Genetic Variability, Bacterial Gene Transfer & Disease Establishment

Vocabulary flashcards covering key microbiology concepts: genetic variation, bacterial gene transfer, routes and stages of disease, transmission terms, virulence factors, enzymes, and toxins.

Genetic Variability

Natural differences in DNA sequences among organisms; essential raw material for natural selection.

Mutation

Random change in DNA sequence that introduces new genetic variation.

Recombination

Creation of new gene combinations in an individual through exchange or rearrangement of DNA.

Vertical Gene Transfer

Transmission of genetic material from parent to offspring during reproduction (e.g., binary fission in bacteria).

Horizontal Gene Transfer

Movement of DNA between organisms without reproduction, generating variability via transformation, conjugation, or transduction.

Transformation

Uptake of free DNA fragments from the environment by a recipient bacterium, followed by homologous recombination.

Conjugation

Direct cell-to-cell DNA transfer in bacteria, usually mediated by an F plasmid and a sex pilus.

F Plasmid (F Factor)

Fertility plasmid that carries genes for sex pilus formation and DNA transfer during conjugation.

Sex Pilus

Hollow appendage produced by F⁺ bacteria to attach to and draw recipient cells close for plasmid transfer.

Hfr Cell

"High-frequency recombination" donor whose F plasmid is integrated into the chromosome, enabling transfer of chromosomal genes.

Generalized Transduction

Lytic phage mistakenly packages random host DNA fragments and transfers them to another bacterium.

Specialized Transduction

Lysogenic phage transfers specific host genes located next to its prophage insertion site.

Plasmid

Small, extra-chromosomal DNA molecule capable of independent replication and frequent exchange between cells.

Symbiosis

Long-term biological association between different species living together.

Commensalism

Symbiosis where one partner benefits and the other is unaffected.

Mutualism

Symbiotic relationship in which both partners benefit (e.g., gut microbiota).

Parasitism

Symbiosis where one organism benefits at the expense of the other, often causing disease.

Opportunism

Condition in which normally harmless microbes become pathogenic when host defenses are compromised.

Virulence

Degree of pathogenicity; the ability of a microbe to cause disease.

Portal of Entry

Specific route by which a pathogen enters the host (e.g., respiratory tract, skin puncture).

Synergy (Microbial)

Interaction where one microbe helps another establish disease.

Antagonism (Syncray)

Interaction where one microbe inhibits another’s ability to cause disease.

Immunocompetent

Having a fully functional immune system capable of normal defense responses.

Immunocompromised

Having weakened or impaired immunity, increasing susceptibility to infection.

Vehicle

Non-living medium (food, water, air) that transmits pathogens indirectly.

Fomite

Inanimate object (doorknob, stethoscope) that passively carries pathogens between hosts.

Vector

Living, usually arthropod carrier that transmits pathogens without being diseased itself.

Zoonosis

Disease of animals that can be transmitted to humans, directly or indirectly.

Reservoir

Natural habitat where a pathogen persists between infections (e.g., soil, water, carrier host).

Carrier

Asymptomatic infected individual who spreads a pathogen over time.

Incubation Period

Time between pathogen entry and onset of symptoms.

Prodromal Period

Early stage of disease with vague, general symptoms such as malaise or mild fever.

Acute Phase

Stage with characteristic, severe, recognizable signs and symptoms.

Decline Phase

Period when symptoms subside in severity or frequency.

Convalescence

Recovery stage when symptoms are gone but body repair and fatigue persist.

Acute Disease

Illness with rapid onset, severe symptoms, a crisis point, and quick recovery.

Chronic Disease

Illness with slow onset, milder symptoms, no crisis point, and prolonged recovery.

Primary Disease

Initial infection occurring in a previously healthy host, usually by a highly virulent pathogen.

Secondary Disease

Infection that follows a primary illness due to weakened host defenses or spread of the original pathogen.

Nosocomial Infection (HAI)

Infection acquired in a healthcare setting such as a hospital or clinic.

MRSA

Methicillin-resistant Staphylococcus aureus, a highly virulent, drug-resistant hospital pathogen.

VRE

Vancomycin-resistant Enterococcus; less virulent but resistant to many antibiotics.

Clostridium difficile

Drug-resistant bacterium causing antibiotic-associated gut infections.

Emerging VSA

Vancomycin-resistant Staphylococcus aureus, a new concern combining high virulence with vancomycin resistance.

Local Infection

Pathogen confined to the portal of entry or a single tissue surface.

Systemic Infection

Infection disseminated throughout the body or multiple organ systems.

Septicemia

Active microbial infection of the bloodstream producing systemic illness.

Bacteremia

Presence of bacteria in the bloodstream (may be transient or lead to septicemia).

Viremia

Presence of viruses in the bloodstream.

Fungemia

Presence of fungi or yeast in the bloodstream.

Focal Infection

Internal site where a systemic pathogen re-establishes and causes localized disease.

Endemic

Disease constantly present at predictable levels in a population.

Epidemic

Sudden increase in disease incidence above normal baseline in a region.

Pandemic

Epidemic that spreads across multiple continents.

Adhesins

Surface molecules (ligands, fimbriae, spikes) that allow pathogens to attach to host cells.

Capsule

Polysaccharide layer surrounding some bacteria that enhances virulence by inhibiting phagocytosis, delaying immune response, and neutralizing drugs.

Coagulase

Bacterial enzyme that forms blood clots to wall off infection, blocking WBCs and drugs.

Streptokinase

Enzyme that dissolves blood clots, enabling bacteria to spread into the bloodstream.

Hyaluronidase

"Spread factor" enzyme that digests hyaluronic acid (cell cement), allowing tissue invasion.

Collagenase

Enzyme that breaks down collagen beneath epithelial layers, facilitating deeper tissue spread.

Leukocidin

Toxin that destroys white blood cells, contributing to pus formation and immune evasion.

M Protein

Streptococcal surface protein that prevents phagocytosis by interfering with WBC attachment.

Hemolysin

Toxin that lyses red blood cells, releasing iron and altering oxygen levels for microbial growth.

Exotoxin

Protein toxin secreted by living Gram-positive or Gram-negative bacteria; highly specific in action.

Endotoxin

Lipid A component of Gram-negative LPS released upon cell lysis; causes fever and shock.

Cytotoxin

Exotoxin that directly kills host cells, producing lesions (e.g., anthrax lethal factor).

Enterotoxin

Exotoxin targeting the digestive tract, causing fluid loss, diarrhea, or cramps.

Neurotoxin

Exotoxin that interferes with nerve function (e.g., botulinum and tetanus toxins).

Botulinum Toxin

Neurotoxin that blocks acetylcholine release at neuromuscular junctions, causing flaccid paralysis.

Tetanus Toxin

Neurotoxin that inhibits inhibitory neurons, leading to constant muscle contraction (rigid paralysis).

Toxoid

Heat-denatured exotoxin used as a vaccine to stimulate antitoxin antibody production.

Botulism

Illness caused by ingestion or infection with Clostridium botulinum producing botulinum toxin.