Introduction to Microbiology: Food Microbiology

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Questions and Answers

What is primarily responsible for the inflammation and permeability changes at tight junctions during EIEC infection?

Toxin production by enterotoxins

Direct lysis of immune cells

Viral replication inside host cells

Lesions caused by changes in cell signal transduction (correct)

How does Enterohemorrhagic E.coli (EHEC) differ from Enteropathogenic E.coli (EPEC)?

EHEC does not adhere to enterocytes

EHEC causes tissue damage without inflammation

EHEC is less virulent than EPEC

EHEC produces Shiga toxins while EPEC does not (correct)

What is a consequence of the Shiga toxin produced by EHEC?

Inhibition of protein synthesis in host cells (correct)

Direct destruction of enterocytes

Increased mucus secretion in the gut

Stimulation of T cell response only

What characteristic is shared between EIEC and Shigella dysenteriae in terms of their pathogenic mechanism?

Both invade host cells and replicate intracellularly Signup and view all the answers

What severe condition is associated with Staphylococcus aureus enterotoxins?

Toxic shock syndrome Signup and view all the answers

Which intrinsic factor is most likely to result in foul odors during food spoilage?

Proteins and fats Signup and view all the answers

What is the impact of low pH on microbial growth in foods?

It favors the growth of yeasts and molds. Signup and view all the answers

How does water availability measured by water activity (aw) affect microbial growth?

High solute environments favor osmophiles. Signup and view all the answers

Which factor is categorized as an extrinsic factor in food microbiology?

Temperature Signup and view all the answers

What type of breakdown results in cadaverine during spoilage?

Decomposition of proteins Signup and view all the answers

What role do phytochemicals found in herbs and spices play in food preservation?

They exhibit antimicrobial properties. Signup and view all the answers

Which intrinsic factor determines how well a food can resist microbial dehydration?

Moisture content Signup and view all the answers

Which scenario would most likely result in microbial growth and food spoilage?

Warm temperatures and high moisture Signup and view all the answers

What type of packaging involves reducing oxygen levels to inhibit spoilage fungi?

Atmospheric modified storage Signup and view all the answers

What is the primary toxic agent produced by Claviceps purpura?

Ergotamines Signup and view all the answers

Which organism is responsible for spoilage of unpasteurized milk by producing lactic acid?

Lactococcus lactis Signup and view all the answers

What is a common effect of aflatoxins produced by Aspergillus flavus?

Hepatocarcinogenesis Signup and view all the answers

Which toxin is associated with ciguatera fish poisoning?

Ciguatoxin Signup and view all the answers

What is the typical incubation period for food-borne infection compared to food-borne intoxication?

Food-borne infections have an incubation period of hours to days Signup and view all the answers

Which organism is associated with Salmonellosis?

S. typhimurium Signup and view all the answers

How do Erwinia carotovora bacteria contribute to the spoilage of fruits and vegetables?

By causing soft rot through hydrolytic enzymes Signup and view all the answers

Which of the following symptoms is common for food-borne intoxication?

Respiratory failure Signup and view all the answers

Which of the following conditions permits the growth of aerobes and facultative anaerobes during spoilage?

High redox potential and lack of reduced conditions Signup and view all the answers

What does 'communicable' refer to in the context of food-borne infections?

Infections can spread between individuals Signup and view all the answers

What is the result of Fumonisin contamination in humans?

Esophageal cancer Signup and view all the answers

Which major food is primarily associated with Listeriosis?

Milk Signup and view all the answers

What is a key difference between bacteria and toxins causing food-borne illnesses?

Bacteria invade the intestine while toxins do not Signup and view all the answers

What is a common cause of both food-borne infections and intoxications?

Inadequate cooking Signup and view all the answers

Which of the following is NOT a characteristic of food-borne infection?

Immediate symptoms after consumption Signup and view all the answers

What is one of the effects of botulinum toxin on the autonomic nerves?

Inhibits respiration Signup and view all the answers

What is the method to destroy botulinum toxin?

Boiling at 80°C for 10 minutes Signup and view all the answers

Which microorganism is primarily associated with the production of Brie cheese?

Penicillium camemberti Signup and view all the answers

Which of the following microorganisms is used in the later stages of producing Roquefort cheese?

Penicillium roqueforti Signup and view all the answers

What is the impact of botulinum toxin on acetylcholine release?

Inhibits the release Signup and view all the answers

Which microorganism is commonly found in the fermentation of Yoghurt?

Lactobacillus bulgaricus Signup and view all the answers

In cottage cheese production, which microorganism is primarily utilized during the earlier stages?

Leuconostoc cremoris Signup and view all the answers

Which type of cheese is associated with the use of Lactococcus lactis in both earlier and later stages of production?

Brie Signup and view all the answers

What is the primary pathogen responsible for enterotoxigenic diarrhea?

Escherichia coli Signup and view all the answers

What type of toxins does ETEC produce that affect host cell functions?

Heat labile and heat stable toxins Signup and view all the answers

Which pathogen is primarily linked to severe hemorrhagic colitis?

Escherichia coli O157:H7 Signup and view all the answers

What is the main source of infection for Yersiniosis?

Pork and milk Signup and view all the answers

Which organism is known to produce toxins leading to travelers' diarrhea?

Enterotoxigenic Escherichia coli (ETEC) Signup and view all the answers

What role do fimbriae play in the pathogenicity of ETEC?

They facilitate adherence to the intestinal lining. Signup and view all the answers

What severe condition can result from infection with Vibrio parahaemolyticus?

Gastroenteritis Signup and view all the answers

Which of the following is NOT associated with Salmonella infection?

Pasteurized milk Signup and view all the answers

Study Notes

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Introduction to Microbiology (MIC60104)

Course taught by Dr. Lee Khai Wooi
Focuses on food and industrial microbiology.

Food Microbiology Subtopics

Food spoilage
Microbial toxins
Microorganisms in fermented foods

Food Microbiology: Intrinsic and Extrinsic Factors

Foods are ideal for microbial growth
Microbial growth in food can lead to both preservation and spoilage.
Contamination from disease-causing microbes occurs during food handling.
Intrinsic factors: pH, moisture, water activity, oxygen potential, physical structure, nutrients, and natural antimicrobial agents.
Extrinsic factors: environmental temperature, humidity, gases, and types of microorganisms present in the food.

Food Spoilage: Relation to Food Characteristics

Spoilage processes differ based on the food substrate (e.g., pectin, protein, carbohydrates, lipids).
Different chemical reactions, including pectinolysis, proteolysis, deamination, hydrolysis, and fermentation, occur and result in specific products.

Approximate Minimum Water Activity (a_w) of Microbial Groups

Data in the document provides the approximate minimum water activity for various microbial groups and specific organisms related to food spoilage.

Intrinsic Factors Affecting Food Spoilage

Carbohydrates: typically do not result in noticeable odors.
Proteins and fats: lead to foul odors due to amine compounds released during protein degradation.
Low pH favors yeasts and molds.
Neutral to high pH favors bacterial growth.
Water activity (a_w) measures water availability. Low a_w inhibits microbial growth. Osmophiles thrive in high solute environments. Xerophiles thrive in dry conditions.

Oxygen Potential (Redox)

Fresh fruits are in a reduced state, inhibiting respiration.
Cooking increases or decreases reducing compounds in various foods.

Physical Structure Affecting Microbial Growth

Grinding or mixing increases surface area, creating a substrate for microbial growth.

Antimicrobial Substances in Foods

Natural substances like coumarins in vegetables and fruits, lysozyme in eggs, and Tabasco/hot sauces contain antimicrobial properties that interfere with bacteria growth.

Herbs and Spices as Antimicrobial Agents

Phytochemicals in herbs and spices (e.g., allicin, eugenol, rosmarinic acid) exhibit antimicrobial properties.

Polyphenol Content in Tea

Green and black tea contain polyphenols.

Extrinsic Factors: Storage Atmosphere

Control of storage atmosphere is critical to reduce microbial spoilage.
Reducing oxygen or increasing carbon dioxide can inhibit microorganisms.
Modified atmosphere packaging (MAP) frequently used to extend shelf life.

Food Spoilage and Microorganisms

Food spoilage occurs through rapid microbial growth, which leads to odors, fermentation, and a change in the appearance of the food.

Ergotism

The fungus Claviceps purpurea affects grains, producing toxic ergot alkaloids that constrict blood vessels and cause uterine muscle contractions.

Aflatoxins

Aspergillus flavus produces toxins called aflatoxins on moist grains and nuts.
These aflatoxins are potent hepatocarcinogens, acting as intercalating agents in DNA and causing mutations, leading to liver cancer.

Fumonisins

Fusarium moniliforme infects grains, especially corn, producing fumonisins.
Fumonisins disrupt metabolism in various animals, and in humans, they are associated with esophageal cancer or pulmonary edema.

Algal Toxins (Summary)

Various organisms produce harmful toxins.
Shellfish, reef fish, and water are associated with contaminated organisms causing syndromes with toxins.

Food-Borne Infection

Foodborne infections involve ingestion of pathogens.
Pathogens may grow in the host and tissue invasion may result.

Food-borne Intoxication

Symptoms appear quickly after consumption of contaminated food.
No growth of microbes necessary; toxins produced by microbes affect the body.

Major Foodborne Infectious Diseases: Organism, Incubation Period, and Characteristics

List of major diseases, organisms involved, associated incubation periods, and symptoms described.

Salmonellosis

Salmonella invades phagocytes and grows intracellularly.
Replication and spread to adjacent cells causes endotoxins, enterotoxins and cytotoxins which cause the host cell to die.

E.coli Infections: Classification and Pathogenesis

ETEC, EPEC, EIEC, and EHEC classifications by pathogenesis.
Briefly described mechanism of pathogenesis.

ETEC (Enterotoxigenic E. coli)

Adheres to the small intestine and produces heat-labile and heat-stable toxins that alter cyclic AMP and GMP levels
Leads to chloride secretion and inhibits sodium absorption, causing water secretion into the gut resulting in travelers' diarrhea.

EPEC (Enteropathogenic E. coli)

Adheres to the enterocytes using intimin.
Involves manipulating actin in the enterocyte (changing cell structure).
Leads to cell lesion and inflammation, causes secretion which leads to diarrhea.

EIEC (Enteroinvasive E. coli)

EIEC use invasins to penetrate the host cells.
Replicates inside cells and invades neighboring cells.
Causes tissue damage and inflammation.
Similar pathogenesis to shigellosis.

EHEC (Enterohemorrhagic E. coli, such as O157:H7)

This strains adheres to cells like EPEC but produces shiga toxins.
These toxins cleave adenine, which affects protein synthesis, in the cell's ribosomes. They cause inflammation and access to the circulatory system.
Damage to the vascular system in the gut, kidneys, and nervous system occur.

Other Important Pathogens and Toxins

Staphylococcus aureus toxins, including toxic shock syndrome toxin 1 (TSST-1) are superantigens which activate T-cells, but cause inflammation and severe illness.
Clostridium botulinum neurotoxins, affecting muscle contraction functions and inhibiting the neurotransmitter release which can cause paralysis or respiratory failure.

Microorganisms in Food Products

Specific microorganisms related to wine (winery), cheese, and yogurt production listed.

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Description

This quiz covers key concepts in food microbiology, focusing on the intrinsic and extrinsic factors that affect microbial growth in foods. Understand the implications of food spoilage and the role of microorganisms in fermentation. It is essential for anyone studying the microbiological aspects of food science.