Microbiology Lecture Exam Review chapter 6

Flashcards covering key microbiology vocabulary related to microbial growth kinetics, environmental factors affecting growth, and methods for controlling microbial growth.

Planktonic growth

Growth in suspension of free-floating/free-swimming cells.

Sessile growth

Growth where cells are attached to a surface, often developing into biofilms.

Biofilm

Cells enmeshed in a polysaccharide matrix attached to a surface.

Biofilm formation stages

Include planktonic cells attaching, colonization with extracellular polysaccharide (EPS) production, development with metabolic changes, and dispersal to new sites.

Microbial mats

Multilayered sheets with different organisms in each layer, found in environments like hot springs or intertidal regions.

Balanced growth

The result of binary fission, producing nearly identical cells.

Budding cell division

Unequal cell growth forming different daughter cells, sometimes with cytoplasmic extensions like stalks or appendages.

Hyphal growth

A type of growth seen in filamentous bacteria like Actinomycetes, where growth occurs only at the filament tip, not directly linked to division.

Mycelia

Weaved hyphae.

Arthrospores

Survival structures formed from mycelia.

Multiple fission

Hyphal filament forming many septa simultaneously.

Cardinal (Principal) Temperatures

The minimum, optimum, and maximum temperatures at which an organism grows.

Psychrophile

An organism with a low growth temperature optimum, typically found in cold environments (optimal growth ≤15°C, maximum < 20°C, minimum ≤ 0°C).

Mesophile

An organism with a midrange growth temperature optimum, found in temperate environments and causing most diseases (optima 20°C to 40°C).

Thermophile

An organism with a high growth temperature optimum, found in hot environments (45°C to 80°C).

Hyperthermophile

An organism with a very high growth temperature optimum, found in extremely hot habitats such as hot springs and deep-sea hydrothermal vents (optima > 80°C).

Extremophiles

Organisms that grow under very hot or very cold conditions.

Psychrotolerant

Organisms that can grow at 0°C but have optimal growth temperatures between 20°C and 40°C.

Taq polymerase

A heat-stable enzyme isolated from Thermus aquaticus, commercially useful in polymerase chain reaction (PCR).

pH

A measure that expresses the acidity or alkalinity of a solution (pH 7 is neutral;

Neutrophiles

Microorganisms that grow optimally at a circumneutral pH range of 5.5–7.9.

Acidophiles

Microorganisms that grow best at low pH (< 5.5).

Alkaliphiles

Microorganisms that have high pH optima for growth (pH ≥ 8), found in highly alkaline habitats.

Water activity (aw)

A measure of water availability in an environment.

Osmosis

The diffusion of water from high to low concentrations across a semipermeable membrane.

Halophiles

Microorganisms that grow best at water activity (aw) = 0.98 (seawater) and have a specific requirement for NaCl (0-12%).

Halotolerant

Microorganisms that can tolerate some dissolved solutes but generally grow best in the absence of added solute.

Extreme halophiles

Microorganisms that require very high levels (15-30%) of NaCl for growth.

Osmophiles

Organisms that live in environments high in sugar as a solute.

Xerophiles

Organisms able to grow in very dry environments.

Compatible Solutes

Highly water-soluble substances (e.g., sugars, alcohols) accumulated by microbes to maintain positive water balance without inhibiting biochemical processes.

Aerobes

Microorganisms that require oxygen for respiration and grow at full O2 tension (~21%).

Microaerophiles

Microorganisms that can use O2 but only at levels reduced from that in air (microxic).

Facultative organisms

Microorganisms that can live with or without oxygen (e.g., facultative aerobes/anaerobes).

Anaerobes

Microorganisms that cannot respire oxygen.

Aerotolerant anaerobes

Microorganisms that tolerate oxygen and grow in its presence, even though they cannot respire it.

Obligate anaerobes

Microorganisms that are inhibited or killed by oxygen.

Reducing agents

Chemicals added to culture media (e.g., thioglycolate) to reduce oxygen to water, creating an anoxic environment.

Resazurin dye

An indicator dye used in culture media that turns pink when oxygen is present.

Toxic oxygen byproducts

Byproducts of oxygen reduction, including superoxide anion (O2⁻), hydrogen peroxide (H2O2), and hydroxyl radical (OH·).

Decontamination

The treatment of an object to make it safe to handle.

Disinfection

A process that directly targets pathogens, killing or severely inhibiting their growth, but not necessarily all microorganisms.

Sterilization

The killing or removal of all microorganisms, including viruses.

Decimal reduction time (D)

The amount of time required at a given temperature for a 10-fold (logarithmic) reduction in the viability of a microbial population.

Thermal death time

The time required to kill all cells in a microbial population at a given temperature.

Autoclave

A sealed heating device that uses steam under pressure (typically at 121°C) to achieve sterilization by killing endospores.

Pasteurization

A heat treatment process that significantly reduces the microbial load in heat-sensitive liquids, killing all known pathogenic bacteria but not achieving sterilization.

Ultraviolet (UV) radiation

Radiation (between 220 and 300 nm) absorbed by DNA, causing mutations or damage, useful for decontaminating surfaces but with poor penetration.

Ionizing radiation

Electromagnetic radiation that produces ions and reactive molecules, with penetrating power, used for sterilizing diverse items.

D10 value (radiation)

The energy dose required to reduce the viability of a microbial population 10-fold by radiation.

Filter Sterilization

A method used for heat-sensitive liquids and gases, where pores of a filter trap living organisms but allow liquid or gas to pass through.

Depth filters

Fibrous sheets (e.g., HEPA filters) made of overlapping paper or glass fibers that trap particles.

Membrane filters

High-strength polymers with many tiny pores, commonly used for liquid sterilization.

Nucleopore filters

Thin irradiated films etched to make holes, used for scanning electron microscopy to observe microorganisms directly on the filter.

Antimicrobial agent

A chemical that kills or inhibits microbial growth.

-cidal

A suffix indicating that an agent kills microorganisms (e.g., bactericidal, fungicidal, viricidal).

-static

A suffix indicating that an agent inhibits microbial growth (e.g., bacteriostatic, fungistatic, viristatic).

Bacteriostatic agents

Antimicrobial agents that inhibit important biochemical processes and bind weakly to the cell, reversibly inhibiting growth.

Bactericidal agents

Antimicrobial agents that bind tightly and kill the cell without causing lysis.

Bacteriolytic agents

Antimicrobial agents that kill cells by causing lysis (e.g., detergents).

Minimum inhibitory concentration (MIC)

The smallest amount of an antimicrobial agent needed to inhibit the visible growth of a microorganism.

Disk diffusion assay

A method where an antimicrobial agent diffuses from a filter paper disk into an agar medium, creating a zone of growth inhibition around the disk if the organism is susceptible.

Sterilants

Chemical antimicrobial agents that destroy all microorganisms, including endospores.

Disinfectants

Chemical antimicrobial agents that kill microorganisms but not necessarily endospores, used on inanimate surfaces.

Sanitizers

Less harsh chemical antimicrobial agents that reduce microbial numbers but do not sterilize.

Antiseptics (germicides)

Chemical antimicrobial agents that kill or inhibit microbial growth and are nontoxic enough to be applied to living tissues.

70% alcohol

An effective antiseptic/disinfectant concentration because it evaporates slower than higher concentrations, allowing more contact time and better penetration to coagulate proteins within cells.