MICROBIOLOGY - Antimicrobials

Question 1

Which antibiotics inhibit bacterial cell wall synthesis? (3)

Answer 1

Penicillins, cephalosporins (ceftriaxone), vancomycin

Question 2

What is the mechanism of action of fluoroquinolones?

Answer 2

BACTERICIDAL
Gram +ve: Inhibit topoisomerase IV

Gram -ve (more potent):
Inhibit DNA replication by action on bacterial DNA gyrase

Question 3

Systemically, what can chloramphenicol cause?

Answer 3

Aplastic anaemia

Question 4

Which antibiotics inhibit protein synthesis? (5)

Which antibiotics inhibit 30S subunit

Which antibiotics inhibit 50S subunit

Answer 4

30S: tetracycline, aminoglycosides (messenger RNA)
50S: Macrolides, Lincosamides, Chloramphenicol

Question 5

What antibiotics inhibit cell wall synthesis?

Answer 5

Beta lactam antibiotics - penicillin, cephalosporins, vancomycin

Question 6

What antibiotics inhibit folic acid synthesis?

Answer 6

Sulphonamides
Trimethoprim

Question 7

What antibiotics inhibit DNA gyrase and transcription?

Answer 7

Fluoroquinolones

Question 8

Which antibiotic is the most retino-toxic when given intravitreally?

Answer 8

Gentamicin (gram negative cover)

Question 9

What are aminoglycosides not effective against?

Answer 9

Streptococcus and strict anaerobes

Question 10

what is the mechanism of action of azole antifungals (fluconazole, itraconazole, ketoconazole)?

Answer 10

inhibit cell membrane synthesis - they inhibit the synthesis of sterols by inhibiting P450 dependent enzymes (C14-demethylase) which are an important constituent in fungal cell membranes (anti-mycotics)

Question 11

What ocular side effect occurs with prolonged use of ciprofloxacin?

Answer 11

Corneal crystalline precipitates

Question 12

What type of bacteria do tetracyclines target? (3)

Answer 12

Gram +ve
Gram -ve
Chlamydia

Question 13

Which drug can be used for infections caused by aspergillus and candida?

Answer 13

Topical amphotericin

Question 14

Which antibiotics are known to be associated with IIH?

Answer 14

1. Tetracyclines
2. Fluoroquinolones

Question 15

Which antibiotics are bacteriocidal? (4)

Answer 15

1. Aminoglycosides
2. B-Lactam
3. Vancomycin
4. Fluoroquinolones

Question 16

Which antibiotics are bacteriostatic? (4)

Answer 16

1. Chloramphenicol
2. Macrolides
3. Tetracycline
4. Sulphonamides

Question 17

What is the mechanism of action of chloramphenicol?

Answer 17

BACTERIOSTATIC
50S subunit:
inhibits peptidyl-transferase and prevents peptide bond formation of to amino acids

Question 18

What is the mechanism of action of macrolides?

Answer 18

BACTERIOSTATIC
50S Subunit: interfering with translocation

Broad spectrum: Gram + ve > atypical (mycoplasma/ chlamydia) > Gram -ve.

Question 19

What is the mechanism of action of tetracyclines?

Answer 19

TETRA blocks tRNA on Thirty Subunit

BACTERIOSTATIC
inhibition of aminoacyltransferase tRNA to 30S subunit preventing binding to A-site.

Question 20

What is the mechanism of action of sulphonamides?

Answer 20

BACTERIOSTATIC
inhibits dihydropteroate synthase –> converts para-aminobenzoic acid to folate

Question 21

What is the mechanism of action of aminoglycosides?

Answer 21

BACTERICIDAL: GRAM -VE.

30S Subunit:
Prevents binding of mRNA to ribosome leading to mRNA misreading and premature termination of protein synthesis

Question 22

What is the mechanism of action of Beta Lactams?

Answer 22

BACTERICIDAL
Inhibits crosslinks of peptidoglycan strands causing cell lysis

Question 23

What is the mechanism of action of vancomycin

Answer 23

BACTERICIDAL
Binds to pentapeptide chains and prevents peptidoglycan assembly

Targets Gram +ve.

Question 24

What is the mechanism of action of fluoroquinolone?

Answer 24

Inhibits bacterial DNA gyrase

Question 25

What is the mechanism of action of metronidazole?

Answer 25

Disrupts DNA synthesis targets anaerobes

Question 26

What are aminoglycosides effective against? What are they not effective against?

Answer 26

1. aerobic gram negative bacili 2. proteus 3. staphylococcus non effective against: 1. streptococcus 2. anaerobes

Question 27

What is the most common side effect of gentamicin?

Answer 27

oscilopsia then cochlear injury then renal toxicity

Question 28

What antimicrobials affect cell wall synthesis? (3)

Answer 28

penicillins cephalosporins vancomycin

Question 29

What antimicrobials affect protein synthesis? (4)

Answer 29

tetracycline gentamicin erythromycin chloramphenicol

Question 30

Which antibiotic has the best ocular penetration when given orally?

Answer 30

ciprofloxacin (fluoroquinolones)

Question 31

What are the second generation fluoroquinolones? (2) What are the third generation fluoroquinolones? (1) What are the fourth generation fluoroquinolones? (1)

Answer 31

Second gen - cipro, ofloxacin, Third gen - levofloxacin, Fourth gen - Moxifloxacin

Question 32

Mechanism of action diagram of anti-microbials

Answer 32

Question 33

What are the 1st generation cephalosporins 2nd generation cephalosporins 3rd generation cephalosporins 4th generation cephalosporins

Answer 33

1 - FA/PHA - cefazolin 2 - Cefuroxime 3 - ONE/IME - ceftriaxone, ceftazidine 4 - PI - Cefepime

Question 34

What are cephalosporins active against which generation?

Answer 34

1st - gram positive (staph/strep) 2nd - gram +ve + some gram -ve (haemophilus, neisseria) 3rd - gram +ve + gram -ve bacilli and pseudomonas

Question 35

What bacteria are cephalosporins NOT effective against (3)

Answer 35

Listeria, Legionella, MRSA

Question 36

What is the mechanism of action of antimicrobials?

Answer 36

Question 37

What is the mechanism of action of micafungin?

Answer 37

Interferers with glucan synthesis, which is an essential component of fungal cell walls.

Question 38

What is the mechanism of action of polyene antifungal drugs (amphotericin, nystatin)

Answer 38

Interact with sterols in cell membrane to form channels through which small molecules leak from inside of fungal cell to the outside.

Question 39

What is the mechanism of action of foscarnet?

Answer 39

pyrophosphate analogue which Reversibly inhibits viral-specific DNA polymerase and reverse transcriptase

Question 40

Which antimicrobial agents are used in the treatment of acanthomoeba keratitis? (4)

Answer 40

Aminoglycosides (neomycin) Diamidines (Brolene) Imidazole (ketoconazole) Antiseptic biocides (polyhexamethylene biguanide)