I suspect all inks to have some sort of biocidal/fungicidal component to it. Considering how many spores and particulates are floating around in our air, and that our pens and inks are not maintained in sterile conditions, I am very much surprised that ink doesn't grow balls of slime/fuzz. I used to work in a microbiology lab, and all our reagents, mediums, and other random fluids were all kept sterile, and even solutions that we didn't think could support life, usually found a way to grow something funky. If our ink didn't have some innate defenses built into it, we'd all have slime and goo.
Water is an amazing medium... psudomonas aeruginosa can grow in contact solution, and serratia marcescens turns your bathroom pink. I wonder what kills things in ink?