Micro Chapter 4

Major elements in microbial cells

C, O, N, H, P, S make up ~96% of the dry weight of bacterial cells.

Macromolecules in microbial cells

Proteins, lipids, polysaccharides, lipopolysaccharides, and nucleic acids comprise ~96% of a microbial cell's dry weight.

Heterotrophs

Organisms that require organic carbon (C) for growth, obtained from the breakdown of organic polymers or uptake of monomers.

Autotrophs

Organisms that synthesize organic compounds from carbon dioxide (CO2).

Nitrogen sources for microbes

Microbes primarily use proteins, ammonia (NH3), nitrate (NO3−), or nitrogen gas (N2) for nitrogen.

Phosphorus (P) in cells

Essential for nucleic acids and phospholipids, usually sourced from inorganic phosphate (PO43−).

Sulfur (S) in cells

Used to produce sulfur-containing amino acids and vitamins like thiamine and biotin; sourced from sulfate (SO4−2), sulfide (H2S), or organics.

Micronutrients

Trace metals and growth factors required in small amounts, necessary for enzyme function.

Growth media

Nutrient solutions used to grow microbes in the laboratory.

Defined media

Growth media with a known exact chemical composition.

Complex media

Growth media made from digests of microbial, animal, or plant products.

Selective medium

Contains compounds that selectively inhibit growth of some microbes, while allowing others to grow.

Differential medium

Contains an indicator, usually a dye, to detect specific metabolic reactions during growth.

Aseptic technique

Methods used to transfer organisms without contamination.

Viable counts

Measurement of living, reproducing microbial population, often done through spread-plate and pour-plate methods.

Turbidity measurement

Estimation of microbial cell numbers based on the cloudiness of a suspension.

Optical Density (OD)

Measurement used to estimate cell numbers, with a standard curve required to relate OD to actual cell counts.

Binary fission

A form of asexual reproduction in which a cell divides into two identical daughter cells.

Generation time

The time required for a microbial population to double in number.

Lag phase

The interval between inoculation and the beginning of growth where cells adapt to new conditions.

Exponential phase

Phase in which microbial cells double at regular intervals.

Stationary phase

Phase where the growth rate of a microbial population is zero due to limited nutrients or waste accumulation.

Death phase

Phase where total microbial numbers decrease due to cell death.

Planktonic growth

Growth of microbial cells in suspension as free-floating cells.

Biofilm

A structured community of microbial cells attached to a surface and enmeshed in a polysaccharide matrix.

Multiple fission

A division process where multiple septa form simultaneously, found in certain filamentous bacteria.

Acidophiles

Microorganisms that thrive in acidic environments with a pH less than 5.5.

Alkaliphiles

Microorganisms that thrive in highly alkaline environments with a pH of 8 or higher.

Aerobes

Microorganisms that require oxygen for growth and metabolism.

Anaerobes

Microorganisms that cannot use oxygen for growth, and in some cases can be harmed by it.

Antimicrobial agents

Chemicals that kill or inhibit the growth of microorganisms.

Bactericidal

Antimicrobial agents that kill bacteria.

Bacteriostatic

Agents that inhibit bacterial growth without killing the cells.

Minimum inhibitory concentration (MIC)

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

Disk diffusion assay

A method to test the susceptibility of microorganisms to antimicrobial agents using filter paper disks.

Sterilants

Agents that destroy all types of microorganisms, including endospores.

Disinfectants

Chemicals that kill microorganisms but may not destroy endospores, used on surfaces.

Sanitizers

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

Antiseptics

Nontoxic agents that can be applied to living tissues to kill or inhibit microbial growth.

Heat sterilization

The most widely used method of sterilization, effective through increased temperature and exposure time.

Pasteurization

The process of using heat to significantly reduce microbial load in heat-sensitive liquids.

ULTRAVIOLET radiation

Type of radiation useful for decontaminating surfaces but with poor penetration.

Ionizing radiation

Radiation that produces ions and reactive molecules used for sterilizing various items.

Filter sterilization

A method used to sterilize heat-sensitive liquids and gases by passing them through a filter.