Microbiology lab quiz #5 Questions With Complete Solutions
Staphylococci - (ANSWER)Gram positive, catalase positive. S epi and S aureus are found in normal flora,
can live on fomites, opportunistic pathogens. Can be acquired nosocomially
S Aureus - (ANSWER)Residents on skin and nasal cavity. Pathogenic due to virulence factors
1) Coagulase: combines with prothrombin causing blood plasma to clot (frbrinogen -> fibrin)
2) Hemolysin/alpha toxin: toxin that causes the complete lysis of RBC's
M-Staphylococcus Medium - (ANSWER)Selective medium. Contains sodium chloride which restricts
growth of many different types of bacteria. Staph can withstand salt concentrations so the medium will
selectively grow them
Streptococci - (ANSWER)Catalase negative, gram positive. Grow well in low O2 high CO2 environments
(anaerobes). Some part of normal flora and some pathogenic
Hemolysis - (ANSWER)alpha: partial (normal flora)
beta: complete (mostly pathogenic)
gamma: none (normal flora)
Carriers - (ANSWER)People that can harbor a pathogen without exhibiting signs of illness and transmit
them to others
Mannitol Salt Agar (MSA) - (ANSWER)Selective medium for Gram+ staph (high salt concentrations inhibit
Gram- bacteria). Medium contains color pH indicator that turns from red to yellow. If bacteria can
ferment mannitol -> produce acids -> turns yellow
-Mainly pathogenic staph
Staphylococcus Medium 110 (SM110) - (ANSWER)Selective medium for Gram+ staph, high salt
concentration. Differential medium, differentiates species of Staph based on pigment production
(different species produce different pigments). S. aureus will produce yellow pigment
Staphylococci - (ANSWER)Gram positive, catalase positive. S epi and S aureus are found in normal flora,
can live on fomites, opportunistic pathogens. Can be acquired nosocomially
S Aureus - (ANSWER)Residents on skin and nasal cavity. Pathogenic due to virulence factors
1) Coagulase: combines with prothrombin causing blood plasma to clot (frbrinogen -> fibrin)
2) Hemolysin/alpha toxin: toxin that causes the complete lysis of RBC's
M-Staphylococcus Medium - (ANSWER)Selective medium. Contains sodium chloride which restricts
growth of many different types of bacteria. Staph can withstand salt concentrations so the medium will
selectively grow them
Streptococci - (ANSWER)Catalase negative, gram positive. Grow well in low O2 high CO2 environments
(anaerobes). Some part of normal flora and some pathogenic
Hemolysis - (ANSWER)alpha: partial (normal flora)
beta: complete (mostly pathogenic)
gamma: none (normal flora)
Carriers - (ANSWER)People that can harbor a pathogen without exhibiting signs of illness and transmit
them to others
Mannitol Salt Agar (MSA) - (ANSWER)Selective medium for Gram+ staph (high salt concentrations inhibit
Gram- bacteria). Medium contains color pH indicator that turns from red to yellow. If bacteria can
ferment mannitol -> produce acids -> turns yellow
-Mainly pathogenic staph
Staphylococcus Medium 110 (SM110) - (ANSWER)Selective medium for Gram+ staph, high salt
concentration. Differential medium, differentiates species of Staph based on pigment production
(different species produce different pigments). S. aureus will produce yellow pigment
