Requirements for Growth Effect of pH and temperature on microbial ...

Lab.3.
Practical Microbial Physiology
<strong>Requirements</strong> <strong>for</strong> <strong>Growth</strong>
<strong>Effect</strong> <strong>of</strong> <strong>pH</strong> <strong>and</strong> <strong>temperature</strong> on microbial growth
<strong>Requirements</strong> <strong>for</strong> <strong>Growth</strong>
a) Physical <strong>Requirements</strong>
b) Chemical <strong>Requirements</strong>
a) Physical <strong>Requirements</strong>
1. Temperature:
Each microbial species requires <strong>temperature</strong> growth range that is determined by the heat
sensitivity <strong>of</strong> its particular enzymes, membranes, ribosomes, <strong>and</strong> other components.
<strong>Growth</strong> Rates <strong>of</strong> Bacterial Groups at Different Temperatures
Microbes are classified into several groups based on their preferred <strong>temperature</strong> ranges:
a. Psychrophiles: “Cold-loving”. Can grow at 0 o C, including two groups:
True Psychrophiles: Sensitive to <strong>temperature</strong>s over 20 o C. Optimum growth at 15 o C or below.
Found in very cold environments (North pole, ocean depths). Seldom cause disease or food
spoilage.
Psychrotrophs: Optimum growth at 20 to 30 o C. Responsible <strong>for</strong> most low <strong>temperature</strong> food
spoilage.
B. Mesophiles: “Middle loving”. Most bacteria.

Include most pathogens <strong>and</strong> common spoilage organisms.
Best growth between 25 to 40 o C.
Optimum <strong>temperature</strong> commonly 37 o C.
Many have adapted to live in the bodies <strong>of</strong> animals.
C. Thermophiles: “Heat loving”.
Optimum growth between 50 to 60 o C.
Many cannot grow below 45 o C.
Adapted to live in sunlit soil <strong>and</strong> hot springs.
Some thermophiles <strong>for</strong>m heat resistant endospores.
Extreme Thermophiles (Hyperthermophiles): Optimum growth at 80 o C or higher.
Archaebacteria. Most live in volcanic <strong>and</strong> ocean vents.
Organism Minimum Optimum Maximum
Bacillus cereus 5 28 - 40 55
Campylobacter spp. 32 42 - 45 45
Clostridium botulinum 10 - 12 30 - 40 50
Clostridium perfringens 12 43 - 47 50
Enterotoxigenic Escherichia coli 7 35 - 40 46
Listeria monocytogenes 0 30 - 37 45
Salmonella spp. 5 35 - 37 45 - 47
Staphylococcus aureus 7 35 - 40 48
Shigella spp. 7 37 45 - 47
Vibrio cholerae 10 37 43
Vibrio parahaemolyticus 5 37 43
Vibrio vulnificus 8 37 43
Yersinia enterocolitica -1 28 - 30 42
2. <strong>pH</strong>:
<strong>pH</strong> dramatically affects bacterial growth, this is because that <strong>pH</strong> affects the activity <strong>of</strong> enzymes
those that are involved in biosynthesis <strong>and</strong> growth.
Each microbial species possesses a definite <strong>pH</strong> growth range <strong>and</strong> a distinct <strong>pH</strong> growth
optimum.

Most bacteria prefer neutral <strong>pH</strong> (6.5-7.5).
Molds <strong>and</strong> yeast grow in wider <strong>pH</strong> range, but prefer <strong>pH</strong> between 5 <strong>and</strong> 6.
Organisms can be classified as:
A. Acidophiles: “Acid loving”.
Grow at very low <strong>pH</strong> (0.1 to 5.4)
Lactobacillus produces lactic acid, tolerates mild acidity.
B. Neutrophiles:
Grow at <strong>pH</strong> 5.4 to 8.5.
Includes most human pathogens.
C. Alkaliphiles: “Alkali loving”.
Grow at alkaline or high <strong>pH</strong> (7 to 12 or higher)
Vibrio cholerae <strong>and</strong> Alkaligenes faecalis optimal <strong>pH</strong> 9.
Soil bacterium Agrobacterium grows at <strong>pH</strong> 12.
Microorganism Minimum Optimum Maximum
Clostridium perfringens 5.5 - 5.8 7.2 8.0 - 9.0
Vibrio vulnificus 5.0 7.8 10.2
Bacillus cereus 4.9 6.0 -7.0 8.8
Campylobacter spp. 4.9 6.5 - 7.5 9.0
Shigella spp. 4.9 9.3
Vibrio parahaemolyticus 4.8 7.8 - 8.6 11.0
Clostridium botulinum 4.6 8.5
Staphylococcus aureus 4.0 6.0 - 7.0 10.0
Enterohemorrhagic Escherichia coli 4.4 6.0 - 7.0 9.0
Listeria monocytogenes 4.39 7.0 9.4
Salmonella spp. 4.2 1 7.0 - 7.5 9.5
Yersinia enterocolitica 4.2 7.2 9.6