Microbial Growth, Control, and Metabolism

Moist heat (like autoclaving) is more effective than dry heat because water molecules conduct heat better and help denature proteins at lower temperatures and shorter times.

Antisepsis refers to the removal or inhibition of pathogens from living tissue, such as skin, using chemical agents.

Autoclaving uses pressurized steam to achieve temperatures above boiling, which effectively kills all microorganisms, including endospores, making it the standard for sterilizing culture media.

The phenol coefficient is calculated by dividing the dilution of the test agent by the dilution of phenol. Here, 500 / 250 = 2.

Aldehydes, such as glutaraldehyde and formaldehyde, act as disinfectants by cross-linking proteins and nucleic acids, which inactivates them.

Disinfection is the process of reducing or eliminating pathogenic microorganisms on inanimate objects or surfaces.

Refrigeration slows down bacterial metabolism and growth without necessarily killing the bacteria, which is defined as bacteriostatic.

The primary elements that make up the biomass of microorganisms (and all living things) are Carbon, Hydrogen, Oxygen, and Nitrogen.

Alkalinophiles are organisms that thrive in high pH environments, typically at a pH of 9 or higher.

Hyperthermophiles are organisms that grow at extremely high temperatures, typically above 80 degrees Celsius, such as in boiling water.

Mesophiles are organisms that grow best at moderate temperatures, typically between 20 and 45 degrees Celsius, which includes the human body temperature.

A chemostat is a bioreactor to which fresh medium is continuously added, while culture liquid containing leftover nutrients, metabolic end products, and microorganisms are continuously removed to keep the culture in a specific growth phase.

Generation time is the time it takes for a population of bacteria to double in number.

Most unicellular organisms, specifically prokaryotes, reproduce asexually through binary fission.

Lyophilization, commonly known as freeze-drying, removes water from biological samples by sublimation under a vacuum, allowing cultures to be preserved stably for years without losing viability.

Catalase is the enzyme that breaks down hydrogen peroxide into water and oxygen, protecting the cell from oxidative damage.

A stab culture is used to test for motility or oxygen requirements. Anaerobes are often cultured in deep agar stabs to minimize exposure to atmospheric oxygen.

Complex media (or undefined media) contain ingredients like yeast extract, peptone, or beef extract where the exact chemical composition is not known. Defined media, by contrast, have a precise, known chemical formula.

Both streak-plate and pour-plate methods are standard techniques for isolating pure cultures. They require agar as a solidifying agent, serial dilutions to reduce cell density, and an initial inoculum of the sample.

A biofilm is a structured community of microbial cells attached to a surface and encased in a self-produced matrix. Dental plaque is a classic example of a biofilm formed on teeth.

Quorum sensing is the mechanism by which bacteria monitor their population density through the secretion and detection of chemical signaling molecules. Once a threshold concentration is reached, the bacteria coordinate group behaviors like biofilm formation.

Obligate halophiles are organisms that require high concentrations of salt (high osmotic pressure) to survive and grow. They would lyse in a hypotonic environment.

Nitrogen is a critical component of proteins and nucleic acids. Because it is often required in large amounts but is not always readily available in a usable form, it frequently acts as a limiting nutrient for microbial growth.

Obligate anaerobes cannot tolerate oxygen because they lack the enzymes necessary to neutralize toxic oxygen byproducts. Therefore, they require an environment with no oxygen.

Chemoheterotrophs derive both their energy and their carbon from organic compounds. Photoautotrophs use light and CO2, while chemoautotrophs use inorganic chemicals and CO2.

While nitrogen is essential for life, it is not strictly required for basic metabolism in the same way that energy, carbon, and electron sources are. Some organisms can fix nitrogen, but the core metabolic processes rely on the other three.

Lithotrophs (or chemolithotrophs) are organisms that use inorganic molecules as their electron donors. Organotrophs, by contrast, use organic molecules.

Photoautotrophs use light as an energy source and carbon dioxide as their sole or principal carbon source. They fix inorganic carbon into organic molecules.

A nutrient is defined as any chemical substance that an organism must acquire from its environment to sustain life and support growth. This includes elements, ions, and complex molecules.

In microbiology, growth refers to the increase in the number of cells in a population, rather than the increase in size of an individual cell. This is typically measured by colony counts or optical density.

A biofilm is a complex community of microorganisms attached to a surface and embedded in a self-produced extracellular matrix. This structure protects the microbes from environmental stressors.