Bacterial Structure, Physiology, Control, and Enumeration

Comprehensive vocabulary flashcards covering bacterial cell anatomy, cell wall distinctions, metabolic classifications, growth phases, sterilization strategies, and enumeration methods based on lecture material.

Prokaryotic cell anatomy

A cellular organization characterized by the absence of membrane-bound organelles and a nuclear membrane, typically composed of an outer envelope (capsule, cell wall, and cytoplasmic membrane), cytoplasm containing ribosomes and a nucleoid, and surface appendages such as pili and flagella.

Nucleoid

The non-membrane-bound region within the bacterial cytoplasm where the chromosomal DNA is localized.

Peptidoglycan (Murein)

A large cell wall polymer consisting of repeating units of two sugars ($N\text{-acetylglucosamine}$ and $N\text{-acetylmuramic acid}$) cross-linked by peptide bridges to confer structural rigidity and shape to bacteria.

Gram stain

A differential staining procedure where bacteria are stained with two dyes; Gram-positive bacteria retain a crystal violet dye complex appearing blue due to a thick peptidoglycan wall, while Gram-negative bacteria decolorize with alcohol and counterstain pink.

Lipopolysaccharide (Endotoxin)

A toxic molecule located in the outer membrane of Gram-negative bacteria that can induce fever, shock, and death when released into the bloodstream of humans or animals.

Teichoic acids

Polymers interwoven throughout the thick peptidoglycan layer of Gram-positive bacterial cell walls that are absent in Gram-negative bacteria.

Bacterial morphology

The structural categorization of bacteria by shape, comprising spheres (cocci, such as diplococci, streptococci, tetrads, and sarcina), cylindrical forms (bacilli, flagellate rods, and spore-formers), and curved or spiral shapes (vibrios, spirilla, and spirochaetes).

Capsule

A tightly adhered, hydrophilic polysaccharide layer with distinct boundaries surrounding a bacterial cell that protects it from desiccation and dehydration.

Slime layer

A loosely associated extracellular secretion surrounding certain bacteria that can be easily washed away.

Chemotaxis

The behavioural process by which a motile bacterium senses chemical gradients and adjusts its flagellar rotation to swim toward attractants or away from repellents.

Fimbriae

Straight, rigid, spike-like surface appendages found only on Gram-negative bacteria that facilitate attachment to specific sugar residues on other cells or surfaces.

Sex pili

Specialized surface appendages that enable one bacterium to recognize, adhere to, and transfer genetic material to another cell during conjugation.

Volutin (Metachromatic granules)

Non-membrane-bound cytoplasmic inclusion bodies composed of polymerized inorganic phosphate that serve as energy and phosphate reserves.

Plasmids

Small, typically circular, non-chromosomal auxiliary DNA molecules residing in the cytoplasm that replicate independently and carry non-essential genes.

Binary fission

The primary asexual reproduction method in prokaryotes wherein an elongated cell synthesizes an inward-growing septum to divide into two identical daughter cells.

Protein FtsZ

A specialized bacterial division protein that forms a contractile ring at the midpoint of an elongated cell, driving the assembly of the division septum.

Endospore

A highly durable, dormant, and metabolically inactive structure formed internally by certain Gram-positive rods, such as $Bacillus$, in response to nutritional deprivation.

Transformation

The process of horizontal gene transfer in which bacteria import naked fragments of free DNA from the surrounding medium and incorporate them into their genome.

Transduction

The transfer of bacterial DNA from a donor cell to a recipient cell mediated by a bacteriophage virus, protecting the genetic material against enzymatic degradation.

Conjugation

The transfer of plasmid DNA between bacterial cells via direct cell-to-cell contact and specialized conjugative machinery.

Bacterial growth curve

The characteristic pattern of population dynamics observed when bacteria are grown in a closed batch system, consisting of lag, exponential, stationary, and decline phases.

Lag phase

The initial adaptation period of bacterial batch culture where individual cells enlarge and actively synthesize RNA, enzymes, and co-enzymes without an increase in population size.

Exponential (Log) phase

The period of bacterial growth during which cells divide at a constant maximal rate, the population doubles predictably over time, and cells exhibit their shortest generation time.

Stationary phase

The growth curve stage reached when nutrient exhaustion or waste accumulation causes the rate of cell division to equal the rate of cell death, yielding a stable viable cell count.

Viable but non culturable (VBNC)

A survival state entered by bacteria during adverse conditions or the death phase characterized by very low metabolism and inability to divide on standard media, with the potential to revive when conditions improve.

Psychrophiles

Cold-loving bacteria with an optimum growth temperature between $-5^\circ\text{C}$ and $15^\circ\text{C}$, typically isolated from Arctic and Antarctic environments or glacial streams.

Mesophiles

Bacteria that exhibit optimum growth at moderate temperatures ranging from $25^\circ\text{C}$ to $45^\circ\text{C}$, encompassing most human body flora and soil bacteria.

Thermophiles

Heat-adapted bacteria possessing an optimal growth temperature between $45^\circ\text{C}$ and $70^\circ\text{C}$, commonly found in compost heaps and hot springs.

Hyperthermophiles

Extreme thermophilic organisms (predominantly Archaea) that grow optimally at temperatures between $70^\circ\text{C}$ and $110^\circ\text{C}$, commonly near deep-sea hydrothermal vents.

Microaerophiles

Organisms that require low oxygen levels of $2\%$ to $10\%$ for aerobic growth, whereas ambient atmospheric concentrations inhibit their proliferation.

Aerotolerant anaerobes

Organisms that cannot utilize oxygen for energy production but can survive in its presence, obtaining all metabolic energy exclusively through fermentation.

Facultative anaerobes

Organisms that grow in both the presence and absence of oxygen, utilizing aerobic respiration when oxygen is available and switching to fermentation or anaerobic respiration when it is absent.

Aquaporins

Channel-forming transmembrane proteins that span the cytoplasmic membrane to facilitate the rapid passive transport of water molecules into and out of the cell.

Plasmolysis

The osmotic shrinking of the bacterial cytoplasmic membrane away from the rigid cell wall caused by the net outward movement of water into a hypertonic medium.

Sterilization

The physical or chemical process of completely eliminating or killing all forms of viable microbial life, including vegetative cells and spores, from a surface, object, or medium.

Autoclave

A moist heat sterilization instrument that utilizes saturated steam under pressure ($15\,\text{psi}$ at $121^\circ\text{C}$ for $15\,\text{minutes}$) to denature proteins and kill all microbes.

Serial dilution plate count

A direct viable enumeration technique in which a culture is sequentially diluted by factors of 10 and plated onto nutrient agar, allowing viable cell density to be calculated from plates bearing $30$ to $300$ colonies.

Colony Forming Unit (CFU)

The reported measure of viable bacterial enumeration representing a single cell or connected group of cells capable of forming a single discrete colony on solid media.

Turbidimetric measurement

An indirect, rapid enumeration technique that evaluates bacterial concentration by measuring the reduction in transmitted light due to scatter by suspended cells using a spectrophotometer.

Petroff-Hauser chamber

A precision microscope slide with an etched grid and a central chamber depth of $0.02\,\text{mm}$ ($\frac{1}{50}\,\text{mm}$) used for direct microscopic counting of total bacterial cells.

Acridine orange

A common fluorochrome dye utilized in direct microscopic counts to stain bacterial nucleic acids on a $0.22\,\mu\text{m}$ membrane filter for visualization under a fluorescence microscope.