the importance of cell biology & AMR for vet med

Question 1

define infection

Answer 1

the invasion and/or colonisation by and subsequent multiplication of pathogenic microorganisms in a bodily part or tissue
- can produce subsequent tissue injury and progression to overt disease through a variety of cellular or toxic mechanisms

Question 2

what is the daily impact of microbiology for veterinarian

Answer 2

• revention of infectious disease (vaccines, probiotics, owner education)
• treatment of infectious disease ( diarrhea, skin infections, bite wounds - do they need antibiotics?)
• sterilisation of instruments
• biosecurity
• epidemiology
• antimicrobial stewardship

Question 3

describe the hierarchy of antibiotics - should we be routinely using critically important human antibiotics in animals

Answer 3

to be able to assess antibiotic usage we need to understand which antibiotics are seen as critically important in human medicine and hence should only ever be a last resort in animal medicine if used at all

Question 4

describe how microbes can cause disease

Answer 4

• infection (colonise or invade tissues)
• produce toxins and poision the host (often associated with infection but sometimes just ingestion of pre-formed toxin)
• cause a host response (allergic reaction)
• combination of above

Question 5

what 3 words can be used to classify the prevalence of pathogens

Answer 5

• sporadic
• enzootic (regularly affecting animals in a particula district or at a particular season)
• endemic ( term that relates to humans but also used in vet med - regularly found among particular group of people or in a certain area)

Question 6

define latency

Answer 6

the pathogen goes inert in the animals. reactivation may occur if the pathogen is switched back on (i.e herpes)

Question 7

define carriage

Answer 7

the animal tolerates the pathogen without disease and is capable of transmitting the organism (host can control pathogen but not clear it or causes disease in one species but is carried in another)

Question 8

define reservoir of infection

Answer 8

any animal, human, environment in which an infectious agent normally lives and multiplies

Question 9

what is an acute infection

Answer 9

pathogen cleared shortly after inefection

Question 10

what is a chronic infection

Answer 10

pathogen is detectable for lifetime of host
- immune response takes effect (or treatment) and reduces but does not clear infection)

Question 11

what is a latent infection

Answer 11

infectious agent disappears (indetectable) but can be reactivated by a number of factors.

Question 12

what features do antibiotics use as points of attack on bacteria

Answer 12

• cell wall synthesis
• cell membrane structure and function
• translation/protein synthesis
• transcription
• DNA synthesis and replication

Question 13

how do antibiotics target the cell wall and give examples of antibiotics that do this

Answer 13

a cell wall is a good target because it contains components unique to bacteria (target peptidoglycan instead of body cell)
- beta lactams inhibit transpeptidation by binding to penicillin binding proteins on maturing peptidoglycan strands (cause decrease in peptidoglycan)
- promote autolysin activity (BACTERICIDAL)

EXAMPLES:
- penicillin (beta lactam)
- ampicillin (beta lactam)
- vancomycin (glycopeptide)

Question 14

describe how antibiotics target the cell membrane. give examples of antibiotics that do this
what are the disadvantages of these antibiotics?

Answer 14

cell membrane is a good target becuase distrupted functional integrity of cell membrane leads to escape of macromolecules and ions from the bacterial cell => bactericidal
disadvantages: high level of similarity between bacterial and animal cell membranes => more toxic to animal cells and often last resort

examples:
polymixin and colistin
- both target the outer membrane of Gram negative bacteria

Question 15

why is nucleic acid synthesis a good target for antibiotics, how does it work and give examples of antibiotics that target this

Answer 15

organisation and replication of bacterial DNA and RNA is different to eukaryotics - bacteriostatic (dont kill but prevent from growing/replicating so immune system can take over)
Examples:
Quinolones and Novobiocin both act on DNA gyrase which separates DNA strands during bacterial replication. quinolones interfere with changes in DNA suoercoiling by binding to topoisomerase II or topoisomerase IV
rifampin interferes with DNA-dependant RNA polymerase activity and prevents RNA synthesis

Question 16

what is protein synthesis a good target for antibiotics, how do they work (give examples of antibiotics)

Answer 16

there are differences in ribosome structure between eukaryotes and prokaryotes - bacteriostatic (doesnt kill, prevents growth and replication so immune system can take over)

examples;
tetracycline blocks tRNA molecule attachment on 30 s subunit
erythromycin and chloramphenicol both block 50 s subunit activity preventing growth of polypeptide chain
aminoglycosides bind to 30 s subunit and inhibit proofreading and initiation (ex. spectinomycin, streptomycin, neomycin)

Question 17

describe the 4 antibiotic resistance mechanisms

Answer 17

1. enzymes that degrade or inactivate antibiotic (beta lactamases that degrade penicillin/ampicillin)
2. alteration of target site (altered ribosome structure)
3. elimination of antibiotic from bacterial cell (efflux pump)
4. bacterial cell impenetrable for antibiotic (gram negative cell wall inpenetrable for penicillin)

Question 18

how does antibiotic use lead to increased antibiotic resistance

Answer 18

antibiotics are an environmental stress and cause selection pressure, leading to only resistant bacteria surviving and subsequently replicating, resulting in the next generation of bacteria being highly resistant as only the strongest survived to divide

Question 19

how can we uphold antimicrobial stewardship

Answer 19

• only use if necessary
• evaluate risk of selecting multidrug resistance
• avoid last resort/critically important antibiotics for human medicine
• prevention rather than cure (herd health)
• “use as little as possible and as much as necessary”