Microbiology Final

Host

Larger organism that supports the survival and growth of a pathogenic microorganism

Infection

- A microbe growing and multiplying on or within.
- May or may not result in overt disease

Pathogen

Any organism that causes disease

Opportunistic pathogen

May be part of the normal microbiota and causes disease when the host is immunocompromised

Pathogenicity

Ability of a pathogen to cause disease

Virulence

Degree of harm (pathogenicity) inflicted on its host.

Incubation Period

Period after pathogen entry, before signs and symptoms

Prodromal Stage

Onset of Signs and symptoms, not clear enough for diagnosis

Illness Period

Disease is most severe, signs and symptoms

Convalescence

Signs and symptoms begin to disappear

What does the Host provide the pathogen?

Protection, nutrients, and energy

What influences transmission from one host to another

Virulence of organism, number of invading
organisms, and presence of adhesion and invasion factors

When does disease occur

-organism produces molecules that directly damage host cells
-stimulates host immune cells to destroy infected tissue

Zoonosis

When an infection can be passed from an animal to a human

Reservoir

Natural environmental location in which the pathogen
normally resides.

Vector

Organism that spreads disease from one host to another EX. Mosquito

Tropism

pathogen must make contact with appropriate
host tissue
-determined by specific host receptors

Droplets

Direct transmission;
•Up to 2 mm in diameter.
•Produced when liquids are placed under force (For example, sneezing, coughing).
•Can travel

Droplet nuclei

Indirect transmission;
•1 to 5 μm in diameter.
•Result from evaporation of the larger droplets.
•May remain airborne for hours or days and travel long distances.

Dust Particles

Indirect transmission;
•Aerosolized—smaller than 1 μm can be dispersed this way farther.
•Microorganisms adhere to dust particles.
•Can survive long periods outside host and can lead to hospital-acquired infections.

Contact transmission

Host touching source/reservoir.
Direct contact (person-to-person).
•Physical interaction
•E.g., kissing, touching, and sexual contact.

Indirect contact

•Involves an inanimate object (fomite) that transfers infectious agent between hosts
•E.g., eating utensils, bedding

Vehicle Transmission

• materials that transmit pathogens.
• E.g., food, water, biological materials (fluids and tissues), air.

Vector-borne Transmission

Pathogen benefit because extensive reproduction and
spread between hosts.
• Highly virulent and cause diseases such as malaria, typhus,
and sleeping sickness.
Important that pathogens do not harm their vectors.

Congenital Infection

Babies born with an infectious disease
EX. Gonorrhea, Syphilis, Herpes, German measles, Toxoplasmosis.

Infectious Dose (ID50)

Number of pathogens that will infect 50% of inoculated hosts.
Varies with pathogen

Lethal Dose (LD50)

Amount of pathogen that will kill 50% of inoculated hosts

Portals of Entry

Skin, respiratory, gastrointestinal, urogenital systems, or conjunctiva of eye.

colonization

A site of microbial replication on or within a host

Adherence Structures

bind complementary receptor sites on host cell surface and are classified as virulence factors.

Active Penetration

occurs through lytic substances that altar host tissue
1. attacking the extracellular matrix and basement membranes of integuments and intestinal linings
2. degrading carbohydrate-protein complexes between cells or on the cell surface
3. disrupting the host cell surface.

Passive Penetration

Not related to the pathogen itself EX. skin lesions, insect bites, wounds

Coagulase

coagulates the fibrinogen in plasma. The clot protects the pathogen from phagocytosis and isolates it from other host defenses

Collagenase

Breaks down collagen that forms the framework of connective tissues; allows the pathogen to spread

Hemolysins

Lyse erythrocytes; Makes iron available for microbial growth

Immunoglobulin A protease

Cleaves immunoglobulin A into Fab and Fc fragments

Phospholipase

destroys the phosphatidylcholine component of plasma membranes, allowing the pathogen to spread

Proteins A and G

Located on cell wall. immunoglobulin G binds to either protein A or protein G by its Fc end, thereby preventing complement from interacting with bound IgG

Streptokinase

a protein that binds to plasminogen and activates the production of plasmin, thus digesting fibrin clots; this allows the pathogen to move from the clotted area

Bacteremia

presence of viable bacteria in the blood

Septicemia

bacterial or fungal toxins in the blood

Formation of Actin Tail

Listeria monocytogenes, Shigella spp., and Rickettsia spp. use actin-based motility to spread between host cells.
• Actin tail propels bacteria to the host’s cell surface where it forms a protrusion.
• Protrusion is engulfed by adjacent cell, allowing the bacteria to enter.

Ways pathogens overcome host defenses

•Produce Type VI secretion system.
•Find shelter to avoid recognition by defense cells.
•Survive and replicate inside host cells.
•Squeeze between host cells.
•Make capsules to avoid phagocytosis.
•Burrow under mucus.
•Secrete exopolysaccharides to form communal shelters within biofilms.
•Produce enzymes that inactivate innate resistance mechanisms.
•Excrete specialized proteins to selectively kill host cells.

How does the Hep B virus evade the hosts defenses

Production of decoy proteins to bind available
neutralizing antibodies.

How does Influenza virus evade the immune system

Change cell surface proteins by mutation or
recombination or down regulate the level of expression
of cell surface proteins.

Antigenic Drift

due to accumulation of mutations in a strain within a geographic area
This is due to the lack of proofreading in RNA-dependent-RNA polymerase

Antigenic Shift

due to reassortment of genomes
when two different strains of flu viruses (from
humans and animals) infect the same cell and are
incorporated into a single new capsid.

Molecular mimicry

Produce capsules that resemble host tissue components
•Capsule of Streptococcus pyogenes
•PANDAS: Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcal Infections

Haemophilus influenzae (defenses)

Some bacterial capsules prevent deposition of host
complement, protecting the pathogen from host defenses.

Neisseria gonorrhoeae (defenses)

Phase variation to alter pili protein sequence and expression.

Neisseria gonorrhoeae (defneses)

produces proteases that degrade IgA

HIV, measles virus, cytomegalovirus (defenses)

Cause host cell fusion

Examples of suppressing the hosts Immune Response

-Infect cells of the immune system and diminish their
function while ensuring their own survival.
• HIV, measles virus
-Some bacteria produce a slippery mucoid capsule that
prevents the host immune cells from effectively
capturing the bacterium.
• Streptococcus pneumoniae, Neisseria meningitidis, and
Haemophilus influenzae
-Eliminate O-antigen on lipopolysaccharide to diminish
immune response and clearance.
• Neisseria gonorrhoeae

Biofilms

• Biofilms protected from nutrient deprivation, predators, environmental shifts, antimicrobial agents, and host immune cells.
• Some pathogenic bacteria within biofilms exchange plasmids, nutrients, and quorum-sensing molecules, altering their behavior.

Frustrated Phagocytosis

Pseudomonas in biofilms prevents penetration of antibiotics & antibodies
•causes downregulation of phagocyte killing mechanisms
•killing enzymes become less effective
•enzymes that create super oxides and nitric oxides are
inhibited

Epidemiology

Science that evaluates occurrence, determinants,
distribution, and control of health and disease in a defined
human population.

CDC

Develop and carry out disease prevention and control.
– Environmental health.
– Health promotion and education activities.

Sporadic Disease

Occurs occasionally or at irregular intervals in human
population.

Endemic Disease

Maintains a steady, low-level frequency at a moderately
regular interval.

Hyperendemic Disease

Gradually increase in frequency above endemic level but
not to epidemic level.

Outbreak

– Sudden, unexpected occurrence of disease.
– Usually in a limited segment of population.

Epidemic

Outbreak affecting many people at once.

Reservoir Host

organism remains healthy while virus thrives.

Index Case

first person identified in an epidemic.

Pandemic

Increase in disease occurrence within a large population
over at least two countries around the world.
• COVID-19—first identified in China and spread to all continents.

Public Health Surveillance

Proactive evaluation of genetic background, environmental
conditions, human behaviors and lifestyle choices,
emerging infectious agents, and microbial responses to
chemotherapeutic agents to monitor the health of a
population.
– Look for cause-and-effect relationships.

Information loop of public health surveillance

Reported information:
• Population morbidity and mortality.
• Disease effect on school attendance.
• Impact on employee absenteeism.
• Animal and vector control policies.

Remote sensing

• Gathers digital images of Earth’s surface from satellites and output from biological sensors, transforming data into maps.

Geographic Information System

Data management system that organizes and displays digital map data from RS and facilitates the analysis of relationships between mapped features.

Incidence

measure occurrence of new cases of a disease during a defined time period.

Disease frequency

Statistics determine risk factors.
• Determining disease frequency requires knowledge on
population, exposed people and affected people.

Prevalence Rate

the proportion of persons in a population who have a particular disease or attribute at a specified point in time or over a specified period of time.

Morbidity Rate

the rate at which a disease or illness occurs in a population and can be used to determine the health of a population and its healthcare needs.

Mortality rate

the number of deaths in a given area or period, or from a particular cause.

Common Source Epidemic

single common contaminated source.

Propagated Epidemic

one infected individual into a susceptible group, infection propagated to others.

Herd Immunity

threshold percentage of the population having immunity so when isolated cases reemerge, there is no escalation of the disease through the population.

Basic Reproduction Number

capacity of an infectious agent to spread.
• Varies depending on environment and pathogen density.
• Helps determine percentage of population that must be immune to achieve heard immunity.

Effective Reproduction Rate

effective reproduction rate with vaccine in population.

Global Pandemics

COVID-19, HIV/AIDS, tuberculosis, H1N1 influenza virus, Zika virus, hepatitis C and E viruses and Ebola virus.

Category A Pathogen

highest threat to public health.
• High mortality rate.

Category B Pathogen

second-highest priority.
• Moderate morbidity and low mortality rates.

Category C Pathogen

third-highest priority.
• Emerging pathogens with potential for high morbidity.

Systematic Epidemiology

• Focuses on ecological and social factors that influence development of emerging and reemerging diseases.
• Numerous factors have been identified.

Reasons for increases in remerging and new infectious diseases

• World population growth and urbanization.
• Increases exposure to microbes.
• Crowded workplaces and public transportation.
• Increased international travel.
• Mass migrations of people.
• Climate change.

Healthcare Acquired infections

From pathogens within a hospital or other clinical care facility, acquired by patients in the facility.
• 5 to 10% of all hospital patients acquire a nosocomial infection.
Often caused by bacteria that are members of normal microbiota.
Many hospital strains are antibiotic-resistant.

Healthcare Acquired infections sources

endogenous, catheter-associated, surgical site, central line-associated, ventilator-associated, exogenous, hospital staff, visitors, flowers, food

Control of epidemics

Reduce or eliminate source or reservoir of infection.
• Social distancing and isolation of carriers, destruction of animal
reservoirs, treatment of water and sewage to reduce contamination.

– Reduce number of susceptible individuals and raise the
general level of herd immunity.
• Immunizations and prophylactic treatment to prevent infection.

Vaccine

Preparation of one or more microbial antigen that induce protective immunity.

Immunization

• Occurs when host’s immune system has responded to the vaccine.
• Vaccines attempt to induce antibodies and activated T cells to
protect host from future infection.

Edward Jenner

•First scientific attempts at artificial immunizations
•1796: extracted pus from milkmaid’s lesions and
injected into arm of 8-year old boy
•Later, inoculated boy with smallpox & no symptoms
•Vaccination: reference to original use of cowpox

Adjuvants

• Are mixed with antigens in vaccines to promote a more
efficient immune response.
• Are nontoxic material that assists in the processing of antigens by antigen-presenting cells.
• EX. Oil in water emulsions, Aluminum hydroxide, Beeswax, Combinations of bacteria

Inactivated Vaccine

Effective, but less immunogenic. Often require boosters.

Attenuated Vaccines (live but avirulent)

Effective at stimulating both humoral and cell-mediated immunity.
– Single dose.
– Can have serious adverse reactions especially in immunocompromised individuals.

Subunit Vaccines

Use of purified macromolecules derived from pathogenic microorganisms.
• Avoids some of the risks of whole-cell vaccines.

Forms of Subunit vaccines

Capsular polysaccharides, Recombinant surface antigens, Inactivated exotoxins (toxoids).

Recombinant-Vector Vaccines

• Pathogen genes that encode major antigens inserted into
nonvirulent viruses or bacteria which serve as vectors and
express the gene product.
• Released gene products (antigens) can elicit antibody -mediated immunity and cellular immunity.
• E.g., J&J COVID vaccine: S gene of SARS-CoV-2 delivered by non-human Adenovirus

DNA Vaccines

• DNA fragments introduced into host cell.
• DNA taken into nucleus and pathogen’s DNA fragment is
expressed.
• Host immune system responds to foreign proteins produced.
• Many DNA vaccine trials are currently under way.
• Very stable vaccines.

mRNA vaccines

• Hurdles overcome in mRNA research over the years:
• Minimized RNA degradation.
• Limited innate immunogenicity.
• Designed a delivery system that would facilitate entry into
the cell.
• E.g., Pfizer and Moderna COVID-19 vaccines

Bioterrorism

“Intentional or threatened use of viruses, bacteria, fungi, or
toxins from living organisms to produce death or disease in
humans, animals, and plants”.