CP2 - Mechanisms of Antibiotic Resistance

Question 1

name some examples of organisms that have developed resistance to antibiotics

Answer 1

1. methicillin resistant streptococcus aureus (MRSA)
2. vancomycin/glycopeptide resistant enterococci (VRE/GRE)
3. mute-drug resistant tuberculosis (MDR-TB)
4. extremely drug resistant TB (XDR-TB)

Question 2

what are the problems associated with antibiotic resistance?

Answer 2

1. under treatment or treatment with excessively broad spectrum antibiotics if the treatment is empirical
2. use of expensive, toxic or last line alternatives for more targeted therapy

Question 3

what is sensitivity testing?

Answer 3

when bacteria is tested to determine which antibiotics it is sensitive to. done in labs using cultures of bacteria with antibiotic-soaked filter paper

Question 4

how is an antibiotic chosen?

Answer 4

size of the zone of inhibition is proportional to the sensitivity of the antibiotic, this is then used to determine if the minimum inhibitory concentration is high enough to kill the organism but not cause significant harm to the patient and if it can be sustained in the body long enough using a practical dosing regime

Question 5

why is sensitivity testing performed?

Answer 5

1. to enable transition from empirical to targeted therapy
2. to explain treatment failures
3. to provide an alternate oral dose while weaning off IV

Question 6

what are the limitations of sensitivity testing?

Answer 6

1. infection may not be caused by the organism that is being tested
2. correlation between antimicrobial sensitivity and clinical response is not absolute
3. some organisms are clinically resistant to treatment even though tests may indicate sensitivity. therefore, clinical interpretation is important.

Question 7

what is the basic principle of the mode of action of antibiotics?

Answer 7

antibiotic + target = cell death

Question 8

what are the types of resistance mechanisms?

Answer 8

1. no target
2. reduced permeability to drug
3. altered target
4. over expression of target to dilute effect
5. enzymatic degradation to destroy the drug
6. efflux pump to expel drug

Question 9

which resistance mechanisms are coded by single genes?

Answer 9

1. antibiotic modifying enzymes

2. altered targets

Question 10

which structures can resistance be encoded in?

Answer 10

DNA, plasmids

Question 11

what enables horizontal transmission of resistance?

Answer 11

transposons and interferons

via plasmids

Question 12

which genes are transferred in vertical transfer?

Answer 12

chromosomal and plasmid

Question 13

what is a consequence of exposing sensitive strains to antibiotics?

Answer 13

chance of survival enhances once resistance is developed. either by spontaneous mutation or acquiring resistant genes. resistant strains will outcompete the sensitive ones and pass the resistance down via vertical transfer