Host-Microbe Interactions

Question 1

General concept

Answer 1

Only a few of the microbial species that exist in nature are found in association with humans. Interactions of microorganism with human or other animal host are determined both ybthe characteristics of microbes and those of the host.

Question 2

Exposed surfaces of the body are…

Answer 2

colonized by a diverse population of microbes that develops in an orderly sequence (succession) after birth, leading to a relatively stable normal flora. Organisms in the normal flora may aid the host, harm the host, or be commensals (neither the microbe or the host is harmed or helped). Humans have about 10^14 BACTERIA in the normal flora (and about 10^13 cells

Question 3

Areas of the body to which microbes can gain access from the environment

Answer 3

respiratory tract, urogenital tract, alimentary tract, mouth, conjunctiva, scratch injury, capillary, skin. Many become colonized with mircobial flora, but some do not. For example, can clear microbes from respiratory tract by cilia. CONSIDER ANATOMICAL REACTIONS

Question 4

Infection

Answer 4

Process whereby a microbe enters into a relationship with the host. It may or may not cause a disease. So remember infection is not synomynous with infectious disease!!!!

Question 5

Infectious disease

Answer 5

A disease caused by an infection with a microbe. Some infections are communicable, others are not and are not transmitted from patient to patient.

Question 6

Microbes cause specific diseases (Koch’s postulate)

Answer 6

1) Specific microbes are present regularly in characteristic lesions of the disease.
2) The specific microbes can be isolated and grown in vitro.
3) Injection of the cultured microbes into animals reproduces the disease seen in humans.
4) The specific microbes can be re-isolated from lesions of the disease in animals.
(the serial dilutions - from animal to animal to animal - IDs the organism and doesn’t point to contaminants)

Question 7

Pathogenicity

Answer 7

Defined as the ability (usually of a microbial species) to cause disease. Microbes that were able to cause disease readily in normal hosts were defined as FRANK pathogens. Microbes that caused disease primarily in compromised hosts but less often in normal hosts were defined as OPPORTUNISTIC pathogens

Question 8

Virulence

Answer 8

Denoted the degree of pathogenicity (usually of a specific strain within a species). A highly virulent microbe was likely to cause disease when it was introduced into a host in small numbers. LIKE DOSE-AFFECT CURVES OF PHARM. Log(# of bacteria/animal)

Question 9

More Contemporary views

Answer 9

recognize that both microbial and host factors contribute to the outcome of an infectious disease. From this “damage- response” framework, a pathogen is a microbe capable of causing host damage, virulence is the relative capacity of a microbe to cause damage in a susceptible host, and a virulence factor is a microbial component that can damage a susceptible host.

Question 10

Stages of infection

Answer 10

Encounter, entry, spread, multiplication, damage, outcome.

Question 11

Encounter: how the agent meets the host

Answer 11

endogenously v exogenously? contact with other ppls, animals, food, air? Route of infection? Infectious dose?

Question 12

Entry: how the agent enters the host

Answer 12

Cross epithelial - but have to deal with tight junctions. Enter actively? 1) COLONIZATION of BODY SURFACES - an important first step in pathogenesis of many microbial infections. 2) ADHERENCE - mediated by specific binding of microbial surface components.

Question 13

Spread: how the agent spreads from site of entry

Answer 13

Microbial products can promote or inhibit spread. Can use lymphatics, use vasculature, or can enter phagocytic cells and use them as a “bus” (if able to survive internal environment of phagosome)

Question 14

Hyaluronidase, elastase, collagenase, etc.,

Answer 14

which facilitate the spread of microbes through tissues, are sometimes called “spreading factors”. Allows to get through tight junctions.

Question 15

Coagulase

Answer 15

is an agent that inhibits spread of microbes by promoting the deposition of fibrin and helping to “wall off” and localize infections.

Question 16

Multiplication: how the agent multiplies in the host

Answer 16

Normal flora and pathogens must REPLICATE in the host at rates that exceed their clearance by defense mechanisms. The growth rate of microbes in the host (in vivo) may be much slower than their maximal growth rate in laboratory cultures (in vitro). NOT there is a relationship btwn population size and onset of symptoms. Can also keep a certain level of microorganism in your body - for example TB and can get recurrent bouts of infection.

Question 17

Damage: How tissue damage is caused by the agent and/or the host response

Answer 17

a) Some microbial products can cause direct damage to the host. b) Some microbial products contribute to host damage by blocking or interfering with host defense mechanisms c) Most of the microbial products that cause direct damage to the host or interfere with host defense mechanisms are either surface components of microbes, products that can be secreted into the microbial culture medium, or products that can be injected by the microbe directly into a target cell. Such microbial products can often be used as protective antigens for development of vaccines.

Question 18

Outcome: does the microbial agent or the host win the battle or do they learn to coexist?

Answer 18

What are the consequences of failure to eliminate the agent? The survival of obligate parasites depends on a satisfactory portal of exit from the infected host as well as on a portal of entry.

Question 19

Some factors that differ among individuals and affect the microbiome include

Answer 19

1. Diet (breast-feeding, bottle feeding, solid food).
2. Suppression of microbial flora by treatment with antibiotics.
3. Anatomic abnormalities (e.g., blind loop syndrome).
4. Genetic differences between individuals (e.g., specific ABO and Se genotypes).

Question 20

Examples of physiologic importance of the microbiome includes

Answer 20

1. Effects on tissue/organ differentiation (normal vs. germfree animals).
2. Production of vitamins by gut flora.
3. Biochemical conversions (e.g., bilirubin degradation, drug metabolism, production of potential carcinogens, etc.)
4. Competition with pathogens for colonization of body surfaces. Source of agents for endogenously acquired infections.

Question 21

Cholera

Answer 21

a toxin-mediated disease that alters the secretory function of the small intestine but does not cause histological damage. So structure remains the same, but function changes.

Question 22

Pneumococcal pneumonia

Answer 22

acute inflammation caused by invasive, extracellular bacteria. has a slimy surface polysaccardie capsule and not easily ingested by neutrophils. immune response allows for phagositosis. ANTIBODY MEDIATED.

Question 23

Tuberculosis

Answer 23

a chronic disease caused by a facultative intra-cellular bacterium and controlled by cell-mediated immunity. T cell mediated!

Question 24

Acute Rheumatic Fever

Answer 24

a disease resulting from immunopathology triggered by the response to a prior group A streptococcal infection. CROSSREACTs. Like in the heart.

Question 25

communicable

Answer 25

(of a disease) able to be transmitted from one sufferer to another; contagious or infectious.

Question 26

Etiologic agent

Answer 26

specific organism that causes a specific disease.

Question 27

Some limitations of Koch’s postulate

Answer 27

1) Some infectious diseases do not have a
characteristic (pathognomonic) lesion
2) Some microbes cause specific infectious diseases
but CANNOT be grown in vitro
3) Traditional concepts of pathogenicity focus
primarily on properties of microbes vs. hosts
4) The characteristics of infectious diseases usually
reflect complex INTERACTIONS between microbes
and their hosts.
SO WHAT IS RECOGNIZED IS THAT THERE IS CONTRIBUTION FROM BOTH THE MICROBE AND HOST ANIMAL THAT LEADS TO THE DISEASE PROCESS. OUTCOME OF DAMAGE TO TISSUE IS SUM OF CONTRIBUTIONS.

Question 28

Shigella dyssenteriae

Answer 28

10 bacteria for contamination. SO EASILY SPREAD!!!!

Question 29

GERD medicine and infection

Answer 29

If take acid reflux medicine you may be making yourself more susecptible to disease as you are changing stomach acid concentration in the stomache.

Question 30

Modes of spread of infectious disease among people and from animals to people

Answer 30

Human to human
1) Respiratory or salivary spread
2) Feacal-oral spread
3) Venereal spread
Zoonoses (animals to humans)
1) vector (biting arthropod) Ex) malaria
2) vertebrate reservoir (ex-rabies)
3) vector-vertebrate resevoir (plague)

Question 31

Sneeze

Answer 31

A sneeze has 20k particles. Large particles fall to ground. Small particles can remain airborne for a while and become a aerosol. The ones that are less than 10 microns can be transmitted to another persons respiratory tract.

Question 32

Upper respiratory tract infections

Answer 32

Most easily transmitted by respiratory secretions then hand to hand contact then by air.

Question 33

In gut contents

Answer 33

There are over 500 species in the microbiome. E.coli and other facultative bacteria represent only 0.1% of the bacteria, whereas most were anaerobes.