Lab: Microbial Effects

Question 1

Three primary means by which to control microbial growth:

Answer 1

1. Temperature
2. UV light
3. Antibiotics & Antiseptics

Question 2

4 categories of temp. requirements for optimal growth

Answer 2

1. Psychrophiles: min. -5c max. 20c; potimum 10-15c
2. Mesophiles: min. 15c max. 45c; optimum 20-45c
3. Thermophiles: min. 45c max. 85c; optimum 55-65c
4. Hyperthermophiles: min. 55c max. unknown; optimum 85-113c

Question 3

Spectrum UV light falls in

Answer 3

4-400nm

Question 4

What makes UV more germicidal?

Answer 4

shorter, higher energy wavelength as compared to visible light or infrared radiation

Question 5

At what wavelength is UV radiation the most germicidal?

Answer 5

260nm because this is where DNA maximally absorbs it causing mutations

Question 6

What are formed upon absorption of UV light by DNA?

Answer 6

pyrimidine dimers. covalent bond formed between adjacent thymine or cytosine molecules, causing a mutant bulk, disallowing DNA polymerase to replicate past the site.

Question 7

What can protect a cell against UV radiation?

Answer 7

• thick peptidoglycan layer on gram + cells
• outer membrane and thin cell wall on gram - cells
• glycocalyx or slime layer can also protect
• spore formulation

Question 8

Photoreactivation repair mechanism

Answer 8

involves photolyase enzyme the breaks the dimer bonds and rematches the purines and pyrimidines

Question 9

SOS repair system

Answer 9

enzymatically removes the dimers and inserts new pyrimidine molecules in their place; excision repair mechanism

Question 10

Antiseptic

Answer 10

chemical agent applied to tissue to prevent infection by killing or inhibiting microorganisms

Question 11

Antibiotic

Answer 11

chemotherapeutic agents of low molecular weight that inhibit or kill other microorganisms.

Question 12

Kirby-Bauer Method

Answer 12

To determine effectiveness of antibiotics
uses Mueller Hinton agar
wafers with antiseptic/
antibiotic placed in growth on agar
determine size of zone of inhibition
corresponds to minimum inhibitory concentration

Question 13

SOS repair enzymes

Answer 13

Endonuclease cuts out bad section
DNA polymerase synthesizes nucleotides
Ligase seals Knicks

Question 14

Listerine

Answer 14

ion channel disrupter, lipid destabilization, protein interference

Question 15

Bactine

Answer 15

yields protein and membrane dissociation

Question 16

Betadine

Answer 16

promotes iodination of lipids and protein structure disruption

Question 17

Ciprofloxacin

Answer 17

HARD CORE

- inhibits DNA gyrase and topoisomerase IV, yields dsDNA breaks

Question 18

Vancomycin

Answer 18

• natural produced by Actinobacteria
• blocks NAM cross-linking
• primarily used to treat gram + infections
• large

Question 19

Tetracycline

Answer 19

• binds to 30s ribosomal subunit
• inhibits RNA binding, therefore blocking translation
• broad spec. against gram +/-
• can interfere with euk. ribosomes as well