Antibiotics and resistance Flashcards
when was there no antibiotics
-There were no antibiotics prior to 1928!
-People did try to use chemicals to treat infection
-Some “natural remedies” probably contained antibiotics
What was the Germ Theory
-1950s Koch and Pasteur showed bacteria caused many infections
-If bacteria can cause disease then by killing them we can cure disease!
who was Paul Ehrlich
-(1854-1915)
-German chemist, studied dyes
-Some chemicals bind to microbes but not to human cells
-If these chemicals can kill then we get Selective Toxicity.
-Use of chemicals to treat clinical conditions is known as Chemotherapy
Antimicrobial Chemotherapy!
who was Alexander Fleming
-Pencicillin 1928
-First clinically useful antibiotic
-Mould contaminated a bacterial culture
-Released a substance that inhibited the bacteria
how do antibiotics act (selective…)
by selective toxicity- more damage to bacterium than host
what is a myth surrounding antibiotics
there are lots and lots antibitoics avaliable- there is acctually lots of brands avaliable- most have the same active ingredient: Amoxicillin
There is NOT a lot of choice!!!
what is used to classify antibiotics
-Different criteria are used
-Effect on the cell
-Type of cellular target
-Types of cells effected
what are bacteriostatic antibiotics
-Arrest growth and replication of bacteria
-Bacteria not killed by the drug
-Can regrow if drug removed
-Need patients to have active immune system to clear the infection (innate and adaptive immunity)
what are bactericidal antibiotics
kill bacteria
look up bacterial cell structure- they are procaryotic- look differences between eu and pro
what makes for a good antibiotic target (inhibits what)
-inhibits something essential to bacterium
-inhibits something not present in the host
-this allows seletive toxicity
what is DNA gyrase involved in
DNA synthesis
what antibiotics act by stopping cross-linking of the peptidoglycan sugar chains (what do they have similar)
-penicillins
-Cephalosporins
-All have a similar chemical structure around the active region
Beta-lactam ring
what happens if a cell wall is disrupted (what happens to cells)
the cells swell, rupture and die
what antibitoics act against the biosynthesis of building blocks of the wall
-Cycloserine
-Vancomycin
how are antibiotics active against the cell wall
-Many act by stopping cross-linking of the peptidoglycan sugar chains
-If the cell wall disrupted cells swell, rupture and die
-Some act against the biosynthesis of building blocks of the wall
what antibitoics affect bacterial membranes (what do they increase)
Polymyxins and gramicidin= interfere with the functioning of the bacterial cell membrane by increasing its permeability
what is gramicidin
one of a family of cyclic decapeptides active against Gram-positive bacteria.
what is polymyxins
-Have a smaller peptide ring attached to a peptide chain ending with a branched fatty acid.
-Primarily against Gram-negative bacteria.
-One of the most toxic groups of antibiotics
Increasing use in recent years= often the only effective antibiotic agent against multidrug-resistant organisms
what is an issue with many drugs that target nucleic acids (too toxic for what)
too toxic for clinical use against infections due to lack of specificity
Have found use as anticancer agents
what are the 4 clinically used antibiotics
- Quinolones- DNA gyrase (step inhibitited)- bacterialcidal
2.Rifampicin- RNA polymerase- bacteriostatic - Trimethoprim- Dihydrofolate reductase- bacteriostatic
- Sulfonamides- Dihydroperoate synthase- bacterialstatic
how do antibiotics inhibit protein synthesis
-Antibiotic targets multistep pathway in the bacterial cytoplasm
-Antibiotic has to get into the cell for activity
what antibiotics inhibit protein synthesis
1.Aminoglycosides-bacteriostatic
2.Tetracyclines- bacteriostatic
3.Chloramphenicol- bacteriostatic
4.Macrolides- bacteriostatic (gram+)
what is the spectrum of activity
Describes the range of different bacterial species that against which an antibiotic is active in vitro- can be narrow or broad
what are the Advantages of narrow spectrum antibiotics
-Will not kill as much of the normal microbiota as broad spectrum antibiotics
-less ability to cause superinfection.
-Should promote less resistance.
what are the disadvantages of narrow spectrum antibiotics
-Can be used only if the causative organism is identified.
-Limited choice of drugs.
what is the Therapeutic Index
The ratio of the dose toxic to the host to the effective therapeutic dose.
The higher the therapeutic index the better the antibiotic.
what is the minimum inhibitory concentration (MIC)
lowest concentration of the antibiotic that results in inhibition of visible growth under standard conditions
what is the minimum bactericidal concentration (MBC)
lowest concentration of the antibiotic that kills 99.9% of the original inoculum in a given time.
how do we select antimicrobial therapy
-Empiric therapy prior to organism identification= The acutely ill patient with infections of unknown origin
Neutropenic patient
Meningitis patient
-Identification of the organism= Differential stains; e.g., Gram stain, Culture
Necessary for conclusive diagnosis and antibacterial sensitivity test
Immunological analysis
PCR of specific target gene
what is synergy
If two antibiotics used in combination have an antibacterial effect much greater than either drug alone
Ex.; Trimethoprim and sulphonamides
what is antagonism
When two drugs in combination have activity less than the better of the two
Ex.; bactericidal and bacteriostatic drugs
what bacteria are inherently drug resistant (M C O)
-Mycoplasma species
Resist Beta lactam drugs
-Chlamydia species
Resist Beta lactam drugs
-Obligate anaerobes
No uptake of aminoglycosides
what is Urticari
a type of rash
what is Anaphylactic shock
rash with much more severe accessory symptoms
what are the complications of antibiotic therapy
-Hypersensitivity= penicillins can cause serious hypersensitivity reactions ranging from urticaria to anaphylatic shock
-Direct toxicity= aminoglycosides can cause ototoxicity, Chloramphenicol linked to fatal aplastic anaemia, 1: 20,000-40,000
-Superinfections= Alterations of the normal microbial flora, permitting the overgrowth of opportunistic organisms
Thrush (Candida albicans)
Clostridium difficile nosocomial/HAI infections
who was William Stewert
-US Surgeon General, 1967
-“time to close the book on infectious diseases”
-30-40 years ago it was thought that antibiotics had conquered bacterial diseases
what did Alexander fleming warn in 1945
the microbes are educated to resist penicillin and a host of penicillin-fast organisms is bred out which can be passed on to other individuals
what occurs in the Kirby-Bauer disk diffusion antibiotic susceptibility test and what type of agar is used
widely used to determine the sensitivity or resistance of bacteria to various antimicrobial compounds, and it uses the Mueller Hinton agar. Mueller-Hinton agar is a non-selective, non-differential medium capable of growing a wide range of non-fastidious organisms
what is the disk diffusion method
-Paper disks impregnated with known amounts of antibiotic
-Bacterial lawns prepared under standard conditions= Important for reproducibility
-Disks placed on lawns and incubation under standard conditions using standard media= Important for reproducibility
-Measure zones of inhibition and compare with standards= EUCAST, important for reproducibility
what is used to test the MIC
-Important Quantitative test
-Different formats available= Tube dilution, Unwieldy, replaced by E test, Automated systems (Vitek)
what is used in the E-test
-Paper strip with a concentration gradient of drug
-Read MIC directly from zone of inhibition
what is Vitek
fully automated system that performs bacterial identification and antibiotic susceptibility testing and MIC determination
what are mechanisms of antibiotic resistance
- Modification of target sites= decrease drug binding
mutation in the penicillin binding proteins in methicillin-resistant S. aureus. - Decreased accumulation of drug= Decreased penetrability due to the presence of lipopolysaccharide layer (gram-negatives) and Efflux system that pumps out the drug
- Enzyme inactivates drug= beta-lactamases destroy many penicillins and cephalosporins, Synthesis of excess target/alternate pathway and Absence of the target
what are beta-lactam antibiotics inactivated by
beta-lactamases= enzymes that hydrolyse beta-lactam ring
why is the beta-lactamases ring important
They stop bacterial growth by inhibiting PBPs that are indispensable for the cross-linking process during cell wall biosynthesis
explain Antibiotic resistance by increased excretion of drug
-Increased awareness of this mechanism in recent decades
-Dependent on “efflux pumps”
-Protein systems that span membranes= Move drugs from the cytoplasm to the external environment
-Can be found in both Gram negative and Gram positive organisms
-Different organisation dependent on membrane structure
Some efflux pumps are antibiotic specific
-Many efflux pumps are able to pump out a range of antibiotics
multiresistance
what genetic alterations lead to drug resistance
- Spontaneous mutations of DNA= Not a major clinical problem for most antibiotics
Exception: Rifampicin resistance in Mycobacterium tuberculosis - DNA transfer i.e movement of drug resistance genes= Major clinical impact as contributes strongly to multiresistance.
- Types of genes involved in transfer of resistance= Genes for drug inactivating enzymes and Genes for efflux pumps
what is MDR
Multi-Drug resistance= MDR: non-susceptibility to at least one agent in three or more antimicrobial categories
what is XDR
Extensively drug-resistant (XDR)
XDR: non-susceptibility to at least one agent in all but two or fewer antimicrobial categories
What is PDR
Pandrug-resistant (PDR)
PDR: non-susceptibility to all agents in all antimicrobial categories
what is multiresistance a consequence of
HGT (HORIZONTAL GENE TRANSFER)
what are examples of categories of antibiotics
Penicillins e.g Ampicillin + Methicillin
Glycopeptides e.g. Vancomycin
Fluoroquinolones e.g. Ciprofloxacin
Aminoglycosides e.g. Gentamycin
Macrolides e.g. Erythromycin
Polymyxins e.g. Colistin
How is antibiotic resistance a natural phenomen
Lechuguilla Cave,
Carlsbad Caverns National Park (USA)
Discovered in 1986
Very little human input
Pristine site, no exposure to antibiotics
Deep recesses of Lechuguilla Cave were isolated from surface input 4–7 million years
Soil samples taken
Various bacteria recovered by cultivation
Recovered bacteria tested for antibiotic resistance
Widespread resistance detected
what is selective pressure for antibiotic resistance
bacteria that have acquired a random change in their DNA that allows them to survive in the antibiotic’s presence outgrow nonresistant bacteria
Sensitive strains of a bacterial species (blue) and resistant (pink) present together.
what happens to the sensitive and resistant strains
1.If no antibiotic present sensitive strains grow a little faster than resistant (resistant have to make more enzymes/efflux pumps etc.)
2.In the presence of antibiotic resistant strains grow and sensitive ones do not, they may even be killed if a bacteriostatic antibiotic used.
3.When sensitive strains eliminated in the presence of a drug the overall population changes and all now resistant.
4.Use of the antibiotic has “selected” for the resistant strains and changed the population
what happened in the experiment for multidrug resistance
Measured selective pressure on a 220 KB multidrug resistance plasmid under various conditions
13 conditions provided selection
8 antibiotics, 2 biocides and 3 heavy metals
Minimal Selective Concentration up to 140x LOWER than MIC
describe antibiotics in the environment
1.Antibiotic resistances are widely distributed
Universal?
2. Selection can take place with very low levels of selective agents
3. Different classes of chemicals can select for antibiotic resistance
how do we prevent drug resistance
Give drug in high concentrations
Give two or more drugs at same time
Use drugs only when necessary
Possible future solutions= continued development of new drugs and the use of bacteriophages to treat bacterial disease???
What is chemotherapy-antimicrobial chemotherapy
Use of chemicals to treat clinical conditions is known as Chemotherapy
Antimicrobial Chemotherapy!
