NOT the William P. McGivern/David W. O'Brien story. This short story had Brown colonized with helpful microbes (from the days before nanites) that did him all sorts of good, however sometimes they decided what his good would be, independent of his 'druthers—-so they would keep him from drinking alcohol or induce him to be aroused by a woman that the microbes themselves wanted to colonize. Probably from the late '60s through the '70s. Thanks.
"Inside John Barth" by William W. Stuart (first published in Galaxy Magazine, June 1960, available at the Internet Archive), which was also the subject of this other question. There is a Project Gutenberg etext.
This short story had Brown colonized with helpful microbes (from the days before nanites)
His name was Barth, not Brown. They were intelligent microbes from outer space. At first, Barth is upset to learn he has been invaded:
"Well, you're trespassing on private property! Get out, you hear me? Get out!"
"Now, now, noble Fatherland. Please, do not become upset and unreasonable. We honor you greatly as our home and country. Surely we who were born and raised here have our rights. True, our forefathers who made the great voyage through space settled first here in a frightful wilderness some four generations back. But we are neither pioneers nor immigrants. We are citizens born."
that did him all sorts of good,
"Oh, please, gracious Fatherland! Permit us to correct you. In the days of our fathers, conditions were, we can assure you, chaotic. Many horrible things lived here. Wild beasts and plant growths of the most vicious type were everywhere."
"What you would call microbes. Bacteria. Fungi. Viruses. Terrible devouring wild creatures everywhere. You were a howling wilderness. Of course, we have cleaned those things up now. Today you are civilized—a fine, healthy individual of your species—and our revered Fatherland. Surely you have noted the vast improvement in your condition?"
however sometimes they decided what his good would be, independent of his druthers—
At ten I had to knock it off to go to bed, get my sleep, keep up my health. They were insistent.
As they put it, even if I didn't care for myself, I had to think about an entire population and generations yet unborn. Or unbudded, which was the way they did it.
—so they would keep him from drinking alcohol
They kept him from drinking to excess:
And all they wanted for me were such fine things as good health, long life, contentment. Contentment, sure. Continued irritation—a sour disposition resulting in excess flow of bile—did not provide just the sort of environment in which they cared to bring up the kiddies. Smoking? No. It wasn't healthy. Alcohol? Well, they were willing to declare a national holiday now and then. Within reason.
Which, as I already knew, meant two to four shots once or twice a week.
or induce him to be aroused by a woman
Sex? Themselves, they didn't have any. "But," they told me with an attitude of broad tolerance, "we want to be fair. We will not interfere with you in this matter—other than to assist you in the use of sound judgement in the selection of a partner."
that the microbes themselves wanted to colonize.
Back in my apartment—my big, new, plush apartment—I sat down to go over the thing with the Department of the Interior. The enthusiast response I got surprised me. "Magnificent," was the word. "Suberb. Great!"
Well, I thought myself that I had turned in a pretty outstanding performance, but I hadn't expected such applause. "It is a first step, a splendid beginning! A fully equipped, well-armed expedition will have the place settled, under cultivation and reasonably civilized inside of a day or two, your time. It will be simple for them. So much more so than in your case—since we now know precisely what to expect."