Gram positive bacteria Flashcards
(35 cards)
What arrangements are:
1. Streptococcus
2. Staphylococcus
usually in?
- Pairs and chains
2. Clusters
General properties of staphylococci
Facultative anaerobes
Catalase +
Found on the skin and mucous membranes
More than 20 species, but 4 are commonly associated with disease
4 species of Staph that are commonly associated with human disease
- S. aureus
- S. ludgunensis
- S. epidermidis
- S. saprophyticus
Catalase test
Determines if the organism produces catalase
This enzyme breaks down H2O2 into water and oxygen
Catalase allows organisms to break down harmful metabolites of aerobic respiration and may be seen in aerobic and facultative anaerobic organisms
Catalase test results for:
- Staph
- Strep
- Enterococcus
- Positive
- Negative
- Negative
S. aureus
10-15% of people carry it in their nose or other mucus membranes - frequency increases in hospitals
Most frequent cause of hospital acquired infections
MRSA is an increasing concern
Slide and tube coagulase +
Golden colour
Slide coagulase
and which organisms are positive
Looking for clumping factor
Latex agglutination test
Positive: S. aureus and S. lugdenensis
Tube coagulase
and which organisms are positive
Looking for free coagulase
Performed in rabbit plasma
Positive: s. aureus and s. pseudintermedius
Only considered coagulase positive if you are tube +
Coagulase negative staphylococci
Every carries CNS on their skin
Virtually impossible to eradicate it, even with disinfectant use and hand washing
Produce slime and have a high affinity for synthetic materials - devices inserted through skin are frequently infected
S. lugdunensis
Coagulase negative Staplococcus spp Considered as virulent as S. aureus Similar clinical spectrum Produces clumping factor (slide coagulase +) PYR + Ornithine decarboxylase +
S. saprophyticus
UTI pathogen associated with young women
Resistant to novobiocin
S. pseudintermedius
Slide coag -‘ve, tube coag +’ve
Animal pathogen that is increasingly being reported in human disease
Methicillin resistant
Used to be misidentified as staph aureus
4 shared characteristics of enterococci
- Growth at 6.5% NaCl at pH 9.6
- Growth between 10-45 degC
- Growth in 40% bile
- Esculin hydrolysis, LAP, and PYR +
4 clinical isolates of enterococci and what are they all resistant to
Common:
E. faecalis (80-90%, and is susceptible to ampicillin)
E. faecium (5-10%, and is resistant to ampicillin)
Less common:
E. casseliflavus
E. gallinarum
All are intrinsically resistant to cephalosporins
Vancomycin resistant enterococci is a concern
3 General characteristics of streptococcaceae
- Gram positive chains/pairs
- Catalase negative
- Facultative anaerobes
3 strep species in Viridans group
S. mutans
S. sanuis
S. salavarius
3 types of haemolysis
Beta: complete
Alpha: partial (greening of agar)
Gamma: none
S. pyogenes
remember: sensitive to..
Group A strep
Highly beta hemolytic
Mid sized colonies with big zone of hemolysis
Use Taxo A disk - has Bacitracin - they are SENSITIVE
PYR +
Never resistant to penicillin or any beta lactam
Beta hemolytic strep are never resistant to…
Penicillin or any beta lactam
PYR test
which organisms are positive, and which are negative
Enterococcus and Grp A = +
S. bovis and other Streptococci = -
S. agalactiae
Grp B Strep Weakly beta hemolytic Colonies tend to be smaller than group A CAMP test + All women should be screened late in pregnancy, because it can cause major problems in newborns
CAMP test
Differentiates Gp B from other strep
Synergistic hemolysis observed between S. aureus and Gp B strep
Positive reaction = arrow head hemolysis
Listeria also positive
Streptococcus anginosus group
3 species Weakly beta, sometimes alpha Primarily group F or A - also C and G Colonies smell like caramel/butterscotch Associated with deep seated abscesses (liver/brain)
3 species in Streptococcus anginosus group
S. anginosus
S. intermedius
S. constellatus
