1. Factors affect growth of bacteria
Indhira Kramomtong
Department of Microbiology, Faculty of Veterinary Science
Chulalongkorn University

2. Cell division by binary fission
generation time (doubling time)

3. And ending at the point of having just completed the next division.
Doubling time is the time it takes a bacterium to do one binary fission starting from having just divided.
And ending at the point of having just completed the next division.

5. Factors affect growth of bacteria Requirement: * Physical environment
* Chemical environment

6. Physical Environment Temperature Bacteria Temp (0C) min op max
Psychrophile <  20
Psychrotroph > 25
Mesophile
Thermophile

8. Physical Environment (cont.)
* Most bacteria grow between pH
* Very few grow below pH 4 acid-producing bacteria
* Proteolytic bacteria can grow in media with alkaline pH
* Molds grow wider range of pH than most yeast ( ) and bacteria

9. Physical Environment (cont.)
Osmotic pressure
* Microbes obtain most of their nutrients in solution from surrounding water plasmoptysis, plasmolysis
* Many foods preserved this way : high sugar or salt draw water out of bacterial cells prevent their growth eg. salted fish, fruits in syrup

11. Chemical Environments
Moisture and water activity (aw)
* The exact amount of water needed for growth varies
* Relative humidity about a food correspond to aw lower than that of food dry surface
* Relative humidity higher than that correspond to the aw increased the surface of food

12. The water activity (aw)
vapour pressure ของสารละลายในอาหาร =
vapour pressure ของ ตัวทำละลาย (น้ำ)
aw x = ERH (%)
aw = ERH

13. Minimum aw of microbes cause food spoilage
Microbes aw
bacteria
yeast
mold
halophilic bacteria
osmophilic yeast

14. aw has its most useful application in predicting the growth of bacteria, yeasts and moulds (Predicting Food Spoilage)

15. The typical water activity of some foodstuffs
Type of products
Water activity(aw)
Bone dry
Pure water
1.0
Fresh meat and fish
Bread
Aged cheddar
Jams and jellies
Plum pudding
Dried fruit
Biscuits
Milk powder
Instant coffee .

16. Chemical Environments (cont.)
Oxygen concentration
From the ability to use free oxygen, microbe has been classified as

17. aerobe presence of O2(20%) mold, most yeast, bacteria
obligate
* anaerobe
* facultative
do not require O2 but do grow better in its presence
* microaerophile require O2 level below %

19. microbe has been classified as

20. Chemical Environments (cont.)
Nutrients
1. Food for energy
2. Food for growth
3. Accessory food substances or vitamins

21. 1. Food for energy carbohydrate - sugar, ester, alc,
- microbes differ in their ability to use soluble sugar
protein
- peptides, amino acid proteolytic bacteria when other energy source is lacking

22. fat
- few microbes obtain their energy from fat
- when usable energy food eg. sugar is absent
- hydrolysed with aid of lipase to glycerol and fatty acid
- aerobic microbes involved than anaerobic ones
- lipolytic organisms usually also proteolytic
- many kinds of molds are proteolytic but few bacteria and yeast are

23. 2. Food for growth Nitrogen
- some microbes cannot get nitrogen from protein without help from proteolytic microbes eg. amino acid, peptide, nitrite and nitrate salts, ammonia
Carbon
- come from CO organic compounds

24. Sulfur
component of cysteine and methionine essential for protein structure within the cell
Phosphorus
metabolism of nucleic acid component of phospholipid, teichoic acid, etc.

25. Minerals:
macroelement
Mg Ca Fe Zn K
metabolism and growth
trace element:
Mn Co Mb Cu
cofactor of enzyme system

26. 3. Accessory food substances or vitamins (growth factors)
- bacteria vary in need for vitamins or accessory growth factors from nutrient
- some synthesize in part (S. aureus) others synthesize all of factors needed (Pseudomonas or E. coli)

27. Inhibitory substances
present in food
added purposely or accidentally
developed by growth of microbes
may prevent growth of microorganisms

28. Inhibitory substances (cont.)
lysozyme in egg white
present in food
added purposely
phenol compound added to meat or fish by smoking
destroy certain mold & bacteria
acid, alc
Inhibit other bacteria
developed by growth of microbe
antibiotic