Antibiotic Resistance 1, 2 & 3 Flashcards
What is an antibiotic?
drug that kills or inhibits growth of microorganisms
Define MIC?
minimal inhibitory concentration. Lowest concentration of antimicrobial that inhibits growth of bacteria.
Defien MBC - minimal bactericidal concentration.
concentration of an antimicrobial that kills bacteria.
Define breakpoint.
the MIC that is used to designate between susceptible and resistant. Generally refers to the maximum achievable serum concentration. You always want breakpoint to be higher than MIC (susceptible). If MIC is higher than breakpoint it is resistant.
How does resistance to aminoglycosides usually develop?
bacteria gain ability to sulfonate, phosphorylate or esterify the drug
which type of bacteria typically gain resistance to B-lactams more easily: Gram+ or Gram-?
Gram- typically have more potent resistance to B-lactams. because of their double membranes. They have an extra pocket they can secrete B-lactamases into to destroy B-lactams, where they can keep the concentration high, whereas Gram+ just pump it out into the environement
What are extended specturm B-lactamases?
B-lactamases capable of hydrolysing extende spectrum cephalosporins, penicillins, and aztreonam. Common in E coli and klebsiells pneumoniae. Usually plasmid mediated. Often have aminoglycoside, ciprofloxacin and trimethoprimsulfamethoxazole resistance encoded on same plasmid
What are class A carbapenemases? Which bacterial species is it most common in?
resistance to carbapenems. Most common in Klebsiella pneumonia, but also found in E coli, and salmonella
Why is vancomycin inneffective against Gram- bacteria?
it is too big to diffuse across the membranes
Antibiotic that targets DNA gyrase?
fluoroquinolones
How is most antibiotic resistance transferred in gram- bacteria?
conjugation
What is empiric therapy?
Use before culture results available. It is the most common type of drug therapy today. Infections are not well defined “best guess”. Uses broad spectrum of multiple drugs based off usually only 2 randomized controlled trials. Leads to more adverse reactions and is more expensive
What is directed therapy?
only used about 15% of the time. Infection is well defined. Usually only one, seldomly two, narrow spectrum drugs are used. Evidence usually stronger than empiric. Fewer adverse reactions and less expensive.
Why is empiric therapy much more common than directed therapy?
there is often a need to immediately treat and not enough time to run the tests before treatment. Cultures often do not provide microbiological definition.
What is telithromycin effect?
drug rejected twice before being approved. started causing severe toxicities so it was labeled with a warning and then banned. Afterwards, FDA required that drug applicants needed to show patients are no more likely to die of any cause within a month of treatment.
