Week 10

Question 1

Classes of bacteria

Answer 1

Gram positive
– Thick peptidoglycan cell wall
– Bacillus, Staphylococcus aureus, Clostridium,
Helicobacter, Streptococcus…
• Gram negative
– Thin peptidoglycan cell wall, plus outer membrane
– E coli , Pseudomonas, Salmonella, Campylobacter

Question 2

MIC:

Answer 2

minimum inhibitory concentration

– Dose of a drug needed to halt bacterial growth

Question 3

MBC:

Answer 3

minimum bacteriocidal concentration

– Dose of a drug needed to kill bacteria

Question 4

narrow spectrum antibiotic

Answer 4

– Attacks only certain types of bacteria

– Often leaves normal gut (or vaginal, or other) flora alone

Question 5

wide spectrum antibiotic

Answer 5

– Attacks many types of bacteria

– May not need to know what kind of bacterium is present

Question 6

C diff (Clostridium difficile)

Answer 6

Wiping out normal gut bacterial flora
can allow superinfection with another pathogen
– Risk with broad-spectrum antibiotics
• C diff (Clostridium difficile)
– causes pseudomembranous colitis
• watery diarrhea, fever, inflammation of colon, distinctive odor
– very difficult to get rid of!
• Clostridium form endospores, not killed by alcohol-based
hand cleansers or routine surface cleaning
– Icky, debilitating, infectious (esp in hospitals)
• kills ~14,000 people a year in U.S.

Question 7

4 ways to kill bacteria

Answer 7

Inhibit cell wall synthesis
– Cells swell/burst due to osmotic pressure
• Inhibit protein synthesis
– Keep bacteria from making essential enzymes etc
• Inhibit DNA synthesis
– Keep bacteria from replicating, or kill them due to
faulty replication
• Increase cell wall/membrane permeability
– Cells swell/burst due to osmotic pressure

Question 8

Bacterial resistance to antibiotics

Answer 8

1. Modified cell wall/membrane is impermeable to
   the antibiotic
2. Enzyme is altered so that antibiotic no longer
   binds to it
3. Acquired enzyme to destroy the antibiotic
   • Societally, reduced use of antibiotics lessens
   overall prevalence of resistant bacteria
   • Insufficient dosage and incomplete course of
   taking abx can encourage resistance
   • Nosocomial infections are often abx resistant
   – Hospital-acquired

Question 9

Preventive antibiotics prior to a dental procedure

may be advised for patients with:

Answer 9

– artificial heart valves
• Possibility of infective endocarditis
– hip and knee replacements
• Possibility of prosthetic joint infection (in 1-2% of
replacements)
• Amoxicillin, 30-60 minutes before the procedure
– Alternatives for patients with penicillin allergies

Question 10

penicillin

Answer 10

Inhibits cell wall synthesis
– Inhibits enzyme called transpeptidase
• Most common (5%) side-effect
– Mild rash to life-threatening anaphylactic shock
• Penicillin V
– Relatively narrow spectrum, vs Gram-positive bacteria
• Amoxicillin
– Broader spectrum, vs Gram pos & some Gram neg
• Augmentin: amoxicillin + clavulanate
– (Potassium) clavulanate inhibits penicillinase enzymes,
combats bacterial a major type of bacterial resistance

Question 11

cephalosporins

Answer 11

Related to penicillins
– Broader spectrum, better vs Gram neg
– less resistance (but becoming more common)
• 1st generation: cephalexin (UTIs, strep throat)
– Most commonly prescribed
• 2nd generation: cefprozil (& others)
• 3rd generation (most by injection only)
– ceftriaxone (Rocephin) (gonorrhea, meningitis…)
– cefazidime (Cefzim) (Pseudomonas…)

Question 12

vancomycin

Answer 12

• Inhibits cell wall synthesis
(not related to penicillin)
• Normally kept for life-threatening Gram pos infections
– MRSA (methicillin resistant Staphylococcus aureus)
– Also used with Clostridium difficile
• As an alternative to metronidazole (Flagyl, see later slide)
• Very few resistant bacteria
– Some VRE (vancomycin-resistant enterococci)
• IV only (except with C diff)
• Thrombophlebitis due to acidic solution
– Infuse slowly, over 1-2 hours
• Ototoxicity, nephrotoxicity
– May be less than what is cited in older literature

Question 13

azithromycin

Answer 13

Selectively inhibits protein synthesis in bacteria
– wide-spectrum among many types of bacteria
• Original was erythromycin,
now mostly replaced by azithromycin
– [also clarithromycin, common for H pylori]
– qdaily dosing, 5-day course for typical infections
• May improve patient compliance
– Lower incidence of nausea, vomiting
• Still significant (3-5% of patients)

Question 14

doxycycline

Answer 14

inhibits protein synthesis in bacteria
– wide-spectrum, but many Gram pos bacteria have become resistant
• often used vs H. pylori, in combo with Flagyl
• also commonly used for severe acne
– Also used vs malaria parasite (eukaryote, diff mechanism)
• Original was tetracycline
now mostly replaced by doxycycline
– qdaily dosing, well absorbed in presence of food
• Common side-effect: GI distubance / gastric pain
– less with food
– Teratogen (FDA category D)
– [disrupts bone/tooth development, also in children < 8yrs]
– Sun-induced rash

Question 15

ciprofloxacin

Answer 15

Inhibits DNA replication
– [breaks DNA chromosome into fragments]
• Very broad spectrum among bacteria
– Especially Gram negative
– [Antibiotic of choice after possible inhalation anthrax
exposure]
• Relatively well-tolerated (mild side-effects)
• [may cause headache, nausea, rash;
rarely may cause tendonitis or tendon rupture]
• Resistant strains of bacteria are becoming common

Question 16

metronidazole (Flagyl)

Answer 16

Inhibits DNA synthesis in protozoans,
amoebae and anaerobic bacteria
– Giardia, H pylori, C diff, others
• Notable side-effect:
inhibits detox of ethanol by the liver
– Tachycardia, headache, vomiting, facial flushing
• Various other side-effects, incl gastric distress
– Take it with food
– Possible carcinogen

Question 17

Triple antibiotic cream

Answer 17

polymyxin B, neomycin & bacitracin
– Neosporin, others
– Topical application for minor wounds etc
• Broad spectrum vs Gram pos/neg bacteria
– Three drugs increase cell membrane permeability
and attack cell wall in different ways
– Triple approach limits bacterial resistance
• [Overuse may be causing increased resistance however]
• Nephrotoxic: not used internally

Question 18

Anti-fungal drugs

Answer 18

Increase cell membrane permeability
• Vs oral thrush, vaginal yeast infections, athlete’s
foot, jock itch…
• “-azole” drugs
– Note: not all “-azole” drugs are antifungals
• Eg. ariprazole (Abilify) is an atypical antipsychotic
– Clotrimazole, ketoconazole, miconazole, fluconazole
• Mainly topical usage, some are OTC

Question 19

metronidazole (Flagyl) works by

Answer 19

inhibiting DNA synthesis

Question 20

azithromycin works by

Answer 20

inhibiting bacterial protein synthesis

Question 21

ceftriaxone works by

Answer 21

inhibiting bacterial cell wall synthesis

Question 22

cephalexin works by

Answer 22

inhibiting bacterial cell wall synthesis

Question 23

amoxicillin works by

Answer 23

inhibiting bacterial cell wall synthesis

Question 24

clotrimazole works by

Answer 24

increasing yeast cell membrane permeability

Question 25

Which one of the following drugs is an antipsychotic, NOT an antifungal/yeast medication?

Answer 25

ariprazole

Question 26

Preventive antibiotic prophylaxis may be helpful before dental procedures for patients who have

Answer 26

an artificial heart valve or hip or knee replacement

Question 27

Which of the following is a side-effect of amoxicillin?

Answer 27

allergic reaction

Question 28

Which of the following is a side-effect of doxycycline?

Answer 28

GI disturbance / nausea