Midterm 1

Question 1

Moist Heat

Answer 1

• Destroys viruses, fungi, and bacteria but NOT spores

- Degrades nucleic acids, denatures proteins, and disrupts membranes

Question 2

Steam Sterilization

Answer 2

Effective against all types `of microorganisms (including spores!)

Question 3

Pasteurization

Answer 3

• 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

Question 4

Dry Heat Sterilization

Answer 4

• Less effective than moist heat sterilization, requiring higher temperatures and often longer exposure times
• Oxidizes cell constituents and denatures proteins

Question 5

Ultraviolet (UV) Radiation

Answer 5

• 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

Question 6

Ionizing Radiation

Answer 6

• Gamma radiation penetrates objects

- Not always effective against viruses but can kill bacterial endospores

Question 7

Phenolics

Answer 7

• Denatures proteins and disrupts cell membranes
• Tuberculocidal, effective in presence of organic material, and long lasting
• Disagreeable odor and can cause skin irritation

Question 8

Alcohols

Answer 8

-Bactericidal, fungicidal, but not sporicidal
-Inactivates some viruses
-Denatures proteins and possibly dissolves membrane lipids
Among the most widely used antisepsis and disinfectants

Question 9

Halogens

Answer 9

• 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

Question 10

Heavy Metals

Answer 10

• Examples are mercury, zinc, copper, silver, and arsenic

- Combine with and inactivate proteins, may also precipitate proteins

Question 11

Quaternary Ammonium Compounds

Answer 11

• Detergents that have antimicrobial activity and are effective disinfectants
• Cationic detergents are effective disinfectants
• Kill most bacteria, but not M. tuberculosis or endospores

Question 12

Aldehydes

Answer 12

• Sporicidal and can be used as chemical sterilants

- Combine with and inactivate nucleic acids and proteins

Question 13

Sterilizing Gases

Answer 13

• Used to sterilize heat sensitive material
• Microbicidal and sporicidal
• Combine with and inactivate DNA and proteins

Question 14

Antimicrobial Drugs - Modes of Action

Answer 14

• Inhibition of cell wall synthesis
• Inhibition of protein synthesis
• Inhibition of essential metabolite synthesis
• Inhibition of nucleic acid synthesis

Question 15

Pencillins

Answer 15

• 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

Question 16

Cephalosporins

Answer 16

• Similar to penicillins
• Broad-spectrum antibiotics that can be used by most patients who are allergic to penicillin
• Inhibits cell wall synthesis

Question 17

Vancomycin

Answer 17

• Glycopeptide antibiotic
• Inhibits cell wall synthesis
• Important for treatment of antibiotic resistant staphylococci and enterococci

Question 18

Aminoglycoside Antibiotics

Answer 18

-Bind to 30S ribosomal subunit, interferes with protein synthesis by directly inhibiting the process and by causing misreading of the mRNA

Question 19

Tetracycline

Answer 19

• Four-ring structure
• Broad spectrum, bacteriostatic
• Combine with 30S ribosomal subunit, inhibits binding of aminoacyl-tRNA molecules

Question 20

Macrolides

Answer 20

• 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

Question 21

Chloramphenicol

Answer 21

• 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

Question 22

Sulfonamides or Sulfa Drugs

Answer 22

• 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

Question 23

Trimethoprim

Answer 23

• 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

Question 24

Quinolones

Answer 24

• 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

Question 25

Antifungal Drugs

Answer 25

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 ```

Question 26

Antiviral Drugs

Answer 26

* 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

Question 27

Anti-HIV Drugs

Answer 27

``` • 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 ```

Question 28

Antiprotozoal Drugs

Answer 28

- Mechanism for drug action not known - Some antibiotics that inhibit bacterial protein synthesis are used against protozoa - Example are chloroquine and mefloquine for malaria

Question 29

Mechanisms of Bacterial Resistance to Antimicrobial Drugs

Answer 29

– 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

Question 30

Electron Carriers

Answer 30

- NAD - NADP - FAD - FMN - Coenzyme Q - Cytochromes - Nonheme iron-sulfur proteins