Factors Affecting Microbial Growth - pp presentation

8/12/2019 Factors Affecting Microbial Growth - pp presentation

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Factors Affecting Growth ofMicroorganisms

So what if the egg salad sat out atroom temperature for two hours!


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Outline

What are microorganisms?

Types of microorganisms

Classifying bacteria Factors affecting bacterial growth


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An organism that istoo small to be seenwith the naked eye

Microorganisms - What are

they?


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If bacteria wereone cm long

A man would be 10.5miles (17 km) tall

How big are

microorganisms?


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The Good, the Bad, the Ugly

Good-Fermentative Microorganisms

Bad-Pathogens

Ugly-Spoilage

Listeria monocytogenes


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Larger than bacteria

Uni- (ie., protozoa) or multi-cellular

(ie., worms)

Needs host to survive

Can go through several developmentastages in life cycle

Some are beneficial to host

Characteristics of

Parasites


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Unicellular

May have structures forpropulsion or movement

Needs host to survive

Can exist in environment or hostduring its life cycle

Characteristics of Protozoa


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Smaller than bacteria

DNA or RNA surrounded by

protein coat

Needs host to replicate but cansurvive outside of host

Characteristics of Viruses


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Molds are commonly found inmoist, nutrient-rich environments

Grow by thread-like filamentscalled hyphae

A tangled mass of hyphae iscalled a mycelium

Characteristics of Molds


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Reproduce by spores

Spores are easily

spread by air or arecarried on insects andanimals

Basidiosporeswww.asm.org


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Can produce mycotoxins

Can produce antibiotics


Penicilliumwww.dehs.umn.edu


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Involved in food spoilage


Involved in food manufact

Bread moldwww.sci.mus.mn.us

Blue cheese


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Usually egg-shaped

Single-celled organisms

Reproduce by budding

Characteristics of Yeasts

Budding yeastwww.phys.ksu.edu/gene


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Easily killed by heating at 58C (136F) for 15minutes

Ferment sugars to alcohol and CO2

Several food uses

Characteristics of Yeasts

www. ars.usda.gov


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Largest group ofmicroorganisms

Thousands of species

Some are pathogenic,others are harmless

(fermentation, spoilage)

Characteristics of Bacteria

www.usda.gov

Salmonella enteriditis
http://www.usda.gov/oc/photo/99c0647.jpg


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Characteristics of Bacteria

Some may produce sporesto survive adverseconditions

Spores are particularlyresistant to heat, drying,and chemicals

Spores can latergerminate and grow intoactive cells

Bacillus breviswith sporesCDC/Dr. William A. Clark

Spores


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Classification of Bacteria

According to cell shape

According to cell grouping

According to ability retain specific stains

According to growth conditions


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According to cell shape

Classifying Bacteria

Rods SpiralCocciwww.asm.orgCDC/Janice Carr CDC/Janice Carr


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According to cell grouping


Pairs ChainsClustersEnterococcus

CDC/Janice Carr

Staphylococcusaureus

www.cellsalive.net

www.asm.gov


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According to ability toretain specific stains

Gram Stain:


GramPositive

GramNegative

CDC/Dr. William A. Clark


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Bacteria reproduce through binaryfission:

How Do Bacteria Grow?


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If bacteria divide every 20 minutes, it wouldtake only 6 hoursfor 1 bacteria cell to

become 1 million bacteria !TIME IS AN IMPORTANT FACTOR IN

MICROBIAL GROWTH!

Bacteria Can Grow Rapidlyto High Numbers

www.cellsalive.net


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Bacterial Growth Curve

Time

Lag

Stationary

Decline

/DeathLog


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What Affects BacterialGrowth?

Intrinsic Factors Those that are integral to the food

Nutrient Content (food)

Acidity (pH or TA) Water Activity (aw)


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What Affects BacterialGrowth?

Extrinsic Factors Those that are external to the food(environmental)

Temperature Level of Oxygen


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Nutrients-Food

Food products (ie. meat, milk, fruit,vegetables, etc.) are high in nutrientsproteins, carbohydrates, fat,

phosphorus, minerals, and water Food products are an excellent sourceof nutrients to support microbialgrowth


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Measure of Acidity or pH

1 4 7 10 1


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Measure of Acidity or pH

Most foods are in the pH range of 5-7

Bacteria typically do not grow below pH 4.6

pH Range for growth in foods

Bacteria 5 - 6

Yeasts 4 - 4.5

Molds < 4


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Water Activity (aw)

0.5 .75 1.

Measure of the free water available for growth


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Water Activity aw=water activity Unbound water available formicrobial growth

aw affected by presence of solutes(salts, sugar bind water andtherefore, unavailable formicrobes)

decreasing aw=increase in lagphase and decrease bacterial


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Water Activity (aw)

Measure of the free water available forgrowth

Scale = (no water) 0 to 1.0 (lots of water)

Minimum awfor growth

Bacteria 0.90

Yeasts 0.87Molds 0.70

170


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-60

-50

-40

-30-20

-10

-0

170-160-150-140-130-120-110-100-90-80-70-60-50-40-30-20-

Psychrotrophs32-68F0-7C

Mesophiles68-113F

15-35C

Thermophiles113-140F43-54C

Degrees Fahrenheit (oF) Degrees Celsius (oC)


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Tolerance to Oxygen

Aerobic Anaerobic FacultativelyAnaerobic


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Summary

Microorganisms may be grouped asbacteria, protozoa, fungi, and viruses

Microorganisms may be classified

according to their physicalcharacteristics or their growthconditions

By changing growth conditions, bacteriamay be controlled


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Test your knowledge:

What is a microorganism?

What are the four stages of bacterialgrowth?

What compounds, when added to foods,affect water activity?

What is meant by anaerobic growth?

What is the temperature danger zone? Bacteria grow best at____ pH.


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Test your knowledge:

What are the four main types ofmicroorganisms?

What are five factors affecting microbial

growth? What are examples of foods made bygood microorganisms?

What are examples of pathogens

considered bad microorganisms? What are examples of uglymicroorganisms?

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Factors Affecting Microbial Growth - pp presentation