Firstly in regards to your other question regarding antibioitcs, they do work on some species but not all. Antibiotic resistance can cause an antibioitc to be inaffective on a species this is due to several machanisms; the lack of structure which the antibiotic inhibits, the orhansims being impermable to the antibiotic, the organsim inactivating the antibiotic, modification of the target structure of an antibioitc, alteration of the biological pathway the antibiotic blocks and releaseing of the antibiotic out of the organism. For mor einfo. google mechanism of anitbitoc resistance.
Reasons why antibiotic resistance occurs; over use, not finishing full prescription. Visit WHO.org for more info on antibiotic resistance
Re: white blood cells they fight off infection through phagocytosis-
Think pacman engulpinginvaders
google it 
Malaria is parasitic infection cause by the spread of sporizoites in the saliva of mosquitoes. Symptoms include fever and flu like symptoms. It is usually hard to treat due to the mechanisms of spreading- treatment consists of antibiotics. for more info. apps.who.int/malaria/docs/Treatme…