W7 Antibiotic resistance mechanisms in bacteria Flashcards
Antibiotics are the basis of modern medicine:
(for info)
What is antimicrobial resistance?
- Antibiotics have transformed human (and animal) medicine
-Saving countless number of lives - Overuse of antibiotics at all levels, has led to the development and spread of drug-resistant bacteria
Antimicrobial resistance (AMR)
* Microbes resistant to one or more antimicrobial agents
-Multidrug resistant (MDR) - Microbes resistant to multiple antimicrobials
* Drug(s) are not effective anymore in inhibiting microbes
* Leading to treatment failure
* Add burden on the healthcare costs
* Increased mortality
Drug resistance in bacteria
What are some of the current serious threats?
- Clostridium difficile - discussed in the GI ISU
- Carbapenem-resistant Enterobacteriaceae (CRE)
- Drug-resistant Neisseria gonorrhoeae
- Methicillin-resistant Staphylococcus aureus (MRSA)
- Extended spectrum β-lactamase producing Enterobacteriaceae (ESBLs)
- Vancomycin-resistant Enterococcus (VRE)
- Multidrug-resistant Pseudomonas aeruginosa
- Multidrug resistant (MDR-TB) and Extensively drug-resistant TB (XDR-TB),
Mycobacterium tuberculosis- lecture 3
What is antibiotic sensitivity testing?
What specific tests measure antimicrobial activity?
- Antibiotic sensitivity testing is the measurement of the susceptibility of bacteria to antibiotics. Essential to understand if bacteria are resistant and the therapy is effective against bacteria isolated from the patients and responsible for the infection.
- Dilution Susceptibility Tests
- Disk Diffusion Tests (Kirby-Bauer Method)
- The Etest
- Detection test based on nucleic acids can identify gene sequence and known mutations encoding drug resistance factors
= no need of bacterial cultivation
Disk Diffusion Tests (Kirby-Bauer Method) – QUALITATIVE TEST
What is done?
Using disks of test antibiotics on an Agar plate spread with the isolated organism.
- Incubation time and practical test need to be standardised!!
- Measurement of the clear zones diameter around disks
- Compared to a standardized chart with reference values (same drug and same bacterial species), determining susceptibility or resistance
Clear zone= bacteria have been killed by solution and cannot reproduce- bacteria isn’t resistant
Dilution Susceptibility Tests and The Etest®
What is an MIC Value?
In both tests, MIC values (quantitative) are experimentally calculated in vitro
* MIC= lowest concentration of drug that prevents growth of the pathogen
*The calculated MIC is then compared to standardized charts with reference MIC values (same drug and same bacterial species) reporting typical values in case of bacterial susceptibility, resistance or intermediate
What are Persisters?
Bacteria that does not respond to a treatment but not involved in drug resistance
Drug-tolerant bacteria (persisters) – distinct from antibiotic resistance
* Rather than “Ignore” the presence of antibiotics,
-Ex. subpopulations of bacteria embedded in biofilms.
-Bacteria in biofilms produce a polysaccharide matrix, representing a physical barrier that antibiotics and immunity struggle to penetrate effectively
* Dormant and slowly-dividing cells = slow metabolism = difficult to be inhibited
* This state is reversible
Origins of drug resistance:
What is intrinsic resistance?
Examples? (2)
Intrinsic
* Common within a bacterial species
* Bacteria are naturally resistant to an antibiotic (existed before the therapy)
-lack of drug target
-the cell wall is impermeable to the drug
Ex. Mycoplasma resistance to β-lactams (cell
wall inhibitors), as Mycoplasma lack cell wall
Ex. Anaerobes are naturally resistant to
aminoglycosides
Origins of drug resistance:
What is Acquired resistance?
-Acquired
* Not uniform within a species
* when there is a change (or gene gain) in the genome of a bacterium acquiring the ability in the presence of a drug by:
a. Mutations
b. Vertical transfer
c. Horizontal transfer
Ex. Mutations occurring during therapy that
alter a bacterial enzyme targeted by antibiotics
Drug resistance acquisition
- Mutations within the bacterial genome
-Most are deleterious - Some are advantageous
-Bacteria can still replicate, and lose the antibiotic susceptibility - Antibiotic pressure tends to select resistance
- Also, bacteria of the normal flora can also acquire drug resistance
- Genetic material exchange between unrelated
bacteria= other than by the (“vertical”) transmission - Transfer of small DNA/plasmids (carries extra genes)
Drug resistance acquisition
Vertical transfer:
- Transmission of DNA from parent to offspring
-Bacterial chromosome and plasmids - Through asexual reproduction
- cell division (binary fission) from the mother cell to 2 daughter cells
- Plasmid DNA replication is independent to the chromosomal DNA and segregate randomly in the daughter cells
Drug resistance acquisition
What is Horizontal transfer?
- Genetic material exchange between unrelated
bacteria= other than by the (“vertical”) transmission - Transfer of small DNA/plasmids (carries extra genes)
- There are 3 types- conjugation, transduction, transformation
1. Plasmid is copied and transferred to a recipient cell
2. Plasmid provides recipient cell with antibiotic resistance
What are the 3 types of horizontal transfer?
- Conjugation
- Transduction
- Transformation
Drug resistance acquisition- Horizontal transfer:
What occurs in Conjugation? (3)
- DNA transfer (plasmids) between bacteria by direct cell-to-cell contact through sex pili (appendages)
- Transfer from a donor cell to a recipient cell
=Genetic variation - Sex pilus (from a donor cell) attaches temporarily to the recipient cell allowing exchange of plasmids
Drug resistance acquisition- Horizontal transfer:
What occurs in Transduction? (3)
- Transfer of genetic material (plasmids) between bacterial cells by viruses (bacteriophages recognising and infecting bacteria)
- No direct contact between cells
- Bacteriophages infecting bacterial cells, pack bacterial DNA into the virion progenies
- Transduction is an in vitro tool used to introduce a foreign gene into a host cell’s genome to correct genetic defects
Drug resistance acquisition- Horizontal transfer:
What occurs in Transformation? (3)
- Bacterial cells taking up DNA from the environment
- Donor cells could release DNA when they are killed
- Recipient cells need to be in a competent state, increased plasma membrane permeability to allow DNA to go across (less common)
- Transformation is a tool used to introduce a foreign gene into bacteria or yeasts to produce
protein-based drugs (e.g. insulin)
