Microbiology: Pathogenic Bacteria, Microbial Growth, Metabolism, and Prokaryotic Structure

Comprehensive vocabulary flashcards covering pathogenic bacteria, microbial growth kinetics and requirements, bacterial metabolism, and prokaryotic structural characteristics and genetics.

Streptococcus pyogenes

A Gram-positive coccus classified as Group A Strep (GAS) that is beta-hemolytic and produces streptolysins; causes strep throat, impetigo, scarlet fever, rheumatic fever, and necrotizing fasciitis.

Streptococcus agalactiae

A Gram-positive coccus classified as Group B Streptococcus (GBS), found in vaginal flora and screened during pregnancy; transmitted perinatally to cause neonatal sepsis, meningitis, and pneumonia.

Streptococcus pneumoniae

An encapsulated, alpha-hemolytic Gram-positive diplococcus carried as normal nasopharyngeal flora by approximately $70\%$ of the U.S. population; causes pneumonia, meningitis, otitis media, and conjunctivitis.

Streptococcus mutans

A Gram-positive coccus of the oral cavity that ferments sugars into acid and produces a dextran slime layer to form biofilms (dental plaque), leading to dental caries and endocarditis.

Escherichia coli O157:H7

The most virulent, enterohemorrhagic serotype of the Gram-negative rod Escherichia coli; possesses endotoxin and causes severe foodborne gastroenteritis, bloody diarrhea, and sepsis.

Borrelia burgdorferi

A weakly staining Gram-negative spirochete transmitted by the Ixodes tick that causes Lyme disease, characterized by erythema migrans ("bull's-eye" rash), joint pain, and neurological and cardiac complications.

Treponema pallidum

A Gram-negative spirochete with endoflagella that cannot be cultured in vitro; transmitted via sexual contact or transplacentally, causing primary (chancre), secondary (rash), tertiary (neurosyphilis), and congenital syphilis.

Shigella dysenteriae

A Gram-negative rod transmitted via the fecal-oral route with an extremely low infectious dose; produces Shiga toxin and endotoxin to cause shigellosis (bacillary dysentery with fever, cramps, and bloody diarrhea).

Vibrio cholerae

A comma-shaped, Gram-negative curved rod transmitted via contaminated water and food; secretes cholera toxin, leading to profuse watery "rice-water" diarrhea and rapid dehydration.

Neisseria meningitidis

An encapsulated Gram-negative diplococcus carried asymptomatically by $10\%$ of the U.S. population; produces potent endotoxin responsible for rapid progression of epidemic meningitis and septicemia.

Neisseria gonorrhoeae

A Gram-negative diplococcus utilizing fimbriae for adherence and undergoing antigenic variation; causes gonorrhea, pelvic inflammatory disease (PID), and neonatal gonorrheal ophthalmia.

Clostridium botulinum

An obligate anaerobic, endospore-forming Gram-positive rod found in soil, wounds, and honey (infants); produces botulinum neurotoxin, which blocks nerve transmission to cause flaccid paralysis.

Clostridium tetani

An obligate anaerobic, endospore-forming Gram-positive rod that enters puncture wounds and produces the neurotoxin tetanospasmin, causing spastic paralysis, lockjaw, and risus sardonicus.

Clostridium perfringens

An endospore-forming Gram-positive rod found in soil, wounds, and contaminated food; produces gas-forming exotoxins causing gas gangrene and food poisoning.

Clostridioides difficile

An endospore-forming Gram-positive rod that proliferates after broad-spectrum antibiotic therapy; produces exotoxins that cause severe antibiotic-associated colitis, requiring strict isolation and terminal spore-killing cleaning.

Bacillus anthracis

An endospore-forming Gram-positive rod and agent of bioterrorism; produces anthrax exotoxin, causing cutaneous, inhalational, or gastrointestinal anthrax.

Corynebacterium diphtheriae

A pleomorphic Gram-positive rod that secretes diphtheria exotoxin, causing respiratory diphtheria characterized by a pseudomembrane in the throat along with potential nerve and heart damage.

Bordetella pertussis

A Gram-negative coccobacillus that adheres to respiratory cilia via filamentous hemagglutinin and releases pertussis toxin; causes whooping cough (severe paroxysmal coughing, inspiratory "whoop," and post-tussive vomiting).

Mycobacterium tuberculosis

An acid-fast rod with a cell wall rich in mycolic acid ($60\%$); survives inside alveolar macrophages and causes chronic pulmonary tuberculosis characterized by chronic cough, night sweats, and weight loss.

Mycobacterium leprae

An acid-fast rod with an exceptionally long generation time ($10\text{--}14\text{ days}$) that cannot be cultured in vitro; grows preferentially in cooler body regions to cause leprosy (Hansen's disease).

Haemophilus influenzae

A Gram-negative bacillus categorized into serotypes a–f (type b prevented by the Hib vaccine); causes epiglottitis, otitis media, and meningitis, but does not cause influenza.

Mycoplasma pneumoniae

A pleomorphic bacterium that naturally lacks a cell wall (making it inherently resistant to $\beta$-lactam antibiotics) and stabilizes its plasma membrane with sterols; causes atypical or "walking" pneumonia.

Listeria monocytogenes

A Gram-positive, intracellular bacillus that can grow at refrigeration temperatures (psychrotroph) and cross the placenta; transmitted via unpasteurized dairy, deli meats, and produce to cause listeriosis and neonatal meningitis.

Psychrophiles

Cold-loving microorganisms whose optimal growth temperature falls between $-10\,^\circ\text{C}$ and $20\,^\circ\text{C}$.

Psychrotrophs

Microorganisms that grow well at refrigerator temperatures ($0\,^\circ\text{C}$ to $30\,^\circ\text{C}$) and frequently cause food spoilage (e.g., Listeria monocytogenes).

Mesophiles

Moderate-temperature-loving microorganisms with optimal growth around human body temperature ($35\text{--}37\,^\circ\text{C}$), encompassing the vast majority of human pathogens.

Thermophiles

Heat-loving microorganisms that thrive at high temperatures, typically with optimal growth between $50\,^\circ\text{C}$ and $60\,^\circ\text{C}$.

Microbial Temperature Classes

The physiological categorization of microbes based on cardinal growth temperatures: psychrophiles, psychrotrophs, mesophiles, thermophiles, and hyperthermophiles.

Temperature Danger Zone

The temperature range between approximately $60\,^\circ\text{F}$ and $130\,^\circ\text{F}$ ($15\,^\circ\text{C}$ to $52\,^\circ\text{C}$) where bacteria proliferate rapidly and may produce toxins in food.

Acidophiles

Organisms that tolerate or thrive in highly acidic environments; for example, Helicobacter pylori survives gastric pH around $2.0$ by secreting urease to break down urea into carbon dioxide and acid-neutralizing ammonia.

Halophiles

Bacteria that tolerate high osmotic pressure caused by high salt concentrations; extreme halophiles specifically require high salt levels to grow.

Oxygen Requirement Classes in Thioglycollate Medium

Categorization of bacteria based on oxygen tolerance: (a) obligate aerobes grow only at top; (b) facultative anaerobes grow throughout but heavier at top; (c) obligate anaerobes grow only at bottom; (d) aerotolerant anaerobes grow evenly; (e) microaerophiles grow in a narrow sub-surface zone.

Generation Time

The time required for a bacterial cell to divide by binary fission, calculated using the formula $\text{Final cells} = \text{Initial cells} \times 2^n$, where $n$ is the number of generations.

Bacterial Growth Curve

A standard curve representing the four distinct phases of a closed bacterial culture over time: lag phase, log (exponential growth) phase, stationary phase, and death (logarithmic decline) phase.

Lag Phase

The initial period in a bacterial culture characterized by intense metabolic activity and enzyme synthesis without significant cell division.

Log Phase

The exponential growth period of a bacterial culture featuring maximum cellular reproduction and metabolic activity; during this phase, bacteria are most susceptible to adverse conditions and antibiotics.

Stationary Phase

The plateau phase in microbial growth where the rate of cell division equals the rate of cell death due to nutrient depletion and toxic waste accumulation.

Death Phase

The logarithmic decline phase where dying cells outnumber newly formed cells due to prolonged toxic environmental conditions.

Anabolism

Metabolic reactions that consume energy (endergonic) to build complex cellular molecules from simpler precursors.

Catabolism

Metabolic reactions that break down complex molecules into simpler substances, releasing energy (exergonic) that is captured as ATP.

Chemoheterotroph

An organism that requires organic chemical compounds (such as glucose) as both its source of energy and its source of carbon (encompassing all animals, fungi, protozoa, and most bacteria).

Aerobic Respiration

Carbohydrate catabolism comprising glycolysis, Krebs cycle, and the electron transport chain using $O_2$ as the final electron acceptor; yields $38\text{ ATP}$ in prokaryotes ($36\text{ ATP}$ in eukaryotes) per glucose molecule.

Anaerobic Respiration

A respiratory pathway that utilizes glycolysis, Krebs cycle, and an electron transport chain where an inorganic molecule other than $O_2$ acts as the final electron acceptor; yields more than $2\text{ ATP}$ but less than $38\text{ ATP}$.

Fermentation

An anaerobic metabolic process relying solely on glycolysis that produces a net yield of $2\text{ ATP}$; uses an organic molecule (such as pyruvate or acetaldehyde) as the final electron acceptor to form acids or alcohols.

Enzyme Inhibition Mechanisms

Modes of slowing enzymatic reactions: competitive inhibitors physically block the active site, whereas noncompetitive (allosteric) inhibitors bind to an allosteric site to alter the active site conformation.

Competitive Inhibitor

A chemical agent that mimics the structure of a substrate to bind directly to an enzyme's active site (e.g., sulfanilamide competing with PABA to prevent bacterial folic acid synthesis).

Catalase Test

A diagnostic enzymatic assay utilizing hydrogen peroxide ($H_2O_2$); catalase-positive organisms (Staphylococcus) produce bubbles ($O_2$), whereas catalase-negative organisms (Streptococcus) do not.

Coccus Arrangements

Morphological groupings of spherical bacteria determined by planes of cell division: diplococci (pairs), streptococci (chains), tetrads (four cells in one plane), sarcinae (cubes of eight), and staphylococci (grape-like clusters).

Bacillus Arrangements

Morphological patterns of rod-shaped bacteria that divide strictly across their short axes: single bacillus, diplobacilli (pairs), streptobacilli (chains), and coccobacillus (short, rounded oval rods).

Curved Bacterial Morphologies

Non-spherical, non-rod bacterial shapes: vibrio (curved, comma-shaped rods), spirillum (rigid corkscrew-shaped helical bodies), and spirochetes (flexible corkscrew-shaped helical bodies).

Transformation

A horizontal gene transfer mechanism where a competent bacterium takes up naked donor DNA fragments released into the environment following cell lysis of a closely related bacterium.

Transduction

A mode of horizontal gene transfer in which a bacteriophage virus accidentally packages donor bacterial DNA and injects it into a recipient bacterium.

Conjugation

Direct transfer of genetic material (plasmid) between two bacteria joined by a sex pilus; can occur between unrelated species and serves as a major pathway for transmitting antibiotic resistance.

Transposons

Transposable DNA segments ("jumping genes") capable of moving and inserting into recipient chromosomes without homologous sequence requirement, often carrying antibiotic resistance and virulence factors.

Glycocalyx

A sticky, gelatinous polymer of polysaccharides and/or polypeptides secreted onto the bacterial exterior; structured as an organized, firmly attached capsule or a loose, diffuse slime layer.

Biofilm

A dense microbial community encased within a self-produced matrix of extracellular polymeric substances (EPS) adhering to surfaces or medical implants, making bacteria up to $1{,}000\times$ less sensitive to antimicrobials.

Flagellar Arrangements

Patterns of flagella distribution on bacteria: monotrichous (single polar flagellum), lophotrichous (tuft of flagella at one pole), amphitrichous (flagella at both poles), and peritrichous (flagella covering the entire cell surface).

Axial Filament

Internal flagellar bundles (endoflagella) located between the cell wall and outer sheath of spirochetes; their rotation drives a corkscrew motion that allows the bacteria to bore through viscous host tissues.

Fimbriae

Fine, hairlike protein bristles extending from the surface of Gram-negative bacteria that facilitate attachment and adherence to host epithelial surfaces for colonization.

Pili

Tubular appendages on Gram-negative bacteria used specifically to bind mating cells together and facilitate the transfer of plasmid DNA during conjugation (sex pili).

Sporulation

The developmental process (sporogenesis) by which an environmentally stressed vegetative bacterium encloses its duplicated chromosome within a protective, multi-layered endospore.

Tetanospasmin

A neurotropic exotoxin produced by Clostridium tetani that blocks inhibitory neurotransmitter release in motor neurons, leading to uninhibited muscle contractions, spastic paralysis, lockjaw, and respiratory failure.

Peptidoglycan

A macromolecular lattice forming the bacterial cell wall, composed of alternating repeating disaccharides (N-acetylglucosamine [NAG] and N-acetylmuramic acid [NAM]) cross-linked by tetrapeptide side chains and peptide bridges.

Gram-Positive Cell Envelope

A cell envelope structure featuring a thick, multi-layered peptidoglycan wall containing wall teichoic and lipoteichoic acids situated directly above a single cytoplasmic lipid bilayer.

Gram-Negative Cell Envelope

A complex envelope consisting of a thin peptidoglycan layer in a periplasmic space between the cytoplasmic membrane and an outer membrane containing lipopolysaccharide (LPS), phospholipids, lipoproteins, and porins.

Blood Agar Hemolysis Patterns

Differential red blood cell lysis zones produced by bacteria: beta-hemolysis (complete clearance of RBCs, e.g., S. pyogenes), alpha-hemolysis (partial, greenish clearance, e.g., S. sanguinis), and gamma-hemolysis (no clearance, e.g., Enterococcus).

Exotoxins

Toxic, soluble proteins actively secreted by living Gram-positive or Gram-negative bacteria into surrounding fluids; potent in minute amounts, heat-labile, specific in tissue action, and convertible to toxoids.

Endotoxins

The toxic lipopolysaccharide (LPS) component of the outer membrane of Gram-negative bacteria, released primarily upon cell death and lysis; stable at $60\,^\circ\text{C}$, stimulates fever and systemic inflammation, and causes septic shock and disseminated intravascular coagulation (DIC).

Toxoid

An inactivated bacterial exotoxin rendered harmless by heat or chemical treatment that retains its antigenicity, stimulating the host to produce neutralizing antitoxins for vaccine protection.

Lancefield Groupings

A serological nomenclature system that categorizes species in the genus Streptococcus into groups (Group A, Group B, Group C, etc.) based on specific carbohydrate antigens located in their cell walls.