Host-microbe Relationship & Infection

These flashcards cover the key concepts of host-microbe interactions, types of infections, transmission methods, clinical stages, and virulence factors based on the lecture notes.

Symbiosis

The living-together and interaction between two different species in such a way that at least one species benefits.

Symbiont

The smaller organism in a symbiotic relationship (e.g., the microbe) that always benefits from the interaction.

Normal flora (microbiota)

Microorganisms normally colonizing the skin and mucous membranes of humans and animals, consisting of about $10^{14}$ bacteria compared to $10^{13}$ human cells.

Transient flora

Members of normal flora that are only occasionally found at a particular site and for short periods.

Colonization resistance

A benefit of normal flora where they occupy space and compete for nutrients, leaving no or little place for pathogens.

Obligate pathogen

A pathogen that causes disease as part of its life cycle, such as Neisseria gonorrhea, obligate intracellular bacteria, and all viruses.

Accidental pathogen

An organism that lives independently of the host (environmental) but causes disease if accidentally introduced, such as Clostridium tetani.

Opportunistic pathogen

A pathogen that causes disease only under unusual circumstances, such as compromised host immunity or transfer to another body part.

Henle-Koch’s postulates

Criteria established in 1891 requiring that a microorganism be found in all diseased subjects, cultivated in pure form, produce similar disease in a lab animal, and be re-isolated.

Colonization

The presence and growth of a microorganism on a host tissue surface without causing damage.

Non-communicable diseases

An infectious disease acquired from the environment, other species, ingestion of bacterial toxins, or caused by self normal flora.

Pathogenesis

The mechanism by which infection and disease develop.

Pathogenicity

The ability of a microorganism to cause disease.

Virulence

The degree of disease a pathogen has the potential to cause.

Infectious dose

The minimum number of a pathogen required to ensure infection.

Subclinical (unapparent) infection

An infection with no clinical symptoms where the individual may still infect others or seroconvert.

Fulminant acute infection

An infection with rapid onset and brief duration that is very severe.

Latent infection

An infection where signs and symptoms appear after a long while, such as herpes simplex.

Oncogenic infection

A viral infection that causes malignant transformation of the infected cell.

Vertical transmission

Transmission from parents to offspring, including prenatal (placenta), perinatal (birth canal), postnatal (milk), and germline (ovum/sperm).

Horizontal transmission

Transmission between individuals through droplets, air, direct contact (skin/mucosa), or fecal-oral routes.

Droplet transmission

Transmission via respiratory particles that are large and fall within $1 \text{meter}$.

Airborne transmission

Transmission via small respiratory particles that remain suspended in the air, such as Mycobacterium tuberculosis.

Zoonoses

Diseases transmitted from animals to humans, such as Rabies, Lyme disease (via ticks), or Toxoplasmosis (via cats).

Incubation period

The period between the entry of the pathogen and the appearance of clinical features.

Prodromal period

A period during which non-specific symptoms and signs may appear.

Acme

The peak of an illness with the most severe signs and symptoms.

Biofilm

An intelligent community of bacteria attached to a solid surface and encased in a polysaccharide matrix.

Exotoxins

Soluble proteins, often enzymes, secreted by viable bacteria that cause direct damage to the host.

Endotoxins

The LPS (lipopolysaccharide) component of the outer membrane of Gram-negative bacteria, released only when the bacteria die.

Septic shock

A systemic effect caused by high quantities of LPS leading to low cardiac output, fever, ARDS, and DIC.

Antigenic mimicry (Camouflage)

An evasion strategy where a microbe covers its surface with material that mimics host material to avoid the immune response.