This document discusses various chemical and physical methods for controlling bacterial growth. It lists chemical agents like phenol, halogens, alcohols and heavy metals that have antimicrobial effects. Physical control methods include heat (through autoclaving, pasteurization, dry heat sterilization), radiation, filtration, cold temperatures, desiccation and high osmotic pressure. The effectiveness of these control methods depends on factors like the number and characteristics of microbes, concentration and type of agents used, and duration of exposure.

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