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.


Bile Solubility: The bile solubility test is a qualitative procedure for determining the ability of bacterial cells to lyse in the presence of bile salts (sodium desoxycholate) under specific conditions of time and temperature. The test is primarily used to differentiate bile soluble Streptococcus pneumoniae from bile insoluble alpha-hemolytic streptococci.


Butyrate: Butyrate is a rapid test for the detection of the enzyme butyrate esterase in bacteria isolated on culture media. It is used for the presumptive identification of Moraxella (Branhamella) catarrhalis.


CAMP: This is a test performed on sheep blood agar to identify Group B β-streptococci based on their formation of a substance (CAMP factor) that enlarges the area of hemoysis formed by streptococcal β-hemolysin.


Campy agar: Campylobacter CVA Agar is a selective medium used in the primary isolation and cultivation of Campylobacter jejuni from human fecal specimens. This selective medium contains cefoperazone, vancomycin and amphotericin B; this combination of antimicrobial agents inhibits the normal fecal flora for easier detection of C. jejuni.


Catalase test: The catalase test is used to differentiate some bacterial species. The test is done by placing a drop of hydrogen peroxide on a microscope slide. Using an applicator stick, a small portion of a colony is then added to a drop of hydrogen peroxide drop.


Coagulase: Coagulase is an enzyme produced by Staphylococcus aureus that converts fibrinogen to fibrin. In the laboratory, it is used to distinguish between different types of Staphylococci isolates. Coagulase negativity excludes S. aureus. S. aureus is coagulase-positive.


Slide coagulase test: The slide Coagulase test detects bound coagulase (clumping factor). This type of coagulase is attached to the bacterial cell walls (surface). This test is usually performed on a glass slide.


Tube Coagulase test: The coagulase test is used to differentiate Staphylococcus aureus from coagulase-negative staphylococci. The test uses rabbit plasma that has been inoculated with a staphylococcal colony. The tube is then incubated at 37 degrees Celsius for 1-1/2 hours. If negative, then incubation is continual up to 24 hours. This test detects free coagulase (coagulase that is released by bacterial cells into culture).

·         Positive (i.e., the suspect colony is S. aureus). The serum will coagulate, resulting in a clot (sometimes the clot is so pronounced that the liquid will completely solidify).

·         Negative, the plasma remains liquid. A negative result may be S. epidermidis.


Choc: Chocolate agar is a non-selective, enriched growth medium. It is a variant of the blood agar plate. It contains red blood cells, which have been lysed by heating. Chocolate agar is used for growing fastidious (hard to grow) bacteria.


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.


Dimorphic fungi:  These  fungi can exist in 2 forms: a mold or filamentous form at room temperature or as a yeast at body temperature.  Dimorphic fungi include Coccidioides immitis, Histoplasma capsulatum, Blastomyces dermatitidis, Sporothrix schenckii, Penicillium.


GC: GC is an abbreviation for gonococcus (Neisseria gonorrheoae).


Germ tube:  Candida albicans can exist as both yeast and mycelial (hyphal) forms.  When yeast cells are incubated with serum at 37 degrees C , tube-like appendages (germ tubes) grow from the cell; these are the beginning hyphal forms as the C albicans converts from yeast to mycelia. (photo from Faculty of Biosciences, Leeds, UK)

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.




Alpha hemolysis (α-hemolysis): Alpha hemolysis is the incomplete lysis of the red blood cells around and under the colonies on a blood agar plate. This area appears dark and greenish. Streptococcus pneumoniae and a group of streptococci (Streptococcus viridans or viridans streptococci) found in oral flora display alpha hemolysis.


Beta hemolysis (β-hemolysis): Beta hemolysis is the complete lysis of the red blood cells around and under the colonies on a blood agar plate. This area appears transparent. Streptococcus pyogenes displays beta hemolysis and is often called Group A beta-hemolytic strep (GABHS).


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.


Hektoen enteric agar: Hektoen agar is a selective and differential agar primarily used to recover Salmonella and Shigella from patient specimens. Hektoen contains indicators of lactose fermentation and H2S production; as well as inhibitors to prevent the growth of gram positive bacteria.


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).


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).


Mucoid: Bacterial colonies that appear moist and sticky (resembling mucus).


Mueller-Hinton: This is a culture medium that is commonly used for antibiotic susceptibility testing.


Non-mucoid: Bacterial colonies that are dry and flat looking.


Latex agglutination - Lancefield groups: Most pathogenic streptococci possess specific carbohydrate antigens, which permit classification into groups (Lancefield’s streptococcal groups A, B, C, D, F and G).  The streptococcal latex agglutination test contains latex particles that have been sensitized with group specific antibody and will agglutinate in the presence of homologous antigen.  In the absence of the particular antigen, the latex particles will remain in a smooth suspension.  


Optochin: Sensitivity to optochin (ethylhydrocupreine hydrochloride) is a well established phenomenon for Streptococcus pneumoniae. A positive presumptive identification of S. pneumoniae is made when a well defined zone of inhibition results around a disk impregnated with optochin. Other alpha-hemolytic streptococci do not display this zone of inhibition when in the presence of optochin.


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.


PYR test: the PYR test is a qualitative procedure for determining the ability of streptococci to enzymatically hydrolyze L-pyrrolidonyl- β-napthylamide (PYR). A positive PYR tests allows for the presumptive identification of group A streptococci (Streptococcus pyogenes) and group D Enterococci.


TCBS: TCBS (thiosulfate citrate bile salts sucrose) enriched agar enhances growth of Vibrio cholerae.


TM: Tm is an abbreviation for Thayer Martin agar. Thayer Martin agar is used for the isolation of Neisseria species, including Neisseria gonorrhoeae and Neisseria meningitides; this medium inhibits the growth of most other microorganisms.


Urease: Urease is an enzyme that catalyzes the hydrolysis of urea into carbon dioxide and ammonia. Urease is found in certain bacteria and yeast. Cryptococcus is urease-positive and Candida is urease-negative.


X and V factor disks: Species of Haemophilus require either or both of the two factors for growth and can be used to differentiate the species. The X factor is haemin and the V factor is nicotinamide adenine dinucleotide (NAD). The factors are incorporated into filter paper disks which are placed on a blood free medium previously inoculated with the organism under test. After incubation, the presence or absence of growth around the disks indicates a requirement for that particular factor.