Question

and Lab Exer n this experiment you will evaluate effect of UV light on bacterial growth. UV light affects growth by interfering with DNA, resulting in thymine dimer formation. The dimerization is confined within adjacent thymine residues on same strand (intrastrand ). These dimmer lesions have consequence on DNA functions including interference in DNA replication, transcription etc, so UV exposure of cells can lead to lethal effects for bacterial multiplications. This forms the basis for UV method to control bacterial growth. 2 common mechanisms operates for repairing the UV induced DNA damage : light and dark repair mechanisms. Please refer to Text page # 218-220 ( Fig 7.25, 7.28) and Atlas pages 114-115. Details of the dark and light repair mechanism will be discussed in lab. Cultures: Serratia marcescenes Bacillus cereus Procedure: This is a class experiment. All results will be compiled to complete lab sheet. 1. Label each plate with the bacteria name and time ( in secs) of UV exposure. Divide the bottom into 2 halves: labeled as uv exposed and control The exposed part is the area which will be irradiated undeř UV source and the other part will be covered with index card to block UV radiation. 2. Dip a sterile cotton swab into appropriate culture tube and swab the plate as demonstrated by your instructor. Swab the agar surface making sure to cover the entire plate evenly so as to obtain a uniform lawn of bacterial cell. Dispose the swab in the appropriate biohazard bag 3. Repeat the above step with the other bacteria. 4. Remove cover (lid) of the first plate and place a index card over part of plate that will not be irradiated (this part is the control, which will be compared to the exposed area). Place plate under UV lamp for the designated time assigned for your table. Make sure, other half of the plate is covered during exposure and plate lid is removed. 5. After exposure, replace the cover and immediately wrap the entire plate with aluminum foil to prevent exposure to white light. Place the plate on tray on instructor's desk. They all will be incubated at 37 Cuntil next lab period. Next lab period: Observe bacterial growth on UV exposed area of the plate and compare it with the covered part of the plate( CONTROL area) Score growth as shown previously and record your result in lab sheet Cultures used:. Tabulate results of class UV experiment here Questions: You may use the back page. 1. Any difficulty you anticipated or experienced when conducting this experiment. 2. List 3 precaution you should be aware of when completing this experiment. 3. Explain how radiation can be effectively used an antimicrobial control method. 4. What are thymine dimmers ? Describe repair mechanism of the thymine dimmers. List all components needed for the repair process and how it corrects the thymine dimmers. 5. List all components of sun blocker lotion and it's protective role. What are the advantages and disadvantages of using PABA?

Answer 1

2)

(a)The culture must be separate from any other bacterial culture avoiding contamination

(b)The culture must be in a dark environment with a 37 C temperature

(c)Avoid any direct contact (without protection) with the culture

(d)Once you recorded every result, you should follow the cleaning protocol for biological waste.

3) Ultraviolet germicidal irradiation has been used as a disinfection method. This method is based on a short wavelength ultraviolet light to kill or inactivate several microorganisms such as bacteria. The light will destroy nucleic acids and disrupt DNA at the same time, leading to a lock of vital cellular functions. For those reasons, UVGI has been used primarily in medical sanitation as well as sterile work facilities (like the laboratory where we are working).