Ch 13 Microbe-Human Interactions Flashcards
Commensalism
An interaction between two species in which one benefits and the other is neutral (not harmed not benefited)
Ex: normal flora
Mutualism
An interaction between two species in which both benefit. Ex: normal flora
Parasitism
An interaction between two species in which one benefits at the expense or harm to the other
Name the four stages of disease
Contact, colonization, infection, disease
Define contact
When exposed to the microbe. can be direct or indirect
Does every exposure lead to colonization
No
Explain colonization
Bacteria is implanted in or on the host as colonies; start to increase growth
Explain infection
The pathogenic bacteria penetrate host defenses, enter the tissues, and multiply; rapid increase in growth
Explain disease
The disruption of a tissue or organ caused by microbes or their products; growth leads to harm. Ongoing process with a deterioration in health, possible death
Another term for normal flora
Resident biota
Describe skin flora
Skin is dry salty; in general gram + bacteria; typically large cocci, xerophile, halophile; ex: strep & staph
Describe the oral flora
Over 30 different species; mixture of aerobic, facultative and obligate anaerobic. Ex: lysozyme in saliva
Describe Gastrointestinal flora numbers
Stomach has very few species due to high acidity; small intestine has a large number due to pH 7; colon Has an even larger number
Examples of G.I. Flora and oxygen requirements
E. coli, salmonella; Colon has 300:1 anaerobes:facultatives
Examples of typical upper respiratory flora
Strep and staph
Is the lower respiratory tract sterile or unsterile
Sterile
Microbial antagonism
The antagonistic effect that good microbes have against intruder microbes
Endogenous infection
Caused by normal flora that are already present in the body that are introduced to a site that should be sterile or is not where it should be. Ex: UTI caused by E. coli
Another term for endogenous infection
Opportunistic
Define pathogen
A microbe whose relationship with the host is parasitic
Pathogenicity
The microbes potential to cause infection and disease
Virulence
The degree of pathogenicity
Three ways to measure virulence
Infectivity, invasiveness, toxigenicity
What is infectivity
The ability to establish itself in the host
What is invasiveness
The ability to spread in the host
What is toxigenicity
The ability to cause damage
What is the number one line of defense for a person against microbes
Normal flora
A true pathogen can cause disease _____
in a healthy person with a normal immune system
An opportunistic pathogen can cause disease ____
only when the host defenses are compromised or if they become established in a part of the body that is not natural to them
How are pathogens classified
By using biosafety levels. Levels are 1, 2, 3 and 4 (with 4 being the worst)
What is the first step in The stages of disease progression
getting in, starts with the portal of entry: The microbe enters the tissues through the characteristic route
Name the 4 types of portals of entry
Skin, G.I. tract, respiratory tract, urogenital tract
What is an infectious dose
Minimum number of microbes to cause an infection. Numbers below that will generally not cause an infection
What is step 2 of the four stages of disease progression
attaching to the host; adherence
Name 4 things that help microbes with adhesion
Fimbriae, slime layer, capsule, viral spikes
Define adhesion
Process by which microbes game a more stable foothold on host tissues
What is the 3rd step in the stages of disease progression
surviving host defenses (the host, not normal flora!!)
Name 4 factors that help bacteria resist phagocytosis
Leukocidins, capsules, coagulase, hiding in the host (intracellular parasite)
What are leukocidins
Substances released by bacteria that are toxic to white blood cells
Pyogenic
Pus forming bacteria, strep and staph are famous for this
Explain how capsules are anti-phagocytic factors
Help bacteria to stick better and is similar enough to self cell that the phagocytes ignore it
Explain how coagulase is an anti-phagocytic factor and give one example of a bacteria that has it
Causes human molecules to clot and cover it up. Ex: staph aureus
Explain how an intracellular parasite resists phagocytosis and give 2 examples of bacteria that do this
parasite is phagocytized then the bacteria stays hidden in white blood cells not being killed, “hiding”
Ex: TB and malaria
Name five digestive enzymes produced by microbes
Mucinase, keratinase, collagenase, hyaluronidase, and fibrinolysin (aka: kinase)
What does hyaluronidase do
Digests the hyaluronic acid (ground substance) between your cells; digests the glue between your cells
Name five bacterial toxins
Neurotoxin, enterotoxin, hemotoxin, nephrotoxin, respiratory toxin
Which hemotoxin causes beta hemolysis
Alpha toxin
What is more damaging digestive enzymes or bacterial toxins
Bacterial toxins
Endotoxin
Gram - bacteria; in certain genera the lipopolysaccharide (LPS) is the endotoxin
How do endotoxins affect a cell
They are not secreted only released when a cell dies and sheds its outer membrane
Describe symptoms of endotoxins
Cause fever, pyrogenic, inflammation, hemorrhage, diarrhea. Could lead to endotoxic shock (aka toxic shock) symptoms tend to be more systemic
Name 4 genera of endotoxin formers and describe their shape
Salmonella, Shigella, Escherichia are all gram - rods
Neisseria is gram - cocci
Endotoxins are typically toxic at what type of concentration (hi or low)
Typically only at high concentrations
200-400 mg/ml
What effect does he have on endotoxins
No matter how long you “cook” it these are stable at high temperatures
How do exotoxins affect a cell
Are secreted by the bacteria cell, have very specific actions. Tend to travel well
Exotoxins are typically toxic at what type of concentration (hi or low)
Toxic at low concentrations (micrograms per milliliter)
Name two types of neurotoxic exotoxins
Clostridium tetani and clostridium botulinum
What does Clostridium tetani cause
Acts at neuromuscular junction causing spastic paralysis
What does Clostridium botulinum cause
Act at neuromuscular junction causing flaccid paralysis
How does bordetella pertussus work
Inactivates respiratory cilia
What does vibrio cholera do
Causes extreme salt and water loss from intestinal cells
Describe a focal infection
Infectious agent breaks loose from local infection and is carried into other tissues. Ex: scarlet fever from strep throat
Example of a localized infection
Wart, pimple
Example of a systemic infection
Chickenpox
Another phrase for mixed infection
Polymicrobial
Name the four stages of clinical infection
Incubation period, prodromal period, Invasive period, Convalescent period
The height of an infection occurs during which stage of infection
Invasive period
Septicemia
Microbes are multiplying in the blood and are present in large numbers
Bacteremia
Small numbers of bacteria are found in the blood but are not multiplying
Passive carrier
Does not become infected but can transmit to others. Ex: typhoid Mary
Asymptomatic vs symptomatic carrier
Infected but shows no symptoms
Infected and shows symptoms
Biological vs mechanical vectors
B: necessary for parasite to survive ex: mosquitos to malaria
M: aren’t infected, just carries it on the outside of its body from place to place.
Zoonosis
Resides in animals and can cross species. Ex: rabies, HIV
4 types of direct transmission
Contact, droplet, vertical, biological vector
3 types of indirect transmission
By vehicle, fomite, or fecal-oral route
Endemic
Cases are concentrated in one area at a relatively stable rate
Epidemic
Increased number of cases that often appear in geographical clusters; rapid increase
Pandemic
Epidemic ranges over more than one continent
