Ultraviolet Radiation and Urea Hydrolysis

Colony-Forming Unit (CFU)

A unit used to estimate the number of viable bacteria or fungal cells in a sample.

OCD - Original Cell Density

The concentration of cells in a sample, typically expressed in CFU/ml.

Urea

A product of the decarboxylation of certain amino acids, identified in Urea Agar.

Urease

An enzyme that hydrolyzes urea to ammonia and carbon dioxide.

Ammonia

A weak base that acts as a proton acceptor in biochemical reactions.

Ultraviolet Radiation

Electromagnetic radiation with wavelengths shorter than visible light, classified into UVA, UVB, and UVC.

UVC

Ultraviolet light with wavelengths from 100-280 nm, most damaging to bacteria.

Thymine Dimers

Errors in DNA caused by adjacent thymines covalently bonding together due to UV exposure.

Photoreactivation (Light Repair)

A bacterial repair mechanism where the enzyme DNA photolyase reverses thymine dimer formation using visible light.

Excision Repair (Dark Repair)

A bacterial repair mechanism that removes a nucleotide fragment and uses the remaining strand as a template for repair.

Urine Streak

A semi-quantitative CFU counting method utilizing a volumetric loop to obtain countable colonies on a blood agar plate.

Urea Agar

A differential media that identifies organisms capable of metabolizing urea.

Phenol Red

A pH indicator that turns pink in basic conditions, used in Urea Agar tests.

Urease Positive Organisms

Organisms that produce urease, resulting in a pink color change in Urea Agar within 24 hours.

Sample Problem #1

OCD = 88 CFU/.001 ml = 88 x 10^3 CFU/ml = 8.8 x 10^4 CFU/ml.

Sample Problem #2

OCD = 62 CFU/.01 ml = 62 x 10^2 CFU/ml = 6.2 x 10^3 CFU/ml.

Longer Wavelengths

Wavelengths that have less energy, such as radiowaves.

Shorter Wavelengths

Wavelengths that have more energy, such as gamma rays and UV rays.

Bacterial Repair Mechanisms

Processes that bacteria use to repair DNA damage caused by UV radiation.

Control No Urease (-)

A control test indicating the absence of urease activity in a sample.