Medical Microbiology: Bacteria and Pathogenesis

Vocabulary terms and definitions covering basic microbiology, cellular differences, bacterial morphology, pathogenicity, and specific bacterial classifications described in the lecture.

Pathogens

Microorganisms that can cause disease, categorized into five basic types: Bacteria, Viruses, Fungi, Parasites, and Prions.

Prokaryotic Cells

Cells that lack a nuclear membrane and have a nucleoid consisting of a single circular molecule of loosely organized DNA; they use binary fission to reproduce.

Eukaryotic Cells

Cells that have a true nucleus with multiple chromosomes surrounded by a nuclear membrane and use mitosis to reproduce.

Peptidoglycans

A polymer of amino acids and sugars found in the rigid exterior cell wall of most prokaryotic cells.

70S Ribosome

The specific size of ribosome found in prokaryotic cells, which differs from the $80S$ ribosomes found in eukaryotic cells.

Cocci

Spherical-shaped bacteria that can be arranged in chains, pairs, or clusters.

Bacilli

Rod-shaped bacteria; short bacilli are referred to as coccobacilli.

Spirochetes

Bacteria that are comma-shaped, $S$-shaped, or spiral-shaped.

Pleomorphic

Bacteria that lack a distinct shape.

Normal Flora (Microbiota)

Communities of microorganisms that colonize skin surfaces, the oral cavity, intestines, and other tracts; they are predominately bacterial species.

Colonization

A state where microorganisms are present but do not cause symptoms or trigger an immune response.

Infection

Occurs when microorganisms invade tissues, leading to symptoms and illness.

Dysbiosis

An imbalance of microbial species and a reduction in microbial diversity within a microbiota, often minimizing beneficial bacteria.

Horizontal Transmission

The spread of an infectious agent from one individual to another, usually by contact with bodily fluids or excretions.

Vertical Transmission

Transmission of an infectious agent from one generation to another, such as from an infected mother to an infant during pregnancy or delivery.

Virulence

The relative capacity of a pathogen to overcome a host’s defenses and cause disease or damage; the degree of pathogenicity.

Pili (Fimbriae)

Adhesion factors on the surface of some prokaryotic cells that help them attach to surfaces or cells.

Capsule

A protective wall surrounding the bacterial cell membrane that disables the ability of neutrophils and macrophages to phagocytize the bacteria.

Endospores

Structures formed by Bacillus and Clostridium that allow bacteria to become metabolically dormant and resistant to heat, cold, and chemical agents.

Biofilms

A community of living microorganisms embedded in a slimy extracellular polysaccharide matrix that protects against antibiotics and the immune system.

Exotoxin

Proteins released by certain gram-positive and gram-negative bacteria, including neurotoxins, enterotoxins, and pyrogenic toxins.

Endotoxin (LPS)

A normal part of the cell membrane of gram-negative bacteria that is shed off and can cause septic shock if it enters the blood.

Bacteremia

The presence of bacteria in the bloodstream; it is frequently transient and self-resolving.

Sepsis

Bacteremia that causes a systemic immune response, characterized by elevated WBC count and temperature changes.

Septic Shock

A life-threatening response to infection causing drops in blood pressure and decreased organ function from lack of perfusion.

Gram-Positive Bacteria

Bacteria with two layers (inner plasma membrane and thick peptidoglycan layer) that appear blue under a microscope after staining.

Gram-Negative Bacteria

Bacteria with three layers (inner plasma membrane, thin peptidoglycan layer, and outer membrane with LPS) that appear red after staining.

Obligate Aerobes

Bacteria that require oxygen to live and possess enzymes such as catalase, peroxidase, or superoxide dismutase.

Obligate Anaerobes

Bacteria that are harmed by oxygen and cannot survive in its presence.

Facultative Anaerobes

Bacteria that can survive with or without oxygen by switching between aerobic and anaerobic metabolism.

Lancefield Antigens

Carbohydrates present in the cell wall used to classify Streptococci into groups designated by letters $A-S$.

MRSA

Methicillin Resistant Staphylococcus aureus; a strain that has acquired multi-drug resistance.

Crepitus

A crackling, crinkly, or grating feeling under the skin caused by gas released by bacteria in gas gangrene.

Pseudomembrane

A gray or white membrane in the pharynx produced by Corynebacterium diphtheriae that serves as a base for secreting exotoxins.

Meningitis

Inflammation of the protective membranes covering the brain and spinal cord, often characterized by a hallmark symptom of a stiff neck.

Erythema chronicum migrans

The characteristic "bull’s eye" rash at the site of a tick bite associated with Lyme Disease (Borrelia burgdorferi).

Acid-fast stain

A specific staining method used to classify Mycobacterium tuberculosis because it is only weakly gram-positive.