Broad-spectrum antibiotic estimated 10-100 trillion multiple organisms that colonize the human body. As a side-effect of therapy, antibiotics can change the body's normal microbial content by attacking indiscriminately both the pathological and naturally occurring, beneficial or harmless bacteria found in the intestines, lungs and bladder. The destruction of the body's normal bacterial flora is thought to disrupt immunity, nutrition, and lead to a relative overgrowth in some bacteria or fungi. An overgrowth of drug-resistant microorganisms can lead to a secondary infection such as "Clostridium difficile" ("C. diff") or candidiasis ("thrush"). This side-effect is more likely with the use of broad-spectrum antibiotics, given
Algae included in Protista, later also abandoned in favour of Eukaryota. However, as a legacy of the older plant life scheme, some groups that were also treated as protozoans in the past still have duplicated classifications (see ambiregnal protists). Some parasitic algae (e.g., the green algae "Prototheca" and "Helicosporidium", parasites of metazoans, or "Cephaleuros", parasites of plants) were originally classified as fungi, sporozoans, or protistans of "incertae sedis", while others (e.g., the green algae "Phyllosiphon" and "Rhodochytrium", parasites of plants, or the red algae "Pterocladiophila" and "Gelidiocolax mammillatus", parasites of other red algae, or the dinoflagellates "Oodinium", parasites of fish) had