Unit 4: Infection chain, microbial pathogenesis & Epidemiology (BIO205)

Includes: infection Chain, Virulence Factors & Epidemiology

Periodontitis (gum disease) is associated with many bacteria, including *Treponema denticola*, causing infection in tissue surrounding teeth. *Treponema denticola* is a ___ in the infection chain.

causative agent

Transfusions and IV drug use are examples of _____ portals of entry.

parenteral

The bacterium *Staphylococcus aureus* is commonly found in the nasal cavity of healthy people. If inhaled into the lungs, however, it may cause pneumonia. *Staphylococcus aureus* is best described as

both resident microbiota and opportunistic pathogen

While in class you notice your teacher sneezes without covering their mouth. This is a form of ___ transmission.

droplet

Fomites are

inanimate objects involved in the indirect contact transmission of pathogens

Romaine lettuce from Yuma, Arizona was contaminated with *Escherichia coli*. This is considered a(n) ___.

outbreak

Valley fever is an example of a(n) ____ infection found in the Southwest U.S.

endemic

What contributes to emerging infectious diseases?

* novel or new pathogens
* spreading of an infectious illness to due international travel
* increase in incidence of an infectious illness

Pandemic

\n A disease increases in frequency worldwide.

Sporadic

A disease occurs relatively rarely, without a geographic focus.

Endemic

A disease occurs at a relatively constant and often low level within a population.

Epidemic

A disease produces more cases than expected within a short time in a localized area.

Factors which contribute to the emergence of infectious diseases may include:

* misuse of antibiotics
* international travel
* war
* disruption of immunization programs
* trade
* evolution of microorganisms
* climate change
* urban development and land use

In which condition does metabolic waste produced by bacteria contribute to pathology?

gas gangrene

Which of the following is a cytotoxin producing organism?

*Corynebacterium diphtheriae*

The definition of pathogenic is____ and virulence is___.

disease-causing, the degree of damage

Which of the following is considered a beta hemolytic pathogen?

*Streptococcus pyogenes*

Upregulated host cell growth or ____ may develop due to certain viral infections.

cancer

viremia =

the presence of viruses in the blood

Tetanus toxin causes ____ paralysis while botulinum toxin produces ____ paralysis.

rigid, flaccid

Adjacent host cells fuse during some viral infections is termed

syncytium

Which infectious disease may lead to rheumatic fever later in life?

strep throat

beta hemolysis

Complete digestion of red blood cells

alpha hemolysis

Partial digestion of red blood cells

gamma hemolysis

No digestion of red blood cells

Normal flora

NO pathology under normal conditions; established before and after birth; aka normal microbes found on/in your skin, eyes, nose and throat, mouth, large intestine, and urinary/reproductive systems.  

Transients

microbes that do NOT normally reside on a specific host tissue; often picked up by contact, do not form long term stable colonies on host, may be present for days, weeks, months, and then disappear 

Strict Pathogens

always cause disease upon colonization of a suitable host; colonization produces infection 

Transformed resident

genetic recombination (through conjugation, transformation, or transduction) of non-pathogenic strains 

Opportunists

often normal flora that cause disease under favorable conditions 

Mutualist

both organisms benefit 

Commensal

 one organism benefits but the other is unaffected 

Parasite

one organism benefits at the expense of the other 

__2 factors__ that contribute to opportunistic infections

1. The host immune system is compromised 
2. normal flora gain entry to to tissues where they do NOT belong 

**Portals of entry for infectious disease**

Mucus membrane, respiratory system, digestive system, and broken skin (punctures, injections, bites, cuts, wounds, surgery, and splitting of the skin), transplacental (crosses placenta), genitourinary tract, gastrointestinal

**Portals of exit for infectious disease**

secretions & excretions (tears, milk, urine, blood, skin flakes, earwax, saliva, sputum, nose secretions, semen, vaginal secretions, feces)

__Causative agent__

disease causing microbes 

__Reservoirs__

Carriers: individuals “carries” microbe but does not present symptoms 

Zoonoses: diseases transmitted to humans by animals

__Modes of transmission =__

direct and indirect contact, droplet, vehicles, and vectors

Indirect contact

 pathogen transmitted via inanimate object (ex: linens, catheters, utensils, etc.)

Direct contact

skin to skin, sexual contact, kissing, hugging, etc. 

Droplet

tiny particles of mucus and saliva expelled from the mouth or nose during coughing, sneezing, laughing, or talking (ex: Influenza)

Vehicles

includes airborne (infectious agents travel through the air more than 1 meter for longer periods of time) and waterborne/foodborne transmission (cross contamination) 

Vectors

biting from an animal or insect (biological transmission), arthropods and flies for example that carry diseases on them onto your food (mechanical transmission) 

**Nosocomial**

healthcare acquired infection (two common: UTI and MRSA); prevented by handwashing, disinfecting equipment between patients, wearing proper PPE

Epidemiology

the branch of medicine which deals with the incidence, distribution, and possible control of diseases and other factors relating to health.

disease occurs at a stable frequency (Common Cold and Valley Fever) 

Endemic 

disease occurs at a greater than normal frequency (Flu typically reaches epidemic level, as well as many STIs)

Epidemic

occurrence of epidemic over a large geographical area or on more than 1 continent simultaneously; oftentimes these are global (ex:COVID-19)  

Pandemic

Outbreak

set of cases that occur during a brief period (ex: E.Coli in lettuce)

occurs only occasionally (ex: tetanus)

Sporadic

the 5 different __stages__ of infectious illness

1. **Incubation**


2. **Prodromal** 


3. **Illness**


4. **Decline** 


5. **Convalescence** 

Incubation

microbe invades and colonizes host; microbes begins to proliferate and reproduce 

**Prodromal**

stage the proceeds illness or onset of severe pathology 

**Illness**

most severe stage of illness where symptoms and pathology are caused by pathogen or immune system  

**Decline**

stage where immune response brings infection under control 

**Convalescence**

final stage where patient recovers from illness and repairs damage

**Acute infection**

rapid onset and short duration 

**Chronic infection**

develops more slowly, microbe persists and causes recurrent infections 

**Latent infection**

symptoms appear long after infection

**Symptoms**

effects of disease reported by patient (pain and malaise)

**Syndromes (AIDS, SARS, etc)**

a group of symptoms 

**Subacute or subclinical**

symptoms not apparent

Pathogenicity

The ability of a microbe to cause a disease 

Virulence

The severity of disease caused by a microbe 

**Virulence Factors def.**

microbial structure/proteins that enhance the ability to invade, proliferate, and damage the host

Virulence Factor Categories

1. Enhanced adherence (attachment aka adhesins) 
2. Immune inhibition and evasion 

a.) masking of microbe

b.) antiphagocytic factors 

c.) inactivation of immune cells and factors


3. Pathology to host

a.) metabolic wastes

b.) toxins

Attachment Factors: **(lock and key)**

– adhesions are viral spikes and bacterial fimbriae/pili/capsules and other structures that allow for attachment to specific host cells

**Bacteria** – use fimbriae, sex pili, biofilms, capsules, hooks on flagella, etc. 

* Coliforms attach to phagocytes and mucosal epithelium (ex: salmonella, shigella, vibrios)
* STI bacteria attach to phagocytes (ex: Neisseria gonorrhea, Chlamydia)

**Viruses** – use spikes to adhere

* Influenza attaches to respiratory epithelium using HA and NA
* HIV attaches to CD4+ Helper T Cells using gp120 & gp41

Masking def.

 the ability to produce external components that are ignored by host immune cells  

Masking includes…

1. viral suppression of host MCHI or of host epitope presentation (ex: herpes viruses)
2. **bacteria capsule (glycocalyx)**


3. **M protein of** ***Streptococcus pyogenes***

**bacteria capsule (glycocalyx)**

secrete extracellular matrix, fibronectin, hyaluronic acid which looks like the host tissues, blocks attachment of bacteria to phagocytes (macrophages or neutrophils)

Capsule = sugar coat that protects bacteria

**M protein of** ***Streptococcus pyogenes***

*mimics connective tissue of heart (rheumatic fever) & inhibits phagocytosis by preventing C3b from opsonizing* 

Antibody or complement inactivators examples…

 Streptococcus pyogenes M protein, Staphylococcus aureus protein A, viral complement inhibitors (Influenza, HIV, Pox)

**Coagulase**

def. clotting enzyme produced by Staphylococcus aureus (bacteria form clots which protect them from phagocytes) 

Abscess: swollen, red, inflamed tissue filled with bacteria and dead phagocytes 

**Hyaluronidase**

produced by Staphylococci, Streptococci & Clostridia; digests hyaluronic acid = the “cement” that helps hold cells together in tissues, allows pathogens to invade tissue; allows pathogens to invade tissue 

**Kinases (Staphylokinase or Streptokinase)**

 enzyme produced by Staphylococcus that dissolves fibrin threads in blood clots, allowing bacteria to escape 

**Antibody receptors (Protein A)**

 antibody receptor which blocks WBC attachment (flip antibody) 

Factors that cause tissue damage

* Toxins 
* Toxemia 
* Septicemia  (Bacteremia + Viremia)

Toxins

poisonous substances produced by microbes that alter host metabolism

Toxemia

presence of toxins in blood 

Septicemia

presence of infection in blood 

* Bacteremia = presence of bacteria in blood 
* Viremia = presence of virus in blood

**Endotoxins**

* a part of the cell membrane; __**membrane bound**__
* part of the outer portion of the cell wall of __**ONLY gram-negative bacteria.**__ 
* They are liberated when the bacteria die and the cell wall breaks apart
* __**lipid**__ A (lipopolysaccharide)
* __**heat-stable**__
* __**not very toxic**__ 
* __**systemic**__
* ex: Salmonella typhi

**Exotoxins**

* __**secreted out**__ of the cell
* produced inside __**mostly gram-positive bacteria (but made by both)**__ as part of their growth and metabolism
* they are released into the surrounding medium
* bacteria is synthesized in the cytoplasm
* mainly made of __**protein**____s__
* inactivated by heat


* __**very potent toxicity**__ 


* are tissue or organ specific with 5 major groups: enterotoxins, neurotoxins, cytotoxins, hemotoxins and super toxins (superantigens) 
* __**local**__
* ex: Clostridium tetani

Bacteria that can cause Toxemia

E. Coli

Toxic shock

 is a rare but life-threatening condition caused by bacteria getting into the body and releasing harmful toxins. (ex: Staphylococcus aureus)

5 categories of exotoxins

1. Enterotoxins


2. Neurotoxins


3. Cytotoxins


4. Hemotoxins


5. Supertoxins aka superantigens

Enterotoxins

* entero = intestines
* causes nausea, vomiting, abdominal cramps and diarrhea
* ex: vibrio cholera
* can be found in food
* food poisoning  

Neurotoxins

* neuro = nerve (most powerful toxin)
* ex: clostridium botulinum (damages excitatory neuron synapse) → causes flaccid paralysis (unable to contact)
* ex: clostridium tetani (damages inhibitory neuron synapse) → causes rigid paralysis (unable to relax)

Cytotoxins

* damage epithelial cell layers
* ex: corynebacterium diphtheria
* “kills” respiratory tract cells that become trapped in mucus and block passageways 
* causes covering die and slough off to form a pseudomembrane which can lead to suffocation

Hemotoxins

* produce hemolysins and leukocidins that lyse blood cells 
* Streptococcus pyogenes, streptococcus pneumoniae, staphylococcus aureus and some E. coli strains 

Supertoxins aka superantigens

* antigen hyper stimulates lymphocytes & induces shock 
* causes immune response 2000x stronger than normal
* toxic shock syndrome: staphylococcus aureus & streptococcus pyogenes (wound infections, tampon use) 

exotoxin that causes GI transport damage

enterotoxin

exotoxin that damages host cell membranes & inhibits protein synthesis

cytotoxin

exotoxin that hyperstimulates immune response

superantigen

 glycocalyx or cell wall components (lipid A) released from dying Gram- bacteria

endotoxin

exotoxin that causes red blood cell damage

Hemotoxin

toxic enzymes secreted by Gram + bacteria

exotoxin

exotoxin that causes motor nerve damage

neurotoxin

pathogens that cause disease when immune system is suppressed or when introduced into an abnormal area of the body

opportunistic

Viral particles observed inside host cells

 inclusion bodies