Gram positive bacteria identification Flashcards
What is the main division between the gram positive cocci?
The ones that grow in chains/pairs and the ones that grow in clusters.
Which genus/genera of bacteria grow in clusters?
Staphylococcus
Which genus/genera of bacteria grow in chains/pairs?
Enterococcus and Streptococcus
What is the catalase test?
determines if the organism produces the enzyme “catalase”, which breaks down hydrogen peroxide (H2O2) to water and oxygen (O2).
What is the usefulness of catalase?
allows organisms to break down harmful metabolites of aerobic respiration and may be seen in aerobic and facultative anaerobic organisms
What are the two forms of the coagulase test? what makes them different?
- Slide coagulase: you’re not actually looking for coagulase, you’re looking for clumping factor
- Tube coagulase: put rabbit plasma and test organism in a tube, if it is positive it will solidify the sample
What makes an organism considered “coagulase negative”
Either negative for both tests or slide positive and tube negative
How common are coagulase negative staph?
Very. Everyone has them on their skin
- almost impossible to get rid of
What are the 4 species of staph that are commonly associated with human disease?
S. aureus, S.lugdunensis, S. epidermidis, and S. saprophyticus
Out of the gram positive cocci, which are positive for the catalase test and which are negative?
Positive for Staphylococcus, Negative for Enterococcus and Streptococcus
What is a key diagnostic (test) feature to identify S. aureus ?
It is both tube and slide coagulase positive
What are 2 common features of all Staphylococci? where are they commonly found?
Facultative anaerobes.
Catalase +
Commonly found on human skin and mucous membranes.
What gram positive cocci is the most frequent cause of hospital acquired infections?
S. aureus
What percentage of people carry S. aureus in their nose or other mucous membranes?
10-15% of people
What are two important coagulase negative Staph species?
S. lugdunensis and S. saprophyticus
What is the testing profile of S. lugdunensis?
Slide coagulase +
Tube coagulase - (considered coag. neg)
PYR +
Ornithine decarboxylase +
S. lugdunensis is considered just as virulent as?
S. aureus, has a similar clinical spectrum
What is S. saprophyticus commonly associated with?
UTIs in young women
What is the coagulase profile of S. pseudintermedius?
Slide coagulase -
Tube coagulase +
What is S. pseudintermedius a pathogen of typically?
Dogs
What is S. pseudintermedius frequently resistant to?
Methicillin
S. pseudintermedius was frequently identified incorrectly as __ before MALDI-TOF?
MRSA
Are the majority of Enterococci pathogenic to humans?
No
What are the common growth characteristics of the enterococci? (3 features)
Growth at 6.5% NaCl at pH 9.6
Growth between 10-45oC
Growth in 40% bile
What is the testing profile of the Enterococci?
PYR +
Esculin hydrolysis +
LAD (?)
What are the Enterococci intrinsically resistant to? What antibiotic is there growing resistance to?
Intrinsically resistant to cephalosporins. Increased resistance to Vancomycin
What are two common clinical Enterococcal isolates ? what percentages?
E. faecalis (80-90%)
E. faecium (5-10%)
- faecium is harder to treat
What are 3 general characteristics of the Streptococci?
Gram positive cocci in chains/pairs
Facultative anaerobes
Catalase negative
What are the 3 groups of Streptococci we discussed (on the chart)? What do they do?
- Pyogenic strep: pus and fever forming
- Anginosis strep: abscess forming
- Viridans strep: “green”, part of the oral flora, includes Strep. pneumoniae
What are the 3 different forms of hemolysis?
Alpha: weakly hemolytic, partial, “greening”
Beta: complete hemolysis
Gamma: no hemolysis
How many different groups of Strep are there?
18
S. pyogenes: what is the hemolysis profile, PYR test result, and antibiotic susceptibilities?
Beta hemolytic
PYR +
Susceptible to ß-lactams and Bacitracin
Why is S. pyogenes susceptibility to Bacitracin important?
Because other Strep are resistant to bacitracin
What is the PYR test looking for?
Tests for the presence of pyrrolidonyl arylamidase (enzyme)
Which organisms are positive for the PYR test/which ones are negative?
Enterococcus and Gp A Strep +ve
S. bovis and other Streptococci -ve
Which population of patients should be screened for Group B strep? Why? What species is an example of this?
Pregnant women because infections with group B strep tend to affect neonates
S. Agalactiae is an example
What is the hemolysis profile of S. Agalactiae ?
Weakly ß hemolytic
What is the result of the CAMP test for S. Agalactiae ?
Positive
What is the CAMP test used for? How does it work? What is a positive result?
Differentiates Gp B from otherStreptococci
Synergistic haemolysis observed between S. aureus and Gp B Streptococci
Positive reaction: arrow head haemolysis pattern
What is another name for the Streptococcus anginosus group?
the milleri group
What 3 species are part of the Streptococcus anginosus group?
S. anginosus
S. intermedius
S. constellatus
What Lancefield group are the Streptococcus anginosus group mainly a part of ?
Group F
- some A, G and C though
What is the growth/hemolysis profile of the Streptococcus anginosus group?
Pinpoint colonies with ß hemolysis
What does the Streptococcus anginosus group smell like when grown in culture?
Butterscotch
What pathology is the Streptococcus anginosus group associated with?
Deep seated brain abscesses
What 4 related species make up the Strep. bovis group?
S. equinus, S. gallolyticus, S. infantarius, and S. alactolyticus
What Lancefield group are the S. bovis group part of?
Group D
What typically harsh conditions are the S. bovis group members capable of growing in?
Bile
What specific test is the S. bovis group members positive for?
Esculin bile test +
What two features of Enterococci differentiates them from the S. bovis group ?
they are PYR + and can grow in 6.5% NaCl
What two tests are used to differentiate S. pneumoniae from the other Viridans strep? What are the results ?
Optochin test and bile solubility
S. pneumoniae is sensitive to Optochin and soluble in bile
other viridans strep are Optochin resistant and insoluble in bile
All viridans strep members display what kind of hemolysis?
Alpha
What group of Strep are biochemically similar to the Viridans group?
Nutritionally variant strep
What is the testing/hemolysis profile of nutritionally variant strep (optochin, bile, PYR)
Optochin resistant
Bile insoluble
PYR+
Alpha hemolytic
What do the nutritionally variant strep require for growth ?
PYRIDOXAL (vitamin B6)
What are 2 gram positive bacilli?
Listeria monocytogenes and Corynebacterium
What are two tests that listeria is positive for?
CAMP and Catalase positive
What is the hemolysis pattern of listeria?
ß-hemolytic
What is listeria intrinsically resistant to ?
Cephalosporins
What is the classic gram stain depiction of Corynebacterium?
Chinese lettering
What test is Corynebacterium positive for?
Catalase
What are 3 pathogenic species of Corynebacterium?
C. diphtheriae
C. pseudodiptheriticum
C. urealyticum
