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.
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
- If bubbles or froth forms, the organism is said to
Staphylococci and microcci are catalase-positive
- If no bubbles form, the organism is catalase-negative.
Streptococci and Enterococci are catalase-negative.
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.
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.
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 enlages the area of hemoysis formed by streptococcal β-hemolysin.
Group A positive
Group B positive
Latex agglutination - Lancefield groups
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.