Pathogenicity, Virulence and Infectious Disease

Comprehensive vocabulary flashcards covering microbial interactions, symbiosis, pathogenicity, virulence factors, toxin types, enzymatic invasins, patterns of infection, and the stages of clinical disease.

Normal flora

Microorganisms usually found at given anatomical sites in a healthy human body without causing infection or disease, conferring mutual benefits to host and microbe without penetrating sterile tissues or fluids.

Microbial antagonism

The mechanism by which normal bacterial flora benefit the host by preventing the overgrowth of harmful microbes.

Resident flora

A category of normal flora that remains part of a person's microflora throughout their entire lifespan.

Transient flora

Microorganisms that can be found in the same body locations as resident flora, but only reside within the body for a brief period of time.

Mutualism

A symbiotic relationship in which both the microbe and the host benefit.

Commensalism

A symbiotic relationship in which the microbe benefits while the host is neither harmed nor helped directly (receives indirect benefits).

Parasitism

A symbiotic relationship in which the microbe benefits and the host is harmed.

Amensalism

A symbiotic relationship in which the microbe is not affected while the host is impeded or restricted.

Pathogen

An infectious agent capable of causing disease by circumventing host defenses, invading sterile tissues, and multiplying to cause infection.

Pathology

The study of the nature of disease, including its causes, development, and outcome.

Etiology

The study of the cause of disease.

Prognosis

A forecast as to the probable outcome of a disease.

Pathogenesis

The cellular events, reactions, and other pathologic mechanisms occurring in the development of disease.

Disease

Any deviation from or disruption of the normal structure or function of any tissue, organ, or organ system, characterized by a specific set of signs and symptoms.

Signs

Any abnormality uncovered upon physical examination that indicates the presence of disease, representing an objective assessment.

Symptoms

The subjective evidence of infection and disease as perceived and reported by the patient.

Syndrome

The collection of signs and symptoms that, taken together, paint a portrait of a specific disease.

Sequela

A morbid complication that follows a disease, such as lesions or scarring.

Pathogenicity

The ability of a pathogen to produce infectious disease in another organism, related to virulence factors, number of microorganisms, portal of entry, and host defenses.

Virulence

The degree or intensity of pathogenicity, determined by specific virulence factors.

Virulence factors

Molecules and regulatory systems that enable microbial pathogens (bacteria, viruses, fungi, and protozoa) to cause infection or harm the host.

Adhesion

The first step in establishing an infection that allows the organism to avoid mechanical removal via ciliary motion, sneezing, coughing, swallowing, urine flow, tears, or peristalsis.

Capsule

A bacterial structure composed of polysaccharide fibres that aids in adherence and prevents phagocytosis by host leukocytes (WBCs).

Fimbriae

Filamentous surface appendages that allow organisms to attach to each other and bear adhesins to enhance attachment to host cell surfaces.

Adhesins

Surface molecules located on microbial appendages like fimbriae that enhance the ability of a pathogen to attach to a host cell surface.

Colonization

The establishment of a pathogen at a portal of entry, specifically in tissues that come in contact with the external environment.

Invasins

Enzymes and toxins produced by pathogens that facilitate tissue invasion by lysing cells or breaking down material between host cells.

Exotoxins

Highly immunogenic toxic proteins with specific targets, produced primarily by Gram-positive bacteria and secreted during their exponential growth phase from genes on plasmids or bacteriophages.

Toxoids

Inactivated forms of exotoxins that resemble the original toxin but are non-toxic, used in immunization to stimulate the production of antitoxins (antibodies).

Leukocidins

Bacterial exotoxins that target and kill white blood cells (WBCs).

Leukostatins

Bacterial exotoxins that inhibit the function of white blood cells (WBCs).

Endotoxins

Bacterial intracellular toxins composed of lipopolysaccharide (LPS) that are released upon cell lysis; they are weakly immunogenic and produce generalized systemic effects.

Hemolysins

Enzymes and toxins that rupture red blood cells to release iron required for microbial metabolism, increasing the organism's virulence.

Hyaluronidase

An enzyme known as the 'spreading factor' that digests hyaluronic acid between connective tissue cells, facilitating pathogen spread into surrounding tissues.

Coagulase

A clotting or 'cementing factor' produced by Staphylococcus aureus that converts fibrinogen into fibrin clots, creating a protective barrier around the bacteria.

Kinase

A bacterial enzyme (such as streptokinase or staphylokinase) that converts plasminogen into plasmin to dissolve host fibrin clots.

Mucinase

An enzyme produced by pathogens that digests the protective coating found on mucous membranes.

Keratinase

An enzyme produced by pathogens that digests keratin, the principal structural component of skin and hair.

Collagenase

An enzyme produced by pathogens that digests collagen, the principal structural fiber of connective tissue.

Infection

The entry, establishment, and multiplication of pathogenic organisms within a host.

Infectious disease

The state of damage or toxicity in the body resulting from an infection by an infectious agent.

Contamination

The presence of microorganisms in or on the body without necessarily resulting in colonization or infection.

Acute infection

An infectious disease classification defined by a sudden onset, short duration, and severe signs and symptoms.

Chronic infection

An infectious disease classification defined by a gradual onset, longer persistence, generally milder signs and symptoms, and potential acute episodes.

Sub-acute infection

An infection with an intermediate status lying between acute and chronic disease courses.

Clinical infection

A symptomatic, obvious infection that allows for clinical diagnosis based directly on visible signs and reported symptoms.

Subclinical infection

An asymptomatic infection diagnosed exclusively through diagnostic laboratory testing, such as blood tests, cultures, or imaging.

Local infection

An infection pattern where the microbe enters and is confined to a single target tissue or area of the body (e.g., an abscess).

Systemic infection

An infection that spreads widely throughout the body via the circulatory system, manifesting as septicemia, bacteremia, toxemia, viremia, or fungicemia.

Focal infection

An infection that originates in one body site and subsequently spreads to another specific tissue site via the blood or lymphatic system, rather than undergoing generalized spread.

Superinfection

A secondary infection occurring during antimicrobial therapy that results from the overgrowth of drug-resistant microorganisms.

Primary infection

An initial infection that may be followed by secondary complications caused by another microbe.

Secondary infection

An infection that follows a primary infection, caused by a different microbe such as opportunistic normal flora.

Latent infection

A persistent infection characterized by a period of inactivity following an episode where no signs or symptoms are present, the pathogen is not multiplying, and disease may recur later.

Slow infection

A persistent infection characterized by a long incubation period before signs and symptoms become visible, such as in Creutzfeld-Jakob disease or AIDS.

Polymicrobial infection

A mixed infection caused by more than one organism at the site of infection, where two organisms that are individually avirulent can cause disease together.

True pathogens

Infectious agents capable of causing disease in healthy individuals with intact, normal immune defenses (e.g., Influenza virus, Ebola virus, malarial protozoan).

Opportunistic pathogens

Organisms that do not cause disease in an immune-competent individual, but cause disease when host defenses are compromised (e.g., Pseudomonas aeruginosa and Candida albicans).

Incubation period

The initial stage of clinical infection spanning from first contact with the pathogen to the appearance of initial symptoms, during which the agent multiplies without producing sufficient damage to cause symptoms.

Prodromal stage

The short stage of clinical infection characterized by vague feelings of discomfort and non-specific complaints.

Period of illness

The clinical infection stage where the pathogen multiplies at high levels, reaches peak numbers, and produces specific signs and symptoms; it includes an acute phase and a decline phase.

Convalescent period

The final stage of clinical infection where symptoms decline as host defenses or medical interventions overcome the pathogen, though lingering fatigue leaves the patient vulnerable to secondary infection.