Which of the following is an example of a direct method for pathogen detection?

The correct choice for an example of a direct method for pathogen detection is PCR (Polymerase Chain Reaction). PCR is a molecular technique that amplifies specific DNA sequences, allowing for the direct detection of the genetic material of pathogens. This method provides precise identification of the organism and can detect minute amounts of DNA, making it extremely sensitive and specific.

In contrast, blood cultures involve growing pathogens in culture media, which is an indirect method since it requires an incubation period and may not detect all pathogens present in the sample at the time of collection. Serological testing measures the immune response to pathogens by detecting antibodies in the blood, thus indicating past or ongoing infections rather than directly identifying the pathogen itself. Antigen testing identifies specific proteins from pathogens but often relies on the availability of a sample that contains these proteins, making it not as direct as PCR in terms of detecting the actual genetic material of the pathogen.

Therefore, PCR stands out as a direct method due to its ability to specifically amplify and detect the presence of pathogen DNA without needing the organism to be in culture or rely on immune responses.