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CLEMSON / Microbiology / MICR 4070 / Why do plants need microorganisms?

Why do plants need microorganisms?

Why do plants need microorganisms?


a. Impact of microbes in food

Why do plants need microorganisms?

i. Fermentation and food production: 22 billion gallons  of beer, 2.2 million tons of cheese, 90 million ponds  of pickles

ii. Foodborned illnesses: 48 million cases, 3,000 death,  128,000 hospitalizations

iii. Spoilage loss: 1/3 of world’s food supply

b. Food Regulatory System


1. FSIS: meat, poultry, and egg products

a. 15% food imported

b. 85% seafood imported

c. 60% fruits/veg imported

2. APHIS: protecting against plant and animal  

pests and diseases

ii. FDA

1. Fresh produce, seafood, imported food

iii. EPA

1. Controls pesticide usage

iv. Department of commerce

What are the sources of microbial contamination?

If you want to learn more check out What two factors influence the amount of circulating hormone levels?

1. National marine fisheries service

c. Food Safety-related Acts

i. 1906: Federal Meat Inspection Act

ii. 1957: Poultry Products Inspection Act

iii. 1997: Pathogen Reduction: Hazard Analysis and  Critical Control Point Final Rule (PR/HACCP)

1. Requires food industry to make sure standard  sanitization policies, and HACCP ahead of time. Required 10 e. Coli tests

iv. 2011: Food Safety Modernization Act (FSMA) v. “inspection acts” – instilled mandatory inspections of meat processing industries based on  


d. Sources of Microbes in Food

i. Classification of foods

1. Stable/Nonperishable: sugar, flour

a. Sometimes these will go bad if too moist  

What are the sources of microorganisms in food?

Don't forget about the age old question of What does anthropology focus on?

of environment, but in general at room  

temperature and dry conditions they are  


2. Semi perishable foods:

a. Potatoes, nutmeats (coconut, shredded  


b. Nutmeats can be oxidized because of  

high fat content

c. Potatoes sprout

3. Perishable foods:  

a. Meats, milk, fish

b. Usually high in water

c. Even if you use some kind of  

preservation method, they will still have  

a shelf life

ii. Sources of microbes in food

1. Plant sources: surfaces of fruits, veggies, crops; pores of some tubers, e.g. radish and onions a. High number of microbes found on  

surface of plants nad areas close to soil

2. Animal sources:

a. Skin, hair, feathers, gastrointestinal, milk  ducts/teats Don't forget about the age old question of What do heterotrophs consume?

b. Outside of the animal associated with  

microbes –skin, fur, etc

c. GI tract also mostly associated with  


3. Environmental sources:

a. Air, water, soil, manure, equipment,  

insects, rodents, food handlers, etc.

iii. Plant microorganisms

1. Most common: molds, yeasts, lactic acid  bacteria, Pseudomonas, Alcaligines,  

Micrococcus, Erwinia (contributes to soft rot),  Bacillus, Clostridium, Enterobacter (GI tract) 2. Type and numbers are affected by:

a. Presence of plant diseases

b. Surface damage

c. Delay between harvesting and washing:  important b/c you have cut surface by  

harvesting which allows unfavorable  

microbes to get in

d. Unfavorable storage

e. Transportation conditions

3. Because of their high nutrient content, plants  can support growth of various microorganisms iv. Animal microorganisms

1. In healthy animals:

a. Internal tissues are sterile

b. Digestive tract has commensal bacteria  and pathogenic bacteria:

i. Salmonella spp.: very powerful,  

cause diarrhea and gasteroenteritis

ii. pathogenic E. coli: ground beef,  

apple cider, fresh produce

iii. Campylobacter jejuni: raw chicken

iv. Yersinia enterocolitica: affects GI  

tract If you want to learn more check out Who taught rhetoric?

v. Listeria monocytogenes: 1:4 people

who get sick will die

c. Animal hides/feathers:  

i. If you clean animal very well before

slaughtering, you can reduce  

number of microorganisms in the  

carcass significantly.

d. Lymph nodes:  

i. Immune defense system of animals

ii. Particles (including  

microbes/pathogens) are  

embedded in fat tissue of animals

iii. If you don’t take these nodes out  

before processing, you risk  


2. Sea animals:

a. Fish: microbes are in scales, gills, and  

digestive tract

b. Shellfish: in digestive tract

i. These animals are filter feeders,  

which concentrates the microbial  

content – more dangerous for  

human consumption

c. Types of microbes affected by water  

quality, feeding habits, seasons

i. Off shore fish/sea animals,  

microbial quality is much better  

because water is cleaner

ii. Bottom feeders have more  

contamination than surface feeder

iii. Water temp increases, more  

microbial growth If you want to learn more check out What is the role of the monasteries?

d. Major Pathogens:

i. Vibrio parahaemolyticus: causes  

liver damage, paralysis

ii. V. vulnificus

iii. V. cholerae

iv. Listeria monocytogenes: more in  

processing environment than the  

fish itself or the water.

v. External sources of microbial contamination

1. Air: dust particles containing bacterial  

endospores, e.g., Bacillus spp., fungal spores,  

Micrococcus spp., Sarcina spp., yeasts

a. Not visible to naked eye but they are  

there – meaning they must be very  

lightweight. Spores are common because

they are dehydrated so therefore very  


2. Soil: molds, yeasts, bacteria, many types; great variations in species and total numbers

3. Sewage: used as a fertilizer for some crops –  can lead to contamination enteropathogenic  

bacteria and viruses

a. Common in developing countries to use  

human waste.  

b. In developed countries, waste is treated  

before use as fertilizer

4. Water: used for production, processing, storage (ice), washing equipment, food handling  We also discuss several other topics like What are the two domains of kingdom monera?

facilities – may contain species of  

Pseudomonas, Alcaligenes and Flavobacterium a. Water is recycled because it is in high  


b. Listed bacteria are common and spore


5. Humans: during processing, restaurants, retail  stores, and homes; Staphylococcus aureus,  

Salmonella spp., pathogenic E. coli, Hepatitis A a. Humans are carriers of many pathogens

b. Importance for sick food service  

employees to stay home

6. Food ingredients: may introduce spoilage and  pathogenic microorganisms, e.g., spices;  

molds, bacterial spores

a. Ex) large outbreak in sausage because of

a spice used in cooking

b. Microbes found in spices/herbs are those  

that can tolerate extremely dry  


7. Equipment: microbes introduced from  

equipment during harvesting, transportation,  

processing, and storage

e. Microbial Classification

i. Eukaryote:

1. Has a membrane-bound nucleus

2. Mold, fungus, and yeast

ii. Prokaryote:

1. Nucleoid

2. Thick/thin cell wall  

3. Gram +/Gram –

4. Gram staining process

5. Some are motile – have flagella

6. Bacillus, spirillus, spherical

iii. Mold

1. Multicellular, many spores produce at the end 2. Pizza crust – ascorbic/propionic acid added as  preservatives to dry and stabilize it. Relies on  moisture free packaging

3. Important mold genera in foods:

a. Aspergillus: spoilage of grains, jams,  

cured hams, nuts, fruits, vegetables;  

some produce mycotoxins

i. A. oryzae: sake production

ii. A. niger: produce many enzymes;  

including beta-galactosidase

1. Mold usually grows very  

slowly and then once you can

see it, it grows very quickly

b. Alternaria: brown to black rots of stone  

fruits (peach, plums); some produce  


c. Geotrichum: “dairy mold” spoilage of  

dairy products

d. Mucor: spoilage of vegetables; used in  

some fermentation; source of enzymes.

i. White/greenish hair looking

ii. Use to make Chinese cheese

e. Penicillium: rot of fruit and vegetables;  

spoilage of grains, bread, meats; some  

species produce mycotoxins; some used  

in food production

i. Spores called “conidia” on  

penicillium, gives blue cheese its  

blue color

f. Rhizopus: spoilage of fruits and  

vegetables; common black mold found  

on bread

i. Also spoils lamb meat

iv. Yeast

1. Single-cellular

2. Yeast is roughly 5-8 micrometer in diameter  (slightly bigger than bacteria)

3. Can grow in a wide range of pH  

4. 55-65% sucrose (grows well in grape because  they have a high sucrose content)

5. Cream to red color  

6. Important yeast genera in foods

a. Saccharomyces: spoilage of some foods;  used for production of bread, wine and  


i. Good in foods with higher sugar  

content like juices

b. Pichia: spoilage of beer, wine, and foods  preserved in brine; some used in  

fermentation of food

i. Arabic yeast

c. Kombucha tea: a product of the  

fermentation of black and/or green tea  

and a mushroom-shaped culture of yeast  

and bacteria

d. Rhodotorula: causing discoloration of  

meats, fish, and sauerkraut

i. Pink/red color

ii. Grows in psychotropic  

environments (cold) – like  


e. Candida: spoilage of food of high acidity,  high salt, high sugar content; forming  

pellicle on liquid surface; causing  

rancidity of butter and dairy products

i. In gut

ii. In clinical setting: causes yeast  


v. Prokaryotes

1. Acinetobacter: G-, rods, widely distributed in  soil, many food, esp. refrigerated fresh  


a. psychrophile

2. Aeromonas: G-, rods, associated with aquatic  products/environment, intestines of fish

a. psychrophile

3. Alcaligenes: G-, rods, widely distributed in  nature and decayed material, raw milk, poultry  products, fecal matter

4. Alteromonas: G-, rods, marine and coastal  water, seafoods

5. Arcobacter: G-, s-shaped rods, poultry, raw  milk, shellfish, cattle, swine, water

a. Used to be in same family as  

campylobacter but not anymore because  they can tolerate more environments

6. Bacillus: G+, sporeforming rods, aerobes, soil,  dust, water, fresh & processed foods

7. Brochothrix: G+, nonsporeforming rods,  processed meat

a. Very similar to listeria monocytogenes

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