Microbiology Chpt. 10 Objectives

Define ID50

ID50 means infectious dose- number of cells needed to establish an infectious in 50% of exposed hosts -The more infectious a disease is, the lower the ID50 is. -Just because an infection is highly infectious doesn't mean it's necessarily dangerous. (ex. a cold is highly infectious but it's not dangerous)

Virulence factors

Include features that help microbes adhere to host, invade host tissues, acquire nutrients, and evade host defenses. -Features include toxins, substances with different ways of thwarting the immune system or damaging our cells -These factors are often linked to transmission

Step 3- A pathogen must invade tissues and obtain nutrients

Several options on which way to invade: It can stay on the surface of the host cell, pass through cells to invade deeper tissues, or enter the cells to reside as a intracellular pathogen -As the pathogen invades, they damage tissues and generate cytopathic effects

Step 4- A pathogen must evade host immune defenses so it can replicate

Hide approach= 1. Antigen masking, mimicry, and variation 2. Intracellular pathogens 3. Latency Undermine approach= 1. Suppress immune function 2. Avoid phagocytosis

Why aren't all pathogens equally virulent?

Some pathogens are asymptomatic in certain people

Define and apply toxin, toxigenic, and toxemia

Toxin= are molecules that, in small amounts, generate a range of host effects like tissue damage, suppressed immune response Toxigenic= A microbe that makes toxins Toxemia= toxins in the bloodstream

TORCH infections

Toxoplasmosis Other agents Rubella Cytomegalovirus Herpes simplex virus (HSV)-2 all these infections can pass to the fetus through transplacental and cause congenital infections -parental entry is used by the pathogens to infect the baby once they cross the placental

Airborne Precautions

tuberculosis, measles (rubella), and varicella (chickenpox) - Limit patient transport - N95 respirator - Place patient in AIIR facility

Define pathogenicity and virulence and provide examples of virulence factors.

-Pathogenicity is the ability of a microbe is cause an infection or disease. This is all-or-nothing -Virulence is the degree of the infection or disease the pathogen causes. There are many virulence factors that allow the microbe to evade our immune system defenses. Determined by microbe, host, and evolves over time -Classic virulence factors are level of toxicity, aggressiveness, transmission

Explain Tropism

A microbe needs a specific host or host feature to establish an infection. The preference for a pathogen for a specific host or tissue. This can limit spread of infection because a pathogen can't cause an infection in someone if it has a preference for the intestine and it's in the stomach -Tropism of microbes can change over time

Hide approach

1. Antigen masking= the pathogen coats itself with host molecules, allowing it to act as part of the body Antigen mimicry= matching host molecules Antigen variation= periodically changing the surface molecules that host immune cells use to recognize a previously met pathogen, so a rapid immune response cannot result 2. Intracellular pathogens= spend majority of their time inside the host cell 3. Latency= ability that lets the pathogen quietly exist inside the host cell. These pathogens usually cause recurrent or persistent diseases

Define attenuated pathogen

A weakened version of the pathogen -Don't cause disease in an immune-competent host

Invasions

Allow the pathogen to invade host tissues and are usually membrane-associated or secreted enzymes Mechanism of action: break down host tissue, form blood clots, induce the host to uptake the pathogen, motility

Maintaining a Reservoir

Any environment in which a pathogen needs to naturally thrive -environmental could be soil, water, or an organism -Organism means some pathogens can only have human reservoir -Some pathogens can survive on fomites, or inanimate objects, for a prolonged period of time

Relate LD50 and ID50 to virulence and infectious transmission

Both of these can change based on the species affect, the host's immune system health, and the route of exposure. Ex. Less botulinum toxin is needed to kill someone when injected than is required if it is inhaled

Tools to Obtain Nutrients

Cellular pathogens require iron to survive and there's very little iron around for them to use Bacteria may produce siderophores that snatch irons Bacteria and fungi can also make extracellular enzymes- such as lipasis(break down lipids) and proteases (break down proteins) - these enzymes break down nutrients in the local environment and allows pathogens to scavenge nutrients as they damage tissue

Respiratory Tract Entry

Coughing and sneezing suspends pathogens in the air as respiratory droplets -These infectious agents could settle in dust or soil and they can get stirred up and inhaled. -Most common tract of entry Example. Pertussis, Measles, Influenza

Discuss why an organism in one host may be a pathogen in another

Differences in host factors. What might be a normal microbe in one person could be an opportunistic pathogen in another because our immune system recognizes our own normal microbiota

Compare and contrast endotoxins, exotoxins

Endotoxins= Made of Lipid by Gram-negative bacteria. It is released when the cell wall divides or dies. As the immune system or antibiotics kill Gram-negative bacteria, the endotoxin levels increase leading to septic shock. Symptoms include fever, chill, hypotension, tachycardia, inflammation, nausea, etc Exotoxins= Made of proteins by both Gram- negative and positive bacteria. It is released from actively growing bacteria. -These protein toxins are often named based on the organism that makes the toxin or the type of cells it targets. Ex. Neurotoxins affect the nervous system -Classified into 3 main families based on mode of action

Urogenital Tract and transplacental Examples

Genitalia- Gonorrhea, Chlamydia, Urinary- E. Coli (bladder, kidney, urethra) transplacental- HIV, Rubella, Toxoplasmosis

Examples of Invasions

Flagella= Motility helps spread and adhere. Ex. E. coli and Vibrio Vulnificus Collagenases= Enzymes that break down collagen which allows for invasion to new host areas. Ex. Neuraminidases= Enzymes that break down neuraminic acid. Damage disrupts normal and immune cell functions Coagulases= Enzymes that promote blood clotting to form a protective layer around the pathogen Kinases=Enzymes that break down blood clots to allow pathogens to spread from clots that may trap them

Why is virulence evolving

For a pathogen to endure, it has to have the ability to promote transmission and establish an infection in the host. - So if the pathogen is transmitted from person to person and kills quickly then it's going to kill itself off. These types of pathogens cause high-morality outbreaks, are short in duration, and are usually geographically isolated

Skin, Ocular, Otic, and Parenteral Entry

Integumentary system is the largest body system and blocks most microbes. -Otic entry means they enter through the ear canal. Ex. Out ear infection by P. aeruginosa -Skin entry means a pathogen will enter through a cut or open wound you have, while certain parasites can physically bore through the skin Ex. S. aureus wound infection -Ocular entry is when pathogens invade the conjunctiva which causes inflammation called conjunctivitis Ex. Conjunctivitis -Parenteral entry is when a pathogen can bypass the skin and can directly invade the underlying subcutaneous tissues, muscles, or bloodstream Ex. Hepatitis B and C

Define LD50

LD50 means lethal dose- amount of toxin needed to kill 50% of affected untreated hosts -Lower LD50 means the disease is more deadly -The lethality of an infectious agent as morality rate, rather than LD50

4 Levels of BSL

Level 1 agents- Low risk, well characterized. Rarely cause disease in healthy people, pose limited if any risk to healthy people Level 2 agents- Cause human disease but mostly cause infections that treatable or preventable with vaccines. Most infectious agents fall into this category. Not airborne -Level 2+ agents= dangerous and incurable, not vaccine preventable. Not airborne but require additional safety measures Ex. HIV Level 3 agents- Serious and lethal human diseases. Many of these are airborne. Some of these pathogens are treated but because of the severity, they are classified at this level. Ex. Tuberculosis Level 4 agents- Dangerous and so called "exotic pathogens. Tend to be lethal in humans and no cures or treatments. Ex. Ebola, viruses with unknown modes of transmission Most laboratories and hospitals at BSL-2

Standard and Universal Precautions

Limit transmission of bloodborne pathogens - Handwashing before and after contact - Change clothes - Proper management of biosharp waste - Barrier clothing - Disinfection of surfaces, laundry, and garment

Undermine Approach

Limits the Immune system defenses 1. Interfering with phagocytosis: make a capsule, block phagosome fusion, neutralize phagocyte, or damage the phagocyte with toxins 2. Suppressing the immune system response -directly targeting immune cells, damage host cell antibodies, interfering with signaling that activates parts of the immune response

Cytopathic Effects

Means damage to the host cells and 2 types: Cytocidal= kills the host cell Noncytocidal= doesn't kill the host cell but damages it -Bacterial induce these effects as they invade the cell, release toxins, and exploiting the host cells nutrients -Viral pathogens generate these effects when hijack cellular machinery and disrupt normal host cell functions. Oncogenic pathogens are viruses or bacteria that transform normal cells into cancerous ones -The immune system also damages the body as a by product of tactics used to the fight the infections

Example of Virulence Transmission

Most STI have evolved virulence factors that have allowed them to be infectious yet minimally symptomatic

Droplet Precaution

Most respiratory infections, Influenza, Pertussis - Limit patient transport - Procedural mask at all times

Urogenital Tract and transplacental Entry

Most sexually transmitted pathogens enter through the mucosal lining of the vagina or cervix in women and through the urethra in men -Some sexually transmitted pathogens can invade through the skin -Some pathogens can do vertical transmission where they cross from the placenta to infect the child

Portals of Exit

Otic= Pus or drainage may contain the infectious agent Ocular=Itchy eyes cause you to rub them which transfer the pathogen to your hands Respiratory Mucosa= Sneezes and coughs, mucus discharges from nose or mouth Skin= Pus or wound discharge may be rich in pathogens GI Mucosa= Infectious agents in saliva, excrements , and mucosal secrements Parenteral= Blood borne pathogens Urogenital= Urine, semen, vaginal secretions

Step 1- Enter the Host

Portal of entry= any site the pathogen uses to enter the host. Mucous membranes are key portals of entry because they line every part of our body -Site where the disease develops but not necessarily the only sit it infects. -Portal of entry is often determined by mode of transmission

Step 5- A pathogen must be transmitted to a new host to repeat the cycle

Sometimes the symptoms a pathogen generates is in order to facilitate transmission to a new host - itchiness: scratching gets the pathogen under the nails which can then be transferred anywhere that person touchs - Sneezing or coughing puts droplets in the air that can spread -Diarrhea lead to scretions, frequent bowel movements -Exiting the host is any route the pathogen leaves the body and typically the it exits the body the same way it enter

Identify the 5 steps to infection

Step 1- Enter the host Step 2- Adhere to host tissue Step 3- Invade tissues and obtain nutrients Step 4- Replicate while evading immune defenses Step 5- Transmit to a new host

Transmission Precautions

Taken in addition to the standard precautions Used to prevent: direct contact, droplet, and airborne disease transmission -Apple when a specific infectious agent is suspected or is known

Step 2- Pathogen must adhere to host tissues

The initial adhesion is often nonspecific and after the agent may target an exact surface molecule on a host cell by tricking the host. -Adhesion are a major part of virulence factors that everyone uses to stick to host cells in specific or nonspecific manners -Adhesion factors tend to be on the surface of pathogens so they make ideal vaccine development targets -Bacterial adhesions include cell wall components, capsules, fimbriae and pili, and a variety of plasma membrane-associated molecules

3 main families of exotoxins

Type I- Membrane-acting extracellular toxins (Surface-acting toxins). These bind to the targeted host cell via specific receptors on the cell surface. Type II- Membrane damaging toxins. These disrupt the host cell plasma membrane by forming pores or by removing phosphate head groups from phospholipids of the lipid membrane. This causes cell lysis Type III- Intracellular toxins. These bind to a receptor and then enter the cell to exert an effect. Most toxins are AB where the B part of the toxin binds to the cell while the A part exerts effects into the cell.

Gastrointestinal Tract Entry

Usually has a fecal-oral transmission -Invade the mucosal surfaces of the GI trace Example- Cholera, Salmonella, C. difficile

Contact Precautions

Wound/skin infection, resistant infection, infectious diarrhea - Limit patient transport - Special attention to hand washing - Gloves at all times - Gown at all times - Single patient use equipment

Biosafety Levels

dictate appropriate on-the-job behaviors in healthcare -based on several criteria: level of infectivity, extent of disease caused and mortality rate, mode of transmission, availability of preventions and treatments