antibiotics and antibiotic resistance Flashcards
(43 cards)
what are disinfectants?
antimicrobial agents applied to inanimate objects – toxic!
what are antiseptics?
antimicrobial agents that are sufficiently nontoxic and can be applied to living tissue
e.g. hand sanitizer
what are antibiotics?
antimicrobial agents produced by bacteria and fungi that are exploited by humans
delivered topically (specific area) and internally
they specifically target microbes and can be applied intramuscularly or intravenously
what’s the most effective therapeutic agent against bacterial infections?
antibiotics
availability enabled chemotherapy, organ transplantation, invasive surgeries & treatment of
premature infants
what are the 2 major problems with developing antibiotics?
bacterial resistance
diminished interest from big pharmaceutical companies to develop new antibiotics (trouble making money)
describe misuse of antibiotics
empiric (blinded) use (treating with any antibiotic on hand)
— may only be used if symptoms are severe & diagnosis is too slow
increased use of broad-spectrum agents (kills off other bacteria)
pediatric use for viral infections
do not complete course of treatment (those that survive may be resistant – bacteria remerges, stronger)
antibiotics in animal feeds (growth promotors)
how is antibiotic activity measured?
via minimum inhibitory concentration (MIC)
^^ the lowest concentration of agent that inhibits bacterial growth
how does one obtain the minimum inhibitory concentration?
series of culture tubes w/ varying concentrations of agent
– check for visible growth
can also use antibiotics strips; faster & multiple
– each strip has a different antibiotic w/ increasing concentration from bottom to
top
– MIC tells tell you antibiotic sensitivity in bacteria & how much you need to kill it
how do antibiotics work?
they target essential bacterial components
– such as cell wall synthesis
– protein synthesis
– DNA/RNA synthesis
– folate or folic acid synthesis
—– folic acid is required for nucleotide synthesis (so it’s starving the microbe)
– cell membrane alteration
describe beta-lactam antibiotics
contains a beta-lactam ring
inhibits cell wall synthesis
what type of antibiotic inhibits cell wall synthesis
beta-lactam antibiotics
how do some bacteria counteract penicillin, the antibiotic?
produces beta-lactamase, enzyme that destroys the beta-lactam ring – and as a result, the antibiotic
what’s methicillin?
chemically modified penicillin
also contains a beta-lactam ring
can’t be cleaved by beta-lactamases
… but some bacteria can produce a different “penicillin-binding proteins” e.g. PBP2a - encoded by ‘mec’ (methicillin resistance) — helps bacteria fight against antibiotics including methicillin
how does penicillin function as an antibiotic?
inhibits cell wall synthesis
it inhibits the penicillin-binding proteins (PBPs) aka transpeptidase in bacteria that help form the cross-links in cell wall – this makes the cell wall toooo weak, causing cell death
what is vancomycin?
a glycopeptide antibiotic that inhibits cell wall synthesis in gram+
— vancomycin can’t get across the cell membrane of gram- so doesn’t work there!
often a drug of “last resort”
how does vancomycin inhibit cell wall synthesis in gram+ bacteria?
binds the peptide linkage at terminal D-Ala-D-Ala residues & inhibits transpeptidation
resistance genes change these to D-Ala-D-Lac
– vancomycin can no longer bind
resistance is encoded by the van genes
what’s antibiotic resistance?
use of antibiotics actively selects for antibiotic resistant bacteria
in many cases, bacteria acquire a new gene (not just a series of single mutations)
antibiotic resistance can increase 1000-fold in a strain
what are some bacterial strategies for antibiotic resistance?
prevention of antibiotic entry
— gram- outer membrane & mycobacteria cell envelope block antibiotics from entering cell
antibiotic modification
— beta-lactamase destroy antibiotic
efflux of antibiotic
— bacteria encode efflux pumps that actively pump antibiotic out of cell
alteration of antibiotic target
— PBPs, ribosome modifications (prevents protein synthesis)
bypassing the antibiotic action
— use environmental folic acid (folic acid synthesis inhibitors)
describe antibiotic resistance genes
many mechanisms of antibiotic resistance are genetically encoded (e.g. mec, beta-lactamase, efflux
pump)
— can produce very high levels of antibiotic resistance
often encoded on mobile genetic elements (e.g. plasmids)
— allows for horizontal gene transfer → “superbugs”
— can be resistant to 10-15 clinically resistant antibiotics
what is horizontal gene transfer?
new genes are acquired from another source, rather than altering gene function via. mutations
what are the 3 ways in which horizontal gene transfer can occur?
bacterial transformation
— cell dies & releases DNA; another cell takes up resistant gene
– least common, requires a lot of energy from bacteria
bacterial transduction
— bacteriophage infects bacteria, packages host antibiotic resistant
gene & injects it into a the recipient cell
bacterial conjugation
— plasmids move DNA from one cell to another via pili (VERY EFFICIENT)
what’s bacterial transformation?
cell dies & releases DNA; another cell takes up resistant gene
least common, requires a lot of energy from bacteria
what’s bacterial transduction?
bacteriophage infects bacteria, packages host antibiotic resistant gene & injects it into a the recipient cell
what’s bacterial conjugation?
plasmids move DNA from one cell to another via pili (VERY EFFICIENT)
