how does antibiotic medication affect our gut microbiota generally, and our alzheimer’s disease risk specifically?
In this context, a treatment which reduced risk would likely be a combination of antibiotics and probiotics to try and shift the biome to a different one.
And this is the exact reason whymost of the time, GI problems come back or are replaced with different symptoms after antibiotics, and why we need more Fecal Microbiota Transplant research.
This is literally the reason I've been on short course antibiotics (<1 week or a single 4 tab dose) at different points, because it eliminates the constant bloating and gives probiotics a chance to work.
Probiotics might help, but a few or a few dozen non-gut-sourced strains simply cannot compare to the hundreds present in healthy stool. The effects on microbiota-dependent conditions are often weak to none.
Long version: It depends on specific antibiotic- generally, they wipe a portion of the strains completely, suppress most of the rest, and give anything resistant the opportunity to grow out of control, a state which persists for weeks to months during which you're extra susceptible to external pathogens, food poisoning, etc. A healthy microbiome is resilient, and sadly if you don't have one, FMT is the only way to do it.