Micrb 265 lec 13
What is food spoilage?
When microbes grow in food and change its appearance or taste
What major factor is food spoilage closely tied to?
Moisture content
Why is moisture so important in food spoilage?
Microbes need water to grow
How does low moisture affect microbial growth in food?
It makes growth less likely
What determines whether microbes will grow on food?
Inoculation size, pH, moisture level, and nutrients
What general group of microbes commonly spoil fruits and vegetables?
Erwinia, Pseudomonas, and Corynebacterium
What general group of microbes commonly spoil meat, seafood, and eggs?
Acinetobacter, Aeromonas, Pseudomonas, Micrococcus, Achromobacter, Flavobacterium, Proteus, Salmonella, Escherichia, Campylobacter, and Listeria
What general group of microbes commonly spoil milk?
Streptococcus, Leuconostoc, Lactococcus, Lactobacillus, Pseudomonas, and Proteus
What general group of microbes commonly spoil high sugar foods?
Clostridium, Bacillus, and Flavobacterium
What is food poisoning?
Ingestion of food contaminated with toxins
What is food infection?
Ingestion of organisms that grow in the host and then trigger symptoms
What is the key difference between food poisoning and food infection?
Food poisoning is caused by ingesting toxins, while food infection is caused by ingesting living microbes that grow in the host
What bacteria were given as examples of food poisoning?
Staphylococcus aureus and Clostridium perfringens
What was the key example of food infection?
Salmonella
Why can food poisoning happen even if the microbes are no longer alive?
Because the toxin may already be present in the food
Are food poisoning toxins acid stable?
Yes
Why is acid stability important for food poisoning toxins?
It lets them survive passage through the stomach
Are some food poisoning toxins heat stable?
Yes
How heat stable is Staphylococcus aureus enterotoxin?
Up to about 60°C or 140°F
How heat stable is Clostridium perfringens toxin?
Up to about 75°C or 168°F
Why are spore-formers a concern in food poisoning?
Spores can survive, germinate later, and produce new toxins
Why is canned food a particular concern for food poisoning?
Spores and anaerobic growth can allow toxin production if conditions are right
How quickly do food poisoning symptoms usually start?
Within hours
How long does food poisoning usually last?
It often resolves on its own, though severe cases can be dangerous
What are five severe food poisoning warning signs from the lecture?
Vomiting so much you cannot keep liquids down, bloody diarrhea, fever higher than 102°F, dehydration, and diarrhea for more than 3 days
Why is symptom onset slower in food infection than in food poisoning?
The organism needs time to grow in the host
How quickly do food infection symptoms usually start?
Usually 12 or more hours later
Can food infection symptoms appear much later than 12 hours?
Yes, they can appear months or even years later in some cases
What does Salmonella do in food infection?
It colonizes the intestinal epithelium, can invade phagocytes, produces toxins, and may spread beyond the intestine
What condition does Salmonella commonly cause in the intestine?
Enterocolitis
Why can food infection be worse than just ingesting toxin alone?
The bacteria continue growing and can keep producing toxin
What are psychrotolerant organisms?
Organisms that grow best above 20°C but can still grow at refrigerator temperatures and sometimes even in frozen foods
Why are psychrotolerant food pathogens important?
They can still grow during refrigeration or freezing
Can microbes grow in frozen food?
Yes, they can grow in small water pockets in frozen foods
What three major variables prevent microbial growth in food?
Temperature, moisture, and pH
How do cold temperatures help preserve food?
They slow microbial growth
Does freezing completely stop microbial growth?
No
What is pasteurization?
A limited heat treatment used to reduce pathogens
What temperature and time range was given for pasteurization?
About 70–90°C for 30–300 seconds
Does pasteurization sterilize food?
No, it only reduces pathogens
What does canning do to help preserve food?
It uses high temperature and also reduces oxygen
Why can canning still be risky for some pathogens?
Some pathogens are anaerobes, such as Clostridium botulinum
Why is Clostridium botulinum dangerous in canned foods?
It is anaerobic and produces botulinum toxin
How can spoiled canned food sometimes be recognized visually?
The can may bulge because gas is produced during microbial growth
What should you avoid consuming when it comes to canned food?
Any can with a bulging lid
How can reducing moisture preserve food?
By making it harder for microbes to grow
What are two major ways to reduce moisture in food preservation?
Dehydration and adding solutes
Why does dehydration need to be done carefully?
Because microbes can still grow during the drying process if conditions are wrong
What kinds of solutes can be added to reduce microbial growth?
Salt and sugar
What is curing?
Preserving food by adding salt
Do high solute levels suppress all microbes?
No, they suppress most but not all
What sugar was specifically mentioned as stimulating Clostridioides difficile?
Trehalose
How can lowering pH preserve food?
Acidic conditions inhibit many microbes
What is pickling?
Using acids to lower pH and preserve food
How else can pH be lowered besides adding acid directly?
By fermentation
What kind of bacteria are most common in acid production during fermentation?
Lactic acid bacteria
Why does fermentation help preserve food?
It produces acids that inhibit the growth of many microbes
What is bioremediation?
The use of organisms to remove environmental pollutants
What is a biofactory?
The use of organisms to produce desirable molecules
What three broad contaminant types were mentioned in bioremediation?
Inorganic contaminants, organic contaminants, and xenobiotics
What is an example of an inorganic contaminant?
Uranium
What is an example of an organic contaminant?
Oil from spills
What is an example of a xenobiotic?
PCBs
Why are microbes useful in bioremediation?
They are metabolically diverse and can absorb, concentrate, or degrade pollutants
What practical advantages do microbes have in bioremediation?
They are cheap, sustainable, and environmentally friendly
What microbe was highlighted for cleaning up oil spills?
Alcanivorax borkumensis
Why is Alcanivorax borkumensis called a hydrocarbon specialist?
It uses alkanes as an energy source
What can Alcanivorax borkumensis not really use as food?
Sugars and amino acids
What enzyme type does Alcanivorax borkumensis use to begin hydrocarbon breakdown?
Monooxygenases
What is the first major chemical step in alkane breakdown?
Oxidation of the alkane to an alcohol
What is the basic hydrocarbon breakdown sequence emphasized in lecture?
Alkane to alcohol to aldehyde to acid to beta-oxidation
Why is oxygen required for hydrocarbon degradation?
It is needed for the initial oxidation step
Why does Alcanivorax borkumensis work well in seawater?
It is halophilic
How does Alcanivorax borkumensis help physically with oil breakdown?
It produces surfactants to break up oil droplets
What extra nutrients does Alcanivorax borkumensis need to grow well?
Phosphorus and nitrogen
What is one disadvantage of Alcanivorax borkumensis for oil spill cleanup?
It is not particularly fast
How can people help Alcanivorax borkumensis clean oil spills more effectively?
By providing absorbent materials plus nitrogen and phosphorus to concentrate oil and support growth
What is bioventing?
A bioremediation method where microbes, nutrients, and oxygen are added to polluted soil or groundwater
Why is oxygen added during bioventing?
To support aerobic degradation of pollutants
What happens after pollutants are cleaned up in bioventing?
Oxygen addition can stop and the added bacteria eventually stop growing
What kinds of useful products can microbes make in biofactories?
Human proteins, biofuels, drugs, enzymes, food or feed products, and small molecules
Why are microbes good biofactories?
They are generally cheaper, faster, and scalable
What medically important proteins can microbes produce?
Blood proteins, hormones, immune modulators, and therapeutic enzymes
What blood protein example was given?
Erythropoietin
What hormone example was given?
Insulin
What immune modulator example was given?
Interferons
What therapeutic enzyme example was given?
Alginate lyase
Why are microbial biofactories useful for mammalian proteins?
Many mammalian proteins are valuable but naturally present in very low quantities
What recombinant animal protein example was discussed?
Recombinant bovine somatotropin
What organism produces recombinant bovine somatotropin in the lecture example?
E. coli
What does recombinant bovine somatotropin do in cows?
It binds the prolactin receptor and increases lactation
How is recombinant protein production in E. coli done at a simple level?
Insert the gene into a plasmid, transform E. coli, then grow the bacteria to produce the protein
What kinds of non-protein products can microbial biofactories also make?
Antibiotics, anti-cancer drugs, pain medication, enzymes, vanillin, indigo dye, and fuels
What enzyme use example was given for paper production?
Xylanase
What enzyme use example was given for laundry detergent?
Lipases
Why is microbial production of indigo useful?
Traditional indigo production is not environmentally sustainable
What biofuel-producing microbe was highlighted?
Caldicellulosiruptor bescii
What kind of organism is Caldicellulosiruptor bescii?
A Gram-positive anaerobic thermophile
What raw material can Caldicellulosiruptor bescii break down?
Cellulose from grasses
What does it turn cellulose into first?
Fermentable sugars