lab 7 - Blood Bile and Starch Agar

hemolysis

break down of RBCs

hemolysin

pore-forming toxins which are able to cause lysis of erythrocytes (RBCs)

strep and staph

both make exotoxins called hemolysins that can break down RBCs

beta hemolysis

complete breakdown of RBCs; generally considered more pathogenic

• ex.) Streptococcus pyogenes

alpha hemolysis

partial break down of RBCs

• ex.) Streptococcus pneumoniae and Streptococcus sanguis

gamma hemolysis

no break down of RBCs

• ex.) Enterococcus faecalis

streptococcus pyogenes

• beta-hemolytic

• resists phagocytosis and produces powerful streptolysins

• member of Group A streptococci

• often called Group A Beta-hemalytic Strep (GABHS)

• major cause of bacterial pharyngitis (Strep throat)

• Responds well to Penicillin or derivatives

• untreated infections can lead to Scarlet fever and Rheumatic fever (life threatening)

streptococcus sanguis

• alpha-hemolytic

• aka viridans (green) strep

• normal flora of the mouth

• can enter the bloodstream during dental procedures and causes infective endocarditis

  • prescribed loading dose of antibiotics to prevent

enterococcus faecalis

• gamma-hemolytic

• normal flora of GI tract

• very antibiotic resistant

• major cause of HAI

• can cause UTIs and bacteremia

• this is VRE (vancomycin resistant enterococci)

alcaligenes faecalis

• gram negative, short rod shaped bacteria

• obligate aerobe

• catalase positive

• oxidase positive

• alpha hemolytic

• lactose fermentation: -/-

• common bacteria in environment, in water and soil and environments in association with humans

• opportunistic pathogen that can cause pneumonia, septicemia, peritonitis, UTIs, and other infections

bile esculin agar (BEA)

both selective and differential agar

• helps identify Enterococci from other members of Streptococci based on the ability to hydrolyze esculin in the presence of bile

• differential ingredient: esculin (if the bacteria can produce an enzyme to hydrolyze esculin in an acidic medium the product will react with iron in the medium and turn brown/black)

• selective ingredient: bile/oxgall (acidic and inhibits the growth of most other gram(+) bacteria, but not Enterococcus)

amylase

an enzyme made by many organisms that causes the bonds of starch to break up into short chains of maltose and other disaccharides

bacillus subtilis

• gram positive, rod shaped bacteria

• facultative anaerobe

• catalase positive

• oxidase positive

• most strains are gamma hemolytic, but certain strains can be beta hemolytic

• lactose fermentation: -/-

• common bacteria in the environment (soil and water), can also be found in GI tract of mammals

• generally non-pathogenic, but can cause opportunistic infections in immunocompromised individuals

starch agar reactions

• iodine reacts strongly with the bonds in starch to create a dark purple or black color

• if a bacteria can secrete extracellular amylase, it will digest the starch around it and no reaction will occur (clear zone)

• can be used to differentiate species of Clostridium, Enterococcus, and Bacillus