1. the verb to become is werden, not bekommen 2. you don't need the sind - in English we have two forms of the present tense which both translate into the same one in German i.e. he is becoming and he becomes would both translate as er wird. 3. In English comparatives we use "more" instead of "-er" when the adjective is three syllables or more long but in German you always use the suffix. So I would say "..., da Antibiotika unwirksamer werden."