# Antibiotics --- **Antibiotics** are a class of [[antimicrobial drugs]] that specifically target [[bacteria]]. When bacteria evolve so that antibiotics can't hurt them, this is called [[antibiotic resistance]]. **Bacteriostatic** antibiotics are those that simply inhibit the growth of a bacteria, but not outright kill them. **Bactericidal** antibiotics are those that do outright kill the pathogens. - [[Broad spectrum antibiotics]] are those effective against a wide range of bacteria, including both Gram positive and negative bacteria. These can be risky as they can harm our helpful bacteria. - **Narrow spectrum** antibiotics are those that are only effective against a select group of bacteria. For example [[penicillin|penicillins]] only act against gram positive bacteria. ## Mechanisms of Action ### Prevention of Cell Wall Synthesis By preventing the formation of the [[cell wall]]—or at least the formation of a *strong* cell wall—the bacteria cannot survive. [[penicillin]] and ampicillin are two antibiotics that work this way. Specifically, they bind to and disable an enzyme called [[peptidoglycan#Transpeptidase|transpeptidase]] that binds together the sugar chains forming the cell wall. A cell wall thus weakened can then fall apart and kill the bacteria. ![[transpeptidase.png]] It's important to note that this will not harm a cell wall that has already been formed, but it *will* prevent the synthesis of a new one. ### Prevention of Protein Synthesis By preventing the [[translation]] of new proteins, the bacteria cannot survive. **Tetracycline** and [[broad spectrum antibiotics|erythromycin]] work by binding to prokaryotic [[ribosome|ribosomes]] and deactivating them. These are selectively toxic because prokaryotic ribosomes have a different structure than eukaryotic ribosomes. Even so, there is a danger of causing harm to our own cells eventually because our [[mitochondria]] are basically their own bacteria living in our cells, and therefore *do* have prokaryotic ribosomes. ### Prevention of Nucleic Acid Synthesis By preventing [[nucleic acid]] synthesis, the bacteria cannot survive. **Quinolones** are a class of antibiotic that work by binding to and deactivating enzymes that are vital to [[DNA replication]], such as topoisomerase. ![[DNA replication.png]] These are selectively toxic because prokaryotic enzymes are slightly different than eukaryotic ones. ### Growth Factor Analogs **Growth factors** are something that a cell needs in order to grow or heal, like a nutrient. Growth factor *analogs* are molecules that are similar enough in shape for the cell to try to take it in an use it, but they don't actually provide any value to the organism. **Sulfonamides** are a class of antibiotic that are PABA (para-aminobenzoic acid) analogs. Bacteria need PABA in order to produce folic acid, which is an ingredient in [[nucleotide|nucleotides]]. The sulfonamide binds to the enzyme that converts PABA into [[vitamin B|folic acid]] and just stays there, blocking up the active site and rendering the enzyme useless. These are selectively toxic because we humans can't actually make folic acid on our own, and we just take it in our diet as [[vitamin B|vitamin B]]. ## Examples - Fluoroquinolones - **Ciprofloxacin** (Brand name: **Cipro**) - generally well-tolerated - used often for [[urinary tract infection|UTI]], [[prostatitis]] **trimethoprim** and **sulfamethoxazole** is a broad-spectrum combo antibiotic called **Bactrim**, it's generally well tolerated and is often used for [[urinary tract infection|UTIs]] ___