Unit 6 Infection

Infection

pathogen

Any microorganism—such as a bacterium, virus, fungus, or parasite—that causes disease in its host.

microorganism

A microscopic organism, such as a bacterium, virus, fungus, or protozoan, that is too small to be seen by the naked eye

normal flora

The community of microorganisms that naturally live on or inside a healthy body without causing disease

microbiome

The entire collection of microorganisms, their genetic material, and the environment they inhabit within a specific habitat, such as the human body.

dysbiosis

An imbalance or disruption in the microbial community of the body, which can impair function and cause disease

opportunistic bacteria

Bacteria that are normally harmless but cause infection when the host's immune system is weakened or normal flora is disrupted

opportunistic infection

An infection caused by pathogens that take advantage of an opportunity not normally available, such as a host with a weakened immune system, altered microbiota, or breached integumentary barriers

colonization

The establishment and growth of microorganisms on or within a host without causing tissue damage or an immune response

virulence

The degree of pathogenicity or the severity of disease that a microorganism can cause in a host

virulence factor

A specific molecule or structure produced by a pathogen that enhances its ability to infect, damage, or evade the host's immune system

immunosuppression

A reduction in the activation or efficacy of the host's immune system, increasing susceptibility to infections

tropism

The specificity of a pathogen for a particular host tissue, organ, or cell type, determined by compatible cell receptors

antibacterial agent

A substance that destroys bacteria or inhibits their growth and reproduction

antibiotic

A specific type of antimicrobial drug derived from natural or synthetic sources that kills or inhibits the growth of bacteria

bacteriostatic

substance that inhibits the growth and reproduction of bacteria without killing them, relying on the host's immune system to clear the infection

bactericidal

A substance that directly kills bacteria

broad-spectrum antibiotic

An antibiotic that is effective against a wide range of both Gram-positive and Gram-negative bacteria

antibiotic resistance

The ability of bacteria to survive and grow despite exposure to antibiotic drugs designed to kill them or inhibit their growth

sensitivity testing

A laboratory method that determines which specific antibiotics or antimicrobial agents are effective at killing or inhibiting the growth of a particular pathogen

culture

A laboratory technique used to grow and identify microorganisms from a patient sample under controlled conditions

penicillin

A class of antibiotic drugs derived from Penicillium fungi that kills bacteria by disrupting their cell wall synthesis

penicillium notatum

The specific species of fungus that produces the natural antibiotic penicillin

plasmid

A small, circular, double-stranded DNA molecule that is distinct from a cell's chromosomal DNA and can replicate independently, often carrying genes for antibiotic resistance

mosocomial infection

An infection acquired by a patient during a stay in a hospital or other healthcare facility that was not present or incubating at the time of admission

adhesion

The process by which a microorganism attaches itself to the surface of a host cell or tissue using specific surface molecules

pili / fimbriae

Hair-like appendages on the surface of bacteria used for attachment to host cells or for transferring genetic material

M protein

A virulence factor found on the surface of Streptococcus pyogenes that inhibits phagocytosis and helps the bacteria evade the host immune system

integrin

A transmembrane receptor protein on human host cells that interacts with bacterial adhesins to facilitate cellular attachment or invasion

fibronectin

An extracellular matrix glycoprotein that pathogens can bind to as a bridge for adhering to and invading host cells

collagen

The primary structural protein in the extracellular matrix of connective tissues that provides strength and support to skin, bones, tendons, and ligaments

extracellular matrix

A complex network of extracellular macromolecules, such as collagen, enzymes, and glycoproteins, that provides structural and biochemical support to surrounding cells

facultative intracellular bacteria

Bacteria that can replicate either inside host cells or outside in the extracellular environment

biofilm

A structured community of microorganisms embedded in a self-produced matrix of extracellular polymeric substances that adheres to a living or non-living surface

bacteriophage

A virus that infects and replicates within bacterial cells

quorum sensing

A system of stimulus and response correlated to population density that allows bacteria to monitor their density and coordinate collective behaviors through signaling molecules

macrophage

A large, specialized immune cell that engulfs and digests cellular debris, foreign substances, microbes, and cancer cells through the process of phagocytosis

phagocytosis

The cellular process by which a cell engulfs and destroys large particles, such as microbes or debris, using its plasma membrane

gram positive bacteria

Bacteria that have a thick peptidoglycan cell wall which retains the crystal violet stain during Gram staining, turning them purple

staphylococcus aureus

A species of Gram-positive, round-shaped bacteria that commonly colonizes the skin and nose but can cause a wide range of infections if it enters deeper tissues

staphylococcus epidermidis

A species of Gram-positive, round-shaped bacteria that is a major component of the normal skin flora but can cause opportunistic infections on medical implants and catheters

streptococcus pyrogenes

A species of Gram-positive, chain-forming bacteria that causes infections such as strep throat, scarlet fever, and necrotizing fasciitis

group A streptococci

A specific serological group of Gram-positive, beta-hemolytic bacteria—primarily Streptococcus pyogenes —that causes a wide range of diseases including strep throat, scarlet fever, and necrotizing fasciitis

corynebacterium diphtheriae

A species of Gram-positive, club-shaped bacteria that produces diphtheria toxin and causes the acute, highly contagious respiratory disease diphtheria

clostridium tetani

A species of Gram-positive, spore-forming, anaerobic bacteria that produces a powerful neurotoxin causing tetanus

clostridium botulinum

A species of Gram-positive, spore-forming, anaerobic bacteria that produces a lethal neurotoxin causing botulism

clostridium perfringens

A species of Gram-positive, spore-forming, anaerobic bacteria that produces tissue-destroying toxins, commonly causing gas gangrene and food poisoning

clostridium difficile

A species of Gram-positive, spore-forming, anaerobic bacteria that causes severe diarrhea and colitis, typically triggered by antibiotic use that disrupts normal gut flora

gram negative bacteria

Bacteria that have a thin peptidoglycan cell wall surrounded by an outer lipopolysaccharide membrane, which does not retain crystal violet stain and turns pink or red during Gram staining

vibrio cholerae

A species of Gram-negative, comma-shaped bacteria that secretes cholera toxin, causing severe watery diarrhea and dehydration through contaminated food or water

escherichia coli

A species of Gram-negative, rod-shaped bacteria commonly found in the lower intestine of warm-blooded organisms, with most strains being harmless but some causing severe food poisoning and urinary tract infections

E. coli O157:H7

A specific pathogenic strain of Gram-negative bacteria that produces Shiga-like toxins, causing severe foodborne illness, bloody diarrhea, and potentially fatal hemolytic uremic syndrome

salmonella enteritidis

A species of Gram-negative, rod-shaped bacteria that is a leading cause of foodborne gastroenteritis, typically contracted from contaminated poultry, eggs, or unpasteurized milk

mycoplasma

A genus of small bacteria that lack a cell wall around their cell membrane, making them naturally resistant to antibiotics that target cell wall synthesis

mycoplasma hemofelis

A specialized, cell-wall-deficient species of bacteria that attaches to and destroys feline red blood cells, causing severe hemolytic anemia in cats

endotoxin

A toxic lipopolysaccharide component found in the outer membrane of Gram-negative bacteria that is released when the bacterial cell dies or disintegrates

exotoxin

A toxic protein produced and actively secreted by a living bacterium into its surrounding environment

enterotoxin

A specific type of exotoxin produced by microorganisms that targets the intestines, causing gastrointestinal symptoms like diarrhea, vomiting, and abdominal pain

lipopolysaccharide (LPS)

a major structural component of the outer membrane of Gram-negative bacteria that acts as an endotoxin to trigger strong immune responses in the host

cytokine

A small protein secreted by immune cells that acts as a chemical messenger to regulate and coordinate immunity, inflammation, and cell communication

chemokine

A specific class of cytokines that acts as a chemoattractant to stimulate the migration and positioning of immune cells toward sites of infection, inflammation, or tissue damage

tumor necrosis factor (TNF)

a major pro-inflammatory cytokine produced by macrophages and other immune cells that regulates inflammation, cell survival, and apoptosis

interleukin-1 (IL-1)

a potent pro-inflammatory cytokine primarily produced by macrophages that induces fever, activates immune cells, and stimulates the acute-phase inflammatory response

vasodilation

The widening of blood vessels resulting from the relaxation of smooth muscle cells within the vessel walls, leading to increased blood flow

endothelial injury

Damage to the inner cellular lining of blood vessels, which disrupts the protective barrier, promotes blood clotting, and triggers inflammation

disseminated intravascular coagulation (DIC)

a serious disorder where widespread blood clots form throughout the body's small blood vessels, depleting clotting factors and platelets, which leads to severe bleeding

acute respiratory distress syndrome (ARDS)

a severe form of hypoxic lung failure caused by widespread inflammation that damages the alveolar-capillary membrane, leading to fluid accumulation in the lungs

acute phase response

A systemic defense mechanism triggered by inflammation or infection that involves fever, increased production of specific liver proteins, and changes in circulating white blood cells

fever

An elevation in core body temperature above the normal range regulated by the hypothalamus in response to pyrogens during infection or inflammation

vasculitis

Inflammation of the blood vessel walls that can restrict blood flow, cause tissue damage, and lead to organ damage or vessel weakness

thrombosis

The formation of a blood clot within a blood vessel that obstructs or restricts the normal flow of blood through the circulatory system

ischemia

An inadequate supply of blood to an organ or tissue, which deprives the cells of vital oxygen and nutrients

ischemic necrosis

The death of cells or tissues resulting from a severe, prolonged lack of blood supply and oxygen

endotoxic shock

A life-threatening condition characterized by severe hypotension and circulatory failure caused by an overwhelming immune response to endotoxins from a Gram-negative bacterial infection

coagulase

An enzyme produced by certain bacteria, such as Staphylococcus aureus, that converts fibrinogen to fibrin to cause blood clotting and shield the pathogen from phagocytosis

fibrinogen

A soluble plasma protein synthesized by the liver that is converted into insoluble fibrin strands by thrombin during blood coagulation

fibrin

An insoluble, fibrous protein formed from fibrinogen during blood clotting that polymerizes to create a meshwork that traps platelets and stabilizes the clot

protease

An enzyme that breaks down proteins and peptides by cleaving the peptide bonds that link amino acids together

hyaluronidase

An enzyme produced by certain pathogens that degrades hyaluronic acid in the extracellular matrix, facilitating the spread of the infection through host tissues

collagenase

An enzyme that breaks down collagen fibers in the extracellular matrix, destroying tissue structure and allowing pathogens to invade deeper into the host

hemolysin

A substance or toxin produced by bacteria that destroys red blood cells by disrupting their cell membranes

lecithinase

An enzyme produced by pathogens that breaks down lecithin, a phospholipid component of cell membranes, causing cell lysis and tissue destruction

alpha toxin

A potent, membrane-damaging exotoxin produced by certain bacteria—such as Clostridium perfringens or Staphylococcus aureus—that destroys host cells by disrupting their cell membranes

necrosis

The premature, unprogrammed death of cells or tissues in a living organism caused by external damage, infection, or lack of blood supply

gas gangrene

A life-threatening, rapidly spreading bacterial infection—typically caused by Clostridium perfringens—that destroys muscle tissue and produces gas bubbles within the affected area

superantigen

A class of antigens that causes non-specific activation of T-cells, resulting in massive cytokine release and a potentially life-threatening systemic inflammatory response

antitoxin

An antibody with the ability to neutralize a specific toxin

toxic shock syndrome (TSS)

a rare and life-threatening condition characterized by sudden high fever, hypotension, rash, and multiorgan failure, typically caused by superantigens produced by Staphylococcus aureus or Streptococcus pyogenes

necrotizing fasciitis

A severe, rapidly progressive bacterial infection that destroys the deep fascia and subcutaneous tissues

diphtheria

An acute, highly contagious bacterial infection caused by Corynebacterium diphtheriae that typically presents with a sore throat, fever, and a characteristic thick gray membrane covering the tonsils and pharynx

tetanus

A serious disease of the nervous system caused by a toxin-producing bacterium, resulting in painful muscle contractions, particularly of the jaw and neck muscles

lockjaw

A medical symptom characterized by severe spasms of the jaw muscles that lock the mouth closed, most commonly associated with tetanus

botulism

A rare, life-threatening paralytic illness caused by nerve-poisoning neurotoxins produced by the anaerobic bacterium Clostridium botulinum

cholera

An acute diarrheal illness caused by infection of the intestine with the bacterium Vibrio cholerae, leading to severe dehydration

hemorrhagic colitis

An acute inflammation of the colon characterized by severe abdominal cramps and intense, bloody diarrhea, most commonly caused by Shiga toxin-producing strains of Escherichia coli

hemolytic uremic syndrome (HUS)

a serious condition characterized by the simultaneous destruction of red blood cells, low platelet counts, and acute kidney failure, typically triggered by a Shiga toxin-producing bacterial infection

Shiga toxin

A potent bacterial exotoxin produced by Shigella dysenteriae and certain strains of Escherichia coli that inhibits protein synthesis in host cells, leading to cell death

hamburger disease

food poisoning caused by Shiga toxin-producing Escherichia coli (specifically the O157:H7 strain), commonly contracted by consuming undercooked ground beef

food poisoning

An illness caused by consuming food or water contaminated with pathogenic bacteria, viruses, parasites, or their chemical toxins

traveler’s diarrhea

A digestive tract disorder that commonly causes loose stools and abdominal cramps, contracted by consuming contaminated food or water while visiting places with different climates, social conditions, or sanitary standards

appendicitis

An inflammation of the appendix, a small pouch attached to the large intestine, that typically requires emergency surgical removal