I know that antibiotics usually have properties affecting specifically bacterial cells, like by inhibiting peptidoglycan synthesis. but do any antibiotics exist affecting eukaryotic cells, like yeast or other fungi? I read in a text that "most" eukaryotic cells are resistant against antibiotics and that confused me.
Regardless of whether it can be used against bacteria or not, is there any kind of antibiotic effective against fungi, or any kind of eukaryotic cell?
Yes. The antibiotic (general microorganism “targeter”) you’re looking for is an antifungal. There are fewer ways to target fungi as opposed to bacteria, but we can target them nonetheless.
The fungal cell membrane has ergosterol to regulate its permeability whereas the mammalian cell relies on cholesterol. Fungi have cell walls which are not present in mammalian cells and are different in chemical composition to bacterial cell walls. A fungal cell wall is made of chitin whereas, as you mentioned before, a bacterial cell wall is made up of peptidoglycan.
We rely on these differences to target fungi. Some antifungals bind to ergosterol (e.g. Polyenes like Amphotericin-B) whereas other agents inhibit ergosterol synthesis altogether (e.g. Azoles like Triazole). Other antifungal agents target the fungal cell wall by inhibiting the synthesis of chitin (e.g. Echinocandins like Caspofungin).
There are more ways to target fungi, like introducing nucleotide analogues (“look alikes” that don’t work) to disrupt their nucleic acid synthesis (e.g. Fluorocytosine 5-FC). Another method is to disrupt the fungal microtubule’s aggregation during mitosis (e.g. Griseofulvin), thus “arresting” the fungal cells in metaphase.
Recommended Textbooks:
Hugo & Russell’s Pharmaceutical Microbiology 8th edition, Wiley- Blackwell. Edited by S.P. Denyer et al. ISBN 9781444330632
Essential Microbiology for Pharmacy and Pharmaceutical Science, Wiley- Blackwell. By Geoffrey Hanlon and Norman Hodges ISBN 978-0-470-66534-3 (pbk.)
The term antibiotic typically refers to chemicals effective against bacteria. There are antimicrobial chemicals effective against fungi, and they are rather aptly called antifungals.
In general, for every organism, there will be a chemical that is toxic to it.
Yes, there is. The Azole class of drugs, for example, are used to treat (eukaryotic) fungal infections. One such drug is clotrimazole which targets cytochrome p450 which is responsible for the synthesis of ergosterol (a mimetic of cholesterol; not found in humans), ultimately leading to excessive fluidity in fungal membranes and their lysis.
https://www.ncbi.nlm.nih.gov/pubmed/3288361
Its not that eukaryotes are inherently resistant to antibiotics; rather, its often difficult to treat serious eukaryotic infections because humans are also eukaryotes and share similar biochemistries. See below. The problem with clotrimazole is that, although ergosterol is not found in human, the cytochrome p450 is (i.e. in the ETC) and it serves other functions which may be affected.
