Chapter 1; PT.2

blue or purple

color of gram-positive bacteria

red or pink

color of gram-negative bacteria

Neisseria, Veilonella, Branhamella

all cocci are gram-positive except

Corynebacterium, Clostridium, Bacillus, Mycobacterium

all bacilli are gram-negative except

Crystal violet

primary stain in gram staining

Gram’s iodine

Mordant

Acetone or 95% alcohol

Decolorizer

Safranin

Counterstain or Secondary stain

Acid-fast stain

stain used for bacteria with high lipid content in their cell wall

Ziehl-Neelsen stain

Kinyoun stain

2 methods used in Acid-fast stain

Ziehl-Neelsen stain

“hot method” requires steam-bathing the prepared smear after addition of the primary dye. primary stain used is aqueous and will not bind to the cell wall of the organism.

appear red on a blue background

Kinyoun stain

“cold method”. oil-based. acid fast organisms will appear red on a green background.

Carbol fuchsin

primary stain in acid-fast staining

Methylene blue

counterstain or secondary stain of Ziehl-Neelsen

Malachite green

counterstain or secondary stain of Kinyoun

Special stains

used to demonstrate specific structures in a bacterial cell

Media

used to grow microorganisms

culture medium

an aqueous solution to which all the necessary nutrients essential for the growth of organisms added.

Physical state

Chemical composition

Functional type

Culture media are classified into 3 primary levels

Liquid Media

suited for the propagation of a large number of organisms, fermentation studies, and other tests

Semi-solid media

best suited for culture of microaerophilic bacteria or for the study of bacterial motility

Solid media

contain a solidifying agent such as 1.5%-2% agar, giving them a firm surface on which cells can form discrete colonies

used for isolation of bacteria and fungi or determining the colony characteristics of the organism under study

liquefiable (or reversible)

non-liquefiable (or non-reversible)

solid media come in 2 forms

Liquid media

Semi-solid media

Solid Media

According to Physical State

Synthetic media

Non-synthetic media

According to Chemical Composition

Synthetic media

contain chemically defined substances which are pure organic or inorganic compounds

may be simple or complex depending on what supplement is added to it

Non-synthetic media

complex media that contain at least one ingredient that is not chemically defined, neither a simple or pure compound

most are extracts of animals, plants, or yeasts.

can support the growth of more fastidious organisms

General purpose media

Enrichment media

Selective media

Differential media

Transport media

Anaerobic Media

According to Functional Type

General Purpose media

are designed for primary isolation of a broad spectrum of microbes and contain a mixture of nutrients that support the growth of both pathogenic and non-pathogenic organisms. Examples are peptone water, nutrient broth, and nutrient agar

Enrichment media

contain complex organic substances such as blood, serum, or special growth factors, and are designed to increase the number of desired microorganisms without stimulating the rest of the bacterial population. These are used to grow fastidious or nutritionally exacting bacteria.

Blood agar

Chocolate agar

2 commonly used enrichment media

Blood agar

contains general nutrients with 5%-10% (by volume)

Beta hemolysis

shows complete lysis of red blood cells resulting in complete clearing around the colonies

Alpha hemolysis

shows incomplete lysis of red blood cells, producing a greenish discoloration of the blood agar round the colonies

Gamma hemolysis

shows no hemolysis, resulting in no change in the medium

Chocolate agar

a type of nutrient medium that is used for the culture organisms such as Haemophilus sp. the medium to turn brown. of fastidious Heat is applied to lyse the red blood cells, causing the medium to turn brown.

Selective media

• designed to prevent the growth of unwanted contaminating bacteria.

  • contain one or more substances that encourage the growth of only a specific target microorganisms

Differential media

allow the growth of several types of microorganism

designed to show visible differences among certain groups of microorganisms

Transport media

used for clinical specimens that need to be transported to the laboratory immediately after collection

prevent the drying of specimen and inhibit the overgrowth of commensals and contaminating organisms

Anaerobic media

media used specifically for organisms that cannot survive in the presence of oxygen and require reduced oxidation-reduction potential and other nutrients.

LAMB

Loeffler Alakaline Methylene Blue

Hiss Stain

capsule of slime layer

Dyer stain

cell wall

Fischer-Conn Stain

flagella

Dorner-Fulton stain

spores

India ink or nigrosine

capsule of the fungus Cryptococcus neoformans

Examples of Selective media

Thayer-Martin agar

Mannitol Salt agar

MaConkey’s agar

Lowenstein-Jensen medium

Saboraud’s dextrose agar

Thayer-Martin agar

- contains antibiotics

- used to isolate Neisseria

Mannitol Salt agar

- contains 10% NaCl

- used for the isolation of Staphylococcus aureus

MaConkey’s agar

promotes growth of gram (-) bacteria primarily belonging to Enterobacteriaceae inhibits growth of gram (+) through addition of bile salts

both Selective and differential

Lowenstein-Jensen medium

used to recover Mycobacterium tuberculosis Selective by the incorporation of malachite green

Saboraud’s dextrose agar

- for the isolation of fungi