCR. Replicated HSV DNA was non-radioactively labeled by random incorporation of digoxigenin-labeled deoxyuridine triphosphate (DIG-dUTP), and the hybrids were detected by the antibody conjugates and the appropriate enzyme-mediated staining reaction (DIG DNA labeling and detection kit non-radioactive, Boehringer Mannheim GmbH).

RESULTS

Non-radioactive labeling of hybridization DNA probes with digoxigenin-dUTP was obtained. HSV DNA was successfully multiplied and detected in the HSV-infected cell culture supernatant; however, it was not detected in the clinical specimen supernatant or sediment. HSV DNA was detected by direct PCR method in non-centrifugated clinical specimens.

CONCLUSIONS

The PCR method could be successfully used for diagnoses of HSV infections. Since the sensitivity of this method is partly limited by the virus quantity in the specimen, we recommend cultivating the virus in the cell culture at least 24 h prior to PCR. The use of non-radioactive labeling of hybridization DNA probes, such as random primed DNA labeling with digoxigenin-dUTP, has proven both sensitive and specific, and more appropriate for diagnostic purposes than radioactive DNA labeling to be used until standardized commercial tests appear.