8th lab physical effect on microbial growth tue

1. 7th Lab
CHEMICAL AND PHYSICAL EFFECTS ON
BACTERIAL GROWTH

2. • Phenol
• Halogens (Chlorine, iodine,
bromine)
• Alcohols (e.g.. isopropyl alcohol)
• Heavy metals (Ag, Hg, Cu, Zn)
• Surface active agents (soaps &
detergents)
• Quaternary Ammonium Cmpds
(quats)
• Aldehydes (e.g.. glutaraldehyde)
• Heat: Moist vs. Dry
• Autoclaving, pasteurization
• Filtration
• Cold
• Desiccation & high osmotic
pressure
• Radiation (UV, gamma rays)
WHAT FACTORS LIMIT MICROBIAL GROWTH
Physical Control Methods Chemical Control Methods

3. Factors that influence effectiveness
 Number of microbes
 Conc.and kind of agents used
 Time exposure
 Microbial characteristics

4. METHODS OF CONTROL
 Chemical
Antimicrobial agents
Chemical depends on circumstances and degree of control
require
 Physical
Heat (Temperature)
Radiation
Filtration

5. PHYSICAL CONTROLS:
HEAT

6. Dry Heat Sterilization kills by oxidation
Dry Heat Sterilization Kills by oxidation
Flaming
Incineration
Hot-air sterilization
Dry Heat

7. • Moist heat
denatures
proteins
• Autoclave:
Steam under
pressure
• 15 min at 121oC
at 15 psi
AUTOCLAVING
PHYSICAL CONTROLS

8. Escherichia colisubtilisBacillusTemperature
60 mins30 mins60 mins30 mins
5C
RT
37 C
55 C
70 C
90C

9. PASTEURIZATION
PHYSICAL CONTROLS
63oC for 30 minutes
72oC for 15 seconds
140oC for 1 second
Pasteurization reduces spoilage organisms and pathogens

10. http://www.mun.ca/biology/scarr/Thymine-
Thymine_Dimers.html
Radiation UV
Physical Controls

11. Radiation
Physical Controls
Ionizing radiation (X rays, gamma rays, electron
beams)
• Ionizing water and other molecules to form
radicals that disrupts proteins and DNA
• surgical supplies, plastic syringes
 Nonionizing radiation UV
DNA damage (260 nm Thymine dimers)

12. Time
1 second
5 second
10 second
30 second
45 second
50 second
60 second
Led on
• Micrococcus luteus
RADIATION

13. Desiccation
Very variable effect on microbes, many can
survive extended times (months), some
endospore for centuries, others die in minutes
Used usually for hospital & nursing home
microbiology,
Osmotic Pressure
High salt or sugar content (hypertonic
conditions)
Other Physical Controls

15. 15% NaCl10%NaCl5%NaCl
Salt
concentration
Figure : The growth of Escherichia coli and Staphylococcus aureus in Nacl concentrations of 5%,10%,15%
respectively

16. Filtration
 For heat sensitive solutions/liquids
 Cellulose esters or plastic polymers (pore
size from 0.01-0.45 µm)
 Used for :
 Culture media
 Laboratory reagents
 Pharmaceutical products
Culture mediaLaboratory reagentsPharmaceutical
products