Basics of Host-Microbe Interactions, Virulence, Steps to Infection, and Biosafety

Comprehensive vocabulary flashcards covering host-microbe interactions, virulence factors, toxin types, steps of infection, immune evasion, and biosafety levels based on chapter 10 lecture notes.

Our normal microbiota has a mutualistic relationship with us. What are three benefits our microbiota gives us?

compete with potential pathogens, make vitamins for us, promote the maturation of our immune system

Which bacterial species causes antibiotic-associated diarrhea?

C. difficile

Up to 30% of women harbor Group B (streptococci) GBS as normal vaginal microbiota, but the same bacterium in newborns is associated with sepsis, meningitis, and pneumonia. Why?

Group B Streptococcus (GBS)

Opportunistic Pathogen

An agent that causes disease when dysbiosis occurs due to a weakened immune system or antibiotic use.

Tropism

The preference of a pathogen for a specific host or tissue.

Emerging Pathogens

Infectious agents that have expanded their host tropism to infect new hosts.

Pathogenicity

The ability of an organism to cause disease.

Virulence

The degree or extent of disease that a pathogen causes.

Virulence Factors

The specific mechanisms pathogens use to overcome host defenses and establish disease.

Basic Reproduction Number ($R_0$)

A measure of a pathogen's contagiousness representing the average number of secondary infections an infected person produces in an entirely susceptible, unprevented population.

Attenuated Pathogen

A pathogen that remains infectious but is weakened to the point that it cannot cause disease in an immunocompetent host.

Infectious Dose 50 ($\text{ID}_{50}$)

The number of pathogen cells or virions needed to establish an active infection in $50\%$ of exposed susceptible hosts; lower values denote higher infectivity.

Lethal Dose 50 ($\text{LD}_{50}$)

The amount of toxin needed to kill $50\%$ of untreated affected hosts; lower values denote greater lethality.

Toxemia

The presence of bioactive toxins circulating within the blood.

Endotoxin

A toxic lipid component (Lipid A) of lipopolysaccharide produced exclusively by Gram-negative bacteria and released upon cell division or death.

Exotoxin

A soluble protein toxin synthesized and actively secreted by growing Gram-positive and Gram-negative bacteria.

Lipid A

The specific lipid region of lipopolysaccharide (LPS) that functions as an endotoxin.

Type I Exotoxins

Membrane-acting extracellular toxins that bind to host cell receptors without penetrating the cell membrane.

Type II Exotoxins

Membrane-damaging toxins, such as hemolysins and cytolysins, that disrupt host cell membranes and cause cell lysis.

Type III Exotoxins (AB Toxins)

Intracellular toxins comprising a binding ('B') component that attaches to host receptors and an active ('A') component that mediates damage within the cell.

Hemolysins

Type II exotoxins that lyse red and white blood cells to impair host immune defenses, such as streptolysins produced by Streptococcus species.

Cytolysins

Type II exotoxins that lyse white blood cells and damage general host tissues, such as pneumolysins produced by Streptococcus pneumoniae.

Superantigens

Type I exotoxins produced by certain Streptococcus and Staphylococcus species that trigger an exaggerated immune response leading to toxic shock syndrome.

Portal of Entry

Any site a pathogen uses to enter the host, the most common of which are the mucous membranes.

Parenteral Entry

A route of entry wherein a pathogen bypasses the skin barrier directly into underlying subcutaneous tissues, muscles, or blood vessels.

Fecal-Oral Transmission

Transmission where pathogens exit the host in infected feces and infect a new host by ingestion through the mouth.

Transplacental Entry

A vertical infection route in which a pathogen crosses the placenta to reach and infect the fetus.

TORCH Pathogens

An acronym referring to organisms capable of vertical transmission across the placenta: Toxoplasmosis, Other agents, Rubella, Cytomegalovirus, and Herpes simplex virus-2.

Adhesins

Cell-surface virulence factors that facilitate specific or nonspecific adherence of pathogens to host cells.

Fimbriae and Pili

Hair-like extracellular protein appendages on bacteria that function in adherence by binding carbohydrates on host cells.

Quorum Sensing

Chemical cell-to-cell communication in biofilms that regulates gene expression to enhance community survival and virulence factor production.

Invasins

Extracellular surface structures or secreted enzymes that facilitate pathogen penetration and invasion into host tissues.

Collagenases

Enzymatic invasins that degrade collagen to breach connective tissues and facilitate deeper invasion.

Siderophores

Iron-binding organic molecules secreted by bacteria to scavenge and strip iron from host iron-transport proteins.

Antigen

Any substance that triggers an adaptive immune response.

Latency

The state in which a pathogen quietly resides within a host without actively causing symptoms, with the potential to reemerge later.

Antigen Masking

An evasion strategy in which a pathogen coats its surface with host-derived molecules to avoid immune detection.

Antigen Mimicry

An evasion mechanism wherein pathogen surface antigens closely imitate host antigens to avoid immune recognition.

Antigenic Variation

The process by which a pathogen periodically changes its surface molecules to stay ahead of host immune defenses.

Bacterial Capsule

A protective carbohydrate coat that prevents phagocytes from engulfing and destroying bacteria with hydrolytic enzymes.

Portal of Exit

Any anatomical site through which a pathogen leaves the host, including feces, urine, wound drainage, vomit, saliva, mucus, or semen.

Fomites

Inanimate objects or materials that harbor and facilitate the transmission of infectious pathogens.

BSL-1 (Biosafety Level 1)

The baseline containment level for well-characterized agents that do not consistently cause disease in healthy humans; does not require healthcare PPE.

BSL-2+ (Biosafety Level 2-plus)

An enhanced containment protocol required when handling dangerous bloodborne pathogens such as HIV.

BSL-4 (Biosafety Level 4)

The highest biological containment level with the most stringent personal protection requirements, utilized for lethal pathogens like Ebola and Marburg viruses.

Standard Precautions

Infection control measures applied to all healthcare scenarios, including hand hygiene, gloves, barrier gowns/face shields for splash risks, and disinfection.

Contact Precautions

Transmission-based precautions implemented for conditions such as wound/skin infections, multidrug-resistant infections, and infectious diarrhea.

Droplet Precautions

Transmission-based precautions used for pathogens spread via respiratory droplets over short distances, including influenza, pertussis, and most respiratory infections.

Airborne Precautions

Transmission-based precautions implemented for aerosol-transmitted pathogens capable of remaining suspended in air, including tuberculosis, rubeola (measles), and varicella (chickenpox).