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Veterinary Bacteriology & Mycology > Antimicrobial Resistance (AMR) > Flashcards

Antimicrobial Resistance (AMR) Flashcards

1
Q

What are the 3 major purposes of antimicrobial prescription? What practice is no longer done?

A
  1. THERAPEUTICS: treating a sick individual
  2. METAPHYLCTICS: one patient in a herd is sick and the whole herd is treated to control spread
  3. PROPHYLACTICS: prescribing a drug to the most vulnerable individuals in a herd to avoid disease

GROWTH PROMOTION: adding antibiotics to feed was proven to increase weight gain (AMR!)

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2
Q

How do AMR bacteria spread to an entire population?

A
  • unregulated use of antimicrobials in humans and animals can lead to the growth of AMR bacteria in the normal (gut) microflora
  • farms use of feces or infected water for fertilizer passes on AMR bacteria onto food
  • food is eaten by an entire population, passing on the AMR to the public
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3
Q

How do bacteria switch from planktonic and structured communities?

A
  • bacteria remain in the movable planktonic life stage until the environmental conditions are unfavorable
  • planktonic bacteria use flagella to attach to a stable surface and become immobile/sessile
  • as the bacteria continue to reproduce, they form a protective biofilm
  • as conditions become more favorable bacteria begin to disperse from the biofilm structure and enter back into the planktonic life stage
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4
Q

What 5 groups can bacteria be classified into based on their cell wall architecture?

A
  1. GRAM POSITIVE: several layers including a thick peptidoglycan layer with lipo/teichoic acid
  2. GRAM NEGATIVE: outer membrane made up of proteins and lipopolysaccharide and a thin layer of peptidoglycan
  3. MYCOBACTERIUM: peptidoglycan layer covered with mycolic acid (wax or lipids)
  4. CHLAMYDIA: cell wall lacking in peptidoglycan, with an outer membrane containing proteins and lipopolysaccharides
  5. MYCOPLASMA: no cell wall, sterols on cell membrane
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5
Q

Why are Mycoplasma clinically important?

A

since they have no cell wall, they are unable to be Gram-stained and are resistant to any antimicrobials that act on the cell wall

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6
Q

What are 4 structures on the bacterium influence their resistance?

A
  1. CAPSULE - protection
  2. PORINS - allow passage of nutrients and antimicrobials
  3. PILI - mating and conjugation
  4. FLAGELLA - movement, chemotaxis
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7
Q

What enzyme is responsible for creating the cell wall in bacteria? What drugs tend to target this enzyme?

A

penicillin-binding proteins (peptidases)

beta-lactams

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8
Q

What 3 enzymes are responsible for bacterial transcription? What proteins are important for translation?

A
  1. DNA topoisomerase - cleaves DNA strands in order to provide torsional-stress relief or to untangle replicating DNA
  2. DNA gyrase - catalyzes the ATP-dependent negative super-coiling of double-stranded closed-circular DNA
  3. RNA polymerase - creates mRNA from a template strand of DNA

30S and 50S ribosomes

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9
Q

What are the main 6 mechanisms of action of antimicrobials?

A
  1. block cell wall synthesis
  2. block metabolism and folic acid synthesis
  3. block 30S ribosomes used for protein synthesis
  4. block 50S ribosomes used for protein synthesis
  5. block RNA polymerase used for RNA synthesis
  6. block DNA gyrase/topoisomerase used for DNA synthesis
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10
Q

What are the 4 major antimicrobial resistance mechanisms employed by bacteria?

A
  1. reduced permeability by constricting porins - keeps antimicrobials outside the cell
  2. efflux pumping - “vomiting” the antimicrobial out of the cell once it enters
  3. drug inactivation - use enzymes to “cut up” drug molecules and make them ineffective
  4. target site change, modification, or protection - move, alter, protect receptors that the antimicrobials would bind to
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11
Q

How does biofilm formation act a mechanism for antimicrobial resistance?

A
  • induced extracellular polymer matrix production as a barrier
  • thick, impenetrable communities as a barrier
  • dormant spore-like cell in the center for persistence

(overall, uptake is limited)

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12
Q

What influences the best antimicrobial resistance mechanism?

A

the type of antimicrobial being used

LIMITED ENTRY BY CONSTRICTED PORINS works best against aminoglycosides, beta-lactams, chloramphenicol, quinolones, tetracycline, and rifamycin
EFFLUX PUMPING works best against tetracycline
ENZYME BREAKDOWN works best on beta-lactams and aminoglycosides
CHANGING DRUG TARGET SITES works best on chloramphenicol, microlides, quinolones, and rifamycin

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13
Q

How do antimicrobial resistance to beta-lactams vary between Gram positive and negative bacteria?

A

G+ - change in binding site of beta-lactams
G- - beta-lactamase production

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14
Q

What are the main 2 origin of antimicrobial resistance in the ecosystem?

A
  1. HORIZONTAL GENE TRANSFER: acquired resistance from free DNA in nature (transformation), plasmids (conjugation), and bacteriophages (transduction)
  2. VERTICAL GENETRANSFER: intrinsic/innate passed from parent cells
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15
Q

What 3 entities create the standardized guidelines for antimicrobial resistance by phenotypic methods?

A
  1. Clinical and Laboratory Standards Institute (CLSI) - USA
  2. European Committee on Antimicrobial Susceptibility Testing (EUCAST)
  3. International Standardization Organization (ISO)
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16
Q

What are the 2 broad categories of bacterial species targeted for antimicrobial resistance testing?

A
  1. grow fast within 24 hours - Enterobacteriaceae (G-), other G- bacilli, non-fastidious G+
  2. don’t grow fast and require special media enrichment and incubation - fastidious organisms, bioterrorism agents, anaerobic microbes
17
Q

What 6 bacterial species are the top antimicrobial bacteria globally?

A
  1. Enterococcus
  2. S. aureus
  3. K. pneumoniae
  4. A. baumannii
  5. P. aeruginosa
  6. Enterobacter
  • fast growing, more time to adapt
18
Q

What 4 media work best for isolating antimicrobial resistant bacteria from sick animals? What species grows best in each?

A
  1. Mannitol salt agar - Staphylococcus
  2. Edward media - Streptococcus
  3. Kenner-fecal agar media - Enterococcus
  4. MacConkey agar - Enterobacteriaceae
19
Q

What broth and media work best for culturing aerobic and anaerobic bacteria for antimicrobial resistance? What is a typical addition to provide nutrients?

A

AEROBIC: cation-adjusted Mueller-Hinton Broth and cation-adjusted Mueller-Hinton agar
ANAEROBIC: Brucella broth and Brucella blood agar

3-5% lysed horse blood

20
Q

How can antimicrobial resistance be detected directly? Indirectly?

A

DIRECT: addition of antimicrobial into broth, agar, or other culture media housing the bacteria
INDIRECT: placing a filter paper soaked with antimicrobial on spread-plated bacteria on agar

21
Q

What kind of antimicrobial resistance detection method is disc diffusion? What are the 6 steps?

A

INDIRECT

  1. dilute various antibiotics at a given concentration as per CLSI guidelines in test tubes
  2. immerse filter paper in each test tube containing the diluted concentration for various drugs
  3. cut immersed filter paper to a diameter of 6 mm
  4. place the disc on an agar plate that is already swabbed with bacteria
  5. incubate overnight
  6. measure diamter of inhibition zone
22
Q

How are the results of disc diffusion read?

A

the larger the inhibition zone, the more effective the antimicrobial is, meaning the bacteria is less resistant to the specific antimicrobial

23
Q

What kind of antimicrobial resistance detection method is the E test? What are the 5 steps?

A

INDIRECT

  1. make a two-fold serial dilution of antibiotics in test tubes
  2. immerse filter paper in each test tube containing the various serial dilutions
  3. cut immersed filter paper snd past them on to a strip of paper
  4. place the strip on an agar plate that has already been swabbed by bacteria
  5. determine the last dilution that inhibits group
24
Q

How are the results of the E test read?

A

the minimum inhibitory concentration can be determined by observing the last place along the strip of paper where the inhibition eclipse ends

25
Q

What kind of antimicrobial resistance detection method is agar dilution? How can minimum inhibitory concentration be obtained?

A

DIRECT

an antimicrobial is added to different agar plates in descending concentrations; once bacteria starts growing, the MIC is the concentration directly before

26
Q

What kind of antimicrobial resistance detection method is macrodilution? What are the 4 steps?

A

DIRECT

  1. load various antimicrobial agents diluted serially in 22-fold concentrations into test tubes
  2. inoculate bacteria into each well
  3. incubate samples
  4. determine last dilution that inhibited growth based on the presence of a cloudy broth

(8 = MIC)

27
Q

What kind of antimicrobial resistance detection method is microdilution? What are the 3 steps?

A

DIRECT

  1. load various antimicrobial agents diluted serially in an increasing 2-fold concentration into a 96-well plate
  2. inoculate bacteria into each well
  3. determine the last dilution that inhibited growth based on the presence of bacterial growth seen as a dot in the plate
28
Q

What part of the usual antimicrobial screening process is not recommended for anaerobic bacteria?

A

disc diffusion —> highly error prone

29
Q

What 3 types of quality control reference bacteria should be used during antimicrobial resistance screening should be used?

A
  1. during survey of beta-lactamases-producing bacteria
  2. for non-fastidious bacteria for agar/broth dilution (MIC)
  3. for testing bacteria of bioterrorism
30
Q

In what 2 instances are antimicrobial tests invalidated?

A
  1. there is no visable and pure growth of the quality control strains
  2. their cut-off value inhibition zone by disc or MIC is not within their range defined by CLSI, EUCAST, or ISO
31
Q

Where do the cut-off MIC values of most antimicrobials fall?

A

0.5-64 μg/mL

32
Q

Why should you only test against a few antimicrobials used in your state or farm/clinic?

A

impossible to do testing on all antimicrobials

33
Q

What are the main 3 ways that the spreading of antimicrobial resistance on a farm and across the nation/world?

A
  1. surveillance
  2. educating to reduce unnecessary drug use and evaluate if the drug is the best
  3. find alternatives to antimicrobials

Veterinary Bacteriology & Mycology (47 decks)

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