Antibiotics in the Food Supply Flashcards
What are the main applications of antimicrobials? Of these, which is the main use in Canada?
Agriculture, human medicine, food processing
agriculture uses 80% of antibiotics in Canada!
What is “AMR?”
Antimicrobial resistance
decreased susceptibility of multiple microbes to a broad spectrum of single/multiple antibiotics
What was the earliest type of antibiotics, and when was this discovered?
Sulfonamides (1930s)
what are the latest type of antibiotics?
Teixobactin (2015)
Name the main types of antibiotics in the 1940s:
aminoglycosides
beta-lactams
Name the main antibiotics in the 1950s:
chloroamphenicol
tetracycline
glycopeptides
macrolides
Name the main antibiotics in the 1960s:
streptogramins
quinolones
lincosamides
Name an antibiotic from the 1970s:
Trimethoprim
Name the antibiotics from the 2000s:
Cycliclipopeptides
oxazolidinones
How can agricultural use of antibiotics affect human health?
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)
True/False: antibiotics used for agriculture are different from those used for human medicine
False; same compounds
*except chloramphenicol (only human)
What are the mechanisms behind antibiotics?
inhibit protein synth (aminoglycosides, chloroamphenicol, macrolides, tetracyclines)
inhibit cell wall synth (beta-lactams, polypeptides)
inhibit DNA synth (fluoroquinones)
inhibit folic acid synth (sulfonamides)
The main purposes of antibiotics in agriculture:
prevent disease
treat disease
growth promotion
antibiotics can be classified as ___ or ____. Describe each category.
bacteriocidal: (kills) - target key structures (cell wall, DNA)
Bacteriostatic: (inhibit growth) - target nonessential process (protein synth)
Give examples of bacteriocidal vs bacteriostatic antibiotics:
bacteriocidal: b-lactams, aminoglycosides, quinolones
bacteriostatic: macrolides, telithromycin, sulfonamides, tetracycline
True/False: the EU bans the use of antibiotics for agriculture
False; banned for GROWTH PROMOTION (can still use therapeutically)
Did the Denmark ban on antibiotics in agriculture have positive outcomes?
Human health: no, incidence of Salmonella and Campylobacter infections stayed the same
But: reduced numbers of virginiamycin-resistant enterococcus in chicken
In ____ farming, there are no antimicrobials used. What outcomes does this have?
organic
higher prevalence of salmonella, toxoplasma, campylobacter
True/False: antibiotics are also used on plants
True (sprayed) - but difficult to know numbers (not kept track of)
What are common antibiotics used on plants?
oxytetracycline, streptomycin
What antibiotics are used in aquaculture?
sulfadimethoxine, ormetoprim, sulfamerizine, oxytetracycline
What is an issue concerning antibiotics with imported food?
other countries have different regulations; imported food may contain antibiotic residues
What evidence suggests that antibiotics in the food chain can lead to AMR infections in humans?
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
What evidence suggests that antibiotics in the food chain DO NOT lead to AMR infections in humans?
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
How do bacteria develop/transmit AMR?
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)
What mechanism spreads AMR very rapidly? How does it happen?
Horizontal gene transfer (HGT)
mobile genetic elements (plasmids, transposons, integrons)
-> transfer by conjugation, transformation, transdution
True/False: HGT is limited to within a species
False
can spread across species, genera, and entire ecosystems
What are the mechanisms of AMR? Are they specific or general?
export (specific or nonspecific) destruction (specific or general) Modification (specific) Altered receptors (specific) membrane composition (general)
What is an old antibiotic not commonly used, and why has it come back into prevalence?
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
What is the significance of the mcr-1 gene?
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!
What methods are used to detect AMR?
Disk diffusion
MIC test strips
Sensititre MIC plate
Gene testing
Describe the Kirby-Bauer test:
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)
What factors affect the zone size in the Kirby-Bauer test?
effectiveness of antibiotic
diffusion rate of antibiotic
How do MIC test strips work?
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
What are sensititre MIC plates?
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
What is an important tool to help with genetic methods for testing AMR?
Comprehansive Antibiotic Resistance Database
take whole genome sequence, compare
