Coccobacilli:
A coccobacillus (plural coccobacilli) refers to an intermediate shape
between coccus (spherical) and bacillus (elongated). Coccobacilli rods
are short and wide and may resemble cocci on a Gram Stain.
Gram stain:
The Gram stain, is a laboratory staining technique that distinguishes
between two groups of bacteria that have differences in the structure of
their cell walls. Standard bacterial taxonomy makes a distinction
between Gram-negative bacteria, which stain red/pink and the
Gram-positive bacteria, which stain blue/purple. Different antimicrobial
agents are directed specifically at gram-positive bacteria and
gram-negative bacteria.
MacConkey: MacConkey agar is a selective medium that
inhibits the growth of Gram-positive bacteria due to the presence of crystal violet and bile salts. Most
Gram-negative bacteria grow well on MacConkey. MacConkey agar also contains neutral red (a pH indicator)
and lactose (a disaccharide). Lactose fermenting bacteria or lactose + bacteria on MacConkey will appear as
bright pink colonies. Non-lactose fermenting bacteria will be colorless (or, if they have any color, will be
their natural color rather than pink).
BAP or SBA:
An abbreviation for blood agar plate or sheep bloog agar. Blood agar contains mammalian blood (usually sheep, rabbit or hrose), typically at a concentration
of 5-10%. Blood agar is an enriched media used to isolate bacteria and to detect hemolytic activity.
Colonies resemble
Enterobacteriaceae on
BAP
but are blue-purple on
MacConkey.
BAP or SBA: An abbreviation for blood agar plate or sheep blood agar. Blood agar contains mammalian blood (usually sheep, rabbit or horse), typically at a concentration
of 5-10%. Blood agar is an enriched media used to isolate bacteria and to detect hemolytic activity.
- Smooth round colonies on
BAP
- Non-lactose fermenters (purple) on
MacConkey
MacConkey: MacConkey agar is a selective medium that
inhibits the growth of Gram-positive bacteria due to the presence of crystal violet and bile salts. Most
Gram-negative bacteria grow well on MacConkey. MacConkey agar also contains neutral red (a pH indicator)
and lactose (a disaccharide). Lactose fermenting bacteria or lactose + bacteria on MacConkey will appear as
bright pink colonies. Non-lactose fermenting bacteria will be colorless (or, if they have any color, will be
their natural color rather than pink).
- Non-hemolytic
Non-hemolytic (γ-hemolysis): If an organism
does not induce any hemolysis on a blood agar plate, it is said to
display gamma or no hemolysis. The agar under and around the colony is
unchanged.
- Fish-like smell
-
Oxidase negative
-
Indole negative
Oxidase: The oxidase test is used to determine
if a bacterium produces certain cytochrome c oxidases. The reagent,
tetramethyl-p-phenylenediamine is used as a redox indicator. The
reagent turns dark blue when oxidized (oxidase positive). The reagent is
colorless when reduced (oxidase-negative). Pseudomonas species
and Aeromonas species are gram-negative bacilli that are oxidase-positive.
Neisseria species are gram-negative cocci that are oxidase
positive.
Indole test: The indole test is a
biochemical test performed on bacterial species to determine the ability
of the organism to split indole form the amino acid tryptophan. The
results of an indole test are indicated by a change in color following a
reaction after the addition of Kovacs reagent. A positive result is
shown by the presence of a red color. A negative result appears yellow.
The Indole test is a key test for separating Proteus mirabilis
(indole-negative) and Proteus vulgaris (indole-positive) and
Klebsiella pneumoniae (indole negative) and K. pneumoniae oxytoca
(indole-positive).
