Antibiotic Resistance

Question 1

Is antibiotic resistance a new phenomenon?

Answer 1

•no it has been around for likely the whole of bacteria existence

Question 2

Can antibiotic resistance occur in the wild?

Answer 2

•yes
•bacteria and other pathogens are always fighting eachother for survival

Question 3

What 3 mechanisms can cause bacterial resistance

Answer 3

•inherent resistance
•mutation
•gene transfer

Question 4

What is inherent resistance

Answer 4

Bacteria know to be naturally resistant to certain antibiotics

Question 5

How does inherent resistance occur

Answer 5

•from year of evolution and possible interactions with that specific antibiotic in the wild long agi

Question 6

Example of inherently resistant organism

Answer 6

•pseudomonas aeruginosa
•inherent resistance to penicillin

Question 7

Mechanism of an advantageous genetic mutation

Answer 7

•non resistant bacteria exist
•multiply (x billion) - some bacteria mutate
•presence of drugs kill usual bacteria but not those with the mutation
•drug resistant bacteria thrive + multiply

Question 8

What causes mutations in bacteria

Answer 8

•random event
•presence of antibiotic does NOT cause mutations
•but it does provide the bacteria with knowledge of what is advantageous

Question 9

Types of gene transfer

Answer 9

•transformation
•transduction
•conjugation

Question 10

Bacterial transformation mechanism

Answer 10

•bacteria die and releases content into surroundings
•dna is taken up by other bacteria cells
•could contains good gene!?

Question 11

Bacterial transduction mechanism

Answer 11

•Bacteriaphage infects bacteria cell
•uptake of bacteria DNA
•release of phage (cell death)
•same phage infects different cell
•releases DNA from other cell into new cell

Question 12

Mechanism of bacterial conjugation

Answer 12

•transfer of plasmid from one living cell to another
•plasmid can contain multiple resistance genes

Question 13

Can conjugation happen between different types of bacteria

Answer 13

•yes
•bacteria of the same species can conjugate
•example E. coli and klebsiella (both enterobacteria)

Question 14

What bacteria love conjugation

Answer 14

•E Coli

Question 15

What bacteria love transformation

Answer 15

•streptococcus

Question 16

5 mechanisms antibiotic resistance

Answer 16

1.inactivation of antibiotic
2.decreased cell permeability
3.efflux pumps
4.modify antibiotic target (receptor)
5.alter metabolic pathway

Question 17

Altering metabolic pathway mechanism

Answer 17

•some antibiotics inhibit receptors the bacteria need
•increase the number of those receptors so they can still use them
•antibiotics function becomes useless

Question 18

What is the minimal inhibitory concentration

Answer 18

Lowest conc of antibiotic required to stop visible growth overnight

Question 19

How can the minimum inhibitory concentration tell us if a bacteria is resistant

Answer 19

•if the found value of a bacteria MIC is higher than the breakpoint the bacteria is resistant
•if it is the same or lower it is susceptible

Question 20

What is the breakpoint

Answer 20

•value of MIC that is decided to be the standard value for that organism
•allows us to see if other organisms go above that so we know it’s resistant

Question 21

2 types of susceptibility testing methods

Answer 21

•phenotypic
•genotypic

Question 22

Phenotypic testing methods for antibiotic susceptibility

Answer 22

•minimal inhibitory conc
•disc diffusion tests

Question 23

What are the types of minimum inhibitory concentration tests

Answer 23

•broth dilutions
•manual/automated
•Etests

Question 24

What are the genotypic methods of susceptibility testing

Answer 24

•PCR
•whole genome sequencing
•to see presence of known resistance genes

Question 25

What is an Etest strip

Answer 25

•strip containing predefined gradient of antibiotic

Question 26

What is the Etest strip used for

Answer 26

Determining MIC value using agar

Question 27

Etest machinism

Answer 27

•agar plate fully inoculated by testing bacteria •strip is placed in middle •antibiotic migrates to surrounding area and will cause an area where no bacteria grows

Question 28

How to read an Etest

Answer 28

•an area of no growth with surround part of the strip •the MIC value is where the bacteria touches the strip for the last time -(where growth zone intersects the strip)

Question 29

Does the disc test show MIC value

Answer 29

•no •only wether the bacteria’s response to antibiotic is more resistant than the breaking point value given

Question 30

Does the breaking point only refer to MIC values

Answer 30

•no •a breaking point can be associated with any testing method •examples diameter of zone of inhibition in disc testing

Question 31

What is the point of disc tests

Answer 31

•to see how bacteria reacts to different concentrations of antibiotics •compare results to breaking point value to determine whether it is resistant to

Question 32

Disc test mechanism

Answer 32

•up to 6 paper disc containing various antibiotic conc are placed on agar inoculated by bacteria •zone of inhibition form around conc the bacteria is susceptible to •results can be compared between strains to test resistance

Question 33

What turbidity are bacterial cultures suspended in for Disc testing

Answer 33

•0.5 McFarland turbidity =150 million cells per mL

Question 34

What is measured during disc testing

Answer 34

•diameter of the zone of inhibition

Question 35

What does horizontal gene transfer mean

Answer 35

•movement of genetic material between organisms that isn’t parent to offspring

Question 36

What does vertical gene transfer mean

Answer 36

Movement of genetic material from parent to offspring

Question 37

Which of these methods tells you an MIC ; disc test, Etest, whole genome sequencing, PCR

Answer 37

Etest

Question 38

what tests can be used to determine the MIC

Answer 38

-Etest -broth dilutions

Question 39

Why would u use Etest over manual broth dilutions

Answer 39

-quicker -broth dilution labour intensive and slow

Question 40

why would u use broth dilutions over Etest

Answer 40

-Etest is expensive and uses more plates

Question 41

how can broth dilutions be quicker

Answer 41

-use automated machines/systems

Question 42

advantages of molecular susceptibility testing

Answer 42

-PCR rapid (no culturing needed) -helpful for slow, hazardous or difficult cultures

Question 43

what is a bacteria that is hard, dangerous or slow to culture

Answer 43

mycobacterium tuberculosis

Question 44

Disadvantages of molecular susceptibility tests

Answer 44

-genes may not be expressed -need to know what genes to look for (some may be missed) -new mutations constantly -expensive -many genes possible per antibiotic (1 PCR per genes)

Question 45

when do clinical labs use disc testing

Answer 45

-most often -practical -low cost -tells us direct if susceptible or not

Question 46

when do clinical labs use Etests

Answer 46

-after disc testing if MIC needed

Question 47

when is molecular testing used in labs

Answer 47

-after disc testing in certain situations

Question 48

what do clinical labs mainly use

Answer 48

-disc testing -automated systems (broth dilutions etc)