Antibiotics II

Question 1

What are the seven classes of protein synthesis inhibitors we learned?

Answer 1

1) Aminoglycosides (only bactericidal)
2) Oxazolidinones
3) Tetracycline/Glycycycline
4) Chloramphenicol
5) Macrolide/Azalide/Ketolide
6) Lincosamide
7) Streptogramins

Question 2

Aminoglycosides are administered via _____

Answer 2

IV (parenteral)

Question 3

What are the two toxicities seen with aminoglycosides?

Answer 3

Ototoxicity

Nephrotoxicity

Question 4

T/F Aminoglycosides cover both aerobic and anaerobic organisms

Answer 4

FALSE

Aminoglycosides require oxygen to enter bacteria, and therefore do not work against anaerobes

Question 5

Aminoglycosides cover _____ rods more than _____

Answer 5

G(-) > G(+)

Question 6

Aminoglycosides have limited coverage against G(+) organisms when combined with _____

Answer 6

A beta-lactam antibiotic

Question 7

Describe the three mechanisms of aminoglycoside action

Answer 7

1) Binds/fixes 30S-50S complex at start codon, blocking INITIATION of protein synthesis
2) Binds 30S, causing MISREADING & PREMATURE TERMINATION
3) Binds 30S, causes incorporation of incorrect amino acid, resulting in the production of a NONFUNCTIONAL PROTEIN

Question 8

What are the mechanisms of resistance against aminoglycosides (3)?

Answer 8

1) Enzymatic modification of drug (cannot bind 30S)
- via acetylases, adenylases & phosphorylases

2) Impaired uptake
3) Ribosomal mutation

Question 9

Which aminoglycoside is used when the infection is resistant to other aminoglycosides?

Answer 9

Amikacin

Question 10

Ampicillin + _____ is used to kill Enterococcus (gram + cocci). Why is this combination effective?

Answer 10

Ampicillin + Gentamicin kills Enterococcus

Ampicillin makes chinks in peptidoglycan layer that gentamicin can enter to kill the organism.

Question 11

What synthetic inhibitor of protein synthesis is especially effective against VRE, MSSA, MRSA? It also has moderate effectiveness against TB.

Answer 11

Linezolid (Oxazolidinone)

Question 12

T/F Linezolid has limited distribution in tissues?

Answer 12

FALSE

Linezolid is distributed widely in all tissues!

Question 13

Linezolid covers only what kind of organisms?

Answer 13

G+ Aerobes

No activity against anaerobes

Question 14

Linezolid binds _____ of bacteria, preventing assembly of _____.

Answer 14

Binds 50S, preventing assembly of ribosomes

Question 15

How do bacteria become resistant against Linezolid?

Answer 15

Ribosomal alteration to prevent binding

Question 16

T/F Tetracyclines only work against G+ organisms

Answer 16

FALSE

Both G+ and G-, though G+ activity > G- activity

Question 17

Which tetracycline is used to treat complicated intraabdominal infections and soft tissue infections, has both G+ and G- activity, and is ineffective against P. aeruginosa and Proteus?

Answer 17

Tigecycline

Question 18

Tetracyclines are effective against intracellular pathogens. What are some of the intracellular infections covered by these drugs (5)?

Answer 18

1) Rickettsial infections
2) Mycoplasma infetions
3) Chlamydia infections
4) Bacillary infections
5) Spirochete infections

Question 19

How is doxycycline used other than as an antibiotic?

Answer 19

As an anti-inflammatory drug.

Subinhibitory concentrations are used to treat rosacea

Question 20

T/F There is more bacterial resistance to tigecycline than tetracycline

Answer 20

FALSE

There’s lots of resistance out there to tetracycline, less so to tigecycline

Question 21

Which tetracycline is particularly effective against Staphylococcus?

Answer 21

Minocycline

Question 22

Which of the following statements are true regarding chloramphenicol?

1) Broad spectrum
2) Treats anaerobes and intracellular
3) No toxicities
4) Bactericidal
5) Crosses BBB

Answer 22

1, 2, and 5 are true

3) Use of chloramphenicol has decreased due to its toxicities.
4) Chloramphenicol is bacteriostatic, not bactericidal

Question 23

What specific infections does chloramphenicol cover (4)?

Answer 23

1) Typhoid Fever (S. typhi)
2) Bacterial meningitis (N. meningitiditis)
3) Anaerobic infections
4) Rocky Mountain Spotted Fever (Ricketssial disease)

Question 24

Chloramphenicol binds to _____, preventing _____.

Answer 24

Chloramphenicol binds to 50S, preventing ADDITION OF AMINO ACIDS to the growing peptide chain

Question 25

What is the most common method of bacterial resistance to chloramphenicol? What are the other methods?

Answer 25

Acetylation is most common (via chloramphenicol acetyl transferase, prevents binding to 50S) Other methods: Efflux, ribosomal mutation

Question 26

Macrolides bind to _____, preventing _____

Answer 26

Macrolides bind to 50S, preventing MOVEMENT OF THE POLYPEPTIDE AT THE A SITE TO THE P SITE

Question 27

What are the methods of bacterial resistance to macrolides (4)?

Answer 27

1) Efflux 2) Methylation 3) *Esterases* (hydrolyze lactone ring of macrolides) 4) Ribosomal mutation

Question 28

Macrolides are _____ spectrum antibiotics that are effective against _____, _____, and some _____.

Answer 28

Macrolides are NARROW spectrum antibiotics that are effective against RESPIRATORY G+ ORGANISMS, ATYPICAL MYCOBACTERIA, & SOME INTRACELLULAR BUGS

Question 29

Which intracellular pathogens does erythromycin cover (4)?

Answer 29

1) Heliobacter/Campylobacter 2) Mycoplasma 3) Chlamydia 4) Legionella

Question 30

Clarithromycin covers the same organisms as erythromycin plus _____ and has better efficiency against _____ & ______

Answer 30

Clarithromycin covers the same organisms as erythromycin plus ATYPICAL MYCOBACTERIA has better efficiency against STAPH AND STREP than erythromycin

Question 31

Azithromycin is slightly less effective against _____ than erythromycin and clarithromycin, but is more effective than them in treating infections by _____. It is also good for use against _____

Answer 31

Less effective against G+ organisms H. influenza Good against atypical mycobacteria

Question 32

Which drug is used to treat macrolide resistant organisms causing CAP? Why is its use limited?

Answer 32

Telithromycin (ketolide) Limited use due to its hepatotoxicity

Question 33

Which macrolide can be used as a single dose STD prescription (chlamydia)?

Answer 33

Azithromycin

Question 34

Which antibiotic works in a similar fashion to macrolides and turns off exotoxin production by staph and strep?

Answer 34

Clindamycin

Question 35

Clindamycin (lincosamide) is a _____ spectrum antibiotic that works against _____ and is excellent against _____

Answer 35

Clindamycin is a NARROW spectrum antibiotic that works against G+ and is excellent against ANAEROBES

Question 36

What is the main method of bacterial resistance to clindamycin?

Answer 36

Alteration of ribosome (via constitutive/inducible methylase

Question 37

Streptogramin binds _____ like macrolides.

Answer 37

50S

Question 38

Streptogramin is a _____ spectrum antibiotic that covers _____ bacteria. It is not effective against _____.

Answer 38

Narrow spectrum Covers G+ bacteria Not effective against E. faecalis

Question 39

Cross resistance to Macrolides, Lincosamides, and Streptogramins (MLS) is mediated by the _____ gene

Answer 39

erm gene

Question 40

When the erm gene (responsible for MLS cross resistance) is turned on, what happens to the bacterial ribosome?

Answer 40

It becomes methylated, preventing the binding of MLS to the 50S subunit

Question 41

T/F There are two kinds of erm methylases

Answer 41

TRUE Constitutive (cMLS) Inducible (iMLS)

Question 42

How is the ability of a bacterial strain to induce methylation assessed in the lab?

Answer 42

D-Test