Antibiotics and resistance Flashcards
What is the purpose of an antibiotic?
To target enzymes and structures that are not present in humans for selective killing of the bacteria.
Which type of antibiotic targets the cell wall?
Beta lactams e.g. penicillin, cephalosporins, carbapenems, monobactams
Which type of antibiotic targets ribosomes?
Tetracyclines and aminoglycosides - inferfere with protein synthesis
Which type of antibiotic targets DNA gyrase?
Ciprofloxacin - Prevents replication
Which type of antibiotic targets folic acid synthesis?
Sulphonamides and trimethoprim - Bacteria cannot use exogenous sources of folic acid.
How does sulphonamide work?
A competitive inhibitor of para-aminobenzoic acid in the folic acid synthesis pathway, to inhibit gram +ve growth.
What is antimicrobial resistance?
Lack of effect on a previously susceptible pathogen.
How is resistance transferred through different species or between the same species of bacteria?
Conjugation through sex pilli.
How is resistance measured?
Consecutively double the concentration of antibiotic within a broth of bacteria. The first tube that fails to show growth is the MINIMUM INHIBITORY CONC of antibiotic for that strain. Can also be done using the zone of inhibition in a petri dish.
What enzyme is secreted by Staphylococus aureus to create resistance?
Secretes beta-lactamase needed to break down the beta-lactam ring. The ring is required for penicillin activity.
What is the target of penicillin?
A beta lactam that binds to peptidase to inhibit the enzymes that form the crosslinks in peptidoglycan polymers of the cell wall.
Which beta lactams were created to overcome this resistance?
Cleaving and adding of new sides chains to the 6-aminopenicillanic acid produced:
Cloxacillin, carbenicillin, ampicillin/amoxicillin.
All can target both gram +ve and -ve.
Why is methicillin no longer used?
Caused sodium overload
What resistance has MRSA developed?
Methicillin resistant Staph A has produced penicillin binding protein 2A which is a beta lactam target enzyme. Methicillin, penicillin, flucloaxcillin are all ineffective against this new enzyme as it is not targeted.
How is MRSA controlled?
Through infection control - Screening, decolonisation and isolation
What resistance did Ecoli originally develop?
Resistant to ampicillin due to the production of beta lactamase TEM. TEM is transferable through plasmids.
What antibiotics were developed against this first resistance and how were they overcome?
Created extended spectrum cephalosporins but the bacteria developed resistance through ESB lactamases and cephalosporinase CTX-M allowed the resistance to spread.
Which type of antibiotic is effective against Ecoli?
Carbapenems as ESB lactamases are ineffective against them
When are carbapenems used?
As a last line for most bacteria
What has led to the high levels of resistance?
Use of antimicrobials in food production and medicine. Megacities, poor public health has helped gram -ve bacteria resistance to spread.
How can the risk of resistance be reduced?
Reduce use of antibiotics.
Use a broad spectrum antibiotic originally but change to narrow spectrum once the strain is identified.
Use carbapenems against gram -ve.
Reduce hospital acquired infections by screening non-UK Pts for carbapenamase genes and use isolation.
Infection control and hygiene.
What are the two most common hospital acquired infections?
C.difficle - imbalance of gut flora causing toxic megacolon
Norovirus - severe vomiting and diarrhoea
What is the main consequence of antibiotics?
Can cause renal impairment and become toxic
In what ways are antibiotics being used inappropriately?
Overprescribing
Extended or uncompleted courses
Use on viral infections
Developing countries do not require a prescription to access antibiotics
