'germ-based' is a modern English compound formed from 'germ' + 'based'. 'germ' in English comes from Latin 'germen' (via Old French 'germe'), where 'germen' originally meant 'sprout' or 'seed'; 'based' is the past participle/adjectival form of the verb 'base', ultimately from Latin/Greek roots related to 'basis' meaning 'foundation'.

'germ' developed from Latin 'germen' -> Old French 'germe' -> Middle/Modern English 'germ', with the specific sense 'microorganism' emerging in the 19th century; 'base' entered English via Old French and Latin/Greek 'basis', and the compound 'germ-based' is a recent formation in Modern English to describe things grounded on germs.

Originally 'germ' meant 'sprout' or 'seed' and 'base' meant a foundation; over time 'germ' acquired the microbiological sense and the compound 'germ-based' came to mean 'founded on microorganisms or their effects'.