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21 Cards in this Set

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What is the number one reason why bacteria become resistant?
- acquire genes that encode resistance
what are the 4 reasons that were discussed about why bacteria become resistant?
1) acquire genes
2) develop resistance by mutation
3) naturally resistant
4) pharmacokinetic Factors
What are 2 examples given about bacteria that acquire resistant genes? How are they combated?
Beta-lactamase that gives resistance to penicillin
-- Augmentin inhibits beta-lactamase
Chloramphenicol acetyl transferase
--chemical modification of original antibiotic
Rifampicin developed resistance by bacterial mutation what is our solution to this?
- triple cocktail drug therapy for TB
What is one example of a naturally resistant bacteria? what is the solution?
aminoglycosides and anaerobic bacteria
--synergism: use penicillin and another antibiotic together
What are some pharmacokinetic factors that induce bacterial resistance?
- Tissue penetration: antibiotic cant get to right area
- Minimal inhibitory concentration (MIC) cannot get high enough concentration in correct area
What are the 4 ways that we discussed about how bacteria become resistant?
1) mobile genetic elements that transfer resistance
2) plasmids
3) transposons
4) phages
What are plasmids? how are they constructed?
- small, circular, episomal, pieces of DNA
- form functional modules, but important part is the replication module
What are the importance of imcompatibility groups?
- 2 plasmids with same replication module cannot exist in same cell
Describe conjugation and plasmids
- male reels in female and burrows hole in her
- male makes a copy of his plasmid and gives it to female--female now is male
- how resistance gene is spread, allows exponential amplification of plasmid
how does the gene get on the plasmid?
- transposons
What are transposons?
- jumping genes
What are 3 important structures of transposons?
1) inverted repeats (identifies as jumping gene)
2) transposase (enzyme)
3) direct repeat at site of transposition
Why was the fertility "F" plasmid important?
- first saw that all isolated R (resistance) plasmids were associated with transposons
- indicated that resistance genes were first part of normal chromosome
What is a phage?
- bacterial virus
Transduction and phages
- virus chops up bacterial DNA, some bacterial DNA gets incorporated into viral DNA and passed on to other bacteria
- what does the new DNA contain?
What are 4 clinical implications of mobile genetic elements causing antibiotic resistance?
1) acquisition is rare: if patient responds to antimicrobial therapy they won't suddenly gain resistance under your watch
2) longer therapy duration wont in itself induce resistance
3) prophylatic administration of antibiotics doesn't promote resistance
4) patients that initially respond to antimicrobials and then get worse most likely have new bug
What is the importance of resistance genes?
some genes have always been there
--penicillins are natural antimicrobials and evolved with bacteria, normal that bacteria developed resistance against
--some resistance genes recruited for double duty
--evolve by mutating the target from antimicrobial
horizontal gene flow: b/c resistance genes recruited by mobile elements
How are resistant bacteria formed?
-SELECTION
- kill off bacteria that can be killed my antibiotics, only leaves resistant ones left
What is piggyback selection?
- may acquire resistance to more than one antibiotic if one resistance gene carries several antibiotic resistance capabilities on one plasmid
How can you cope with antibiotic resistance?
- new antibiotics
- altruism (reduces selective pressures, and lower use of antibiotics lowers antibiotic resistance frequencies
- limit use of antimicrobials on farm