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Microbiology Lab Techniques Cheat Sheet (DRAFT) by

Lab techniques discussed in BIOL 308

This is a draft cheat sheet. It is a work in progress and is not finished yet.

Microscopy Techniques

Name
Uses
Light Microscopy
Uses visable light to magnify specimens; helps visualize bacteria and their morphology
Bright­-field Microscopy
Common light microscopy technique where bacteria appear dark against a bright backgr­ound; used for stained bacteria
Phase-­con­trast Microscopy
Enhances contrast in unstained samples, useful for observing live bacteria and their internal structures
Dark-field Microscopy
Illumi­nates specimens against a dark backgr­ound; useful for observing thin, live bacteria
Fluore­scence Microscopy
Uses fluore­scent dyes that bind to bacterial compon­ents; allows identi­fic­ation of specific bacteria using labeled antibodies
Differ­ential Interf­erence Contrast (DIC) Microscopy
Enhances contrast and depth perception in unstained samples; useful for observing bacterial structures in detail
Scanning Electron Microscopy (SEM)
Produces 3D images of bacterial surfaces
Transm­ission Electron Microscopy (TEM)
Provides detailed images of internal bacterial structures

Bacterial Quanti­fic­ation Techniques

Name
Uses
Optical Density (Turbidity Measur­ement)
Measures bacterial growth in liquid culture using a spectr­oph­oto­meter
Counting Chamber
A micros­copic grid for estimating bacterial concen­tra­tion; viable cell counting
CFU Dilution Plating (Serial Dilutions)
A method to count bacteria by diluting and plating them; viable cell counting

Antimi­crobial Testing Techniques

Name
Uses
Kirby-­Bauer Assay
Tests bacterial suscep­tib­ility to antibi­otics by measuring zones of inhibition around antibiotic disks
Minimum Inhibitory Concen­tration (MIC)
Determines the lowest antibiotic concen­tration that inhibits bacterial growth
 

Staining Techniques

Name
Uses
Gram Stain
Differ­ent­iates bacteria into Gram-p­ositive (purple) and Gram-n­egative (pink) based on cell wall compos­ition
Simple Stain
Uses a single dye to highlight bacterial shape and arrang­ement
Negative Stain
Stains the backgr­ound, leaving bacteria unstained; useful for visual­izing capsules
Capsule Stain
Specif­ically stains the protective capsule around some bacteria, aiding in virulence identi­fic­ation
Acid-fast Stain
Identifies mycoba­cteria by staining waxy cell walls
Spore Stain
Detects bacterial endosp­ores, which are resistant survival structures

Culture & Media Technqiues

Name
Uses
Culture Media
Provides nutrients for bacterial growth in the lab
Defined Media
Has precisely known chemical compos­itions; used for studying specific bacterial metabolic needs
Complex Media
Contains unknown amounts of nutrients; commonly used for general bacterial growth
Agar
Solid medium for growing bacterial colonies
Broth
Liquid medium for growing bacteria
T-streak
A technique for isolating pure bacterial colonies from a mixed culture
Spread Plates
Used for counting and isolating bacteria by spreading a diluted sample on an agar plate
Mixed Cultures
Contain multiple bacterial species
Pure Isolates
A single bacterial species obtained from a mixed culture

Bacterial Growth & Metabolism

Name
Uses
Microbial Growth Curve
Describes bacterial population changes over time (lag, expone­ntial, statio­nary, decline phases)
Expone­ntial Growth & Generation Time
Determines bacterial replic­ation rate under given conditions

Oxygen Requir­ements & Special Growth Conditions

Name
Uses
Thiogl­ycolate Broth
Used to test bacterial oxygen requir­ements by creating a gradient from aerobic to anaerobic conditions