Lecture 5 - Antibiotic Resistance Flashcards
(T/F) It is common to be resistant to all antibiotics.
False!
It is rare to be resistant to ALL antibiotics.
A rare case: woman killed by a superbug (K. pneumoniae) resistant to all antibiotics available in US.
What are antibiotics?
When are they called antibiotics?
Antibiotics are compounds produced by bacteria or plants (NATURAL) and chemists (SYNTHETIC) that kill or inhibit the growth of bacteria.
They are called antibiotics when we use them in the CLINIC to treat patients but they originated as ANTIMICROBIAL AGENTS (general term for compounds that kill or inhibit the growth of bacteria) in the env.
Antibiotics are compounds that bacteria need to _____ themselves from.
Producers of antibiotics (trying to establish a _____) will have ______ mechanisms to protect themselves from what they are producing.
Other bacteria need to respond to these compounds by:
protect
niche; resistance
1) moving away
2) expressing resistance mechanisms
3) get eliminated from the env (ie get killed by the antibiotics)
What is the general mechanism of antibiotics?
When does resistance occur?
Antibiotics have TARGETS in the bacterial cell. They interact with a target that is specific to a bacterial cell (cell wall, bacterial ribosome) and PREVENT PROPER FUNCTION resulting in either the death or growth inhibition of bacterial cell.
Resistance occurs when this interaction (between the antibiotic and the target) no longer occurs.
Briefly describe how Fleming discovered penicillin in 1929.
Discovery was a chance observation, where contamination of a culture plate of staphylococci by mold led to the observation that the staph were lysing (zone of inhibition).
Penicillium notatum was the mold that produced penicilin.
Several years of study, a few publications and the discovery of other antibacterial agents led to use of penicillin in the clinic.
(T/F) Fleming warned of resistance of penicillin through overdosage.
False!
Fleming warned of resistance of penicillin through UNDERDOSAGE.
“It is not difficult to make microbes resistant to penicillin in the laboratory by exposing them to concentrations not sufficient to kill them, and the same thing has occasionally happened in the body.”
What was the first antibiotic discovered? by who? to treat what?
Salvarasan was discovered by Paul Ehrlich to treat SYPHILIS.
(T/F) Resistance to penicillin was seen 10 years after it was put into widespread use in 1946.
False!
Resistance to penicillin was seen IMMEDIATELY after it was put into widespread use in 1946.
There was an outbreak of shigella in 1953 with a strain that was resistant to three antibiotics.
What are these antibiotics?
streptomycin, chloramphenicol and tetracycline
What are some bacterial structures/processes targeted by antibiotics?
cell wall synthesis/integrity
cytoplasmic membrane
DNA replication
transcription
translation
*there are many antibiotics that target the same structures/processes
What are the four general antibiotic resistance mechanisms?
1) alteration of outer membrane (prevent an antibiotic from getting into the gram - cell)
2) up-regulation of drug efflux pumps (remove the antibiotic once it gets inside the cell)
3) alteration of the target (prevent the interaction between antibiotic and target -> prime mechanism that relies on mutations; primarily the target)
4) inactivation of the antibiotic (prevent the interaction between the antibiotic and target)
How does antibiotic resistance arise?
1) mutation and selection - random mutations naturally occur at low frequency n antibiotic resistant mutants can be selected for by the environment
2) bacterial cells that produce antibiotics will have INTRINSIC (part of their genome - no mutations) resistance mechanisms (or else they will be killed by antibiotic that they produce)
these are sources of antibiotic resistance genes. THESE GENES CAN BE TRANSFERRED TO OTHER BACTERIA.
How do random mutations occur?
DNA polymerase makes mistakes (natural evolution) !!
the average mutation rate for bacterial genes is 10^8. these mutations can be selected for in the environment if they provide a growth advantage to the organism.
How do bacteria transfer resistance genes?
transformation (acquisition of DNA from the evn - released by other cells)
transduction (transfer of DNA via a virus - bacteriophage)
conjugation (cell-cell contact using a pilus to transfer DNA)
THIS IS VERY IMPORTANT - without these mechanisms, antibiotic resistance would be a much smaller issue!!
The _____ often bacteria are exposed to antibiotics, the _____ likely they will be able to develop resistance to the antibiotic. (Is this entirely true?)
Antibiotics serve as a _______ _____ for bacteria that have a resistance mutation.
more
*this is true but it is a LIMITED VIEW - bacteria don’t have to be exposed to antibiotics to become resistant (intrinsic resistance)
selective agent
1) What are actinomycetes?
2) Where do most clinically relevant antibiotics originate from?
3) Why did D’Costa et al looked for resistance elements in soil dwelling bacteria?
1) Broad group of bacteria that form thread like filaments in the soil and are responsible for the distinctive scent of soil.
2) Most clinically relevant antibiotics originate from soil-dwelling actinomycetes.
3) These antibiotic producers harbour resistance elements for self-protection and these can be transferred to other bacteria.
1) What did D’Costa et al do to study the antibiotic resistome?
2) What did they find?
3) What are the conclusions from their study?
1) They went out to different sites around Hamilton, ON to collect soil samples and isolated actinomycetes from the soil. They created a library of 480 actinomycetes to screen against 21 antibiotics.
2) They found widespread resistance! These isolates were not exposed to these clinical antibiotics before!!! Every strain isolated from the soil was resistant to several drugs (average 7 or 8). Two strains were resistant to 15 out of the 21 drugs. They identified characterized resistance mechanisms and uncharacterized resistance mechanisms.
3) The study was done with env isolates. Potential exists that these mechanisms will be transferred to pathogenic bacteria (and that this has happened in the past) and we need to study the soil resistome and understand the resistance mechanisms.
Define antibiotic resistome.
the group of all existing antibiotic resistance genes (known or unknown) in the world.
Does it make sense that there would be resistance in the absence of exposure to a particular clinically relevant antibiotic?
Yes! Intrinsic resistance mechanisms!!!
Producers need these genes to protect themselves and there can be transfer of these genes.
*bacteria don’t need to be exposed to clinically impt antibiotics to be resistant
*but when they are exposed, we will see resistance!
What are some factors that can cause the development of resistance related to exposure to antibiotics?
1) Overuse of antibiotics (in humans and agriculture)
2) non-compliance (patients often stop taking the antibiotic too soon because the symptoms improve - allows resistant bacteria to proliferate)
3) natural exposure to antimicrobial agents
Give examples of overuse of antibiotics in humans.
- physicians often prescribe antibiotics for illnesses due to a VIRUS
- individuals are put on long-term antibiotic treatment for conditions like acne, recurrent ear infections and UTIs (biofilm based; no response but other bacteria in body can develop resistance)
Which statement is true?
1) Resistant strains spread pretty slowly.
2) The use of fluoroquinolone prophylaxis (giving antibiotics to prevent the development of an infection) increased between 1986-1993 and frequency of fluoroquinolone-resistant bacteria in cancer patients also increased.
2!
Resistant strains spread RAPIDLY.
Livestock producers feed healthy animals antibiotics to promote ______ and to compensate for ______ and _______ conditions found in the industry.
in 2001, it was estimated that __% of all antibiotics in the US are used to feed ______ pigs, poultry and beef cattle.
humans can become ______ by eating undercooked, contaminated meat (antibiotic resistant bacteria)
farm workers are continually in contact with ______ and ______-_______ bacteria
antibiotics and antibiotics-resistant bacteria enter the ________ through farm waste (flows into lakes, rivers, ground water)
growth; unsanitary; stressful
70%; healthy
infected
antibiotics; antibiotic-resistant
environment
What are two ways antibiotics are found in the environment and cause resistance?
1) Humans and animals excrete antibiotics that make their way into our environment where the antibiotics continue to exert their selective pressure.
2) Soil organisms produce antimicrobial agents NATURALLY, creating an environment for the selection of resistance.
Differentiate acquired vs intrinsic resistance.
Acquired: resistance gene was not present in genome - it was acquired either through mutation and selection OR it was transferred from other bacteria.
Intrinsic: resistance gene is part of the genome - no mutations or DNA transfer occurred.
*resistance genes can be transferred to clinically relevant bacteria
What are the 4 classes of antibiotics and what do they target?
1) b-lactams (target cell wall)
2) macrolides (target protein synthesis)
3) aminoglycosides (target protein synthesis)
4) quinolones (target DNA replication)
Briefly describe the structure of peptidoglycan.
Chains of NAG and NAM.
Lateral tetrapeptide chains fixed to NAM.
Chains crossed-linked through peptide interbridges = TRANSPEPTIDATION (through the action of penicillin-binding proteins)
Briefly answer the following questions about b-lactams:
1) what are b-lactams?
2) give examples of b-lactams that are natural, have broad spectrum and have narrow spectrum
3) what is their mechanism of action?
1) beta-lactams are bactericidal (kill bacteria).
2)
natural: penicillin (work against gram + bacteria)
broad spectrum (work against both gram + and - bacteria): ampicillin, piperacillin, cephalosporins and carbapenems
narrow spectrum: methicillin
3) inhibit peptidoglycan synthesis by binding penicillin-binding proteins (transpeptidases). prevent the transpeptidation step.
*there are different classes within each 4 class of antibiotics. though they have the same target, they have different structures and functions.
What are the 3 mechanisms of b-lactam resistance displayed in resistant clinical isolates?
1) loss or diminished expression of OM proteins (OM becomes less permeable and b-lactams cant get inside the cell)
2) alteration in penicillin binding proteins so that they have reduced affinity for b-lactams
3) production of b-lactamases (enzymes that hydrolyze the b-lactam ring) - major form of resistance
1) What are b-lactamases?
2) How many have been identified?
3) Do b-lactamases provide resistance to just one specific b-lactam or multiple ones?
1) enzymes that hydrolyze the b-lactam ring. major resistance mechanism to b-lactams
2) over 2700 b-lactamases identified as of 2018
3) b-lactamases can mediate resistance to one specific b-lactams or more than one.
