Week 7 Identification and treatment of microorganisms Flashcards
How can bacteria be identified
- clinical samples grown on agar plates
- using bacteria specific characteristics (gram stains, aerobic/anerobic) - use dichotomous keys
What is selective media
chemical compounds that have been added to an agar to prevent the growth of certain microorganisms but not others (e.g. high salt concentration)
What is differential media
Agar which has an indicator on it which is usually a dye that allows differentiation of bacteria on the basis of the chemical reactions that occurs during growth
How are viruses identified
Diagnosed by blood test because viruses live inside of cells, and if the infection has been there for a while antibodies would be present, and you may also be able to identify the viral particles in the blood
How are funguses identified
- Fungal infections are superficial and usually lie on the skin so samples can be taken and grown or looked under a microscope.
- Light microscopy of stained or unstained preps
How are protozoa identified
- easily seenby light microscopy using certain stains e.g. Trichrome
def cidal activity
antimicrobial that kills the organism
def static activity
antimicrobial that inhibits the growth of an organism
what are the types of antimicrobial range of activity
- Broad spectrum antibiotics are effective against a wide variety of organisms
- Narrow spectrum antibiotics are only effective against a limited number of organisms
(narrow spectrum is preferred to not damage the rest of the host cells)
What is the concept of selective toxicity
Selective toxicity refers to the ability of a substance to selectively target and inhibit or kill specific organisms or cells while causing minimal harm to others.
This is achieved by the drug targeting specific differences which is only found in the specific microorganism which is being targeted.
What are the 4 main target sites for antibacterial drugs
- Cell wall synthesis
- Protein synthesis
- Nucleic acid synthesis
- Cell membrane function
How is cell wall synthesis targeted by antibacterial drugs
In bacteria drugs target peptidoglycan as it is a major component of bacteria and not present in humans. It’s more effective in gram positive than gram negative as gram positive has a greater amount of peptidoglycan
e.g. penicillin weakens the cell wall leading to lysis
How is protein synthesis targeted by antibacterial drugs
Protein synthesis is essential for bacterial growth and replication. Antibacterial drugs that target protein synthesis interfere with the bacterial ribosome, the cellular machinery responsible for translating mRNA into proteins.
e.g. Prokaryote Ribosomes - they interfere with binding of mRNA to ribosome or translation
How is nucleic acid synthesis targeted by antibacterial drugs
Nucleic acid synthesis is necessary for bacterial DNA replication and RNA transcription. Antibacterial drugs that target nucleic acid synthesis interfere with DNA replication or RNA transcription processes because the structure of DNA between prokaryotes and eukaryotes is the same.
Example
- Fluoroquinolones: Fluoroquinolones inhibit bacterial DNA gyrase and topoisomerase IV enzymes, which are involved in DNA replication and supercoiling, leading to DNA strand breaks and inhibition of DNA synthesis.
How is cell membrane function targeted by antibacterial drugs
Bacterial cell membranes maintain the integrity of the cell and regulate the passage of molecules in and out of the cell. Antibacterial drugs that target cell membrane integrity disrupt the structure or function of the bacterial cell membrane.
- structure of plasma membrane is similar between prokaryotes and eukaryotes
polymixins e.g. Colisitn
- Bind to LPS and interact with phospholipids in the outer and inner membranes hence is only effective against gram negative bacteria
What is the target of penicilin
cell wall
What are the drug target sites for fungus
- cell membrane
- b-glucan synthesis
What are the drug target sites for viruses
- stages of life cycle e.g. release of new virions
How does drug resistance occur
- innate/intrinsic - inherent characteristics of microorganisms that make them naturally less susceptible to certain antimicrobial agents
Acquired - developed after exposure or spontaneous mutation or horizontal gene transfer
What are some characteristics bacteria may have which gives it innate/intrinsic resistance
- no mechanism to transport drug into cell
- do not contain or reply on the antibiotic’ target process or protein
- gram positive and colistin (attached to lipopolysaccharide)
- Pseudomonas (has low membrane permeability and efflux pumps)
How may acquired resistance occur
- spontaneous chromosomal mutation (altered protein, selective advantage)
- horizontal gene transfer
What are the mechanisms of resistance (4)
- altered target
- alteration in access to the target site (altered uptake)
- Drug inactivation
- Horizontal gene transfer
Explain altered target as a mechanisms of resistance
The drug has target molecules such as enzymes or receptor, and the active sites of the enzyme or receptor may of been modified into different shapes where the drug no longer fits and inhibits
- lowered affinity for the antimicrobial drug
Explain alteration in access to the target site (altered uptake) as a mechanisms of resistance
Decreased permeability - the cell wall is modified and the drug cannot pass into the cell
gram negative contains porins which are pores in the outer membrane which can close making it harder for antibiotics to reach the membrane or cell
-Active transport which removes the antibiotic such as efflucx pumps that actively pump antimicrobial agents out of the cell
Explain drug inactivation as a mechanisms of resistance
Microorganism may contain an antibiotic degrading enzyme which destroys or inactivates the drug.
e.g. beta-lactamases inactivates beta lactams
Explain horizontal gene transfer as a mechanisms of resistance
Microorganisms can acquire resistance genes from other microorganisms through processes such as conjugation, transformation or transduction
These resistance genes may encode efflux pumps, enzymes or altered target proteins that confer resistance to antimicrobial agents.
What are solutions to counteracting resistance
- developing new drugs
- better management ( using appropriate drugs for the infection. rapid diagnosis, test for resistance)
What are solutions to developing resistance
- Phage therapy (targets bacteria phage)
- Silver nanoparticles (silver is toxic and disrupts metabolic processes in the bacteria, uses small amounts)
What is synergy
combination of drugs which enhances their activity
What is antagonism
A combination of drugs which decrease the activity of either or both drugs
