Microbiology Test 1, Ndaluka, Georgia Southern

Magnification

ability to enlarge objects

resolving power

ability to show detail

what does magnification result from?

an interaction between visible light waves and the curvature of a lens

what does the objective lens form?

magnified real image

when the real image is projected to the ocular, what does it form?

virtual image

what makes up total magnification?

objective power x ocular power

what provides a better resolution?

shorter wavelength and larger numerical aperture

bright field microscopy

most widely used; specimen is darker than surrounding field; used for live and preserved stained specimens

fluorescence microscopy

ultraviolet radiation source and filter, uses dyes that emit visible light when bombarded with shorter UV rays, useful in diagnosing infections

electron microscopy

uses electrons instead of light, the shorter wavelength of electrons gives greater resolution, doesn't show natural color

Transmission Electron Microscope (TEM)

transmits electrons through the specimen, dark= thick and dense, light= transparent, less dense

Scanning Electron Microscope (SEM)

provides detailed 3D view

Wet mounts

allow examination of characteristics of live cells: size, motility, shape, and arrangement

Fixed mounts

made by drying and heating a film of specimen. This smear is stained using dyes to permit visualization of cells or cell parts.

staining

dyes are used to create contrast by imparting color

Basic dyes

cationic, positively charged chromophore

Positive staining

surfaces of microbes are negatively charged and attract basic dyes

Acidic dyes

anionic, negatively charged chromophore

Negative staining

microbe repels dye, the dye stains the background

Simple stains

one dye is used; reveals shape, size, and arrangement

Differential stains

uses a primary stain and a counterstain to distinguish cell types or parts

structural stains

reveal certain cell parts not revealed by conventional methods: capsule and flagellar stains

What are the 6 I's of culturing microbes?

inoculation, isolation, incubation, inspection, information gathering, identification

Specimen Collection of Microorganisms

microbiologists sample the object of their interest

Inoculation of Microorganisms

the sample is placed into a container or medium that will support its growth

Incubation of Microorganisms

inoculated media are placed in a controlled environment to promote growth

Isolation of Microorganisms

separate microbes to create isolated colonies that each contain a single type of microbe

Inspection of Microorganisms

cultures are observes for the macroscopic appearance of growth characteristics

Information Gathering of Microorganisms

additional tests for microbial function and characteristics may include inoculations into specialized media that determine biochemical traits, immunological testing, and genetic typing

Identification of Microorganisms

one goal of these procedures is to attach a name or identity to the microbe, using info gathered from the inspection and investigation

Isolation techniques

streak plate, pour plate, spread plate

Streak plate technique

a loop is used to streak the mixed sample many times over the surface of a solid culture medium in a petri plate

Pour plate technique

a small amount of diluted sample is mixed with melted agar and poured into empty, sterile Petri dishes

Spread plate technique

a small amount of a previously diluted specimen is spread over the surface of a solid medium using a spreading rod

what are the 3 ways media can be classified according to three properties?

physical state, chemical composition, and functional type

physical states of media

liquid (broth), semisolid (contains a solidifying agent), solid (firm surface for colony formation)

Agar

The most commonly used solidifying agent, Solid at room temperature, liquefies at boiling (100oC), does not re-solidify until it cools to 42oC, Provides framework to hold moisture and nutrients, Not digestible for most microbes

most commonly used media

nutrient broth and nutrient agar

chemical content of media

synthetic (contains pure organic and inorganic compounds), complex/nonsynthetic (contains at least one ingredient that is not chemically definable, general purpose media (grows a broad range of microbes), enriched media (contains complex organic substances)

selective media

contains one or more agents that inhibit growth of some microbe and encourage growth of the desired microbes

Carbohydrate fermentation media

contains sugars that can be fermented, converted to acids, and a pH indicator to show this reaction

what are the basic shapes of cells?

spherical, cubical, cylindrical

internal content of cells

cytoplasm, surrounded by a membrane

external structures of cells

appendages (fimbriae, pili, flagella, and axial filaments, and glycocalyx (surface coating)

what is fimbriae?

Fine, proteinaceous, hairlike bristles emerging from the cell surface, VELCRO

what makes up flagella?

filament (long, thin, helical structure), hook (curved sheath), and basal body (rings anchored in the cell wall)

what is pili

rigid tubular structure made of pilin protein, found only in gram-negative cells

Glycocalyx

coating of molecules external to the cell wall, made of sugars and/or proteins

what are the two types of glycocalyx?

slime layer (loosely organized and attached), capsule (highly organized and tightly attached)

what is the cell envelope?

external covering outside the cytoplasm, cell wall and cell membrane

gram positive bacteria

thick cell wall composed primarily of peptidoglycan and cell membrane

gram negative bacteria

outer cell membrane, thin peptidoglycan layer, and cell membrane

gram positive stain

retain crystal violet and stain purple

negative gram stain

loose crystal violet and stain red