Antibiotics in the Food Supply

Question 1

What are the main applications of antimicrobials? Of these, which is the main use in Canada?

Answer 1

Agriculture, human medicine, food processing

agriculture uses 80% of antibiotics in Canada!

Question 2

What is “AMR?”

Answer 2

Antimicrobial resistance

decreased susceptibility of multiple microbes to a broad spectrum of single/multiple antibiotics

Question 3

What was the earliest type of antibiotics, and when was this discovered?

Answer 3

Sulfonamides (1930s)

Question 4

what are the latest type of antibiotics?

Answer 4

Teixobactin (2015)

Question 5

Name the main types of antibiotics in the 1940s:

Answer 5

aminoglycosides

beta-lactams

Question 6

Name the main antibiotics in the 1950s:

Answer 6

chloroamphenicol
tetracycline
glycopeptides
macrolides

Question 7

Name the main antibiotics in the 1960s:

Answer 7

streptogramins
quinolones
lincosamides

Question 8

Name an antibiotic from the 1970s:

Answer 8

Trimethoprim

Question 9

Name the antibiotics from the 2000s:

Answer 9

Cycliclipopeptides

oxazolidinones

Question 10

How can agricultural use of antibiotics affect human health?

Answer 10

use in animals -> selects for presence of ARGs (antibiotic resistance genes) and ARBs (antibiotics resistant bacteria)

manure -> environment (gain more ARG and ARB) -> vegetables -> consumed
(genes for resistance have entered body)

Question 11

True/False: antibiotics used for agriculture are different from those used for human medicine

Answer 11

False; same compounds

*except chloramphenicol (only human)

Question 12

What are the mechanisms behind antibiotics?

Answer 12

inhibit protein synth (aminoglycosides, chloroamphenicol, macrolides, tetracyclines)
inhibit cell wall synth (beta-lactams, polypeptides)
inhibit DNA synth (fluoroquinones)
inhibit folic acid synth (sulfonamides)

Question 13

The main purposes of antibiotics in agriculture:

Answer 13

prevent disease
treat disease
growth promotion

Question 14

antibiotics can be classified as ___ or ____. Describe each category.

Answer 14

bacteriocidal: (kills) - target key structures (cell wall, DNA)

Bacteriostatic: (inhibit growth) - target nonessential process (protein synth)

Question 15

Give examples of bacteriocidal vs bacteriostatic antibiotics:

Answer 15

bacteriocidal: b-lactams, aminoglycosides, quinolones
bacteriostatic: macrolides, telithromycin, sulfonamides, tetracycline

Question 16

True/False: the EU bans the use of antibiotics for agriculture

Answer 16

False; banned for GROWTH PROMOTION (can still use therapeutically)

Question 17

Did the Denmark ban on antibiotics in agriculture have positive outcomes?

Answer 17

Human health: no, incidence of Salmonella and Campylobacter infections stayed the same

But: reduced numbers of virginiamycin-resistant enterococcus in chicken

Question 18

In ____ farming, there are no antimicrobials used. What outcomes does this have?

Answer 18

organic

higher prevalence of salmonella, toxoplasma, campylobacter

Question 19

True/False: antibiotics are also used on plants

Answer 19

True (sprayed) - but difficult to know numbers (not kept track of)

Question 20

What are common antibiotics used on plants?

Answer 20

oxytetracycline, streptomycin

Question 21

What antibiotics are used in aquaculture?

Answer 21

sulfadimethoxine, ormetoprim, sulfamerizine, oxytetracycline

Question 22

What is an issue concerning antibiotics with imported food?

Answer 22

other countries have different regulations; imported food may contain antibiotic residues

Question 23

What evidence suggests that antibiotics in the food chain can lead to AMR infections in humans?

Answer 23

AMR Foodbourne pathogens are common

AMR in commensal bacteria on food is very common

AMR genepool in food is high

humans continuously exposed to AMR genes through food chain

Question 24

What evidence suggests that antibiotics in the food chain DO NOT lead to AMR infections in humans?

Answer 24

actual # of pathogens in food is small

actual # of AMR pathogens is very, very small

No evidence that genes actually move to organisms in GI tract

Question 25

How do bacteria develop/transmit AMR?

Answer 25

mutated genes (error in DNA synth, induced by mutagens, or incorrect repair) - occurs spontaneously at 10^-6 to 10^-10 bp/generation passed on VERTICALLY (mother-daughter), or HORIZONTALLY (gene transmission)

Question 26

What mechanism spreads AMR very rapidly? How does it happen?

Answer 26

Horizontal gene transfer (HGT) mobile genetic elements (plasmids, transposons, integrons) -> transfer by conjugation, transformation, transdution

Question 27

True/False: HGT is limited to within a species

Answer 27

False | can spread across species, genera, and entire ecosystems

Question 28

What are the mechanisms of AMR? Are they specific or general?

Answer 28

``` export (specific or nonspecific) destruction (specific or general) Modification (specific) Altered receptors (specific) membrane composition (general) ```

Question 29

What is an old antibiotic not commonly used, and why has it come back into prevalence?

Answer 29

Colistin (polymyxin E) - not used due to kidney toxicity increase in AMR -> use as last-resort in multi-drug resistant Pseudomonas aeruginosa, K. pneumoniae, Acinetobacter

Question 30

What is the significance of the mcr-1 gene?

Answer 30

discovered in E. coli from pig (China) - gives plasmid-mediated resistance to colistin (last-resort antibiotic) has been found in E. coli, Salmonella, K. pneumonia, enterobacter, in 30 countries!

Question 31

What methods are used to detect AMR?

Answer 31

Disk diffusion MIC test strips Sensititre MIC plate Gene testing

Question 32

Describe the Kirby-Bauer test:

Answer 32

place antibiotic infused disks on agar inoculated with lawn of bacteria -> incubate -> observe for zone of inhibition -> measure and compare to database of zone standards (susceptible, mod. susceptible, resistant)

Question 33

What factors affect the zone size in the Kirby-Bauer test?

Answer 33

effectiveness of antibiotic | diffusion rate of antibiotic

Question 34

How do MIC test strips work?

Answer 34

strip infused with antibiotics (in a concentration gradient) -> place on bacteria lawn on agar -> observe for growth (elliptical shape; as conc decreases along strip, bacteria will grow closer) strip contains markings indicating conc., MIC is concentration at which bacteria can touch strip

Question 35

What are sensititre MIC plates?

Answer 35

96 well plates, different antibiotics per row Add dilutions of bacteria + usable carbon source in each well Incubate -> measure with plate-reader to determine MIC

Question 36

What is an important tool to help with genetic methods for testing AMR?

Answer 36

Comprehansive Antibiotic Resistance Database | take whole genome sequence, compare