Week 10 Flashcards
Classes of bacteria
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
MIC:
minimum inhibitory concentration
– Dose of a drug needed to halt bacterial growth
MBC:
minimum bacteriocidal concentration
– Dose of a drug needed to kill bacteria
narrow spectrum antibiotic
– Attacks only certain types of bacteria
– Often leaves normal gut (or vaginal, or other) flora alone
wide spectrum antibiotic
– Attacks many types of bacteria
– May not need to know what kind of bacterium is present
C diff (Clostridium difficile)
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.
4 ways to kill bacteria
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
Bacterial resistance to antibiotics
- Modified cell wall/membrane is impermeable to
the antibiotic - Enzyme is altered so that antibiotic no longer
binds to it - 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
Preventive antibiotics prior to a dental procedure
may be advised for patients with:
– 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
penicillin
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
cephalosporins
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…)
vancomycin
• 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
azithromycin
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)
doxycycline
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
ciprofloxacin
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
metronidazole (Flagyl)
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
Triple antibiotic cream
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
Anti-fungal drugs
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
metronidazole (Flagyl) works by
inhibiting DNA synthesis
azithromycin works by
inhibiting bacterial protein synthesis
ceftriaxone works by
inhibiting bacterial cell wall synthesis
cephalexin works by
inhibiting bacterial cell wall synthesis
amoxicillin works by
inhibiting bacterial cell wall synthesis
clotrimazole works by
increasing yeast cell membrane permeability
