Microbiology Exam 3

chapters 31 and 32

In general, infectious diseases that are commonly fatal are newly evolved relationships between the parasitic organism and the host. Why is this?

• the immune system has not recognized a disease, so it is not ready to fight it off. it has never seen it before

• viruses / the pathogen mutate to a less severe form, leading to coexistence

parasite

organism that lives on or within a host organism

• metabolically dependent on the host

• causes disease

pathogenicity

ability of parasite to cause disease

virulence

• degree or intensity of pathogenicity

• determined in part by pathogen’s ability to survive outside host

what are the three characteristics that determine virulence?

infectivity

invasiveness

pathogenic potantial

infectivity

ability to establish focal point of the infection

invasiveness

ability to spread to adjacent tissues

pathogenic potential

ability to cause damage to host

explain the observation that different pathogens infect different parts of the host

• different parts of the body have different environmental conditions so some grow more optimally in different places

• viruses need to attach to specific receptors

• mode of transportation or spread

Three factors impacting the outcome of host-parasite relationships

1. number of organisms infecting the host

2. the degree of pathogenicity (virulence)

3. host’s defenses or degree of resistance

signs

objective changes in body that can be directly observed

symptoms

subjective change experienced by patient

disease syndrome

set of characteristic signs and symptoms

course of infectious disease

• incubation period

• prodomal stage

• period of illness

• convalescence

incubation stage

period after pathogen entry, but before signs and symptoms appear

prodomal stage

onset of signs and symptoms

not clear enough for diagnosis

period of illness

disease is most severe and has characteristic signs and symptoms

convalscence

signs and symptoms begin to disappear

understand this graph

how to tell what pathogen caused the disease

Koch’s postulate

clinical micro lab

• important for isolation and identification

• determines susceptibility to antimicrobial agents

source

location from which pathogen is immediately transmitted to host

can be inanimate or animate

period of inactivity

time during which source is infectious or is disseminating the organism

reservoir

site or natural environmental location in which pathogen is normally found

sometimes functions as the source of pathogen

carrier

infected individual who is a potential source of infection for others

(human)

4 types of carriers

active

healthy

incubatory

convalescent

(all human)

active carrier

has overt clinical case of disease

healthy carrier

harbors the pathogen but is not ill

incubatory carrier

is incubating the pathogen in large numbers and is in the beginning stages of disease

convalescent carrier

has recovered but continues to harbor large numbers of the pathogen

zoonoses

animal diseases that can be transmitted to humans

(animal)

zoonoses transmission to humans

direct or indirect

• contaminated milk

• inhaling dust particles contaminated by animal excreta

• eating insufficiently cooked meat

vectors

organisms that spread disease from one host to another

e.g. mosquitoes, ticks, flies

(animals)

4 main routes of transmission

• airborne

• contact

• vehicle (indirect mode)

• vector-borne

airborne transmission

pathogen suspended in air and travels up to 1m from source to the host

droplet nuclei

• can remain airborne for long time, travel long distances

• usually propelled from respiratory tract (sneeze, cough, vocalization)

contact transmission

coming together or touching of source/reservoir and host

direct and indirect contact

direct contact

person to person

physical interaction between source/reservoir and host

e.g. kissing, touching, sexual contact

indirect contact

involves an intermediate (usually inanimate)

e.g. eating utensils, bedding, door handles

vehicle transmission

inanimate object involved in pathogen transmission

common: single vehicle spreads pathogen to multiple hosts

e.g. water, food, surgical instruments, bedding, etc.

fomites

object that is not harmful itself but is able to harbor and transmit pathogenic organisms

vector-borne transmission

Transmission can be either external or internal

external (mechanical):

• passive carriage of pathogen on body of vector

• no growth of pathogen during transmission

• e.g. flies carry Shigella on their feet from a fecal source to a plate of food

internal:

• pathogen is carried within the vector

• e.g. rat fleas carry Yersinia pestis (cause of plain)

2 factors effecting susceptibility

• defense mechanism of the host

• pathogenicity of the pathogen

nutrition, genetic predisposition, and stress also play a role

how do pathogens leave the host

active or passive escape

active escape

active movement of the pathogen to portal of exit

e.g. parasites migrate through the body, reach the surface, and exit

passive escape

most common

excretion in feces, urine, droplets, or saliva

non-specific immune system

• acts as first line of defense, acts immediately

• offers resistance to any microbe or foreign material

• lacks immunological memory

• occurs to the same extent each time a microorganism is encountered

another name for non-specific immune system

innate immune system

specific immune system

• resistance to specific foreign agent

• has memory

• effectiveness increases on repeated exposure to agent

another name for specific immune system

adaptive immune system

antigens

something recognized as foreign

specific in shape

invoke immune responses

cause specific cells to replicate

innate immune system cells & tissues

granulocytes

macrophages

dendritic cells

NK cells

(inflammation & cell cooperation)

innate immune system physical barriers

skin

mucous membranes

(resident responders)

• prevent pathogens from entering the body

• first line of defense

• effectiveness impacted by age, genetics, nutrition, and personal hygiene

innate immune system chemical mediators

defensins

lysozyme

complement

(opsonization)

acquired immune system cells & tissues

T cells

B cells

(opsonization, resident responders, inflammation)

leukocytes

white blood cells

involved in both immune systems

hematopoesis

development of white blood cells in bone marrow

(leukocytes)

comparison of white and red blood cells

there are way more red blood cells, but white blood cells fight infections

monocyte

immature macrophage

macrophage

• highly phagocytic

• reside in tissues

• variety of surface receptors

• toll-like receptors

toll-like receptors

recognize LPS (gram negative bacteria)

granulocytes

cytoplasm contains granules, during an infection/infalmmation granulocytes rush to the area and release granules, these can kill microorganisms

3 classes of granulocytes

basophil

eosinophil

neutrophil

basophil

allergies and hypersensitivity reactions

eosinophils

allergies and parasitic infections

neutrophils

migrate to sites of tissue damage and attack bacteria

dendric cells

contain more surface area

contact invading pathogen

uses 3 Ps

3 Ps

phagocytosis

process (break into smaller pieces)

presentation (on outer surface)

lymphocytes

specific population of white blood cells

major cells of the immune system

what two populations are included in lymphocytes

B cells & T cells

lymphocytes in action

require a specific antigen to bind to a surface receptor (B or T cell)

lymphocytes divide once activated

some form memory cells

memory cells

subset of lymphocytes that will respond later in host’s life when antigen is present again

B lymphocytes

B cells

mature in bone marrow

after maturation and activation, these are called plasma cells and produce antibodies

T lymphocytes

T cells

mature in the thymus (next to heart)

require antigen binding to surface receptors for activation and replication

primary organs and tissues

sites where lymphocytes mature and differentiate into antigen-sensitive mature B and T cells

includes bone marrow and thymus

secondary organs and tissues

area where lymphocytes may encounter and bind antigen

• followed by proliferation (dividing) and differentiation into fully mature effector cells

includes spleen (filters blood) and lymph nodes (filters lymph)

understand and talk through this diagram

Lymphocyte cells develop into B cells (bone marrow) and T cells (thymus). When exposed to an antigen, both undergo clonal expansion (make identical copies).

• B cells → become plasma cells (produce antibodies to neutralize pathogens) and memory B cells (enable faster response if the same antigen returns).

• T cells → become:

  • Helper T cells (TH): release signals that regulate and activate other immune cells

  • Cytotoxic T cells (CTL): directly kill infected or abnormal cells

  • Memory T cells: allow a faster response to future infections

phagocytosis

engulf

process by which phagocytic cells recognize, ingest, and kill extracellular microbes

e.g. macrophages, dendritic cells, and neutrophils

mechanisms for recognition of microbe by phagocyte

opsonin-independent recognition

opsonin-dependent recognition

opsonin-independent pathogen recognition

Common pathogen components are non-specifically recognized to activate phagocytes

• pathogen-associated molecular patterns (PAMPs) detected by pattern recognition receptors (PRRs)

  • example: toll-like receptors

PAMP meaning

pathogen associated molecular patterns

PRR meaning

pattern recognition receptors

PAMPs

• conserved microbial molecular structures that occur in patterns

• detected by phagocyte

• unique to microbes, not present in host

  • LPS of gram-neg, peptidoglycan of gram-pos, or flagella

• recognized my PRRs on phagocytic cells

toll-like receptors (TLRs)

PRRs that function exclusively as signaling receptors

recognize and bind unique PAMPs of viruses, bacteria, or fungi

• binding is communicated to the host cell nucleus which initiates the host response

steps of phagocytosis

1. binding of specific microbial components to receptors of phagocyte

2. microbes can be internalized as part of a phagosome

3. toxic oxygen products are produced which can kill invading microbes

what happens to microbial invaders once they have been killed and digested

• exocytosis

• antigen presentation

exocytosis

after neutrophils break down microbes, the fragments are expelled

opsonin-independent mechanism of pathogen recognition

• PAMPs (on microorganism) are recognized by toll-like receptors (on the phagocytic cell)

• PAMPs are molecular signatures of infection

• allows innate immune system to distinguish self from microbial non-self

how do opsonins promote phagocytosis?

by tagging foreign pathogens, bridging them to phagocytes (like macrophages and neutrophils), and overcoming negative electrical charges that cause repulsion

inflammation

nonspecific response to tissue injury

• can be caused by a pathogen or physical trauma

• acute inflammation is the immediate response of body to injury or cell death

4 cardinal signs of inflammation

redness

warmth

pain

swelling

acute inflammatory response: chemical mediators

chemokines

selectins

integrins

chemokines

released by injured cells

activate the endothelium on nearby capillaries

selectins

cell adhesion molecules on activated capillary endothelial cells

integrins

adhesion receptors on neutrophils

attach selectins

acute inflammatory response: processes

margination

diapedesis

extravasation

margination

neutrophils stick to endothelium

stop rolling

diapedesis

neutrophils change shape and squeeze through the endpthelial wall

extravasation

neutrophils move into the tissue and migrate to the site of injury

skin - how do they protect

inhospitable environment for microbes

• shedding of outer layers

• pH is slightly acidic

• high NaCl conc.

• drying

mucous membrane - how do they protect

form a protective coating that resists penetration and traps microbes

often bathed in lysozyme, which breaks down peptidoglycan

where are mucous membranes found

eye, respiratory, digestive, and urogenital system