Antibiotics

Question 1

How do antibiotics act on Gram+ bacteria?

Answer 1

By blocking the cross-linking reaction:
cell walls w.out cross linking have no strength and rupture when the cell reproduces

Question 2

What type of antibiotics work by disrupting the cell wall?

Answer 2

Penicillins/beta-lactams (penicillin binding protein)
glycopeptides (cell wall peptidoglycans)

Question 3

Which antibiotics work by inhibiting protein biosynthesis of 30s ribosomal subunit?

Answer 3

Tetracyclines
aminoglycosides

Question 4

Which antibiotics work by inhibiting the protein biosynthesis of 50s ribosomal subunit?

Answer 4

Macrolides
chloramphenicol

Question 5

Which antibiotics work by inhibiting DNA synthesis?

Answer 5

quinolones
fluoroquinolones

Question 6

Which antibiotics work by interfereing with metabolic pathways?

Answer 6

Trimethoprim
sulfonamides

Question 7

What type of bacteria do beta-lactams work best against?

Answer 7

Gram positives and some anaerobes

Question 8

What are third generation cephalosporins good for treating?

Answer 8

Resistant gram-negative infections in particularly compromised cases

*IM injections can be painful
**repeated IV administration may lead to local phlebitis

Question 9

You have a case involving a nasty anaerobic infection with Bacteroides fragilis. What antibiotic do you reach for?

Answer 9

Carbapenems!

(new class beta-lactams)

Question 10

Gentamicin, tobramycin, and amikacin belong to which class?

Answer 10

Aminoglycosides

Question 11

What facilitates the passive movement of aminoglycosides across bacterial cell membranes?

Answer 11

Alkaline pH

(low pH may increase membrane resistance 100x +!)

Question 12

What bacteria are susceptible to aminoglycosides?

Answer 12

Aerobic - generally Gram-negative - bacilli

(including Pseudomonas aeruginosa)

Question 13

Where is a fraction aminoglycosides filtered and absorbed into?

Answer 13

the brush border of the
proximal tubule and loop of Henle cells

Question 14

How does excessive accumulation of aminoglycosides in the cytosol of the cell (mainly in the renal cortex) lead to a characteristic tubular cell necrosis?

Answer 14

once filtered and absorbed into PT and LoH cells; binding effect is facilitated by ionization
once transported into the cell, sequestered in lysosomes…

rupture of lysosomes results in release into cytosol

Question 15

Besides nephrotoxicity, what other 2 negative side effects have been reported with the use of aminoglycosides?

Answer 15

Ototoxicity,
Neuromuscular blockade

Question 16

How early can changes or evidence of nephrotoxicity from the use of aminoglycosides, be detected?

Answer 16

Early: 3-5 days
more overt signs: 7-10 days

Question 17

How do fluoroquinolones work and what is an example?

Answer 17

They inhibit necessary enzymes for synthesis of bacterial DNA and RNA;
enrofloxacin (Baytril)

Question 18

What antibiotic should we use to treat Salmonellosis?

Answer 18

Enrofloxacin (Fluoroquinolones)

Question 19

What type of bacteria do fluoroquinolones work best against?

Answer 19

Aerobic;
gram-negatives
(genitourinary, gastrointestinal tracts, respiratory tract, bone infections, and skin and soft tissue infections)

Question 20

What bacteria are macrolides more effective against?

Answer 20

Gram-positive

(Aerobic and anaerobic)

Question 21

Which class of antimicrobials are generally bacteriostatic, but demonstrate bactericidal activity at high concentrations, and are considered to be time-dependent in terms of efficacy?

Answer 21

macrolides!

Question 22

Macrolides act synergistically with what other antimicrobial against R. Equi?

Answer 22

Rifampin

Question 23

What are a couple “dont’s” of using sulfonamides?

Answer 23

Don’t put a pneumonia patient on sulfa drugs…

don’t mix SMZ with beta-lactams; this will kill significant bacteria in the GI tract and lead to colic

Question 24

How do potentiated sulfonamides work? Examples?

Answer 24

Inhibit dihydrofolate reductase in bacteria and Protozoa;
trimethoprim, pyrimethamine

Question 25

What bacteria do sulfonamides inhibit?

Answer 25

Gram-positives and gram-negatives;
some protozoa

Question 26

How do tetracyclines work?

Answer 26

Bind to the 30S ribosomal subunit, which prevents ribosomal translation

Question 27

What is the antimicrobial of choice to treat Rickettsia and Mycoplasma?

Answer 27

Tetracyclines!

(specifically Oxytetracycline)

Question 28

What type of bacteria do tetracyclines work against?

Answer 28

Aerobic/anaerobic,
gram-positive/gram-negative,
some protozoa

Question 29

Which antimicrobial can cause contracted tendons in foals?

Answer 29

Tetracyclines

Question 30

How do phenicols exhibit their effects on bacteria?

Answer 30

Inhibit microbial protein synthesis;
bind to the 50S subunit of 70S ribosome
and impairing peptidyl transferase activity

Question 31

What type of bacteria do phenicols work best against?

Answer 31

Many genera of gram-positive and gram-negative bacteria and several anaerobes (such as Bacteroides fragilis)

Question 32

Where are phenicols absorbed and how are they metabolized?

Answer 32

Absorption: promptly from the upper GI tract

Metabolism: extensive hepatic metabolism

Question 33

Which class of antimicrobials does vancomycin fall under and how does it work?

Answer 33

Glycopeptides;
binds to precursors of the peptidoglycan layer in bacterial cell walls

*this prevents cell wall synthesis and produces a rapid bactericidal effect in dividing bacteria*

Question 34

Which bacteria are glycopeptides most active/effective against?

Answer 34

Gram-positive

Question 35

What is the only indication for use of parenteral vancomycin?

Answer 35

Serious infections due to methicillin-resistant Staphylococcus aureus

Question 36

Which bacteria are nitroimidazoles active against?

Answer 36

Anaerobic;
anti-protozoal effects too

extra-label use is prohibited in food animals in the USA

Question 37

Which antimicrobial is active against B.fragilis, B.melaninogenicus, Fusobacterium spp, and Clostridium spp.?

Answer 37

metronidazole