lecture 9) antibiotic resistance mechanisms

Question 1

what is antibiotic resistance?

Answer 1

resistance of a microorganism to an antimicrobial drug that was originally effective for treatment of infections caused by that microorganism

Question 2

how can you measure antibiotic resistance?

Answer 2

antiobiotic resistance can be reflected by an increase in MIC

Question 3

what is MBC?

Answer 3

minimum bacterial concentration

the minimum concentration of an antimicrobial that kills in vitro

Question 4

what is the process of determining the MBC?

Answer 4

grow bacteria at different concentrations
plate bacteria on drug free plates
only bacteria that havent been killed will grow back

Question 5

what is the difference between MIC and MBC?

Answer 5

MIC just looks at growth

MBC is a 2 step process (grow and plate)

Question 6

how are the values of MIC and MBC correlated with what is used in a clinical setting?

Answer 6

using breakpoints

Question 7

what is a breakpoint?

Answer 7

the chosen concentration of an antibiotic which defines whether a species of bacteria is resistant to the antibiotic
determines how the antibiotic will be administered

Question 8

using breakpoints and MIC how is antibiotic resistance determined?

Answer 8

if the MIC is less than the BP the bacteria is susceptible to the antibiotic
if the MIC is greater than the BP the bacteria is resistant to the antibiotic

Question 9

what are the units for breakpoints?

Answer 9

mg/L

Question 10

what is a bacteriostatic agent in relation to antibiotic resistance?

Answer 10

an agent that reaches MIC levels in blood or tissues

Question 11

what is a bacteriocidal agent in relation to antibiotic resistance?

Answer 11

an agent that reaches cidal levels in blood/tissues

Question 12

describe a broad-spectrum agent in terms of MIC/BP

Answer 12

low MIC for many different bacteria types

Question 13

describe a susceptible microbe in terms of MIC/BP

Answer 13

inhibited by an agent at a low MIC

Question 14

describe a resistant microbe in terms of MIC/BP

Answer 14

inhibited by an agent at a high MIC

resistant microbes will only be killed at a dose higher than what a clinician will use

Question 15

generations are used as an indication for the level of resistance of an antibiotic. describe this method of indication

Answer 15

the higher the generation of antibiotic used to treat the resistant bacteria, the worse the resistance
4 generations: 4th generation is the very very last resort as there is no generation after this and it is likely that the bacteria will become resistant to this one too

Question 16

name 3 mechanisms of resistance

Answer 16

drug efflux pumps
drug inactivation - enzymes modify drug
drug inactivation - enzymes modify receptor

Question 17

what mechanism of resistance do beta lactams use?

Answer 17

inactivation of drugs by enzymes - modify drug
beta lactamase (enzyme produced by host) 
breaks down the beta lactam ring in penicillins that binds to a surface protein to prevent the formation of peptide bonds in the peptidoglycan later 
no beta lactam ring = no inhibiton of infection = bacteria resistant

Question 18

what makes staphylococcus aureus resistant to penicillin?

Answer 18

presence of penicillinase which is a beta lactamase so will hydrolyse the beta lactam ring

Question 19

what was used to treat S. aureus infections after they became resistant to penicilin?

Answer 19

methicillin

Question 20

what infection is induced if S. aureus strains are resistant to methicillin?

Answer 20

MRSA (methicillin resistant staphylococcus aureus)

Question 21

describe the mechanism of resistance that S. aureus has for methicillin

Answer 21

inactivation of drug using enzymes - modify receptor
resistant strains have an altered pen binding protein that prevents methicillin from binding to the protein. transcription not inhibited so neither is the infection

Question 22

what genetic components make MRSA resistant?

Answer 22

staphylococcal casette chromosome is mec (SCC-mec)
SCC-mec = mobile genetic elements
each SCC-mec has a casette chromosome recombinase (CCr) and a mec gene complex
mecA encodes for a varient penicillin binding protein (PBP)
PBP has a lower affinity for beta lactams = resistant to virtually all beta lactams

Question 23

what type of antibiotic is streptomycin?

Answer 23

aminoglycoside

Question 24

what is streptomycin used to treat?

Answer 24

streptomyces ssp.

Question 25

how does streptomycin act against streptomyces spp.?

Answer 25

protein synthesis inhibitor | targets 30S subunit that strep ssp. produces

Question 26

why doesnt streptomycin kill the producer strain?

Answer 26

something attaches to the producer strain making it inactive

Question 27

what is characteristic about aminoglycoside phosphotransferase (APH) in streptomycin resistance?

Answer 27

chromosomally acquired streptomycin resistance

Question 28

what is the chromosomally acquired resistance to streptomycin commonly due to?

Answer 28

mutations in gene encoding ribosomal protein s12 and rpsL

Question 29

what does rspL gene encode for in streptomycin resistance?

Answer 29

encodes for a protein that will be incorporated into a ribosome strep will want to go there to inhibit the infection if this gene is modified then the protein wont be there

Question 30

what is chloraphenicol?

Answer 30

man-made antibiotic | protein synthesis inhibitor targeting 50S subunit

Question 31

what is the method of resistance bacteria have against chloraphenicol?

Answer 31

modifies acetylation of chloraphenicol by chloraphenicol acetyltransferase

Question 32

what is the secondary method of resistance bacteria have adapted against chloraphenicol?

Answer 32

chromosomally encoded cmIA produces more OmpA leading to decreased permeability of membrane preventing the action of chloraphenicol

Question 33

where are drug efflux pumps present?

Answer 33

gram positive and negative bacteria except from the RND family of gram negative bacteria

Question 34

what is the mechanism of resistance for drug efflux pumps?

Answer 34

TolC and AcrA are genes involved in forming the transporter part of the efflux pump that removes the antibiotic from cell

Question 35

why is the TolC and AcrA channel needed in gram negative bacteria?

Answer 35

dont have periplasmic intermediate therefore if the antibiotic was pumped out of the cell it would come straight back in again as there would be no control mechanism

Question 36

what makes efflux pumps multifunctional tools?

Answer 36

they can make secretion systems

Question 37

in E.coli, AcrA and TolC have been shown to extrude what antibiotics?

Answer 37

``` chlorampenicol fluoroquinolone tetracycline novobiolin beta lactams ```

Question 38

AcrA and TolC in S. typhimurium can expel what antibiotics?

Answer 38

quinolons chloramphenicol tetracycline nalidixic acid

Question 39

describe the role of TolC

Answer 39

outer membrane bound protein attaches and hooks any protein fuse components in inner and outer membrane

Question 40

how many rings are there in tetracycline?

Answer 40

4

Question 41

what does tetracycline specifically target?

Answer 41

30S subunit in protein synthesis

Question 42

what is a plasmid?

Answer 42

extra chormosomal material can replicate at the same or different time as chromosom contains all the genes needed to make an efflux pump

Question 43

what is an R plasmid?

Answer 43

resistant plasmid

Question 44

how would you detect anomalies in plasmids?

Answer 44

each plasmid has different GC content | plot GC content to detect abnormalities

Question 45

what is GC content?

Answer 45

guanine-cytosine content of a chromosome

Question 46

what are transponons?

Answer 46

mobile genetic elements that regenerate into a chromosome

Question 47

why would transponons be considered dangerous?

Answer 47

mediator of resistance excise from chromosome and integrate elsewhere can also excise from chromosomes and integrate into plasmids

Question 48

where can antibiotic genes be found?

Answer 48

chromosomes | plasmids

Question 49

how can antibiotic resistant genes be transferred?

Answer 49

horizontal and vertical transmission

Question 50

explain vertical transmission of antibiotic resistant genes

Answer 50

selective advantage means a spontaneous strain arise antibiotic is added susceptible cells will die resistant cells will remain alive, grow, replicate and propagate their selective advantage onto subsequent generations

Question 51

explain horizontal transmission of antibiotic resistant genes

Answer 51

genetic material is transferred between 2 different bacterial cells in the presence of antibiotic the suscpetible cells will die (majority are susceptible) resistant cells will remain alive resistance genes transfer from cell to cell

Question 52

what type of gene transfer is the main reason for antibiotic resistance?

Answer 52

horizontal gene transfer

Question 53

what is the main difference between horizontal and vertical gene transfer of antibiotic resistance?

Answer 53

vertical transmission is genes being propagated on to subsequent generations therefore there is an increase in number of cells horizontal transmission is when genes are transferred from cell to cell so there is no increase in overall cell number but there is an increase in the number of cells that are resistant to antibiotic

Question 54

what is the main driver of vertical and horizontal gene transmission?

Answer 54

selective advantage

Question 55

name the mechanisms of horizontal gene transfer

Answer 55

natural transformation | conjugation and transduction

Question 56

what happens to the bacteria during natural transformation of horizontal gene transfer?

Answer 56

manipulation of bacteria = can take up DNA

Question 57

what species is natural transformation of horizontal gene transfer found in?

Answer 57

neisserria bacillus streptococcus haemophillus

Question 58

what do the bacteria develop during natural transformation of horizontal gene transfer and when does this happen?

Answer 58

develop T6SS when in competition for food, water etc

Question 59

what do certain species in vibrio use T6SS for in regards to natural transformation of horizontal gene transfer?

Answer 59

use it to kill cells around it and then take up their DNA | use it as a survival mechanism

Question 60

what mediates natural transformation in horizontal gene transfer?

Answer 60

competence proteins

Question 61

what is a competent bacteria?

Answer 61

bacteria that can take up DNA

Question 62

what does the secretin do in competence proteins in natrual transformation of horizontal gene transfer?

Answer 62

forms a ring in outer membrane that is part of protein secretion system pairs with something involved in protein synthesis that will pull in DNA

Question 63

what is the ring in the outer membrane formed by secretin normally involved in?

Answer 63

extrusion of material

Question 64

what is conjugation with regards to antibiotic resistant gene transfer?

Answer 64

mechanisms of transferring antibiotic resistant genes from one cell to another via horizontal gene transfer

Question 65

what type of replicate are involved in conjugation of horizontal gene transfer?

Answer 65

chromosome replicates only even though plasmids can integrate into the chromosome and replicate

Question 66

what does transduction use during horizontal gene transfer?

Answer 66

bacteriophage

Question 67

how are bacteriophages used in gene transfer?

Answer 67

go into cell and attack it inject their DNA into host's DNA to hijack the host phage DNA integrates into host chromosome/plasmid phage particles released from bacteria package DNA from host

Question 68

name the gene for conjugation and efflux pumps

Answer 68

F factor

Question 69

what is the F factor?

Answer 69

gene for conjugation and efflux pumps | fertility factor: origin of transfer

Question 70

what type of enzymes are antibiotic degrading enzymes?

Answer 70

beta lactamases

Question 71

where can you find efflux pumps?

Answer 71

inner and outer membrane

Question 72

what can beta lactamases modify?

Answer 72

their own target, different target or can break target down

Question 73

what is the consequence of altering the permeability of the membrane?

Answer 73

prevents things entering the cell