Not quite true. Antimicrobial doesn't mean quite what you think; it means anti-some-microbes. Honey, for instance, has several antimicrobial or antibiotic aspects. Some honey is so because enzymes in it produce hydrogen peroxide, while other honey is so for different reasons, not fully understood. If you feed mice a lot of honey, their intestinal flora rebalance -- in one study, for instance, feeding mice honey as a food supplement increased their bifidobacteria and lactobacilli counts. This is actually probably good for digestion.