While I read that the Apollo spacecraft had to be decontaminated from potential lunar microbes, I wonder whether also probes were taken to investigate later on whether there had been any?
Biomedical Results of Apollo has an entire chapter devoted to that topic: section IV chapter 2, pp 425-434. There is much detail, but in summary:
- Fifteen species of animals, in five phyla, were exposed to lunar soil. After allowing time for something to grow, light and electron microscopy of tissues from the subjects revealed no evidence of replicating agents, other than identifiable, normal Earth microbes.
- A variety of growth media and atmospheres was inoculated with lunar soil. Nothing grew.
- Tissue cultures from humans, monkeys, cows, pigs, ducks, trout, minnow, and grunt(?) were inoculated with lunar soil. There were no differences from control samples. Many of the cultures were then infected with Earth viruses; the lunar soil had no effect on the Earth diseases.
- Seeds, seedlings, spores, and tissue cultures of 39 different species of crops, trees, other plants, and algae were grown in lunar soil. No diseases were found, but the lunar soil was determined to be an excellent growth medium.
- No plant or animal exhibited mutations or changes in growth.
And of course, the astronauts of the first three lunar surface missions spent 3 weeks in quarantine, with no observable negative effects. In summary, no microbes were found.