Antibiotics 3 Flashcards
When does a bacterial superinfection occur?
- when resistant bacteria are allowed to grow and thrive, leading to the super infection of resistant bacteria
What are the most common causes of antibiotic resistance?
- overuse of antibiotics in humans
- overuse of antibiotics in non-humans
- use in developing countries
- world travel
- critically ill patients
- promotion of antibiotics
What increases the risk of antibiotic resistant infections?
- patient related factors (increasing age, increasing severity of underlying disease)
- hospital related factors (increased length of stay, admission to the ICU, proximity of infected patients)
- treatment related factors (prolonged use of broad spectrum antibiotics, contaminated devices or procedures)
How is antibiotic use in developing countries contributing to resistance?
- antibiotics are available OTC
- poor patient compliance
- cost (take sub therapeutic course)
- antibiotic quality is low, with a lot of counterfeit and poor quality Abs
What are the different ways that a bacteria can become resistant? (genetics of mutation)
- spontaneous mutation
- -acquisition of new DNA
- via transformation: DNA comes from the environment after being released by another cell (plasmid DNA)
- transduction: virus transfers DNA between bacteria
- Conjugation: contact between cells as DNA crosses from donor to the recipient
What are the two general mechanisms of antibiotic resistance?
- alteration of the target site
- decreased uptake by bacteria
What strategies could we use to overcome the problem with beta lactamases?
- can develop inhibitors of beta lactamases (clavulanic acid)
- combine the penicillin with the use of other antibiotics
- can add bulkier side chains to the penicillin structure, hindering the access of the Beta lactamase enzyme
By using a beta lactam antibiotic along with a beta lactamase inhibitor, you get a _____ effect
synergistic
What is the resistance to tetracyclines caused by?
- resistance is due to decreased uptake or increased extrusion of the Ab
- widespread resistance to tetracyclines limits clinical use
- bacteria have cross resistance
- Mg dependent active efflux is mediated by the TetA gene is the most common resistance mechanism
- other mechanisms of bacterial resistance
- — bacterial enzymes that inactivate tetracyclines
- — expression of bacterial proteins that inhibit binding of tetracycline to the ribosome
What is the bacterial resistance mechanisms against aminoglycosides?
- decreased uptake of the drug
- – absence of porin channels
- – absence of oxygen dependent transport system
- enzymes that inactivate aminoglycosides
- – acetyltransferases
- – nucleotidyltransferases
- – phsophotransferases
- cross resistance is rare
What is the bacterial resistance mechanisms to macrolides?
- decreased uptake of the drug
- increased efflux of the drug
- reduced affinity for the 50S ribosomal subunit
- – methylation of an adenine in the 23 S bacterial ribosomal RNA
- enzymes that inactivate macrolides
- – erythromycin esterase
- cross resistance is common
What is the resistance mechanism against fluorquinolones?
- alterations to DNA gyrase
- decreased uptake
- increased efflux
- cross resistance amount quinolone is common
Describe resistance to ciprofloxacin?
- widespread resistance by S aureus, S pyogenes, enterococcus and K pneumonia
- once considered a powerful Ab of last resort
- widespread use to eat minor infections and unapproved used promoted resistance
- – ear infections
- – acute respiratory illness
- – widespread veterinary usage
Describe bacterial resistance to sulfonamides and trimethoprim
- bacteria that obtain folate from the environment are inherently resistant to sulfonamides
- resistance is due to mutations that alter key functions in bacteria
- – sulfonamides: altered dihydropteroate synthase
- — trimethoprim: altered dihydrofolate reductase
- — reduced cellular permeability to the drugs
- — enhanced production of folates
Describe bacterial resistance to cotrimoxazole?
- bacteria that obtain folate from the environment are inherently resistance to sulfonamides
- cotrimoxazole resistance is rare since bacteria must have simultaneous resistance to both the sulfonamide and trimethoprim drug
- emergence of antibiotic resistant bacteria has recently renewed interest in cotrimoxazole
