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BIO 207 > Biology 207 Exam #4 > Flashcards

Biology 207 Exam #4 Flashcards

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1
Q

Symbiosis

A

Close, prolonged physical or metabolic interactions between two or more populations

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2
Q

The Human Microbiome

A

The indigenous microbial communities of the human body
*exist on all external and internal surfaces of the body

Significant positive effects of this symbiotic relationship
*useful metabolites, digestion, colonization resistance, immune responses

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3
Q

Microbial Load vs. Body Site

A

Human to microbial cells ~ 1:1

Microbial cells are not even distributed at body sites, not typically associated with disease, often present in vastly diverse communities

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4
Q

The Human Microbiome is dominated by four phyla of bacteria

A

Bacteroidetes & Firmicutes > Actinobacteria & Proteobacteria

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5
Q

The Human Microbiome Cont.

A

Each body site is colonized predominantly by only certain bacterial species

The composition and diversity of the human microbiome is strongly determined by habitat

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6
Q

The Human Microbiome Cont.

A

Carriage of microbial taxa varies between sites and between individuals while metabolic pathways for each site remain stable within a healthy population

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7
Q

Genomics and the Human Microbiome

A

The humane intestinal microbiome contains at leas 100 times as many different genes as our own genome
*significantly enriched for metabolism of exogenous substrates

Numerous examples of genetic susceptibilities in animals manifesting only in the presence of a microbiome or specific microbiome composition

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8
Q

Pregnancy and Human Microbiome

A

Acquisition of the microbiome in early life by vertical transmission and factors modifying mother-to-child microbial transmission

Birth mode, diet shape microbiome composition during early life

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9
Q

Microbiome of the Skin

A

The skin surface varies greatly in chemical composition and moisture content

Three micro-environments: dry skin, moist skin, sebaceous skin

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10
Q

Microbiome of the Skin Cont.

A

Each micro-environment shows a unique microbiota
*composition influenced by environmental factors and host factors

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11
Q

Aerodigestive Tract

A

A tube that permits the external environment passage through the body
*epithelial cell lining that is covered with mucus, except the lowest part of the airways

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12
Q

Bacterial Abundance

A

Increases as you move through the GI tract, with different sections providing distinct habitats for microbial growth

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13
Q

Mucosal Layer

A

Prohibits microorganisms from engaging directly with the epithelial surface in healthy individuals

Enterocyte = epithelial cell

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14
Q

Epithelium

A

The single layer lining the aero-digestive tract and is made up predominantly of epithelial cells, with lesser numbers of secretory cells and a small number of a variety of other cells

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15
Q

Epithelium

A

The single layer lining the aero-digestive tract and is made up predominantly of epithelial cells, with lesser numbers of secretory cells and a small number of a variety of other cells

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16
Q

Mucins

A

Proteins that are the major components of the extracellular mucus layer that protects and lubricates the epithelium

High-molecular-mass glycoconjugates with oligosaccharide chains in O-glycosidic linkages to a protein backbone
*form a mesh layer that absorbs water/forms gels

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17
Q

Intestinal Mucus

A

Protected by mucus, forms a single, easily removable mucus layer, and in the colon forms a double layer, with the inner mucus layer firmly attached to the epithelium

Major building blocks giving mucus its properties are large glycoproteins called mucins

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18
Q

Intestinal Mucus Cont.

A

In the small intestine, the mucus layer is penetrable, but the bacteria are kept away from the epithelium by antibacterial mediators

In the large intestine, the inner mucus layer is impenetrable to bacteria whereas the outer mucus layer is expanded and serves as the habitat for the bacteria

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19
Q

Gut Microbiome

A

Architecture of the gut microbiome is largely determined by diet and physiochemical conditions in the gut
*pH gets higher when going from stomach to colon
*as pH increases, so does load of bacteria

Acidity of stomach and duodenum prevent many organisms from colonizing these regions

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20
Q

Gut Microbiome Cont.

A

Mucosal layer prohibits microorganisms from engaging directly with the epithelial surface in healthy individuals
*mucosal layer = mucus + host defense molecules

In individuals with IBS, etc, disruption of the mucosal barrier allows bacteria to engage with the epithelium

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21
Q

Colonization Resistance

A

How the gut microbiome prevents the invasion of new pathogenic species
*loss of colonization resistance by antibiotics can lead to intestinal infection, etc.

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22
Q

Fecal Microbiota Transplant (FMT)

A

A procedure in which feces is collected from a tested donor, mixed with a saline, strained and placed in a patient

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23
Q

The Healthy Lung is not conducive to…

A

Microbial colonization by mucosal anaerobes, Gram + bacteria and others

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24
Q

Heathy Lungs

A

Aerobic, cilia, lower surface temperatures in trachea and bronchi

Surfactant in alveoli, surfactant proteins and anti-microbial peptides, very little mucin in alveoli, home of the only phagocytes to actively patrol an external surface

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25
Q

Healthy Lungs Cont.

A

The lung is a low microbial biomass site

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26
Q

Monosaccharides

A

The most basic units of carbohydrates and cannot be hydrolyzed to simpler compounds
*glucose, fructose, galactose

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27
Q

Polysaccharides

A

Polymeric carbohydrate molecules composed of long chains of monosaccharide units bound together by glycosidic linkages

Range in structure from linear to highly branched, often quite heterogenous, may be soluble or insoluble
*starch and cellulose are polysaccharides composed of a or b glucose monomers

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28
Q

What makes all polysaccharides different?

A

The types and rations of different monosaccharides in the polysaccharide

The chemical linkages that join all the monosaccharides

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29
Q

Dietary Fiber

A

The edible parts of plants or analogous carbohydrates that are resistant to digestion and absorption in the human small intestine, with complete or partial fermentation in the large intestine

Includes polysacc, oligosacc, lignin, plant substances
*carbohydrate polymers with >10 monomeric units are not hydrolyzed by the endogenous enzymes in the small intestines of humans

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30
Q

Digestion Cont.

A

Only short glycan substrates can penetrate bacterial cell walls -> as consequence, the digestion of dietary polysacc
requires export of sugar-cleaning enzymes into the intestinal lumen

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31
Q

Digestion Cont.

A

A secretion signal is needed on the gene sequence to target the enzyme to outside the bacterial cell

Among all genes encoding hydrolases with predicted signal peptides, 72% belong to Bacteroidetes members

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32
Q

Digestion Cont.

A

Through the action of bacterial polysaccharide digestive enzymes, significants amounts of free monosaccharides can be liberated in the GI tract

These monosaccharides can be used as metabolic precursors by bacteria in the colon (anaerobic)
*either anaerobic respiration or fermentation

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33
Q

Carboxylic Acids

A

The general formula of a carboxylic acid is R-COOH, with R referring to the rest of the molecule

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34
Q

Colon

A

Firmicutes are the primary source of fermentation by-products in the intestine (colon)

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35
Q

Colon

A

Firmicutes are the primary source of fermentation by-products in the intestine (colon)

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36
Q

The Microbiome, Fermentation and Fiber Metabolism

A

Increased epithelium health/function

Decrease inflammation

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37
Q

Acquisition of function in GI tract bacteria by horizontal gene transfer

A

Agar degradation locus what discovered

Homologs were found in the gut bacterium that was isolated from Japanese individuals who consume seaweed

Frequent in Japanese population, absent from other data

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38
Q

Fermentation in Food

A

Fermentation historically important method of food preservation
*acid produced inhibits growth of many spoilage organisms and food-borne pathogens
*bacteriocins and some secondary metabolite can also inhibit the growth of other microbes

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39
Q

Other important preservation methods

A

Salting, drying, addition of various herbs or spices, canning

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40
Q

Lactic Acid Fermentations

A

By lactic acid and acetic acid producing bacteria
*tastes due to in part of the production of lactic and/or acetic acid, as well as other molecules produced by fermentation and/or secondary metabolism

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41
Q

Fermented milk products

A

Milk is sterile in cow’s udder
*rapidly becomes contaminated during milking and handling (lactic acid bacteria reside on cow’s udder)

Aesthetic features of milk change due to production of acid, proteases, exo-polysaccharides and flavor compounds (secondary metabolites)
*causes milk proteins to coagulate or curdle, sours flavor, thickens the liquid

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42
Q

Fermented milk products Cont.

A

Production of fermented milk products no longer rely on naturally occurring lactic acid bacteria
*starter cultures are added to milk

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43
Q

Starter Cultures

A

A preparation of living microorganisms, which are deliberately used to assist the beginning of fermentation, producing specific changes in the chemical composition and sensorial properties of the substrate
*carefully selected to produce desirable flavors/textures
*must be carefully maintained and protected against contamination by other microbes

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44
Q

Cheese Production

A

Made from a wide variety of animals
*classification is based on percentage of water content

Cottage cheese easiest cheese to make
*pasteurized milk inoculated with starter culture -> culture causes milk proteins to coagulate -> heated and cut into small pieces to facilitate drainage of liquid

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45
Q

Cheese Production Cont.

A

Most all cheeses undergo further microbial processing termed ripening or curing

Enzyme “rennin”, a protease is added to fermenting milk to hasten protein coagulation

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46
Q

Cheese Production Cont.

A

Curds salted after whey is separated and pressed, ripened to encourage changes in texture and flavor
*can take weeks to years

Long ripening produces more acidic cheese
*certain organisms produce certain characteristics

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47
Q

Yogurt

A

Milk is inoculated with starter culture -> incubated 40-45 for several hours
*controlled incubation ensures proper levels of acid production, proteolytic activity and flavor compound generation

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48
Q

Probiotics

A

Most common: Lactobacillus, Bifidobacterium, Bacillus coagulans, Saccharomyces boulardii

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49
Q

Variation in Probiotic Activity

A

Not all strains and species of probiotic microbes will have the same activity in all aspects of probiosis

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50
Q

Pickling

A

Originated as way to preserve vegetables
*uses naturally occurring lactic acid bacteria residing on vegetables (unlike using starter culture)

Vast majority today are used with vinegar

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51
Q

Alcoholic fermentation by yeast

A

Some yeasts ferment sugars to produce ethanol and carbon dioxide
*yeasts are used to make variety of alcoholic beverages as well as vinegar and bread

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52
Q

Bread

A

Rises due to carbon dioxide produced through fermentation of sugars by baker’s yeast

Characteristic flavor of sourdough bread due to addition of lactic acid bacteria to the bread making mixture

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53
Q

What factors influence the growth of microorganisms in food?

A

Conditions naturally present in food -> “intrinsic” factors
Environmental conditions -> “extrinsic” factors

Combine to determine which microbes grow in particular foods and at what rate

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54
Q

Intrinsic Factors

A

Water availability, pH, nutrients, biological barriers, antimicrobial chemicals

Microbes multiply most rapidly in moist, nutritionally rich, pH neutral foods

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55
Q

Water Availability

A

Foods vary dramatically in terms of water availability
*milk have higher water content -> supports microbes
*bread has low water content -> defined pops. can grow

Water activity (aw) used to designate amount of water available in foods
*most bacteria require above 0.90 aw
*most fungi require above 0.80 aw

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56
Q

pH

A

Important in determining which organisms can survive and thrive on specific foods
*many microorganisms inhibited by acid conditions

Lactic acid bacteria not inhibited by low pH
*used in fermentation of milk products, can cause spoilage of unpasteurized milk

Yeast and other fungi are able to survive a low pH
*most acid foods spoil from fungal contamination as opposed to bacteria

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57
Q

Nutrients

A

Nutrients present in food determine organisms that can grow in foods

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58
Q

Biological Barriers

A

Rinds, shells and other outer coverings help protect foods from microbial invasion
*microorganisms will eventually breakdown coverings and cause spoilage

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59
Q

Antimicrobial Chemicals

A

Some foods and spices naturally contain antimicrobial chemicals that inhibit growth of organisms responsible for spoilage

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60
Q

Extrinsic Factors

A

Extent of microbial growth largely dependent on storage of food
*microbes multiply rapidly in warm, oxygen-rich environments (also in low oxygen anaerobic con.)

Include storage temperature, oxygen levels, humidity

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61
Q

Storage Temperature

A

Affects the rate of microbial growth
*below freezing water availability is significantly decreased
*at low temperature, growth is very slow or non-existent

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62
Q

Atmosphere

A

Presence of absence of oxygen affects type of microbial population
*moisture promotes the growth of spoilage microorganisms

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63
Q

Preservation methods include:

A

Canning, pasteurization, cooking, refrigeration, freezing, drying/reducing water availability

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64
Q

Cooking

A

Can destroy non-spore forming organisms, alters characteristics of food
*if heat is uneven, some organisms may survive in undercooked portion of food

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65
Q

Refrigeration

A

Preserves food by slowing growth rate of spoilage organisms
*many organisms unable to multiply in low temperatures

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66
Q

Freezing

A

Stops microbial growth (water unavailable due to ice formation)
*portion of organisms remaining can grow when food is thawed

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67
Q

Drying/reducing water availability

A

Inhibits microbial growth by decreasing available moisture
*molds may grow eventually

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68
Q

Irradiation

A

Damages microbial DNA

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69
Q

Filtering

A

Will not remove viruses

0.2 micron (microbial cell filtering) vs. cheesecloth (particulate filtering)

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70
Q

Heating

A

Efficacy depends on temperature and time at that temperature

Boiling may not kill endospores

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71
Q

Pasteurization

A

Process of heating a liquid to below the boiling point to destroy microorganisms

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72
Q

Heating/Boiling Milk

A

Has been recognized since the early 1800s
*was used to reduce milk-borne illness

Increased milk production and distribution led to outbreaks of milk-borne diseases

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73
Q

Heating/Boiling Milk Cont.

A

Common milk-borne illnesses included typhoid fever, undulent fever, scarlet fever, etc

Tuberculosis can also be transmitted via un-pasteurized milk

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74
Q

Heating/Boiling Milk Cont.

A

1918, drinking unpasteurized milk could transmit the bacterium that caused brucellosis from domestic farm animals to humans

In combination with improved management practiced on dairy farms, milk-borne illnesses were virtually eliminated with commercial implementation of pasteurization

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75
Q

Heating/Boiling Milk Cont.

A

At very high temperatures, micelles of the milk protein casein irreversibly aggregate and impart a cooked flavor to the milk

Pasteurization reduced the pathogenic bacteria in milk without changing flavor
*includes high temper, short-time pasteurization
*HTST: 161 for 15 secs

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76
Q

Types of Pasteurization

A

Ultra-pasteurization holds the milk at a temp of 140 C fro two seconds (refrigerated, extended storage)

Ultra-heat-treating processing holds the milk at a temp of 140 C (sterilized, not pasteurized)
*lets people store milk for months without refrigeration

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77
Q

What else is pasteurized?

A

Any juice sold on the shelf at room temperature has been sterilized, not pasteurized (usually by UHT)
*all truly pasteurized need to be refrigerated

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78
Q

What else is pasteurized?

A

Any juice sold on the shelf at room temperature has been sterilized, not pasteurized (usually by UHT)
*all truly pasteurized need to be refrigerated

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79
Q

Sterilization

A

Refers to any process that eliminates, removes, kills or deactivates all forms of life and other biological agents present in a specified region

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80
Q

Does boiling a liquid sterilize it?

A

Depends on what was the liquid was to start with and how long you boil the liquid

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81
Q

Food Spoilage

A

Encompasses any undesirable physical change in food
*generally not harmful

Considered unsafe because high numbers of spoilage organisms indicate that conditions have favored microbial growth, which may include potential food-borne pathogens

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82
Q

Food Spoilage Cont.

A

Range of bacteria important in food spoilage
*psychrophilic organisms can multiply in refrigerator

Endospore forming organisms can survive cooking and in some cases canning processes (Clostridium, Bacillus)

Range of fungi spoil foods
*fungi grow in readily acidic and low-moisture environments

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83
Q

Food-borne Illness

A

Results from a failure in proper use of preserving, preparation or cooking techniques to avoid growth of microbial pathogens

Intoxication and Infection

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84
Q

Intoxication

A

Disease that results from ingestion of foods containing preformed microbial toxins
*microorganism that produce toxins do not have to infect the host

4-12 hrs for time of onset

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85
Q

Infection

A

Results from the ingestion of pathogen-contaminated food followed by growth of pathogen in the host

24-48 hrs from time of onset

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86
Q

Risk Factors for Foodborne Illness

A

Type of microbe or toxin ingested
Inoculum size
Inadequate stomach acidity
Reduction or change in normal microbiota of host
Susceptible populations include

87
Q

How do you tell if there has been an outbreak of a food-borne illness?

A

Cluster cases by symptoms
Isolate pathogen from cases
Identify common food to all cases
Isolate pathogen from suspected food
Re-trace distribution of suspected food
Isolate pathogen from suspected food at common distribution point

88
Q

Food Intoxication

A

Illness resulting from consumption of an exotoxin produced by organisms growing in food product
*toxin is responsible, not organism

89
Q

Heat Stable Enterotoxins

A

Produced by strains of Staphylococcus aureus
Stable upon heating at 100C for 30 min

Protected from hydrolysis by duodenal/jejunal enzymes
Elicit net secretion of ions and water (rapid onset of diarrhea, no fever)

90
Q

S. aureus Food Poisoning

A

Generally a human carrier
*common skin and nasal commensal microbe

Inoculated into food during preparation
*food left at room temperature allows organisms to grow and produce toxin

Toxin is heat stable and not inactivated by cooking!

91
Q

Canning

A

An extremely effective method of food preservation

Heat processing at high temps for fixed time -> destroys microbes -> inactivates endogenous spoilage enzymes -> oxygen driven out -> vacuum is formed upon cooling that prevents recontamination

92
Q

Canning Cont.

A

Designed to destroy endospores
*improper canning can promote germination of endospores (when temp is not high enough, etc.)

93
Q

Botulism

A

Paralytic disease caused by ingestion of a neurotoxin
*produced by Clostridium botulinum, gram + spore forming anaerobic rod

Growth of organism or production of toxin may not result in change in taste or appearance of food

94
Q

Botulism Cont.

A

Disease characteristics (adults, 12-14 hrs after ingestion)
*nausea, fatigue, visual impairment, etc.

Disease characteristics (infants, days-weeks)
*constipation, facial expression, weakness, etc.

Widely found in soil, dust, honey
*mainly impact infants

95
Q

Bacillus Cereus

A

Gram positive spore forming rod (fac. anaerobe)
Widely disseminated in nature

Can cause diarrheal disease (found in grains)

96
Q

Food-borne Infection

A

Requires consumption of living organisms
*invasion of the large intestine mucosal surface by the infection

Symptoms do not appear for a least one day after ingestion
*major symptom is diarrhea

97
Q

Food-borne Infection Cont.

A

Thorough cooking of food immediately before consumption will kill microbes responsible for infection
*prevents infection

98
Q

Salmonella and Campylobacter

A

Commonly associated with poultry products
*inadequate cooking can result in food-borne infection

Cross-contamination can result in transfer of pathogens to other foods

99
Q

Salmonellosis

A

Symptoms: Gastroenteritis and Food Poisoning
*nausea, vomiting, abdominal pain, fever, etc.

Generally short lived and range from mild-moderate
*vary depending of virulence of strain and # of infecting organisms

100
Q

Salmonellosis Cont.

A

Causative Agent: Salmonella (motile, gram -, enterobac.)

101
Q

Campylobacter jejuni

A

Most common cause of bacterial diarrhea in the world
*inadequately cooked poultry, untreated water, unpasteurized milk, exposure to animals with diarrhea

Self-limiting, antibiotics not needed, causes fever, nausea, cramps, etc
*low infectious dose, replicates in the small intestine

102
Q

Campylobacter jejuni Cont.

A

Curved s-shaped gram - rods
*motile with a singular polar flagellum at one or both ends, micro-aerophile, grows best 42C

Toxins: adenyl cyclase activating cholera toxin-like enterotoxin, cytotoxin

103
Q

Pathogenic E. coli

A

Can cause food poisoning (intoxication) or food-borne infection
*depends on strain of E. coli, depends on pathogenic mechanisms encoded in the accessory genome of that strain

104
Q

Listeriosis

A

Listeria monocytogenes is the cause
*may lead to bacteremia and meningitis

Found in soil and water
*psychrotolerant - grows at refrigeration temperatures

Listeria is killed by cooking and pasteurization
*transmitted to people by food

105
Q

Listeria mococytogenes

A

Tolerates high salt concentration
*can survive a pH range of 4.4-96

Primary food-borne sources: unpasteurized milk, deli meats, etc.

106
Q

Listeriosis Cont.

A

Infection causes severe disease in vulnerable groups
*L. monocytogenes in an intracellular pathogen (uptake by phagocytes results in growth of the bacterium)

Mortality rate is high
*non-invasive: diarrhea, chills
*invasive: septicemia, meningitis

107
Q

Other causes food-borne/waterborne illness

A

Vibrio cholerae
*gram -, toxin producing, safe water is critical to control
Amoebic dysentery
Traveler’s diarrhea
Clostridium perfringens
Norovirus

108
Q

Infection

A

The invasion of an organism’s body tissues by a disease causing agents, the persistence of those agents and the reaction of host tissues to the infectious agents

109
Q

Infectious Disease

A

The disease that results from infectious by a transmissible agent (from host to host, via intermediate, etc.)

*all infectious diseases are infections, not all infections are infectious diseases

110
Q

Passive barrier to infection

A

Skin
Normal Microbiota
Mucus, phagocytes, peptides
Blood and lymph nodes
Rapid pH change
Flushing of urinary tract
Epithelial cells

111
Q

Anti-Microbial Peptides

A

Small, typically positively charged, peptides with potent antimicrobial activities
*produced by many cells in the body, including neutrophils and cells of the mucosa

Many AMPS display a direct and rapid antimicrobial activity by causing disruption of the physical integrity of the microbial membrane and/or by translocating across the membrane into the cytoplasm of bacteria to act on intracellular targets

112
Q

Host Response to Infection

A

Barrier Function -> Primary Innate Defenses -> Activated Innate Defenses -> Immune Defenses

113
Q

Bone Marrow

A

Source of the white blood cells that are the major mediators of host defense

114
Q

Mast Cells

A

Found throughout the body in all tissues
*are increased in the tissues of allergic individuals

115
Q

Macrophages

A

Found throughout the body in all tissues and many are derived from monocytes that have left the blood

116
Q

Neutrophils

A

Most abundant white blood cell in body
*predominant cell in pus

Granulocyte: polymorphonuclear leukocytes

Ambulance of the immune system: produced in high numbers quickly in bone marrow upon infection and travel to site of infection to exert anti-microbial activity

117
Q

Phagocytosis

A

Carried out primarily by macrophages and neutrophils

Attachment of phagocyte to microbe can be mediated by specific receptor interactions or by charge interactions

118
Q

Killing Ingested Microbes

A

Phagocytic cells use reactive oxygen radicals to kill ingested bacterial cells by oxidizing key cellular constituents of the ingested microbe

Respiratory burst is a series of catalyzed reactions in the phagolysosome that creates reactive oxygen metabolites

119
Q

Killing Ingested Microbes Cont.

A

Occurs within the phagocytic vacuole of the phagocyte, which is not damaged by the toxic oxygen products

Degradative enzymes are also found in the phagolysosome

120
Q

Neutrophils Cont.

A

Neutrophils also “throw” neutrophil extracellular traps around nearby pathogens

After interacting with bacteria, neutrophils can undergo an unusual form form of cell death
*spews a latticework of DNA impregnated with antimicrobial peptides into the immediate area that traps bacteria in this mesh

121
Q

Innate Immunity

A

Multicellular organisms have evolved the ability to recognize microbes and to eliminate them without causing damage to self

The recognition system is a host receptor - microbial ligand interaction

122
Q

Microbe-Associated Molecular Structures

A

Ex.
Lipopolysaccharides
Teichoic acids
Unmethylated CpG motif
dsRNA
Mannans
Flagellin

123
Q

Pattern Recognition Receptors

A

Host-encoded receptors that bind MAMPs
Expressed on phagocytes and many cells in the body

Include a number of receptors: TLR, NLR, CLR. etc.

124
Q

Pattern Recognition Receptors Cont.

A

Stimulation of PRRs activates transcription factors in a host cell to induce production of cytokines and other factors

125
Q

Cytokine

A

Protein
Binds to a specific receptor
Intercellular signaling molecule
Can act locally or systemically
Can have multiple effects, depending on the target cell binding the cytokine

126
Q

Intercellular Signals Induced by the MAMP-PRR Interactions

A

Signals that mediate inflammatory responses
Signals that control induction of leukocyte effector functions
Signals that function in activation of adaptive immunity

127
Q

Acute Inflammation

A

Redness, warmth, pain, swelling and altered function

Inflammation is the process of leukocyte movement from the blood into a tissue and/or increased localized vasodilation

128
Q

Bone Marrow Cont.

A

The bone marrow pumps out more leukocytes in response to inflammation

129
Q

Pathogens have specific mechanisms to

A

Gain access to the body and attain a unique niche
Acquire necessary nutrients in vivo
Multiply and persist
Avoid, subvert or circumvent innate host defenses
Evade acquired specific immune responses
Cause tissue damage or disease
Exit and transmit infection to new hosts

Mechanisms of virulence are genetically encoded virulence genes and having these genes distinguishes pathogens from non-pathogens

130
Q

Adherence in Infection

A

Pathogenic bacteria and viruses often adhere specifically to epithelial cells through interactions between molecules on the surfaces of the pathogen and the host cells

Can be facilitated by fimbriae, pili, flagella, capsule, other cell-surface adhesions

131
Q

Biofilms and Infections

A

Biofilms play an important role in chronic infections by enabling persistent adherence and resistance to bacterial host defenses and antimicrobial agents

132
Q

Pathogen Colonization

A

Pathogens may grow locally at the site of invasion or may spread throughout the body

The availability of appropriate nutrients is the most important parameter affecting pathogen growth

133
Q

In vivo

A

Nutrients can be limiting
*iron is a growth-limiting nutrient

Host-derived transferrin, lactoferrin and lipocalin are very high affinity iron-binding molecules that function to sequester iron in the host to limit infection

Many pathogens produced iron-chelating compounds caused siderophores to counter iron sequestration

134
Q

Avoiding host defenses

A

Capsules and biofilms help protect against phagocytosis

135
Q

Pathogens can block phagocytosis

A

Some pathogens can stop phagocytosis by injecting phagocytes with effectors (T3SS)

Ex. Yersinia uses t3SS to inject host phagocytic cells with infectors -> precent actin polymerization, block phagocytosis

136
Q

Some pathogens hide out inside host cells

A

Complement and antibodies act only within extracellular spaces

Some pathogens remain intracellular after being ingested

137
Q

Pathogens and Phagocytosis Cont.

A

Some pathogens stop the phagolysosome from maturing

Some can escape the phagosome before it fuses with a lysosome

138
Q

Virulence Factors

A

Promote pathogen infection and host cell damage

Enzymes that break down host tissue: proteases, nucleases, lipases
Toxins: exotoxins, endotoxins

Sometimes clustered together on pathogenicity islands

139
Q

Endotoxins

A

Lipopolysaccharides found in the outer membrane of most gram-negative bacteria
*released as bacteria die

Serves as a MAMP which binds to certain PRRs on leukocytes
*causes cytokine release

140
Q

Endotoxins Cont.

A

Repeating O-antigen side chain that faces out from the microbe and the membrane proximal core glycolipid and lipid A

141
Q

Damage-Framework Hypothesis

A

Microbial pathogenesis is an outcome of an interactions between a host and a microorganism

The host-relevant outcome of the host-microorganism interaction is determined by the amount of damage to the host

Host damage can result from virulence factors and/or the host response to the presence of the microorganisms

142
Q

Damage-Framework Hypothesis

A

Top weak of a host response can result in disease
*opportunistic infections

Too strong of a host response can result in disease
*sepsis, hypersensitivity, cytokine storm

143
Q

Horizontal Transmission

A

Individual to individual

144
Q

Vertical Transmission

A

Maternal to neonatal

Infectious agent may cross placenta from the mother to fetus

145
Q

Direct Contact Transmission

A

Person to person spread of microorganisms through actual physical contact

146
Q

Indirect Contact Transmission

A

Occurs when a susceptible person comes in contact with a contaminated object or contact with contaminated material

Fomite - an inanimate object or substance that is capable of transmitting infectious organisms from one to another

147
Q

Ingestion

A

Food, water, “fingers”
Fecal-oral transmission

Infection is via the gastrointestinal tract

148
Q

Giardiasis

A

Ingestion of water or food contaminated with cysts
*can survive for months with exposure to cold water

Spreads very easily

149
Q

Human to Human Disease Transmission

A

Fecal-oral Spread
Respiratory or Salivary Spread
Venereal Spread

150
Q

Routes of Transmission

A

From:
Oropharynx
Respiratory
Gastrointestinal
Urogenital tract
Skin
Milk
Blood

151
Q

Inhalation

A

Infection is via the respiratory tract
Aerosol transmission

152
Q

Droplet vs. Aerosol Transmission

A

Although droplets produced by an infectious individual through coughing or sneezing may convey infection at short distance, the number and viral load of aerosols produced through speaking and other expiratory activities are much higher than those of droplets

Aerosols are small enough to linger in air, accumulate in poorly ventilated spaces, and can be inhaled at both short and long ranges

153
Q

Factors affecting airborne transmission

A

Movement of aerosols is more strongly influenced by airflow direction and pattern, type of ventilation and air filtration and disinfection

154
Q

Routes of Acquisition

A

Dose of infectious inoculum is a critically important variable!

Route of transmission has to match up with the route of acquisition and the infectious agent’s mechanism of infection for the disease to occur

155
Q

Arthropod/Vertebrate to Human Disease Transmission

A

Vector
Vertebrate Reservoir
Vector-Vertebrate Reservoir

All can be controlled by controlling vectors or by controlling animal infection

156
Q

Direct inoculation

A

Vector-mediated transmission
*insect bite

Animal or human bite
Needle stick, blood transfusion

157
Q

Ro

A

Average number of people who will contract a transmissible infection from one person with the disease

If Ro > 1, number of people with the disease will rise
If Ro < 1, the number will decline

SARS CoV-2 Ro: 4-7

158
Q

Infection versus Disease

A

Contact with an infectious agent does not guarantee that a person will actually contract the disease

159
Q

Parabolic Curve of the Damage-Response Framework

A

The dose of the infectious agent slides the damage-response framework curve up or down

Each infectious agent has its own damage-response framework curve

160
Q

Disease Outcome

A

The dose received of a pathogen, as well as the immune status of the host, makes a significant difference in the disease outcome

Thus, simply being exposed will not necessarily cause disease

161
Q

Iceberg Concept of Infectious Diseases

A

Infection and disease after exposure is determined by route of transmission, length of exposure, dose of inoculum, route of acquisition, type of infectious agent and level of pre-existing immunity

162
Q

Virus

A

Genetic element that cannot replicate independently without a living a host cells
*infect bacteria, archaea, eukaryotes

Virus particle (virion): extracellular form of a virus
*exists outside host and facilitates transmission

163
Q

Virion

A

It consists of a nucleocapsid
*capsid (protein coat), nucleic acids

Two main categories:
*naked, enveloped

164
Q

Enveloped Viruses

A

Have membrane surrounding nucleocapsid
*lipid bilayer with embedded proteins

Envelope makes initial contact with host cell
*much of the membrane is picked from host cell, most infect animal cells

165
Q

Virus Cont.

A

Do not carry out their own metabolism
*some still need to carry enzymes with them to carry out certain function (lysozyme-like, cleavage, etc.)

RNA viruses ~ also need RNA replicases
Retroviruses ~ need reverse transcriptase

166
Q

Baltimore Scheme to classify viruses

A

Based on relationship of viral genome to its mRNA

***mRNA must be made in order to make protein so no matter what the viral genome looks like, mRNA somehow has to be made from it

167
Q

Positive strand RNA

A

The sequence of the genome and the mRNA are the same
*mRNA can be translated immediate after entering the cell

These viruses encode RNA replicase, which is an enzyme that replicates viral RNA

168
Q

Coronaviruses

A

Enveloped viruses
Single stranded, + sense RNA genome
Respiratory or fecal-oral transmission

Spike protein mediates ACE2-dependent cell entry

169
Q

Coronaviruses Cont.

A

Viral shedding peaks rapidly after SARS-CoV-2 challenge but qPCR remains positive for at least a week beyond detectable live virus

170
Q

Influenza Virus

A

Causes infection of the upper/lower respiratory tract
Enveloped
- sense, ssRNA

171
Q

Influenza A Viruses

A

Exists in many species
Different strains of Influenza A viruses infect different animals species like birds, humans and pigs (strains remain largely species-specific)
*pig as an intermediate host

Considered zoonotic pathogens because genetic reassortment in an intermediate host allows emergence of new hybrid strains
*type A flue virus is constantly changing its genome and is generally responsible for large flu epidemics

172
Q

Influenza B Viruses

A

Only found in humans
*causes a less severe reaction than type A flue virus
*more limited host-range

173
Q

Structure of Influenza Virus

A

The virions of influenza A and B viruses contain 8 different RNAs
*in influenza A, the 8 genomic RNA segments code for 11 proteins

Virus replicates in the cell nucleus, not cytoplasm, because the virus requires host machinery to cap the mRNAs

174
Q

Structure of Influenza Virus Cont.

A

Surface glycoproteins determine subtype

H -> binds sialic acid
N -> cleaves sialic acid

175
Q

Antigenic Drift

A

Small genetic changes in surface-exposed proteins that alter a few individual epitopes on an antigen

Occurs in all types of influenza

176
Q

Antigenic Shift

A

Large genetic change that allows the virus to evade host immunity, resulting in an epidemic/pandemic

Only occurs in influenza A

177
Q

Influenza-induced Tissue Destruction & Disease

A

Primary site of viral infection is the upper part of the lower airways and replication in these cells

178
Q

Influenza-induced Tissue Destruction & Disease Cont.

A

Innate followed by adaptive immune response to the virus is important for viral clearance, but can cause significant damage to lung tissue

Inflammation in the bronchial tree and Cytokine Storm during the inflammatory response causes symptoms of the flue

179
Q

Influenza-induced Tissue Destruction & Disease Cont.

A

The entire process leads to increased susceptibility to secondary bacterial infection due to unregulated inflammatory response in the lungs

180
Q

Vaccines

A

Manipulation of adaptive immune system in an antigen-specific manner to mimic infection by a specific pathogen

Results in stimulation of protective immunity against a pathogen without causing the disease of that pathogen

181
Q

Principle of Vaccination

A

To induce a “primed” state so that on first contact with the relevant infection, a rapid and effective secondary immune response will be mounted, leading to prevention of disease

*should contain some of the antigens of the microbe that the immune response is directed against

182
Q

Types of Modern Vaccines

A

Attenuated microbes - “live vaccine”
Killed micro-organisms
Subcellular microbial fragments or toxins
Micro-organism DNA
Micro-organism RNA

183
Q

mRNA Vaccines

A

Have been genetically modified to optimize physical stability and translatability, including reducing the induction of an interferon/anti-dsRNA response

184
Q

Antibody

A

Heterodimeric bivalent receptor specific for an antigen (Ag) …can bind two identical Ag molecules

A protein complex, made up of four polypeptides, two heavy chains and two light chains joined by disulfide bonds

185
Q

Where do antibodies come from?

A

B lymphocytes secrete antibodies into the circulation and tissues of the body

186
Q

How do antibodies work?

A

Receptor-Ligand Interactions: the primary mechanism of the immune system
*receptor specificity: only one ligand binds a specific receptor

187
Q

Antigen

A

A molecule recognized by the antigen receptors of the adaptive immune system: antibodies and T cell receptors
*usually a protein

An allergen is an antigen derived from a non-infectious source, etc.

188
Q

Antigens & Epitopes

A

Epitope: the specific molecular structure on an antigen that is specifically bound by antigen receptors

Antigen receptors: Immunoglobulin, T cell receptor

189
Q

Genomic rearrangements to generate an antibody

A

A single B cell randomly selects which light chain gene locus to use and the other light chain locus is silenced for the life of that cells and all its subsequent clones

190
Q

How many possible novel Ag receptors can be made by B cells in the body?

A

Combinatorial diversity and Junctional diversity
*as a result of the potential number of DNA recombination possibilities

In the periphery, the DNA in that region of the B cell is subject to high levels of mutation, resulting in even more DNA sequence possibilities in the variable regions of immunoglobulin loci

Recombination of V, D, J regions produces unique antigen receptors

191
Q

B cell development cont.

A

Clonal selection & B cell differentiation is an antigen-dependent process that occurs in the periphery

192
Q

TcR rearrangement

A

Very similar to Ig rearrangement

T cell development occurs in the thymus and is similar (but very different) to B cell development in the bone marrow

193
Q

Antigen Binding: Immunglobulin vs. TcR

A

Antibody (Ig) binds directly to an Ag - binds epitope on the antigen

The T cell receptor (TcR) binds to only a fragment of an Ag, when it is held in place by an MHC molecule
*binds to Ag peptide plus MHC in a very specific way

194
Q

Major Histocompatibility Complex (MHC)

A

Whole Ag does not bind to an MHC molecule: a peptide fragment derived from the native Ag binds to an MHC molecules

Length of the antigen peptide bound in the MHC groove depends on the type of MHC molecule

195
Q

MHC I

A

Found on all nucleated cells in the body

MHC I presents Ag peptides derived from intracellular compartments after cleavage of Ag into peptides

Restricted recognition of both the APC and target cell for destruction by CD8+ T cells

196
Q

MHC II

A

Found on antigen-presenting cells at baseline at high levels and inducible to even higher levels in presence of inflammation & cytokines

MHC II presents Ag peptides derived from extracellular compartments after cleavage of the Ag into peptides

197
Q

CD8 T cell Activation

A

The CD8 molecule aids in stabilization of the TcR-peptide-MHCI interaction

198
Q

Why would a B cell undergo switching of the heavy chains that it produces?

A

The function, not the antigen binding, of antibody is due to its heavy chain. B cells will switch their heavy chains when they receive a special signal from a Th cell that also reacts to the same antigen
*the helper T cell helps determine the fate of what the immune system does when an antibody binds to its Ag

199
Q

CD4 T cell Activation

A

The CD4 molecule aids in stabilization of the TcR-peptide-MHCII interaction

200
Q

T Cell Activation - 2 step process

A

MHC ~ AgPeptide ~ TCR Binding

Co-stimulation of T Cells by Dendritic Cells
*cytokines & secondary receptor signaling

201
Q

Lymphatic System

A

Open-ended second circulatory system in the body and connects the tissue sites to the lymph nodes, spleen and circulatory blood system

202
Q

Where do APC-T cell and T cell-B interaction occur?

A

Spleen and Lymph nodes

203
Q

Th-B cell Interactions & Ab Isotype Switching

A

CD4 Th Cell Help for B Cell Proliferation and Memory Development

CD4 Th Cell Help for Isotype Switching

204
Q

Isotype Switching

A

Gene rearrangement of the constant region genes in the heavy-chain locus results in isotype switching

205
Q

Fc Receptor

A

Cell surface receptor that binds the Fc region of an antibody (does nit bind the Fab region)

206
Q

Antibody Isotype Switching

A

Isotype switching of an antibody produced by a B cell retains the same Ag binding specificity but changes the function of that Ab because the constant region of the heavy chain is switched out

207
Q

Immunity Against Intestinal Parasites

A

B cells
Th cells
IgE
Mast cells

208
Q

Allergic Responses

A

B cells
Th cells
IgE
Mast cells

209
Q

Symbiosis in the GI tract: Microbial Co-Existence without Tissue Damage

A

slgA is made in the intestine and one of its major functions is binding to the bacterial microbiota and preventing it from invading the mucus layer and adhering to the epithelium, without inducing inflammation

210
Q

Immune Responses

A

B cells, CD4 T cells and CD8 T cells can all undergo primary and secondary responses, depending on the Ag stimulus, due to clonal expansion and the development of memory cells

211
Q

Immune Responses

A

B cells, CD4 T cells and CD8 T cells can all undergo primary and secondary responses, depending on the Ag stimulus, due to clonal expansion and the development of memory cells

212
Q

Immune Memory after SARS CoV2 Infections

A

Consists of antibodies, memory B cells, memory CD8+ T cells and memory CD4+ T cells

213
Q

Microbial Metagenome vs. Human

A

Human genome only encodes 17 glycoside hydrolases (GH) that are involved in digestion

In contrast, the microbial metagenome in the gut encodes >9,000 glycoside hydrolases, polysaccharides lysases, glycosyltransferases and carbohydrate esterases

BIO 207 (2 decks)

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