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What is Staphylococcus?
gram positive cocci (in clumps like grapes)
all members are highly resistant to drying, extremes in pH, and high temperatures
increase in community acquired cases, with infections associated with schools, prisons, and shared athletic equipment
S. epidermis
common cause of hospital-acquired infections in immunocompromised patients
S. saprophyticus
an occasional cause of UTIs
S. aureus
common cause of hospital-acquired skin infections
normal flora of humans: nasal membranes & skin
opportunistic infections
Latex Agglutination Test
rapid identification for S. aureus
Protein A is a virulence factor found on the cell wall of only S. aureus
antibodies in the test solution bind antigens on Protein A, resulting in a positive result of clumping
Latex Agglutination Test Results
positive = S. aureus
clumping occurs because the antibodies in the test solution bind with the antigens found on Protein A which is located on the cell wall of only S. aureus
negative = not S. aureus
no clumping occurs due to the absence of Protein A
Catalase Test
key test in differentiating Gram (+) cocci
substrate is hydrogen peroxide
distinguishes Staph from Strep
Catalase Test Results
positive = Staph
bubbling will occur due to the presence of catalase
the catalase reacts with the hydrogen peroxide, resulting in oxygen to be released as seen by the bubbling
negative = Strep
no bubbling occurs due to the absence of catalase and thus no release of oxygen
Mannitol Salt Agar
Selective & differential media for Staphylococcus
contains 7.5% salt to inhibit the growth of most bacteria
contains phenol-red dye to detect mannitol fermentation
highly selective for S. aureus and some strains of S. saprophyticus
Mannitol Salt Agar Test Results
positive = S. aureus or S. saprophyticus
a color change from red to yellow indicates the fermentation of mannitol, which S. aureus and some strains of S. saprophyticus are able to do
negative = S. epidermis
no color change indicates the inability to ferment mannitol
Blood Agar Plates
Tests for hemolysis ability
contains Tripticase Soy Agar (TSA) and 5% sheeps blood
beta, alpha, and gamma
Blood Agar Plates Results
beta = S. aureus
indicates complete breakdown of red blood cells
if the plate is held up to a light, you will be able to see through it
partial = none
indicates partial breakdown of red blood cells
seen by a green tint around the growth
gamma = S. saprophyticus & S. epidermis
indicates no breakdown of red blood cells
if the plate is held up to a light, you will not be able to see through it
Novobiocin Susceptibility
Distinguishes coagulase-negative Staph species
does not apply to S. aureus
Novobiocin Susceptibility Test Results
positive for coag-negative = S. epidermis
seen by a zone of inhibition
negative for coag-negative = S. saprophyticus
seen by no zone of inhibition
What is Streptococcus?
gram positive cocci (in a chain-like pattern)
highly environmentally sensitive
normal human commensal
mouth, skin, intestine, and upper respiratory tract
Strep. mutans
most common cause of dental plaque
Strep. pneumoniae
most common cause of bacterial pneumonia
Strep. pyogenes
common cause of throat infections; “Strep throat”
responsible for pharyngitis and systemic infection like scarlet fever
able to completely lyse RBC
4 Streptococcus strains identified in lab
S. pyogenes
S. agalactiae
S. equi
E. faecalis
CAMP Test
Identification for Group B or S. agalactiae
Bacitracin Susceptibility Test
Identification for Group A or S. pyogenes
Bacitracin Susceptibility Test Results
positive = S. pyogenes or Group A
seen by a zone of inhibition around the disk
negative = not S. pyogenes or Group A
seen by no zone of inhibition around the disk
SXT Sensitivity Test
Identification for Group C or S. equi
enzyme inhibitor (blocks folic acid synthesis)
SXT Sensitivity Test Result
positive = S. equi or Group C
seen by a zone of inhibition around the disk
negative = not S. equi or Group C
seen by no zone of inhibition around the disk
Optochin Sensitivity Test
Identification for S. pneumoniae
was not performed in lab
a zone of inhibition indicates a positive result for S. pneumoniae
Bile Esculin Media
Identification for Group D or E. faecalis
bile salts inhibit non-Group D species
esculin hydrolysis forms black precipitate
Bile Esculin Media Results
positive = E. faecalis or Group D
seen by the formation of black precipitate
bacteria is able to hydrolyze esculin
negative = not E. faecalis or Group D
seen by no change in the test tube
bacteria is unable to hydrolyze esculin