Microbiology- Chapter 13 (Microbe- Human Interactions)

Front 1

What is normal microbiota?

Back 1

• Normal Microbiota- microorganisms colonizing the human body without harming it

Front 2

What are • Transient microbes?

Back 2

• Transient microbes- rapidly lost

Front 3

WHat are Pathogenic microbes?

Back 3

• Pathogenic microbes- invade and damage the cells and tissue

Front 4

How do we acquire resident biota?

As fetus-newborn.

Back 4

• The uterus is germ-free
• First exposure to microbes during the passage through the birth canal
• Feeding
• Contact with the environment and family members

Front 5

How does an infection start and on what does it depend for success?

Back 5

• Infection starts with an invasion of a pathogen
• How successful this invasion will be depends on:
o Pathogenicity- the ability of a microbe to cause disease in another organism
- Virulence- the degree of pathogenicity; relative ability of a microbe to cause disease
- Virulence factors (enzymes, toxins, capsule…)

Front 6

How is an infection established?

Back 6

“Establishing the Infection”
• The microbes enter the body through- portal of entry
• Attaching to the host
• Surviving host defenses
• Causing disease

Front 7

What is the portal of entry of microorganisms into the body?

Back 7

“How Microorganisms enter a Host”
Portals of entry:

• Mucous membrane (lines the body cavities that are open to the environment)
• Skin (openings or cuts)

Front 8

Describe agents that enter through the skin.

Back 8

“Infectious agents that enter the skin”
• Skin is a tough barrier
• Broken skin enables penetration of microbes
• The common infectious agents:
o Staphylococcus
o Streptococcus
o Clostridium

Front 9

What are ways of penetrating the skin?

Back 9

• Other ways of penetrating the skin
o Digestive enzyme of microbes
o Insect bites
o Hypodermic needles

Front 10

what are the mucus membranes?

Back 10

• Mucus membranes (respiratory, gastrointestinal, genitourinary tract)

o Respiratory tract is the most common portal of entry. Inhalation (common cold, influenza, pneumonia, tuberculosis…)
• Gastrointestinal tract- through food, water and contaminated hands
• Genitourinary tract- through sexual contact (STD’s)

Front 11

Is the number of invading microbes important?

Back 11

• A certain (minimal) number of microbes have to enter the body in order to cause an infection- infectious dose
• Infectious dose for:
o Q fever- 1 cell
o Tuberculosis- 10 cells
o Gonorrhea- 1,000 cells
o Cholera- 1,000,000,000

Front 12

True or false.

• Pathogens have preferred portal of entry

Back 12

True.

• Pathogens have preferred portal of entry
o Ex: streptococcus that is : inhaled can cause pneumonia, when swallowed it does not show symptoms

Front 13

How does a microorganism attach to the host?

Back 13

• Microorganisms attach themselves to the host cell through:

o Fimbriae (Bacteria)
o Capsules (bacteria)
o Spikes (viruses)

Front 14

Describe the adherence in infections.

Back 14

“Adherence”
• Attachment is based on binding of specific molecules on both host and pathogen
• Surface molecules of the pathogens bind to the specific molecules of host tissue cells
• Ligands are located on Glycocalyx or on Fimbriae

Front 15

How do microorganisms survive host defense?

Back 15

“Surviving Host Defense”
• Pathogenic microbes are recognized by white blood cells
o Phagocytes
• Phagocytes engulf and destroy the pathogen
• Some microbes know how to evade Phagocytosis
o Produce toxins that kill phagocytes
o Produce capsule
o Can survive inside the phagocyte

Front 16

How Virulence Factors Contribute to Tissue Damage?

Back 16

“Causing Disease”

How Virulence Factors Contribute to Tissue Damage?

• Virulence factors:
o Exoenzymes and
o Toxins directly affect the host tissue
o Capsules

Front 17

What are exoenzymes?

Back 17

“Exoenzymes”

• Some pathogens produce Exoenzymes that can dissolve structural chemicals in the body
o Hyaluronidase- hydrolysis of hyaluronic acid, a substance that cements animal cells together
o Kinases- digest the blood clots- formed to isolate the infection
o Coagulases- coagulate (clot) the fibrinogen (protection against phagocytes)

Front 18

What are the two types of bacterial toxins?

Back 18

• Exotoxins
o Actively excreted by a living bacterial cell

• Endotoxins
o Part of the cell wall of Gr- bacteria

Front 19

Describe exotoxins.

Back 19

“Exotoxins”
• Are released from bacterial cells (Gr+ or Gr-)
• They are proteins, some are enzymes

Naming Exotoxins:
• Hepatotoxins
• Cytotoxins
• Neurotoxins
• Entertoxins
• Botulinum toxin

Front 20

What effects do Botulinum toxin- Clostridium Botulinum cause?

Back 20

• Botulinum toxin- Clostridium Botulinum
o Nuerotoxin that prevents the transmission of impulses from the nerve cell to the muscle
o Flaccid paralysis

Front 21

What effects do Tetanus toxin- Clostridium Tetani cause?

Back 21

• Tetanus toxin- Clostridium Tetani
o Blocks the relaxation pathway of muscles; uncontrollable muscle contraction

Front 22

Describe endotoxins.

Back 22

“Endotoxins”
• Is part of the outer layer of the cell wall of Gr- bacteria
• Endotoxins are Lipopolysaccharides
• Endotoxin has to be released from the cell wall in order to cause the symptoms
• The symptoms are: chills, fever, weakness aches, shock and even death

Front 23

How is the potency of a toxin expressed?

Back 23

“Potency of Toxin”
• Expressed as lethal Dose- LD50
- Botulinum toxin- 0.03 ng/kg (mice)
- Shiga toxin- 250 ng/kg

Front 24

FIll in the blanks.

• Microbial toxins can cause:

Back 24

• Microbial toxins can cause:
- Fever, diarrhea, cardiovascular disturbance, shock , inhibition of protein synthesis, disrupt the nervous system

Front 25

What are the three types (patterns) of infection?

Back 25

“The Patterns of Infection”

• Localized infection- infection that is limited to a small area of body (abscesses)
• Systemic infection- microbes are spread throughout the body (measles)
• Focal infection- infectious agent migrates from a local infection to other tissues
• Mixed (polymicrobial) infection- more than one infectious agent is involved
• Primary infection- infection that causes the initial illness
• Secondary infection- infection by opportunistic pathogen
• Acute infection- develops rapidly but lasts a short time (influenza)
• Chronic infection- develops slowly but lasts for long period of time

Front 26

What are the stages of clinical infections?

Back 26

“Stages of Clinical Infections”
• Incubation period- time period between initial infection and first symptoms of disease (several hours in pneumonic plague; several years leprosy)
• Prodromal stage- feeling of discomfort (1-2 days)
• Period of invasion- expression of all symptoms
• Convalescent period- decline of symptoms- recovery

Front 27

What are the symptoms and signs of an infection?

Back 27

• Inflammation- swelling of the tissue
o Edema- accumulation of fluid
o Granulomas and abscesses- walled-off cells of damaged cells and microbes
o Rashes, skin eruption
• Signs of infection in the blood
o Leukocyotsis- increased level of blood cells
o Bacteremia- bacteria present in the blood; do not multiply
o Septicemia- microorganisms multiply in the blood
• Unnoticed infections
o Asymptomatic, subclinical

Front 28

What are the portals of exit of an infectious microorganism?

Back 28

“The Portal of Exit”
The discharged microorganisms are the source of a new infection
• Respiratory or salivary portals
• Skin
• Fecal exit
• Urogenital tract
• Blood


• Respiratory or salivary portals
o Moist secretion-coughing, sneezing, laughing and talking
• Fecal
o Intestinal infection causes rapid peristalsis- diarrhea
• Urogenital tract
o Vaginal discharge, semen, urine
• Blood
o When removed for testing purposes or when released during tissue injury

Front 29

What are the two reservoirs from which a microbe can start an infection?

Back 29

• Microbes start an infection from the reservoirs

• Reservoir:
o Living reservoir
- Human body
- Animal body

o Non-living reservoir
- Soil
- Water
- Plants

Front 30

What is the source of infection of a living reservoir?

Back 30

“Living Reservoirs”

Source of infection:

• Diseased person or animal
• Carrier- people that harbor pathogens without any signs of illness
o Incubation carriers- spreads the disease during the incubation period
o Convalescent carriers- recuperating patients
o Chronic carries- carry the agent for long period of time
o Passive carriers- medical personnel

Front 31

How do animals act as reservoirs?

Back 31

“Animals as Reservoirs”
• Animals are vectors- they transmit the infectious agent from one organism to another
• Biological vectors
o The agent multiplies within the vector
• Mechanical vectors
o Mechanically transmits the agent to food or directly to humans

Front 32

What are Communicable diseases?

Back 32

• Communicable diseases- infected host transmits the agent to another host

Front 33

What are Non-communicable diseases?

Back 33

• Non-communicable diseases- infection acquired through:
o Contact with an agent from its own body
o From nonliving reservoir

Front 34

Describe contact transmission of infection.

Back 34

• Contact transmission- microbes directly transferred
o STDs
o Droplet contact- sneezing

Front 35

Describe indirect transmission of infection.

Back 35

• Indirect transmission

o Contaminated materials
- Vehicle: food water, biological products and fomites
o Air as vehicle
- Droplet nuclei- dried material (mucus) generated by sneezing

Front 36

what is a nosocomial infection?

Back 36

“Nosocomial Infectious- hospital acquired”
• 5-15% of hospital patients acquire nosocomial infection
• Factors responsible for nosocomial infections:
o The characteristics of microbes in the Hospital
o Weakened status of the hosts
• Patients are compromised by:
o Broken skin or mucous membranes
o Suppressed immune system
• Chain of transmission
o Transmission from hospital staff to patient
o From patient to patient
o From fomites to patients
o Through ventilation system

Front 37

What is epidemiology?

Back 37

“Epidemiology”
Study of frequency and distribution of disease in human population
• Frequency of cases:
o Incidence of a disease- number of new cases of a disease during a given time interval, usually one year
• Prevalence of a disease- total number of current cases in the entire population regardless of when it first appeared

Front 38

What is an endemic disease?

Back 38

• Endemic disease- constantly present in a population

Front 39

What is a Sporadic disease?

Back 39

• Sporadic disease- occurs occasionally

Front 40

What is an Epidemic disease?

Back 40

• Epidemic disease- many people in a given area acquire a disease in a short period of time

Front 41

What is a Pandemic disease?

Back 41

• Pandemic disease- epidemic disease but occurs in a large geographic region