How do antibiotics work?
Drugs capable of inhibiting/destroying disease-causing bacteria.
Prevent the formation of bacterial cell walls – peptidoglycan – can inhibit synthesis of peptide links that hold molecules together. Cell wall is weakened and osmotic lysis occurs.
OSMOTIC LYSIS: water enters cells by osmosis, pressure builds up if too much water enters, cells burst.
Antibiotics can work by:
· Bind to bacterial ribosomes & inhibit protein synthesis – not dangerous to humans, because bacterial ribosomes & protein synthesis aren’t same as in humans
· Disrupt DNS synthesis during DNA replication
· Disrupt cell membranes
Resistance due to chance mutation within bacterium. Bacteria have new allele enabling them to make a new protein that can break down antibiotic before it kills bacteria. – some resistance alleles change membrane permeability/bypass metabolic process that a antibiotic blocked. Alleles present in plasmid.
Plasmid = small extra loop of DNA that can copy itself & transfer genetic info. from one cell to another.
Mutation occurs AT RANDOM, but this gives an advantage. This is only an advantage in presence of antibiotics, so increased use of antibiotics = more likely resistant bacterium will encounter drug. Drug will kill non-resistant bacteria but not resistant = resistant reproduces & pass on resistant allele to offspring. = VERTICAL GENE TRANSMISSION.
Horizontal gene transmission
Bacteria can also pass on copies of plasmid, containing resistance allele, to other species of bacteria by conjugation = horizontal gene transmission through conjugation tube. = bacteria accumulating multiple resistance to range of antibiotics.
Increased use of antibiotics = increased resistanc
· Mutation causing resistance is a random event but increased use of antibiotics = greater likelihood resistant bacterium exposed to it.
· Use of antibiotics creates a selection pressure for resistant bacteria
· More resistant bacteria survive than non-resistant
· More resistant bacteria pass on allele to non-resistant bacteria
· Frequency of resistance allele increases in population
Treating TB & MRSA
TB has several different strains, treated by giving different antibiotics – taken over months. Kill off least resistant strains + patient = feels better. If stop taking drugs, selects most resistant strains to be unaffected & multiply + pass on alleles by vertical & horizontal gene transmission = new strains with further resistance.
MRSA usually harmless bacteria on skin/throat. In lungs/under skin = major health risk (hospital patients reduced immunity). Lots of antibiotics used in hospitals = mutant strain more likely to be exposed & selected. Became resistant to almost every known antibiotic.
Reduced by: screening patients & staff/ isolating patients with MRSA/ improving hygiene e.g. sterilising equipment & hands
Treatment of diseases to prevent resistance
· Rotate use of different antibiotics (GPs)
· Don’t allow people to buy antibiotics/ prescribe themselves
· Antibiotics shouldn’t be given routinely to cows (make a strain of bacteria resistant that can be passed to humans)
If shown a circular disk with wells in of where bacteria grow. HSW Q = how to plot graph. Answer = measure the diameter/ area of the clear zone where the bacteria can’t grow. Larger zone = better antibiotic.