Micriobiology Practical

Cocci (Round)

Spherical-shaped cells

Bacilli (Rod)

Cylindrical or rod-shaped cells

Spirilli (Spiral)

Long, flexible or rigid spiral-shaped cells

Vibrios (Comma)

Curved, comma-shaped cells

Coccobacillus

Short, plump rod shape

Diplobacilli

pairs of bacilli

Palisades

V-shape or parallel fence-like stacking rows

Streptobacilli

Long chains of bacilli

Diplococci

pairs of spheres

Staphylococci

Irregular grape-like clusters

Streptococci

Chains of spheres

Sarcina

Cube-like packet of eight cells

Tetrad

Square grouping of four cells

Gram-Positive

Deep purple
Thick peptidoglycan cell wall layer

Gram-Negative

Reddish-pink
Thin peptidoglycan layer surrounded by an outer membran

Selective Media

Inhibits the growth of some organisms while encouraging the growth of others

Differential Media

Contains indicators to expose metabolic differences betweeen organisms

Undefine Media

Contains one or more components with an unknown chemical composition

Defined Media

All chemical components and their exact amounts are known

Components of Media

Nutrients
Inhibitors
Substrates
Indicators

Nutrients

Provide nutrition for optimal growth of bacteria

Inhibitors

Make a medium selective; prevent the growth of unwanted organisms

Substrates

Make a medium differential; rely on chemical reactions and include a substrate only certain organisms can utilize or ferment

Indicators

Make chemical reactions visible (pH-sensitive dyes; reactions must be dramatic because slight color shifts cause false readings)

Punctiform

Circular/Round

Filaments

Irregular

Rhizoid

Spindle

Elevation

Flat
Raised
Convex
Pulvinate
Umbonate

Flat

Raised

Convex

Pulvinate

Umbonate

Margin

Entire
Undulate
Filamentous
Lobate
Erose
Curled

Entire

Undulate

Filamentous

Lobate

Erose

Curled

Mannitol Salt Agar (MSA) (lighter red)

Selective, differential, and undefined media
High salt 7.5%

Yellow (acidic)

pH<6.8

Red (neutral)

6.8<pH<7.4

Pink (basic)

pH>7.8

A

Yellow colonies and agar color change
Mannitol was fermented
Acids are produced that lower pH

B

No growth
Ihibited by high salt concentrations

C

Growth with no color change
Mannitol was not fermented
No pH change

Blood Agar (dark red)

5% sheep’s blood
Different bacteria based on their hemolystic properties

Hemolysis

Beta
Alpha
Gamma

Beta

Complete lysis of red blood cells

Alpha

Partial Lysis of red blood cells

Gamma

No lysis of red blood cells