17 - Antibiotics in the food supply Flashcards
where are antimicrobials applied?
- human medicine
- agricultural production
- food processing
where are most antimicrobials used?
- agriculture (80% in canada)
antibiotics used in food-producing animals help select for the presence of _____ and _____
antibiotic resistance genes (ARGs); antibiotic resistant bacteria (ARBs)
when ARGs and ARBs mix with environmental ARGs and ARBs, what can potentially happen?
can select to increase antimicrobial resistance
expand AMR
antimicrobial resistance
describe AMR
decreased susceptibility of microbes to a broad spectrum of single or multiple antibiotics
antibiotics can be classified into what 2 categories?
bactericidal, bacteriostatic
define bactericidal
- kills bacteria
- targets cell structures (biosynth of cell wall or DNA)
what are some examples of bactericidal antibiotics?
- B-lactam family
- aminoglycosides
- quinolones
define bacteriostatic
- inhibit further growth
- target protein synth
what are some examples of bacteriostatic antibiotics?
- macrolides
- telithromycin
- sulfonamides
- tetracycline
what’s the purpose of antimicrobials in food production?
- treat infected animals
- prevent onset of infection
- promote growth
what interesting thing did Denmark do in Nahyeon’s birth year? (1997)
banned total use of antibiotics (saw desirable results for enterococcus faecium resistance)
true or false: organic products can use antimircobials
false
is prevalence of pathogenic bacteria higher in organic products?
yes, for salmonella, toxoplasma, and campylobacter
what antimicrobials are used on plants?
- oxytetracycline
- streptomycin
what antimicrobials are used for aquaculture in the US?
- sulfadimethoxine
- ormetoprim
- sulfamerazine
- oxytetracycline
true or false: foreign agricultural commodities are tightly monitored
false - apparently not. use of imported seafood is a common reason for seizure
can the food chain affect AMR infections in humans?
there’s 2 schools of thought:
- yes: AMR foodborne pathogens are common; AMR genepool in food must be very high; it’s very likely humans are being continuously exposed to AMR genes through food chain
- no: the actual number of pathogens in foods is very small; the actual number of AMR pathogens in food is even smaller; can ARGs really move to organisms in the GI tract?
how can ARGs be transmitted?
vertical or horizontal gene transmission
mutated and acquired AR genes are spread via….
vertical transmission to offspring
what causes mutations?
errors in DNA synthesis, chemical change induced by mutagens, or incorrect repair of damage induced single strand breaks
antibiotic usage appears to be (increasing/decreasing) rate of mutation overall
increasing
what is vertical gene transfer?
transfer of genetic information, including any genetic mutations, from a parent to its offspring.
what is horizontal gene transfer?
spreads genes using mobile genetic elements (plasmids, transposons, integrons)
what processes can cause HGT?
- conjugation (direct contact)
- transformation (uptake DNA from environment)
- transduction (bacteria to phage to new bacteria)
vertical transmission is relatively (rapid/slow)
slow - mutations must accumulate & cells must divide
HGT is (rapid/slow)
rapid
true or false: HGT can cause genes to be spread across species
true
which transfer (vertical or horizontal) plays a larger role in AMR?
horizontal
what are the mechanisms of AMR?
- export
- destruction
- modification
- altered receptors
- membrane composition
which AMR mechanisms are specific?
- export (sometimes)
- destruction (sometimes)
- modification
- altered receptors
what is Colistin?
- old antibiotic not used in humans bc it’s toxic to the kidney
- is used as a last-resort for multi-drug resistant pseudomonas aeruginosa, klebsiella pneumoniae, and acinetobacter
what gene is colistin resistant? what kind of gene transfer can it undergo?
MCR-1; horizontal
what methods are there for detecting AMR?
- disk diffusion method
- Minimal Inhibitory concentration (MIC), strips and plates
- genome sequencing
describe the disk diffusion method
uses antibiotic discs placed on agar; plate incubates; sensitive bacteria show a zone of inhibition
what factors influence the size of the zone of inhibition?
- effectiveness of the antibiotic
- rate of diffusion of antibiotic in the agar
- molecular configuration of the antibiotic
what do you do once you have the zone of inhibition measured?
consult a database to determine the bacteria’s level of antibiotic sensitivity
using the disk diffusion method, bacteria can be concluded to be…..
susceptible, intermediately susceptible, or resistant
what is MIC?
Minimal Inhibitory Concentration; defined as lowest concentration of a drug with no visible growth
how do you use a MIC test strip?
- put strip on agar
- incubate plate
- an ellipse shaped growth inhibition area is manifested
- where ellipse meets the strip, that the MIC
what’s a sensititre mic plate?
- 96-well plates containing lyophilized antibiotics configured to determine the MCI to a variety of antibiotics
- dilutions of bacteria are inoculated into each well
- plates can be inspected visually or with a plate-reader
