Lab 4 - Microbiology of Foods Flashcards
What are some examples of things that are allowable defects?
Insect filth, rodent filth, parasites, mildew, cigarette butts, and mammalian excreta.
Where are these “allowable defects” stated?
In an FDA booklet
What does the NY times estimate?
They estimate that you’re probably infesting 1-2 lbs of flies, maggots, and mites without knowing it.
What are mites?
Small arthropods, similar to ticks
How many people in the US get sick every year from contaminated food?
76 million
What are some symptoms of eating contaminated food?
Upset stomach Abdominal cramps Nausea and vomiting Diarrhea Fever Dehydration
Where do contaminants often come from?
From the animal itself, or from the utensils and equipment used
What types of bacteria can be found in contaminated meat?
Non-pathogenic
Pathogenic
Pathogenic that produce toxic waste products in the meat
What are coliform bacteria used for?
They are an indicator of sanitary quality of foods and water. Since they are often found in feces, their presence often indicates that other microorganisms of faecal origin may be present.
What is a coliform bacteria?
Rod-shaped Gram negative non-spore forming microorganisms. They can be aerobic or facultatively anaerobic.
What do coliforms ferment?
Some enterobacteriaceae can ferment lactose with the production of acid and gas when incubated at 35-37 C
Others can ferment glucose
Where can coliforms be found?
In the feces of warm-blood animals, in the aquatic environment, soil, and vegetation.
What bacteria are common causes of nosocomial illnesses?
Coliforms
What are some examples of faecal pathogens?
Bacteria, viruses, protozoa, and many multicellullar parasites
What does VRBA stand for?
Violet red bile agar
What is in VRBA?
Peptone = C and N source for growth
Yeast extract = B-complex vitamins for growth
Bile + Crystal violet = inhibit gram positive growth
Lactose = carbohydrate source
Neutral red = pH indicator
What are the different results one can expect with a VRBA?
Lactose fermenters = Purple-red colonies (w/ or w/o zone of precipitate)
Non-fermenters = Colorless to transparent colonies
Gram positive cocci = Colorless, pinpoint colonies
What are the limitations of using VRBA?
Other gram-negative bacilli might grow (not Entero)
Some coliforms might have unique nutritional requirements so they won’t grow
VRBA may not be completely inhibitory to gram positives
VRBA plates should not be incubated longer than 24 hours, as bacteria that are only partially inhibited may start to grow lot
What is the other test used for coliforms? What is it for?
Brilliant green lactose bile broth (with Durham tube)
Tests for presence of coliform bacteria in foods
What does brilliant green lactose bile broth contain?
Two inhibitors of both gram positive and selected gram negative species: oxgall and brilliant green dye
What can grow in brilliant green lactose bile broth?
Anything that is resistant to both of the inhibitors and is able to ferment lactose (primarily coliforms)
What is oxgall?
Dried bovine bile
What result is observed for a positive test in brilliant green?
Gas production (via fermentation) within 2 days
How does bile inhibit gram positive growth only?
Because gram positive have lipoteichoic acids on the outside. Bile is able to interact with these and act as a detergent.
How does crystal violet only inhibit gram positive growth?
Because it interacts with the peptidoglycan (which is exposed in +ve). This causes inhibition of enzymes that are responsible for inserting new peptidoglycan monomers, thereby not allowing cells to replicate.
