New Methods For Identification and Detection of Microbial Pathogens
Traditional Methods For Pathogen Identification
- Cultivation of organism in laboratory, and subsequent characterization.
- Detection of host immune response (e.g., antibodies) to known organism.
- Visual detection of "typical" microbial form in host.
Problems With Traditional Methods
- Cultivation-based methods insensitive for detecting some organisms.
- Cultivation-based methods limited to pathogens with known growth requirements.
- Poor discrimination between microbes with common behavioral features.
- Failure to detect infections caused by uncultivated (e.g., novel) organisms, or organisms that fail to elicit a detectable host immune response.
- Visual appearance of microorganisms is nonspecific.
Examples of Failures With Traditional Approaches
- Detection and speciation of slow-growing organisms takes weeks (e.g., M. tuberculosis).
- A number of visible microorganisms cannot be cultivated (e.g., Whipple bacillus).
- Diseases presumed to be infectious remain ill-defined with no detected microorganism (e.g., abrupt fever after tick bite).
New Molecular Methods
- Use of genetic (DNA or RNA) sequences to identify microorganisms plus DNA amplification procedures (e.g., polymerase chain reaction, PCR) leads to development of specific and consensus PCR methods.
- Other experimental sequence-based molecular methods for detection of novel microorganisms (e.g., "representation difference analysis").
Advantages
- Rapid (hours).
- Specific (can distinguish among different strains of same species).
- Sensitive (can detect one microorganism in some cases).
- Can be automated.
Examples of Successes With New Methods
Identification and characterization of...
- Agents of bacillary angiomatosis and cat scratch disease.
- Agents of human ehrlichiosis.
- Agent of Whipple's disease.
- Hantaviruses associated with human pulmonary disease (e.g., Sin Nombre Virus).
- Agent of Kaposi's sarcoma (Human Herpesvirus 8).
- Novel Babesia-like piroplasm (tick-borne protozoan).
- Novel viral hepatitis agents.
Future Applications
- Rapid, automated identification of known microbial pathogens on routine basis.
- More rapid and sensitive detection and identification of emerging, novel microbial pathogens (via active surveillance network?).
Research Priorities
- Optimize methods for extracting and amplifying DNA directly from clinical samples.
- Expand sequence databases.
- Look for microbial DNA/RNA in various chronic inflammatory diseases of unclear cause.
May 1996
