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1. PHYSICAL METHODS OF MICROBIAL CONTROL
Presented To: Dr Noroza Umer
Presented By:
Fatima Niaz (447-BS-CHEM-22)
Mubarrah Shehzadi (444-BS-CHEM-22)

2. Contents
Introduction
Physical Methods of Microbial Control
1) Filtration
 HEPA Filters
 Membrane Filters
2) Radiation
 Ionizing Radiation
 Ultraviolet Radiation
 Microwave Radiation

3. Early civilizations practiced salting, smoking, drying, and exposure
of food and clothing to sunlight to control microbial growth.
In mid 1800s Lister helped developed aseptic techniques to
prevent contamination of surgical wounds by using Carbolic acid
(Phenol Compound).
• Nosocomial infections caused death in 10% of surgeries.
• Up to 25% mothers delivering in hospitals died due to infection
Introduction
Need for Microbial Control

4. Physical Methods of Microbial Control
Filtration
Removal of microbes by passage of a liquid or gas through a
screen like material with small pores.
A vacuum is created in the receiving flask ; air pressure then
forces the liquid through the filter.
Used to sterilize heat sensitive materials like vaccines,
enzymes, antibiotics, and some culture media.

5. High Efficiency Particulate Air Filters (HEPA): Used in
operating rooms and burn units to remove bacteria from
air.
 They remove all microorganisms larger than about 0.3µm
in diameter.
 They are constructed of borosilicate microfibres in the
form of pleated sheets.

6. HEPA Filters
High-Efficiency Particulate Air Filters
I. Operating Rooms
II. Burn Units
III. Fume Hoods

7. Membrane Filters:
Uniform pore size. Used in industry and research.
0.22 and 0.45μm Pores: Used to filter most bacteria.
Don’t retain spirochetes, mycoplasmas and viruses.
0.01 μm Pores: Retain all viruses and some large proteins.
Membrane-based separation processes make use of
selective permeability.

9. Radiation: Three types of radiation kill microbes:
1. Ionizing Radiation: Gamma rays, X rays, electron beams, or
higher energy rays. Have short wavelengths (less than 1
nanometer).
 Dislodge electrons from atoms and form ions.
 Cause mutations in DNA and produce peroxides.
 Used to sterilize pharmaceuticals and disposable medical supplies.
Food industry is interested in using ionizing radiation.
Disadvantages: Penetrates human tissues. May cause genetic
mutations in humans.

10. Forms of Radiation

11. Radiation
Electromagnetic radiation includes (in decreasing order of
wavelength=energy) electron beams, gamma-rays, x-rays,
UV light, visible light and infrared light.
All radiation with wavelength < 1 nm are ionizing = have
sufficient energy to knock electrons off an atom
Most non-ionizing radiation is not sufficiently energetic to
kill microbe, except UV light, which injures DNA, but
does not penetrate well
Microwaves kill by secondary heat effect

12. Radiation
1. Ionizing Radiation
1. High Degree of
Penetration
2. Examples
- Gamma Rays
- X-rays
- High Energy
Electron Beams
2.Ultraviolet Radiation
1. Nonionizing
2. Low Degree of
Penetration
3. Low Penetration
4. Harmful / Skin / Eyes
5. Cell Damage /
Thymine
6. Germicidal / 260 nm

13. 3. Microwave Radiation:
 Wavelength ranges from 1 millimeter to 1 meter.
 Heat is absorbed by water molecules ( ionized water).
 May kill vegetative cells in moist foods.
 Bacterial endospores, which do not contain water, are not
damaged by microwave radiation.
 Solid foods are unevenly penetrated by microwaves.
Kill Microbes Indirectly
with Heat

14. References
 https://openstax.org/books/microbiology/pages/13-2-using-physical-methods-to-control-
microorganisms
 Cutter, C. N. (2002). Microbial control by packaging: a review. Critical reviews in food
science and nutrition, 42(2), 151-161.
 Ngadi, M. O., Latheef, M. B., & Kassama, L. (2011). Emerging technologies for microbial
control in food processing. Green technologies in food production and processing, 363-
411.
 Li, L., Wilson, C. B., He, H., Zhang, X., Zhou, F., & Schaeffer, S. M. (2019). Physical,
biochemical, and microbial controls on amino sugar accumulation in soils under long-term
cover cropping and no-tillage farming. Soil Biology and Biochemistry, 135, 369-378.
 Schimel, J. P., & Schaeffer, S. M. (2012). Microbial control over carbon cycling in
soil. Frontiers in microbiology, 3, 348.