1. CONTROL OF MICROBIAL GROWTH
CHAPTER 9
CONTROL OF MICROBIAL GROWTH

2. Terminology of Microbial Control
Sepsis/ Asepsis
Aseptic techniques
Sterilization
Commercial Sterilization
Sanitization

3. Antisepsis vs Disinfection
Biocide vs Biostatic
Degerming
Chemotherapy

4. Factors that influence the effectiveness of anti-microbial procedures:
microbial characteristics
number of microbes
Decimal reduction time (D value)
environmental influences
time of exposure
concentration or intensity of treatment

6. Physical or Mechanical Methods
Heat (moist & dry)
Filtration
Low temperature
High pressure
Desiccation & Osmotic pressure
Radiation

7. Heat Moist Heat Dry heat Boiling kills most vegetative forms in 10 min
Autoclave – steam under pressure
Sterilization - 15 psi, 121OC for 15 min
Pasteurization
Standard methods do not sterilize
higher temp, shorter exposure time
Dry heat
Incineration
Flaming
dry heat sterilization
Requires higher temp and longer exposure
170°C for 2 hours is equivalent to autoclaving

8. 2. Low Temperatures 3. Filtration Slows metabolic rate
Freezing forms ice crystals that can damage cells
Slow freezing then thawing does most damage
3. Filtration
Mechanical sterilization of heat-sensitive material
HEPA filters (high efficiency particulate air filters)
Membrane filters have pores as small as 0.01 microns

9. 4. High Pressure Up to 130,000 psi Endospores are resistant
Commercially pasteurize foods
Preserves flavor, taste, appearance, and nutritional value

10. 5. Desiccation Resistance varies by species
can’t reproduce or grow, but may remain viable
Osmotic pressure
create a hypertonic environment; dehydrates cells
Preserved fruits (sugar), cured meat (salt), and pickles (salt)

11. 6. Radiation depends on wavelength, intensity and duration
Ionizing vs non-ionizing
Sterilization of food products and disposable medical equipment; water treatment

12. Evaluating Anti-microbial Compounds
Phenol coefficient test
Use-dilution test
Current industry standard

13. Disk-Diffusion Method

14. Types of Anti-microbial Chemicals
Phenol (carbolic acid)
Rarely used, irritating qualities and bad odor
Penolic compounds more common
Disinfect for surfaces (Lysol) and antiseptic (antimicrobial soaps and lotions)
Halogens
Iodine – antiseptic or disinfectant
May be available as a tincture or iodophore
Chlorine - disinfectant (water treatment)

15. Alcohols
Affect vegetative forms of bacteria, fungi, and enveloped viruses
ethanol and isopropanol - degermer (hand sanitizer) and disinfectant
70% solution typically is most effective
Heavy metals
Silver; mercury; copper
antiseptic, algicide, mildew control paints, placed in newborn’s eyes to prevent spread of gonorrhea

16. Surfactants Soap Emulsification; degerming
Least effective of all chemical methods
Anionic Detergents
Commercial sanitizers
Cationic Detergents
disinfectant and antiseptic

17. Peroxygens Aldehydes Disinfectants
Ozone – supplements chlorine in water treatment
Hydrogen peroxide – good disinfectant not antiseptic
Where do the bubbles come from?
Aldehydes
Disinfectant and preservative
Formaldehyde – formalin
Irritating and carcinogenic
Glutaraldehyde
Liquid chemical sterilant

18. Biguanides Ethylene oxide Chlorohexidine most effect class
antiseptic in lotions, soaps and impregnated into surgical meshes and plastics
Ethylene oxide
Gaseous chemo-sterilizer
4 -18 hours exposure kills all microbes
Useful for heat sensitive materials

19. Food preservatives Organic acids – Sodium benzoate, Sorbic acid
Inhibit mold growth in acidic foods
Calcium propionate - fungicide used in bread
Inhibit mold growth
Nitrates- added to many meat products
prevents germination and growth of botulism endospores
preserves the pleasing red color ????

20. Antibiotics
Nisin- added to cheese to inhibit growth of endospore formers
Natamycin – antifungal used in food (mostly cheese)
Why should medical antibiotics not be used in food preservation?