Exam 2 Prep Flashcards
Describe the relationship between “contamination”, “infection”, “disease”, ‘pathogenicity”, and “virulence”
“Contamination” is simply the presence of microbes in/on the body. Some microbes are capable of causing disease/harm and are known as pathogens. This ability to cause disease is known as “pathogenicity”.
When these pathogens successfully invade/enter the host body, this is known as “infection”. Once inside, if the pathogen alters or interferes with the normal body functions, “disease” results.
Pathogenicity does not guarantee a resulting disease or injection. “Virulence” is the degree of pathogenicity/relative ability of a pathogen to infect a host and cause disease.
Signs vs. symptoms? Name some examples.
Signs: objective manifestations of disease that are observable or measurable by others.
- Fever (temperature)
- Vomiting
- Swelling/rash
- WBC count
- Tachycardia/bradycardia (increased/decreased heart rate)
Symptoms: subjective characteristics felt only by the person with the disease
- Pain
- Nausea
- Headache
- Itching
Why can signs and symptoms be helpful?
A group of signs and symptoms (known as a “syndrome”) can characterize a disease or abnormal condition and be useful in diagnosis.
Do infections and disease always present signs and symptoms?
No. Infections/disease can show no symptoms but still have signs. “Asymptomatic/subclinical” cases show no symptoms (i.e. headache/pain) but have signs (i.e. patient with leukocytosis has a sign, increased WBC count, but feels completely normal).
Define: etiology and epidemiology
Etiology - study of the cause of disease
Epidemiology - study of the occurrence, distribution, and spread of disease
What are some types of relationships between microbes and hosts?
What relationship do humans have with most of their microbiota?
Mutualism - both members benefit
Commensalism - one member benefits while the other is not affected
Parasitism - one member benefits at the expense/harm of the other
Humans/microbiota are mostly mutualistic in nature.
Describe the “human microbiome/normal flora”.
It is the collection of all normal microbes that live in and on a human and are important to our health and functioning.
“Resident” microbiota remain part of a human for most of their life and typically live on the skin, in mucous membranes, and GI or respiratory tracts. They normally do not cause disease (dysbiosis can influence disease)
“Transient” microbiota are only found on the body for short periods of time (hours, days, months) and found in the same area of resident microbes.
Describe “microbial antagonism”
Normal flora reduce the ability of arriving pathogens to grow in the body. This is due to their normal activities such as:
- consuming nutrients
- taking up space
- releasing toxic waste
- providing vitamins to promote health
- stimulation of body’s immune system
Name some discoveries from the “Human Microbiome Project”
- Microbes were found in locations previously thought to be sterile
- 100 million viruses per gram of human feces
- Healthy people normally harbor low numbers of potential pathogens
- Intestinal biota influences overall health
Some human flora locations?
Main locations:
- Skin
- Mucous membranes
- Upper respiratory tract
- GI tract
- Mouth
- Genitals
- Eye lids/membrane
Possible flora or their DNA locations:
- Lungs (lower resp. tract)
- Bladder and urine
- Breasts and milk
- Amniotic fluid and fetus
Possible DNA (of flora) locations:
- Brain
- Bloodstream
Unique facts about normal resident biota locations?
don’t need to memorize, this list not all-inclusive
Upper resp. tract: nose is cooler than the rest of resp. system
Upper GI tract: teeth and cheeks
Lower GI tract: mostly strict anaerobes found here
Reproductive systems: microbiota changes as acidity changes during menstrual cycle. Flow of urine prevents colonization of bladder/urethra.
Eyes: Tears wash away most microbiota
Skin: Mostly live on outer dead layers of skin.
When do we acquire normal microbiota?
During the birthing process. The birthing method also affects the ratio of microbiota a baby acquires.
Where can babies get their microbiome? (sources)
Utero, birth, milk, ,caregivers, environment
Factors that increase susceptibility to infection?
- Weakened host defenses/immunocompromised
- Old age/extreme youth
- Surgery/organ transplants
- Underlying disease
- Chemotherapy
- Physical and mental stress
- Pregnancy
- Other infections
Describe opportunistic pathogens
Normal microbiota that cause disease under certain conditions:
- When normal microbiota are introduced to unusual site in body
- Under immune suppression
- Normal microbiota are decreased or changed in population
Polymicrobial infections - contributions from more than one microbe
What is virulence of a microbe determined by?
It’s ability to:
- Establish itself in a host
- Cause damage
Describe virulence factors
Characteristics or structures that contribute to the ability of a pathogen to establish itself in a host and cause disease
Name some examples of virulence factors
- Adhesion factors (structures or molecules)
- Biofilms
- Extracellular enzymes
- Toxins
- Antiphagocytic factors
Describe the 5 steps in the Microbial Disease Process
- ) Find portal of entry
- Respiratory tract, skin/wounds, etc. - ) Attach firmly and negotiate the microbiome
- Adhesion factors - ) Survive host defenses
- Avoid phagocytosis, death, hide from immune system - ) Cause damage
- Damage due to toxins, enzymes, induce extreme response, epigenetic changes - ) Exit host
- Usually through portal of entry, fluids, feces
Name some portals of entry
Skin:
- Thick salty layers of dry, dead cells
- Cuts/wounds/hair follicles/sweat glands
Mucous membrane:
- Thin, moist, warm, living cell layers
- Respiratory tract, conjunctiva, GI tract
Parenteral route:
- Normal tracts are circumvented (i.e. nails, thorns, needles, bites)
Placenta:
- Less than 2% of pregnancies
Exogenous vs. Endogenous microbes
Exogenous: originates from source outside the body (i.e. environment, person, animal)
Endogenous: already exists inside or on the body
What is an inoculating dose?
The minimum number of microbes needed to cause an infection to proceed. The smaller the number, the higher virulence.
(“ID50: 20” means 20 cells would result in infection in 50% of healthy adults)
Characteristics of adhesion?
- Glycoproteins/lipoproteins (called ligands) can bind to complementary receptors (usually glycoproteins) on host cells. These ligands can be found on fimbriae, glycocalyces in bacteria or envelopes/capsids in viruses (AKA spikes).
- Structures such as fimbriae, capsules, hooks(eukaryotes) can also adhere.
- Adhesion is necessary to cause disease because the body has mechanisms to flush microbes such as tears.
What are phagocytes?
Cells that engulf and destroy pathogens with enzymes and chemicals.
- An example is WBCs (AKA macrophages)
How do pathogens survive host defenses?
- Virulence factors (help avoid phagocytes/macrophages)
- Ability to kill phagocytes
- Extracellular layer (capsule) makes it difficult to engulf
- Adaption to survive within phagocyte after being engulfed
What are some antiphagocytic factors?
Capsule - not recognized as foreign and is slippery making it difficult to engulf
Chemicals - prevent fusion of lysosome with phagocytic vesicles, allowing bacteria to survive inside phagocytes.
Leukocidins - chemicals capable of killing WBCs/macrophages
What ways can pathogens cause damage?
- Enzymes and toxins
- Inducing excessive/inappropriate host defense response
- Epigenetic changes
Examples of damage causing enzymes?
Hyaluronidase - breaks down hyaluronic acid, the “glue” that holds animal cells together
Collagenase - breaks down collagen, the body’s chief structural protein
Coagulase - causes blood to clot, provides pathogens a “hiding place” within clots
Kinases - digest blood clots, releasing “hidden” or trapped pathogens to cause damage
Keratinase/Mucinase - digest keratin/mucus lining of GI tract, respectively
How to toxins cause damage?
- Harm tissues or trigger host immune responses that cause damage
- Toxemia refers to presence of toxins in bloodstream
How to extracellular enzymes cause damage?
Most dissolve/digest structural chemicals in the host
Types/categories of toxins?
Exotoxins - secreted by microbes to destroy host cells or interfere with metabolism
Endotoxins - the lipid A portion of membrane’s lipopolysaccharide (gram negative cell walls) that is released when these cells die/divide/are digested
How do endotoxins affect the host?
Dead gram-negative bacteria release lipid A which cause systemic damage - cause fever, inflammation, diarrhea, hemorrhaging, shock, blood coagulation
How to exotoxins affect the host?
Cytotoxins - kill host cells
Neurotoxins - interfere with nerve cell function
Enterotoxins - affect lining of GI tract
Nephrotoxins - damage kidneys
Hemotoxins - lyse RBCs
Some characteristics of exotoxins?
- Toxic in small amounts
- Specific to cell type
- Composed of small proteins
- Stimulates antitoxins
- Usually no fever
Some characteristics of endotoxins?
- Toxic in high doses
- Systemic reaction (fever, inflammation)
- Composed of lipid A
- Doesn’t stimulate antitoxins
- Gram-negative only sources
Classify infectious diseases/infections
Local infection - limited to small area of body
Systemic infection - throughout the body
Focal infection - begins as local infection and spreads through body
Primary infection - acute infection that causes initial illness
Secondary infection - opportunistic infection arises due to primary infection
Subclinical disease - no noticeable symptoms or signs
Types of infections in the blood
Leukocytosis - increase in WBC levels
Leukopenia - decrease in WBC levels (ex. HIV)
Septicemia - microorganisms are multiplying in blood and present in large numbers
Bacteremia/viremia - bacteria/viruses are present in blood but not multiplying
How do pathogens exit the body?
Often leave in the same way they entered or leave in materials the body releases:
- Secretions: tears, saliva, respiratory droplets, earwax
- Excretions: feces, urine
- Blood: arthropod bites, needles, wounds
- Milk, semen
What are the 5 stages of infection?
- ) Incubation period - time between infection and first signs/symptoms
- ) Prodromal period - short time of mild symptoms, pathogens are reproducing
- ) Illness - most severe stage of disease, pathogens are highest in number
- ) Decline - immune system responds, body returning to normal state
- ) Convalescence - patient recovers and tissues are repaired. Returns to normal
How is the incubation period influenced?
Host resistance, degree of virulence, distance between target organ and portal of entry
What is the acute phase of infection?
Can occur after prodromal period:
- pathogen/agent multiplies at high levels
- greatest virulence, becomes well established
- fever occurs
What is a continuation phase in an infection?
Only some chronic infections:
- lingers for months or years
What are the reservoirs of infectious diseases?
Most pathogens can’t survive for long outside of host:
Animal reservoirs
Human carriers
Nonliving reservoirs
