The antibiotic penicillin can kill invading bacteria without harming human cells because it targets bacterial:

Penicillin works by inhibiting the synthesis of peptidoglycan, a key component of the bacterial cell wall. Without a functional cell wall, bacteria cannot maintain their structure and lyse due to osmotic pressure. Since human (animal) cells do not have cell walls, penicillin does not harm them, making it selectively toxic to bacteria. Plasma membranes, ribosomes, and chromosomes are present in both bacterial and human cells (though with differences), so targeting them would not provide the same selectivity.