toxins
  are classified by:
1. their structure
2. their mechanics of infection
3. their target tissue

        infectious dose 50 (ID50)
= how many of the pathogens must be present in order to infect 50% of exposed susceptible hosts.   

review question:
what is meant by LD50?

review question:
what is dysbiosis?

how can antibiotics cause this conditi0on?

        lethal dose 50 (LD50)
= amount of toxin needed to kill 50% of affected hosts who are not treated. 

review question:
what is meant by ID50?

        Botulinum toxin:
 Clostridium botulinum produces this neurotoxin
 which causes botulism = muscle paralysis. 

​                                         Virulence factors include:
 1. adhesins: help pathogens attach to host cells (ex: fimbriae in bacteria) 
 2. invasion factors: help pathogens enter host cells 
 3. toxins: damage host cells or tissues (ex: exotoxins/endotoxins) 
 4. capsules: protect pathogens from the host's immune system 
 5. spike proteins: help entry into host cells 
 6. immune evasion factors: help pathogens evade the host's immune response 

 virulence

 Dysbiosis
is an imbalance in the gut microbiota.
it's been linked to mood/mental health disorders due to its negative impact on serotonin levels

​  capsules

Serotonin
 your gut microbiota produces over 90% of the body's serotonin. 
Gut bacteria modulate tryptophan supplies needed for serotonin production.
Serotonin produced in the gut influence your brain via your Vagus nerve.
 The Vagus nerve is a communication highway between the gut and the brain. 

Escherichia, Enterococcus, Candida, and Streptococcus ​have been found to produce serotonin in your gut. 

the measles virus
 R0 = 12-18
each person with measles, on average, infects 12-18 other people

 exotoxins

normal
​gut microbes 

how do we manage a pathogen that is
​ super virulent?

 compare Ro to Rt
Rt = the effective reproduction number (also called Re or just R)

ex:

review question:
describe the different types of virulence factors.

     Tetanus toxin:
 Clostridium tetani produces this neurotoxin causes   tetanus = muscle spasms and rigor. 

review question:
describe what is meant by t he gut-brain axis.

vs

Your gut microbiota (microbiome/gut flora)
​are the microbes that live in your digestive tract.
This microbiota influences our resistance to pathogens, the health of intestinal tissues, the production of important molecules, and emotional health via the gut–brain axis.
Your colon contains the most microbes with between 300 and 1000 different species present, most of them anaerobic bacteria.  99% of your gut bacteria come from about 30 or 40 species.
55% of your poo is bacteria.

                                   host factors are characteristics of the host that influence
                                   its susceptibility or resistance to infection including:

a. Immune status: weakened immune systems/immunocompromised individuals                                                  cause hosts to be more susceptible to infection
b. Genetics: specific genes can confer resistance or susceptibility to specific pathogens
c. Age: very young and very old people are often more vulnerable to infections
d. Nutrition: malnutrition weakens immune systems
e. Co-infections: being already sick impairs a host's ability to fight off other pathogens
f. Gut microbiome: the gut microbiome can influence susceptibility to certain
​                                         infections

toxin producing microbes = toxigenic microbes

the gut - brain axis

review question:
explain why the risk group designation of a pathogen determines the BSL that must be followed. 

 gut microbes
      normal   v   pathogenic   

review question:
 infection control practices are designed to prevent the transmission of infectious diseases in a healthcare setting.

List 5 standard precautions all health care workers should practice. 

pathogenicity vs virulence

review question:
 in addition to infection control practices previously cited,
what are three ways you can help manage the outbreak of infections in a healthcare setting?

review question:
how do endotoxins differ from exotoxins?

R0 =
the reproduction rate
of a pathogen
Ro quantifies the contagiousness and transmissibility of pathogens.

    adhesins

      and...
Clostridium perfringens produces toxins causing gas gangrene = a severe infection that destroys tissue

Clostridioides difficile produces these toxins causing
C. diff infection = diarrhea /colitis.

Corynebacterium diphtheriae produces exotoxin
 which causes respiratory failure. 

 E coli and Shigella produces this cytotoxin which
 damages red blood cells and causes severe diarrhea and kidney failure

microbes that are normally not pathogenic may prove to be opportunistic pathogens should the opportunity present itself. 

risk group determines
biosafety precautions

review question:
explain why endotoxin producing bacteria are
Gram (-)

review question:
describe three host factors that affect a host's susceptibility to a pathogen.

pathogenic
gut microbes

                             standard precautions
       infection control practices designed to prevent the transmission of   infectious diseases in a healthcare setting based on the assumption that all          patients may have bloodborne pathogens or other infectious agents.

1. sharps safety:
properly handling and disposing of sharps (needles etc)

2. respiratory hygiene and cough etiquette:
covering coughs/sneezes, wearing a mask 

3. environmental cleaning and disinfection:
Regularly cleaning/disinfecting surfaces/equipment 

4. waste management:
Properly disposing of contaminated materials (blood, excretions, sharps) 

5. safe injection practices:
preventing needle contamination and infection 

6. hand hygiene:
soap/water or an alcohol-based hand rub before and after
​patient contact

7. personal protective equipment (PPE):
gloves, gowns, masks, eye protection 

  and a deep dive into 
  bacterial      toxins

review question:
what is meant by pathogenic tropism?
​ Why would a pathogen have a preference the  type of cell or tissue it infects?

review question:
what is meant by a pathogen's Ro value?

If a pathogen has an Ro value of 3, how many people will be infected after three rounds of transmission?

 pathogens can interfere with the ability of host cells to activate T cells
 pathogens can survive and inside host cells so the immune system can't "see" them
 pathogens can produce molecules that mimic host proteins
 pathogens can change their cell surface structures to avoid immune recognition.
 pathogens can produce proteins that bind to immune molecules

bottom line...

Understanding how the gut microbiota, serotonin, and the brain-gut axis is critical as we developing new ways to treat mood disorders. Probiotics designed to improve the gut microbiota may be a useful therapy aimed at improving serotonin levels. 
and addressing related health issues. 

risk group 4 

threshold exposure

the lower the ID50 for a pathogen,
the more infectious that pathogen is. 
ID50 is not related to virulence.
ex: adenovirus (causes the common cold) has a low ID50 but is not very virulent

      health care workers can help manage outbreaks of infectious 
    disease by maintaining these standard precautions plus...

 1. following isolation precautions
 2. reporting potential outbreaks to public health authorities
 3. communicating with fellow healthcare workers, patients, and families
 4. maintain proper vaccination
 5. remain isolated is you are ill or exposed to infectious diseases

review question:
give one example
​ of a commensal gut microbe and a pathogenic gut microbe.  

            Virulence Factors

 are molecules or structures used by a pathogen to infect           and damage a host and overcome host defenses

virulence and the host
​|it's not just about the pathogen...

the host matters too

​  fimbrae

Biosafety levels (BSL) classify pathogens by their potential hazard.
BSL-1 = least hazardous BSL-4 = most hazardous
examples:
non-path E. coli (BSL-1)
 Staph aureus (BSL-2)
 M. tuberculosis (BSL-3)
Ebola (BSL-4)

chapter 10

pathogenicity

review question:
why does the evolution of viruses favor transmission?

risk group 3 

​    spikes

gut microbes and your health

other Ro values:
Chickenpox – 10-12
Polio – 10-12
HIV/AIDS – 2-5
SARS – 0.19-1.08
MERS – 0.3-0.8
Common Cold – 2-3
Ebola – 1.56-1.9

review question:
explain how virulence differs
from pathogenicity.

microbes have a preference for which cells/tissues/
​organisms they colonize. 

pathogens more easily transmitted from host to host become common in a population

virulence factors are often linked to transmission

be careful
be vigilant

the evolution of virulence
​favors transmission

 LPS molecules (lipopolysaccarides) in cell wall of Gram (-) bacteria

review question:
what five tasks must pathogens complete?

microbe/host interactions

           the host-microbe
     relationship is complex
bacteria, viruses, fungi, parasites
 interact with hosts in ways that             aren't always negative: 
 1. commensalistic: microbes                                              benefit                                                  without                                                causing harm
2. mutualistic: host and microbes
                           both benefit
3. parasitic: microbes harm the
                       host

risk group 1 

                                     in order to be virulent,
              pathogens must complete five tasks:
1. enter the host via portal of entry
    respiratory/GI mucosa, wound, otic, ocular, urinary, parenteral, transplacental 
2. adhere to host tissues
3. invade tissues and obtain nutrients
4. replicate while avoiding immune defenses
5. transmit to a new host. 

                            two main categories:
 1. exotoxins: released by living bacteria 
 2. endotoxins: released as bacteria die and break up

virulence and transmission

Enterotoxins: target the gut
Cytotoxins: inflame tissues
Neurotoxins: target the nervous system

review question:
what are four methods of pathogenic transmission?

Dysbiosis

​    immune evasion factors

review question:
how does a pathogen's Ro value differ from its Rt value?

​  invasion factors

Dysbiosis and antibiotics

review question:
if a pathogen A has an
LD50 lower than pathogen B, is pathogen A more or less contagious tan pathogen B?

review question:
Ebola is designated RG4.
​What are two safety protocols that must be followed?

 endotoxins

risk group 2