Staphylococci (ex. 52)
differentiation of 3 species of staphylococci
(note- focus on S. aureus and S. epidermis; toxin, Mannitol, coagulase, and DNase
DNase test
nuclease that digests DNA
Coagulase test
•Definitive test for confirming presence of S. aureus (97% coagulase positive) •Forms a clot •Place 0.3 ml of rabbit plasma on a clean microscope slide. Then mix with a colony of S. aureus. Observe during class period.
Mannitol Salt Agar (MSA)
•Selective medium for Staphylococcus growth •Contains the sugar mannitol, 7.5% salt (NaCl), and the pH indicator phenol red (acid turns yellow) •Differential medium for mannitol fermenters
Staphylococcus medium 110 (SM110)
Also contains mannitol and 7.5% NaCl, but lacks phenol red Favors colony pigmentation by different strains of S. aureus
coagulase test
definitive test for confirming S. aureus (97% coagulase positive) forms a clot place .3 mL of rabbit plasma in a clean test tube. then mix with a colony of S. aureus - turns gel like
Staphylococcus aureus growing on blood agar
α toxin (causes beta-hemolysis on blood agar) lyses red blood cells, etc.
Staphylococcus aureus Staphylococcus epidermidis
Procedure: Inoculated Mannitol Salt Agar, SM110 Agar, and Blood Agar plate with the two known organisms, dividing the plate in half. Also incubate in the room temperature bin.
The Staphylococci
Staphylococcus is derived from the Greek, meaning "bunch of grapes." Grouped with other Gram-positive cocci including Micrococcus, Enterococcus, and Streptococcus Consist of 40 different species with 24 subspecies Non-motile non-spore forming can grow in media with high-salt concentration Most are facultative anaerobes.
Staphylococcus aureus
The most clinically significant staphylococcal pathogen Has developed resistance to many antibiotics MRSA: Methicillin resistant Causes skin infections, wound infections, bone tissue infections, toxic shock syndrome, and food poisoning Ferments mannitol to produce acid Grow culture on Mannitol salt agar (MSA)
Staphylococcus aureus Virulence factors:
•Coagulase production: cause serum to form a clot (clot forms around staphyloccocal infections and protects bacterium from host defenses) •Dnase: nuclease that digests DNA •Produces a hemolysin: α toxin (causes beta-hemolysis on blood agar) lyses red blood cells, etc. •Produce a pigment: staphylxanthin-golden color antioxidant properties which prevent reactive oxygen produced by the host immune system from killing bacteria
