Microbiology Flashcard Study Guide: Physical Control of Microbes and Tools of the Laboratory

Vocabulary study cards covering physical methods of microbial control, the 5 I's of culturing, media types, and light microscopy magnification.

Resistance Ranking of Microbes

Ordered from MOST to LEAST resistant: Prions > bacterial endospores > Mycobacterium > Staphylococcus/Pseudomonas > protozoan cysts > protozoan trophozoites > most Gram-negative bacteria > fungi/fungal spores > nonenveloped viruses > most Gram-positive bacteria > enveloped viruses.

Sterilization

Removal or destruction of ALL microbial life, including endospores and viruses. Used mostly for inanimate objects.

Disinfection

Removal or destruction of most vegetative microbes on INANIMATE surfaces. Does NOT reliably destroy endospores.

Antisepsis (degermation)

Inhibition or destruction of microbes on LIVING tissue using an antiseptic agent.

Decontamination (sanitization)

Mechanical removal of microbes from animate or inanimate objects to lower microbial load, spoilage, and infection risk.

-cidal

Suffix meaning KILL (e.g., bactericidal, virucidal, fungicidal). Sporicides may function as sterilants.

-static / -stasis

Suffix meaning STOP/steady. Growth is inhibited rather than killed, and growth can resume after the agent is removed.

Log (exponential) phase

The bacterial growth phase in which cells are actively growing and are most susceptible to microbicidal agents.

Cellular Targets of Antimicrobial Control

The 4 major targets in microbial cells: cell wall, cell membrane, nucleic acid synthesis/DNA, and proteins.

Moist Heat Control Mechanism

Physical method of control that functions by denaturing and coagulating proteins.

Boiling / Steam

At about $100^\text{o}\text{C}$ at sea level, it kills vegetative cells, some viruses, fungi, and spores within ~$10\text{ min}$, but is not a reliable sterilization method because it does not destroy all viruses or endospores.

Autoclave

Device using steam under pressure (standard conditions: $121^\text{o}\text{C}$ for $15\text{ minutes}$). It is the preferred heat method of sterilization because pressure allows temperatures above $100^\text{o}\text{C}$.

Pasteurization

Mild heating that kills spoilage microbes and pathogens without seriously damaging the product; used for milk, wine, beer, and yogurt.

HTST Pasteurization

High-temperature, short-time pasteurization performed at $72^\text{o}\text{C}$ for $15\text{ seconds}$.

UHT Treatment

Ultra-high temperature sterilization performed at about $134^\text{o}\text{C}$ for $1\text{--}2\text{ seconds}$, followed by vacuum cooling.

Dry Heat Control Mechanism

Physical method of control that dehydrates cells and denatures proteins (e.g., direct flaming, incineration, and hot-air oven sterilization at $170^\text{o}\text{C}$ for $2\text{ hours}$).

Filtration

Method where liquid or gas is forced through pores to trap microbes larger than the pore size (e.g., ~$0.22\text{ }\frac{1}{1000000}\text{m}$ or 0.22\text{ }\text{μm} for bacteria and 0.01\text{ }\text{μm} for viruses); ideal for heat-sensitive liquids like antibiotics.

HEPA Filter

High-efficiency particulate air filter used to remove particles and microbes from air.

Desiccation

Removal or loss of water that inhibits growth (bacteriostatic) and preserves materials, though many microbes survive and resume growth when water returns.

Plasmolysis

Loss of water from a microbial cell in a hypertonic environment, causing the cytoplasm and cell membrane to shrink away from the cell wall.

Ionizing Radiation

High-energy radiation with short wavelengths (gamma rays, X-rays, electron beams) that causes ionization, generating free radicals that damage molecules like DNA.

Non-ionizing (UV) Radiation

Lower-energy, longer-wavelength radiation with low penetration (useful for surface treatment) that is absorbed by DNA and forms thymine dimers.

Thymine Dimers

UV-induced abnormal bonds between adjacent thymine bases in DNA that interfere with normal DNA function and replication.

The Five I's of Culturing Microbes

The five basic techniques used to manipulate, grow, and study microorganisms in the laboratory: Inoculation, Incubation, Isolation, Inspection, and Identification.

Inoculation

Introduction of a sample/inoculum into a container of nutrient medium to begin growth.

Incubation

A period of controlled conditions (such as temperature, pH, and oxygen) that allows cells to grow.

Isolation

Separating one microbial species from another so individual cells can reproduce into separate colonies and pure cultures (e.g., using the streak-plate technique).

Inspection

Observation of microbial growth; colonies are viewed macroscopically and cells are viewed microscopically.

Identification

Determining an organism's identity, typically to the level of species and sometimes strain.

Bacterial Colony

A visible macroscopic pile or mass of many cells that are descendants of the same ancestral cell and genetically identical.

Pure Culture vs. Mixed Culture

A pure culture contains only one kind/species of organism; a mixed culture contains multiple kinds/species of microbes.

Aseptic Technique

Sterile technique used to prevent unwanted contamination of media, tools, cultures, or specimens.

Chemically Defined Media

Media in which the exact chemical composition and concentrations of all ingredients are fully known and consistent.

Complex (Chemically Undefined) Media

Media containing materials such as yeast, meat, or plant extracts or peptones, where the exact molecular composition is not fully known.

Peptones

Sources of amino acids and short protein breakdown products used as nutrients in complex media.

General-purpose Media

Media designed to grow a wide variety of non-fastidious microbes without intentionally selecting a specific group.

Enrichment Media

Media that supports fastidious microbes by supplying specific nutrients or growth factors they cannot synthesize themselves (e.g., blood agar).

Selective Media

Media formulated with ingredients or conditions that allow certain microbes to grow while inhibiting others.

Differential Media

Media that tests for a specific biochemical trait and distinguishes positive vs. negative organisms, often through a visible color change.

Mannitol Salt Agar (MSA)

A medium that is both selective (high salt selects for salt-tolerant organisms) and differential (distinguishes organisms based on mannitol fermentation traits).

Sabouraud's Agar

A selective medium formulated at a pH of $5.6$ to select for the growth of fungi.

Compound Light Microscope Magnifications

Calculated as Ocular ($10\times$) multiplied by Objective ($4\times$ scanning, $10\times$ low power, $40\times$ high power, $100\times$ oil immersion), producing total magnifications of $40\times$, $100\times$, $400\times$, and $1000\times$.