antibiotics and antibiotic resistance

Question 1

what are disinfectants?

Answer 1

antimicrobial agents applied to inanimate objects – toxic!

Question 2

what are antiseptics?

Answer 2

antimicrobial agents that are sufficiently nontoxic and can be applied to living tissue

e.g. hand sanitizer

Question 3

what are antibiotics?

Answer 3

antimicrobial agents produced by bacteria and fungi that are exploited by humans

delivered topically (specific area) and internally

they specifically target microbes and can be applied intramuscularly or intravenously

Question 4

what’s the most effective therapeutic agent against bacterial infections?

Answer 4

antibiotics

availability enabled chemotherapy, organ transplantation, invasive surgeries & treatment of
premature infants

Question 5

what are the 2 major problems with developing antibiotics?

Answer 5

bacterial resistance

diminished interest from big pharmaceutical companies to develop new antibiotics (trouble making money)

Question 6

describe misuse of antibiotics

Answer 6

empiric (blinded) use (treating with any antibiotic on hand)
— may only be used if symptoms are severe & diagnosis is too slow

increased use of broad-spectrum agents (kills off other bacteria)

pediatric use for viral infections

do not complete course of treatment (those that survive may be resistant – bacteria remerges, stronger)

antibiotics in animal feeds (growth promotors)

Question 7

how is antibiotic activity measured?

Answer 7

via minimum inhibitory concentration (MIC)

^^ the lowest concentration of agent that inhibits bacterial growth

Question 8

how does one obtain the minimum inhibitory concentration?

Answer 8

series of culture tubes w/ varying concentrations of agent
– check for visible growth

can also use antibiotics strips; faster & multiple
– each strip has a different antibiotic w/ increasing concentration from bottom to
top
– MIC tells tell you antibiotic sensitivity in bacteria & how much you need to kill it

Question 9

how do antibiotics work?

Answer 9

they target essential bacterial components

– such as cell wall synthesis
– protein synthesis
– DNA/RNA synthesis
– folate or folic acid synthesis
—– folic acid is required for nucleotide synthesis (so it’s starving the microbe)
– cell membrane alteration

Question 10

describe beta-lactam antibiotics

Answer 10

contains a beta-lactam ring

inhibits cell wall synthesis

Question 11

what type of antibiotic inhibits cell wall synthesis

Answer 11

beta-lactam antibiotics

Question 12

how do some bacteria counteract penicillin, the antibiotic?

Answer 12

produces beta-lactamase, enzyme that destroys the beta-lactam ring – and as a result, the antibiotic

Question 13

what’s methicillin?

Answer 13

chemically modified penicillin

also contains a beta-lactam ring

can’t be cleaved by beta-lactamases

… but some bacteria can produce a different “penicillin-binding proteins” e.g. PBP2a - encoded by ‘mec’ (methicillin resistance) — helps bacteria fight against antibiotics including methicillin

Question 14

how does penicillin function as an antibiotic?

Answer 14

inhibits cell wall synthesis

it inhibits the penicillin-binding proteins (PBPs) aka transpeptidase in bacteria that help form the cross-links in cell wall – this makes the cell wall toooo weak, causing cell death

Question 15

what is vancomycin?

Answer 15

a glycopeptide antibiotic that inhibits cell wall synthesis in gram+
— vancomycin can’t get across the cell membrane of gram- so doesn’t work there!

often a drug of “last resort”

Question 16

how does vancomycin inhibit cell wall synthesis in gram+ bacteria?

Answer 16

binds the peptide linkage at terminal D-Ala-D-Ala residues & inhibits transpeptidation

resistance genes change these to D-Ala-D-Lac
– vancomycin can no longer bind

resistance is encoded by the van genes

Question 17

what’s antibiotic resistance?

Answer 17

use of antibiotics actively selects for antibiotic resistant bacteria

in many cases, bacteria acquire a new gene (not just a series of single mutations)

antibiotic resistance can increase 1000-fold in a strain

Question 18

what are some bacterial strategies for antibiotic resistance?

Answer 18

prevention of antibiotic entry
— gram- outer membrane & mycobacteria cell envelope block antibiotics from entering cell

antibiotic modification
— beta-lactamase destroy antibiotic

efflux of antibiotic
— bacteria encode efflux pumps that actively pump antibiotic out of cell

alteration of antibiotic target
— PBPs, ribosome modifications (prevents protein synthesis)

bypassing the antibiotic action
— use environmental folic acid (folic acid synthesis inhibitors)

Question 19

describe antibiotic resistance genes

Answer 19

many mechanisms of antibiotic resistance are genetically encoded (e.g. mec, beta-lactamase, efflux
pump)
— can produce very high levels of antibiotic resistance

often encoded on mobile genetic elements (e.g. plasmids)
— allows for horizontal gene transfer → “superbugs”
— can be resistant to 10-15 clinically resistant antibiotics

Question 20

what is horizontal gene transfer?

Answer 20

new genes are acquired from another source, rather than altering gene function via. mutations

Question 21

what are the 3 ways in which horizontal gene transfer can occur?

Answer 21

bacterial transformation
— cell dies & releases DNA; another cell takes up resistant gene
– least common, requires a lot of energy from bacteria

bacterial transduction
— bacteriophage infects bacteria, packages host antibiotic resistant
gene & injects it into a the recipient cell

bacterial conjugation
— plasmids move DNA from one cell to another via pili (VERY EFFICIENT)

Question 22

what’s bacterial transformation?

Answer 22

cell dies & releases DNA; another cell takes up resistant gene

least common, requires a lot of energy from bacteria

Question 23

what’s bacterial transduction?

Answer 23

bacteriophage infects bacteria, packages host antibiotic resistant gene & injects it into a the recipient cell

Question 24

what’s bacterial conjugation?

Answer 24

plasmids move DNA from one cell to another via pili (VERY EFFICIENT)

Question 25

what’s klebsiella pneumoniae? what type of bacteria is it? what does it cause? etc.

Answer 25

a gram- bacterial pathogen

important cause of nosocomial pneumonia (hospital-acquired pneumonia)

produces a capsule
— commonly resistant to multiple antibiotics

Question 26

what’s NDM-1?

Answer 26

New Delhi Metallo-beta-lactamase-1 aka cabarpenemase, an enzyme

its first documented source was Klebsiella pneumoniae

NDM-1 is now widespread in other Gram negatives

= CRE (carbapenem resistant Enterobacteriaceae) is a fairly new problem

Question 27

what are carbapenem antibiotics?

Answer 27

beta-lactamase resistant beta-lactams w/ broad-spectrum activity

– antibiotics for NDM-1 aka carbapenemase which is found in Klebsiella pneumoniae and other gram- bacteria

Question 28

what was the first documented source of NDM-1?

Answer 28

Klebsiella pneumoniae

Question 29

what’s clostridia? what type of bacteria is it? where is it found? what can it cause?

Answer 29

gram+

rod-shaped

endospore formers! (forms endospores)

strict anaerobes (no oxygen for them! or else they die…)
— generally found in soil and intestinal tracts of animals

can cause life threatening diseases mediated by exotoxins

Question 30

where can clostridia be found?

Answer 30

generally found in soil and intestinal tracts of animal

strict anaerobes (no oxygen for them! or else they die…)

Question 31

what does clostridioides difficile (c. diff) cause?

Answer 31

mild to moderate diarrhea

life-threatening pseudomembranous colitis (aka antibiotic-associated diarrhea)

or it can be asymptomatic in the large intestine (carrier state)

Question 32

what does clostridium tetani cause?

Answer 32

tetanus

Question 33

what does clostridium botulinum cause?

Answer 33

botulism

Question 34

what does clostridium perfringens cause?

Answer 34

food-borne illness & gas gangrene (in soldiers)

Question 35

where is clostridioides difficile (c. diff) often found?

Answer 35

nursing homes and hospitals

its endospores are difficult to eradicate from the environment

Question 36

what’s the mode of transfer for clostridioides difficile (c. diff)?

Answer 36

spores thru the fecal-oral route

Question 37

what is pseudomembranous colitis?

Answer 37

inflammatory condition of the large intestine

most important risk factor is having recently received an antimicrobial agent which may develop this bacterial infection
— symptoms may occur 1-2 days after antibiotics or several weeks after the antibiotic is continued

lesions can enlarge to cover substantial portions of inflamed mucosa and can be stripped off – this is the pseudomembrane (“false membrane”)

Question 38

what are the symptoms of pseudomembranous colitis?

Answer 38

offensive smelling diarrhea

abdominal pain

fever

nausea

dehydration

Question 39

how does pseudomembranous colitis occur?

Answer 39

antibiotics cure infections, but also kill normal microbiota

suppression of normal microbiota + persistence of C. difficile endospores

after antibiotic is stopped, spores germinate, leading to the overgrowth of C. difficile which occurs w/
production of toxins

C. difficile is not considered an invasive bacterium (it does not invade itself), but the
exotoxins cause damage and inflammation to the intestinal
lining of the large intestine – its exotoxins are invasive!!

Question 40

describe the exotoxin produced by clostridioides difficile (c. diff)

Answer 40

A-B toxins aka large clostridual cytotoxins

“A-B” serves to designate two domains

A domain denotes the active portion of the toxin that carries the enzymatic activity that inactivates key regulatory proteins of the host cells, causing dysregulation of multiple cell processes including cytoskeletal rearrangements, cell death, and inflammation

B domain denotes the portion of the toxin molecule responsible for binding and uptake by the host cell

Question 41

how is clostridioides difficile (c. diff) diagnosed?

Answer 41

history (antibiotic use), symptoms and laboratory tests to confirm C. difficile

endoscopy and toxin detection assays

Question 42

what is treatment for clostridioides difficile (c. diff)?

Answer 42

discontinue antibiotic if still being used

provide fluids

antibiotics more specific for “C. diff” –– oral vancomycin or I.V metronidazole
— vancomycin is not a very good antibiotic; not absorbed well when taken orally, BUT… we want that here ??

avoid antidiarrheal agents as this would cause decreased toxin clearance

this is essentially using different antibiotics to treat a disease initially caused by antibiotics

Question 43

what is fecal microbiota transplantation?

Answer 43

replaces unhealthy bacteria in the colon with healthy bacteria from a donor

helps to rebalance the microbiota, or bacteria and other organisms, in the intestines.