Hospital acquired infection and antibiotic resistance Flashcards Preview

MCD - Microbiology > Hospital acquired infection and antibiotic resistance > Flashcards

Flashcards in Hospital acquired infection and antibiotic resistance Deck (28)
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Reasons for high rate of hospital-acquired infection

- High numbers of ill people
- Very crowded wards
- High amounts of pathogen nearby
- Broken skin from surgical wounds, IVs, catheters
- Antibiotic therapy allows antibiotic-resistant pathogens to accumulate
- Transmission by staff who don't wash hands properly


Antimicrobial definition

A chemical that selectively kills or inhibits microbes


Bactericidal definition

Kills bacteria


Bacteriostatic definition

Stops bacteria growing


Antiseptic definition

A chemical that kills or inhibits microbes, usually used topical to prevent infection


Minimal inhibitory concentration definition

The lowest concentration of antibiotic required to inhibit growth


Tetracycline mechanism of action

- Targets protein synthesis
- Binds to 30s ribosomal subunit
- Prevents peptide elongation


Chloramphenicol mechanism of action

- Targets protein synthesis
- Binds to 50s ribosomal subunit
- Prevents peptidyl transfer step


Erythromycin mechanism of action

- Targets protein synthesis
- Gram positive bacteria affected
- Truncation of polypeptides


Sulphonamides mechanism of action

- Inhibition of essential metabolites
- Targets specific enzymes


List of important bacteriostatic antimicrobials

- Tetracycline
- Chloramphenicol
- Erythromycin
- Sulphonamides


List of important bactericidal antimicrobials

- Beta-lactams (penicillin, methicillin)
- Quinolones
- Gentamicin
- Streptomycin


Penicillin/methicillin (beta-lactams) mechanism of action

- Targets cell wall synthesis
- Bind to Penicillin Binding Protein (PBP) and inhibit function
- No peptidoglycan synthesised


Quinolones mechanism of action

- Inhibit nucleic acid replication and transcription
- Target DNA gyrase in Gram negative
- Target topoisomerase in Gram positive


Gentamicin/Streptomycin mechanism of action

- Target protein synthesis
- Targets 30s ribosomal subunit


Reason for antimicrobials acting as selective pressure on microbes

Antimicrobial usage will kill all bacteria who do not possess resistance genes in a population. However, those that do will survive, and thus proliferate further until the new population is entirely resistant to that antimicrobial. Thus here the antimicrobial has acted as a selection pressure.


Genetic mechanisms of resistance

- Altering target site for antimicrobials, e.g. encoding an alternative PBP
- Inactivation of antibiotic, e.g. enzyme degradation of antibiotic molecules, encode beta-lactamase which breaks down beta-lactams
- Antibiotic efflux, e.g. encoding for efflux pumps which pump antibiotic molecules back out of cell
- Altered metabolism, e.g. increasing production of substrate to out-compete antibiotic as inhibitor, can switch to other uninhibited metabolic pathways
- Decreased drug accumulation, e.g. reduced penetration of antibiotic into bacteria


Non-genetic mechanisms of antibiotic resistance

- Forming a biofilm
- Changing intracellular location of targeted sites
- Slow growth
- Spores
- Persisters


Penicillin resistance mechanisms

- Penicillinases break down antibiotic, gained from plasmid transformation
- Modification of PBP, gained from point mutation


Tetracycline resistance mechanism

Efflux pump, gained by plasmid conjugation


Quinolone resistance mechanism

Target site modification, gained by point mutation


Cefotaxime resistance mechanisms

Target site modification, gained by point mutation


Sources of antibiotic resistance genes

- Plasmids
- Transposons, integrate into chromosomal DNA, allows transfer of genes from plasmid to chromosome and vice versa
- Naked DNA from dead bacteria in environment


Mechanisms of antibiotic resistance gene spread

- Transformation, uptake of extracellular DNA
- Transduction, phage inserts resistance gene into cell
- Conjugation, DNA transferred from cell to cell by a conjugation bridge


Examples of important antibiotic-resistant bacteria

- Methicillin-resistant staph.aureus (MRSA)
- Vancomycin-insensitive S.aureus (VISA)
- Clostridium difficile
- Vancomycin-resistant enterococci (VRE)
- E.coli
- P.aeruginosa


Reasons for longer hospital stays, more medical costs and increase in mortality and morbidity caused by antibiotic-resistant bacteria

- New resistant strain must be treated
- More specific/expensive treatment required to eliminate resistant strains
- Mortality and morbidity increased because disease is more severe and some may have no treatment


Strategies for decreasing antimicrobial resistance rate of increase

- Tighter controls on prescribing strategies
- Temporary withdrawal of certain antibiotic classes
- Restriction of antibiotics for certain serious infections
- Reducing use of broad-spectrum antibiotics
- Quicker identification of infections caused by resistant strains
- Combination therapy
- Better knowledge of local strains/resistance patterns


Strategies for overcoming resistance

- Modification of existing medications, preventing cleavage of beta-lactams and enhancing efficacy of methicillin
- Combinations of antibiotic and inhibitor of resistance mechanism e.g. beta-lactams with augmenting (inhibits beta-lactamases)