▁the ▁qu in ol ones , ▁and ▁the ▁ox az olid in ones — are ▁produced ▁sole ly ▁by ▁chemical ▁synth esis . ▁Many ▁ant ib acter ial ▁comp ounds ▁are ▁relatively ▁small ▁mole cules ▁with ▁a ▁mole cular ▁weight ▁of ▁less ▁than ▁ 1 0 0 0 ▁d alt ons . ▁ ▁Since ▁the ▁first ▁pione ering ▁efforts ▁of ▁Howard ▁Fl ore y ▁and ▁Ch ain ▁in ▁ 1 9 3 9 , ▁the ▁importance ▁of ▁ant ib iot ics , ▁including ▁ant ib acter ial s , ▁to ▁medicine ▁has ▁led ▁to ▁inten se ▁research ▁into ▁producing ▁ant ib acter ial s ▁at ▁large ▁scales . ▁Following ▁screen ing ▁of ▁ant ib acter ial s ▁against ▁a ▁wide ▁range ▁of ▁b acter ia , ▁production ▁of ▁the ▁active ▁comp ounds ▁is ▁carried ▁out ▁using ▁fer ment ation , ▁usually ▁in ▁strongly ▁aer ob ic ▁conditions . ▁ ▁Res istance ▁ ▁The ▁emer gence ▁of ▁resistance ▁of ▁b acter ia ▁to ▁ant ib iot ics ▁is ▁a ▁common ▁phenomen on . ▁Emer gence ▁of ▁resistance ▁often ▁reflect s ▁evolution ary ▁processes ▁that ▁take ▁place ▁during ▁ant ib i otic ▁ther apy . ▁The ▁ant ib i otic ▁treatment ▁may ▁select ▁for ▁b acter ial ▁stra ins ▁with ▁phys i olog ically ▁or ▁gen et ically ▁en hanced ▁capacity ▁to ▁surv ive ▁high ▁dos es ▁of ▁ant ib iot ics . ▁Under ▁certain ▁conditions , ▁it ▁may ▁result ▁in ▁prefer ential ▁growth ▁of ▁resist ant ▁b acter ia , ▁while ▁growth ▁of ▁sus