Lecture 3- Hospital Acquired Infections Flashcards
What is an antibiotic?
An antimicrobial agent produced by microorganisms which kill or inhibit other microorganisms
What is the difference between bactericidal and bacteriostatic?
Bactericidal= kills bacteria Bacteriostatic= inhibit bacterial growth
What is an antiseptic?
Chemical that kills or inhibits microbes that is used topically to prevent infection
What is the ‘minimal inhibitory concentration’ (MIC)?
The lowest concentration of AB required to inhibit growth
What is ‘resistance’?
The ability of an organism to replicate in the presence of an AB at a particular concentration
What is the ‘breakpoint’?
An estimate of the concentration that might be achieved clinically
What were the misconceptions at about antibiotics
- resistance against more than one class of antibiotic at the same time would not occur
- horizontal gene transfer would not occur
- resistant organisms would be less’ fit’
When does resistance emerge?
Soon after the arrival of a new AB
How do antibiotics work?
SELECTIVE TOXICITY- inhibit specific pathways in certain types of bacteria
How do beta-lactams work as an antibiotic? Give examples of Beta lactams.
- E.g. penicillin and methicillin
- penicillin binds to Penicillin binding protein (PBP) and catalyses pathways
- Beta lactam ring is similar in shape to peptidoglycan precursor and interferes with cell wall synthesis
Which bacteria is resistant to the action of beta- lactams and how?
MRSA
- has a different PBP (PBP2a) which doesn’t bind to beta-lactams
What sort of antibiotic is Tetracycline?
Bacteriostatic
Broad spectrum
How does Tetracycline work as an antibiotic?
Inhibits protein synthesis
- Binds to the 16S component of the 30S ribosomal subunit
- prevents interaction of charged aminoacyl tRNA with the mRNA ribosome complex
- prevent elongation
What sort of antibiotic is Chlormaphenicol?
Bacteriostatic
Broad spectrum
What is the mechanism of action of Chloramphenicol?
Inhibits Protein Synthesis
- Binds to 50S ribosomal subunit and blocks peptidyl transferase step
Why is Chloramphenicol mainly used topically?
Because of its toxicity
What sort of antibiotic are quinolone?
Synthetic
Broad spectrum
Bactericidal
Which enzymes do quinolone target?
DNA gyrase-= Gram -ve
topoisomerase IV= Gram +ve
What sort of ‘antibiotic’ are sulphonamides?
Bacteriostatic
Synthetic
What are sulphonamides used to treat?
UTI’s, RTIs, bacteraemia
Interferes with folate pathway
What sort of antibiotic are ahminoglycosides? give examples
Gentamicin, streptomycin
Bactericidal
How do aminoglycosides work?
Target protein synthesis
- targets RNA proof reading–> msfolded proteins–> incorporated into cell membrane –> leakage –> rupture
Give an example of a macrolide. Which sort of bacteria do they target and what is their mode of action?
- Erythromycin
- Gram positive infections
_ Target 50S ribosomal subunit and prevent aminoacyl transfer
What are the four main mechanisms of resistance?
- altered target site
- inactivation of antibiotic
- altered metabolism
- decreased drug accumulation (reduced uptake or increased efflux)
Give an example of antibiotic inactivation
1) Beta- lactamase for beta-lactams
2) Chloramphenicol acetyl-transferase
How might bacteria alter their metabolism to confer resistance to antibiotics?
- increase enzyme substrate synthesis to out-compete the inhibitor
- switch metabolic pathways
How might AB resistant genes be acquired?
- Transformation
- Conjugation
- Transduction
What are the consequences of antibiotic resistance?
- Increased morbidity
- Increased mortality
- increased length of hospital stay
- increased cost
What are the reasons of the high rate of hospital acquired infections?
- High density of susceptible people
- crowded wards
- presence of pathogens
- bone skin- surgical wounds/ IV catheter
- Indeling devices (intubation)
- AB therapy presses normal flora (commensals)
- staff vectors
How do you prevent the emergence of drug resistant bacteria?
- prescribing strategies
- reduced used of broad-spectrum antibiotics
- quicker identification of infections caused by resistant strains
- combination therapy
- knowledge of resistance patterns
