Midterm 1 Flashcards
Moist Heat
- Destroys viruses, fungi, and bacteria but NOT spores
- Degrades nucleic acids, denatures proteins, and disrupts membranes
Steam Sterilization
Effective against all types `of microorganisms (including spores!)
Pasteurization
- Controlled heating at temperatures well below boiling
- Process does not sterilize but does kill pathogens present and slow spoilage by reducing the total load of organisms present
- Ultra High Temperature Method can sterilize
Dry Heat Sterilization
- Less effective than moist heat sterilization, requiring higher temperatures and often longer exposure times
- Oxidizes cell constituents and denatures proteins
Ultraviolet (UV) Radiation
- Causes thymine dimers preventing replication and transcription
- UV limited to surface sterilization because it does not penetrate glass, dirt films, water, and other substances
- Has been used for water treatment
Ionizing Radiation
- Gamma radiation penetrates objects
- Not always effective against viruses but can kill bacterial endospores
Phenolics
- Denatures proteins and disrupts cell membranes
- Tuberculocidal, effective in presence of organic material, and long lasting
- Disagreeable odor and can cause skin irritation
Alcohols
-Bactericidal, fungicidal, but not sporicidal
-Inactivates some viruses
-Denatures proteins and possibly dissolves membrane lipids
Among the most widely used antisepsis and disinfectants
Halogens
- Iodine, for example, is an antiseptic
- Oxidizes cell constituents and iodinates proteins
- At high concentrations can kill spores
- Chlorine also oxidizes cell constituents and destroys vegetable bacteria and fungi
- Chlorine has is sporicidal
Heavy Metals
- Examples are mercury, zinc, copper, silver, and arsenic
- Combine with and inactivate proteins, may also precipitate proteins
Quaternary Ammonium Compounds
- Detergents that have antimicrobial activity and are effective disinfectants
- Cationic detergents are effective disinfectants
- Kill most bacteria, but not M. tuberculosis or endospores
Aldehydes
- Sporicidal and can be used as chemical sterilants
- Combine with and inactivate nucleic acids and proteins
Sterilizing Gases
- Used to sterilize heat sensitive material
- Microbicidal and sporicidal
- Combine with and inactivate DNA and proteins
Antimicrobial Drugs - Modes of Action
- Inhibition of cell wall synthesis
- Inhibition of protein synthesis
- Inhibition of essential metabolite synthesis
- Inhibition of nucleic acid synthesis
Pencillins
- Most crucial feature is the beta-lactam ring
- Blocks the enzyme that catalyzes transpeptidation (formation of cross-links in peptidoglycan)
- Prevents synthesis of complete cells walls leading to lysis of cell
- Acts only on growing bacteria that are synthesizing new peptidoglycan
Cephalosporins
- Similar to penicillins
- Broad-spectrum antibiotics that can be used by most patients who are allergic to penicillin
- Inhibits cell wall synthesis
Vancomycin
- Glycopeptide antibiotic
- Inhibits cell wall synthesis
- Important for treatment of antibiotic resistant staphylococci and enterococci
Aminoglycoside Antibiotics
-Bind to 30S ribosomal subunit, interferes with protein synthesis by directly inhibiting the process and by causing misreading of the mRNA
Tetracycline
- Four-ring structure
- Broad spectrum, bacteriostatic
- Combine with 30S ribosomal subunit, inhibits binding of aminoacyl-tRNA molecules
Macrolides
- Contain 12-to 22-carbon lactone rings linked to one or more sugars
- For example, Erythromycin – broad spectrum, usually
- binds to 23S rRNA of 50S ribosomal subunit
- inhibits peptide chain elongation during protein synthesis
- Used for patients allergic to penicillin
Chloramphenicol
- Now is chemically synthesized
- Binds to 23S rRNA on 50S ribosomal subunit and inhibits peptidyl transferase reaction
- Toxic with numerous side effects so only used in life-threatening situations
Sulfonamides or Sulfa Drugs
• Structurally related to sulfanilamide, a p-aminobenzoic acid (PABA) analog
• PABA used for the synthesis of folic acid and is made by many pathogens
– sulfa drugs are selectively toxic due to competitive inhibition of folic acid synthesis enzymes
Trimethoprim
• Synthetic antibiotic that also interferes with folic acid production
• Broad spectrum
• Can be combined with sulfa drugs to increase efficacy of treatment
– combination blocks two steps in folic acid pathway
Quinolones
- Synthetic drugs containing the 4-quinolone ring
- Nalidixic acid was the first quinolone synthesized
- Acts by inhibiting bacterial DNA gyrase and topoisomerase II
- Broad spectrum, bactericidal, wide range of infections
Antifungal Drugs
Superficial mycoses
– Candida albicans
• causes “yeast infections” of the vagina, skin, etc.
• Nystatin – binds to sterols and damages the membrane
– Griseofulvin – disrupts the mitotic spindle and inhibits cell division
• Used to treat other superficial fungal infections – skin and nails
Treating Systemic Mycoses • Difficult to control and can be fatal • Three common drugs – Amphotericin B - binds sterols in membranes – 5-flucytosine – disrupts RNA function – fluconazole • low side effects, used prophylactically
Antiviral Drugs
- Drug development has been slow because it is difficult to specifically target viral replication
- Drugs currently used inhibit virus-specific enzymes and life cycle processes
Amantidine
– used to prevent influenza
infections
– blocks penetration and uncoating of influenza virus
Tamiflu
• anti-influenza agent
• a neuraminidase inhibitor
– an enzyme that is essential for the release of virus particles from the host cells
• though not a cure for influenza, has been shown to shorten course of illness
Anti-HIV Drugs
• Reverse transcriptase (RT) inhibitors – nucleoside RT inhibitors – non-nucleoside RT inhibitors • Protease inhibitors – mimic peptide bond that is normally attacked by the protease • Fusion inhibitors – prevent HIV entry into cells • Most successful are drug cocktails to curtail resistance
Antiprotozoal Drugs
- Mechanism for drug action not known
- Some antibiotics that inhibit bacterial protein synthesis are used against protozoa
- Example are chloroquine and mefloquine for malaria
Mechanisms of Bacterial Resistance to Antimicrobial Drugs
– an enzyme is produced that destroys or deactivates the drug
• example: β-lactamase
– the drug is inhibited or prevented from entering the cell
• example: alteration in cell wall porin
– the antimicrobial drug is pumped out of the cell before it can act
• example: efflux pumps
– there is an alteration of the target for the drug, so that the drug can no longer bind or attach to the target
• example: mutation in ribosome
– a metabolic pathway is shut down or an alternative pathway is used
Electron Carriers
- NAD
- NADP
- FAD
- FMN
- Coenzyme Q
- Cytochromes
- Nonheme iron-sulfur proteins
