Enumeration of Microbes and Microbial Growth

Vocabulary practice flashcards covering bacterial cell replication, binary fission, growth curves, culture media types, sterilization methods, and direct/indirect microbial enumeration techniques.

Binary Fission

The most common mechanism of cell replication in bacteria, wherein a single bacterial cell increases in size, replicates its genome, and divides into two identical daughter cells.

FtsZ Ring

A ring formed at the center of a dividing bacterial cell by the assembly of the protein FtsZ and anchored by FtsZ-binding proteins to direct cytokinesis and septum synthesis.

Divisome

A bacterial protein complex formed when additional division proteins join the FtsZ ring; it directs the synthesis of new peptidoglycan wall material to construct the septum.

Generation Time

Also called doubling time; the time required for a bacterial population to double in number through one complete round of binary fission.

Fragmentation

An alternative pattern of cell division seen in filamentous bacteria such as cyanobacteria, where multiple nucleoids accumulate along a filament before it breaks into independent cells.

Bacterial Growth Curve

A graphical representation of the growth of a bacterial population over time in a closed culture, consisting of the lag phase, log phase, stationary phase, and death phase.

Log Phase

The phase of the bacterial growth curve during which cells divide rapidly by binary fission and the number of living cells increases exponentially.

Intrinsic Growth Rate

The genetically determined generation time of a bacterial species under specific growth conditions such as nutrients, temperature, and pH.

Stationary Phase

The phase of the growth curve where the rate of cell division equals the rate of cell death, causing the total number of living cells to reach a plateau as cells switch to survival metabolism.

Persisters

A small subpopulation of surviving bacterial cells in the death phase characterized by a very slow metabolic rate.

Barophiles

Microorganisms that require high hydrostatic or atmospheric pressure to grow, typically found in deep-sea environments.

Selective Media

A type of culture media containing substances that inhibit the growth of certain microorganisms while permitting or promoting the growth of others, such as MacConkey Agar.

Differential Media

Culture media designed to distinguish between different bacterial species based on recognizable biochemical reactions, such as EMB Agar or Blood Agar.

Enriched Media

Culture media containing added growth factors and nutrients (such as blood or hemoglobin) to support the growth of nutritionally fastidious organisms, such as Chocolate Agar.

Fastidious Organisms

Organisms that have complex, sophisticated nutritional requirements and are comparatively difficult to grow in standard laboratory media.

ChromAgar

A differential diagnostic medium containing proprietary chromogenic compounds that produce specific colors upon interaction with target pathogens, aiding rapid presumptive identification.

Defined (Synthetic) Media

Culture media in which every single chemical constituent is precisely known along with its exact molar concentration, such as Minimal Salt Medium.

Undefined (Complex) Media

Culture media composed of ingredients derived from natural extracts (e.g., yeast, plant, or animal digest) whose exact chemical formula and molar amounts are not fully known.

Transport Media

Formulations containing pH buffers, preservatives, and minimal nutrients designed to maintain pathogen viability during transport to a clinical lab without permitting overgrowth.

Autoclave

A moist heat sterilization device that applies pressurized steam, standardly at $121\,^\circ\text{C}$ for $15\,\text{minutes}$, to kill all viable microorganisms.

Syringe Filter

A disposable filtration device (commonly with a $0.22\,\mu\text{m}$ pore size) used to sterilize heat-sensitive liquid solutions such as antibiotics by physically retaining bacteria.

Petroff-Hausser Chamber

A specialized ruled microscope slide used to perform direct microscopic cell counts of prokaryotic populations.

Spread Plate Method

A viable plate count technique where a measured volume of bacterial sample ($0.1\,\text{mL}$) is pipetted onto solid agar and spread evenly across the surface using a sterile hockey-stick spreader.

Colony-Forming Unit (CFU)

A unit of measurement used in viable counting that estimates live bacterial cell numbers per milliliter ($\text{CFU/mL}$), accounting for the fact that single colonies can originate from clumps, chains, or single cells.

Countable Plate Guideline

A statistical threshold stating that only agar plates yielding between $30$ and $300$ colonies are considered reliable for calculating viable cell counts.

Dilution Factor

The inverse or reciprocal of the dilution ($1 \div \text{dilution}$), used as a multiplier to determine original cell concentration in viable count formulas.

Most Probable Number (MPN)

A statistical direct estimation technique used to enumerate microbial populations in very dilute liquid samples, such as water.