Lab #2 Flashcards
(60 cards)
1
Q
Phenylethyl Alcohol Agar (PEA)
A
- Selective medium
- selective for G(+) bacteria; inhibits G(-) growth
- interferes with DNA replication in G(-) bacteria
2
Q
Catalase test
A
- putting drops of Hydrogen Peroxide on a bacteria
- reaction is: H2O2 -> H2O + O2
- catalase-positive bacteria will bubble immediately
- Hydrogen peroxide is more effective (toxic) against catalase-negative bacteria
- Staphs are catalase-positive
- Streps are catalase-negative
3
Q
Blood Agar Plate (BAP)
A
- Differential medium (everything grows)
- differentiates on the basis of rbc hemolysis
- must stab agar plate
4
Q
Beta hemolysis
A
- complete hemolysis
- results in clearing around colonies and/or stabs
- Streptococcus pyogenes
- Streptococcus agalactiae
5
Q
Alpha hemolysis
A
- incomplete hemolysis
- results in green halos around colonies and/or stabs
- green color is causes by hydrogen peroxide produced by bacterium, oxidizing hemoglobin to green methemoglobin
- Streptococcus sanguinis
- Streptococcus pneumoniae
6
Q
Gamma hemolysis
A
- no hemolysis
- agar is unchanged
- Enterococcus faecalis
- Streptococcus bovis
7
Q
What exoenzyme, which is produced by the bacteria, results in hemolysis?
A
hemolysin
8
Q
hemolysis
A
- breakdown of red blood cells
- certain bacteria produce an exoenzyme (hemolysin) that causes hemolysis.
- when placed on a Blood Agar Plate, creates a clear space around the bacteria.
9
Q
What causes the green color seen around colonies exhibiting alpha hemolysis?
A
The bacterium produce hydrogen peroxide that oxidizes hemoglobin to green methemoglobin.
10
Q
Mannitol Salt Agar (MSA)
A
- Both selective & differential medium
- indicator is phenol red
- selective based on salt tolerance (bacteria grows on this if it’s salt tolerant)
- differential based on mannitol fermentation, which produces acid, thereby lowering the pH
- phenol red is a pH indicator:
stays red: when neutral
turns yellow: when acidic
11
Q
Generally, Staphylococcus bacteria are salt ___________ (tolerant/intolerant).
A
tolerant
They live on our skin (very salty).
12
Q
Generally, Streptococcus bacteria are salt __________
tolerant/intolerant).
A
intolerant
13
Q
One “strep” is an exception to the rule about being intolerant to salt. Which one?
A
Entercoccus faecalis, which is normal flora of the colon.
14
Q
Coagulase test
A
- differential medium that contains blood plasma
- a test for production of exoenzyme coagulase
- Coagulase reacts with prothrombin in plasma. The result is staphlyothrombin, which enables the enzyme protease to convert fibrinogen to fibrin. This clots the plasma & lets the bacteria multiply in the clot w/out being detected by the host’s immune system.
If serum clots = Coagulase (+) “jello blob” [Staphylococcus aureus]
If no clot = Coagulase (-) [Staphylococcus epidermidis]
15
Q
Bile Esculin Test (BEA = Bile Esculin Agar)
A
- selective for bile salt
- differential for esculin hydrolysis (splitting w/water)
if bacteria produces the enzyme, esculin is broken down into glucose & esculetin. Esculetin then combines with indicator ferric citrate to form a black precipitate.
16
Q
When hydrolyzed, esculin splits into ________ and ___________.
A
glucose
esculetin
17
Q
Esculetin combines with __________ __________ in the medium to produce a _______ (color) precipitate.
A
ferric citrate
black
18
Q
What color indicates a negative test for esculine hydrolysis?
A
gold
19
Q
Enterococcus faecalis
A
- actually a Streptococcus
- acts like a Staphylococcus in that it’s salt tolerant up to 7% salt solution (Streps are NOT salt tolerant)
- Group D Strep
20
Q
Streptococci Lancefield Groups
A
named after specific Lansfield antigens (carbohydrates) in cell envelope. Rebecca Lansfield, American microbiologist, established this method.
21
Q
Group A Streptococcus (GAS)
A
- Streptococcus pyogenes
- Beta hemolytic
- strep throat
- rheumatic fever
- impetigo
- sinusitis
- otitis media
22
Q
Group B Streptococcus (GBS)
A
- Streptococcus agalactiae
- Beta hemolytic
- pregnant women are tested for this; can be passed on to baby during birth
- neonatal meningitis
- septicemia
23
Q
Group D Streptococcus (GDS)
A
- Enterococcus faecalis & Streptococcus bovis
- Gamma (non-hemolytic)
- urinary tract infections
- intra-abdominal infections
- septicemia
- endocarditis
24
Q
Viridans Group
A
- Streptococcus pneumoniae & Streptococcus sanguinis
- Alpha hemolytic w/no Lancefield antigens
- S. pneumoniae is most common cause of pneumonia & otitis media; also causes bacteremia & meningitis
- S. sanguinis causes dental cavities
25
Diseases caused by Staphylococcus aureus
- most common cause of opportunistic infections in hospitals & community
- pneumonia
- osteomyelitis
- septicemia
- endocarditis
- impetigo
- conjunctivitis
- food poisoning
- uti's
- TSS
- cellulitis
- otitis media
- scalded skin syndrome in infants
26
Diseases caused by Staphylococcus epidermidis
- less common cause of opportunistic infections
| - nosocomial infections (catheters, shunts, surgery)
27
Bacitracin Antibiotic Sensitivity Test (Kirby Bauer plate)
- will show a "zone of inhibition" if Strep is sensitive to the antibiotic
Bacitracin inhibits growth of beta-hemolytic Group A streptococci (Streptococcus pyogenes)
Does NOT inhibit growth of beta-hemolytic NON-Group A Streps (Streptococcus agalactiae)
28
Optichin Antibiotic Sensitivity Test (Kirby Bauer plate)
- for testing Alpha-hemlytic Streps
- will show a "zone of inhibition" if sensitive to antibiotic
Streptococcus pneumoniae is SENSITIVE to Optichin
Streptococcus sanguinis is RESISTANT to Optichin
29
Effects of Osmotic Pressure on Growth
Staphylococcus are SALT TOLERANT
Streptococcus are SALT INTOLERANT, with the exception of Entercoccus faecalis (it is SALT TOLERANT up to 7% salt solution)
Staphs live on our skin (salty) & Enterococcus lives in the colon (a salty environment)
30
What does MRSA stand for?
Methicilin Resistant Staphylococcus Aureus
31
Give 2 examples of diseases commonly caused by Staph aureus.
pneumonia
| impetigo
32
What does VRE stand for?
Vancomycin Resistant Entercoccus
33
Give 2 examples of diseases commonly caused by Enterococcus faecalis.
UTI
| intra-abdomonal infections
34
Give 3 examples of diseases commonly caused by Streptococcus pyogenes
strep throat
scarlet fever
sinusitis
35
Give 3 examples of diseases commonly caused by Streptococcus pneumonia.
pneumonia
otitis media
meningitis
36
ID Lancefield group & type of hemolysis:
| Strep pyogenes
Group A Strep (GAS)
| beta
37
ID Lancefield group & type of hemolysis:
| Strep. agalactiae
Group B Strep (GBS)
| beta
38
ID Lancefield group & type of hemolysis:
| Enterococcus faecalis
Group D Strep (GDS)
| gamma, but can look like alpha if left too long
39
ID Lancefield group & type of hemolysis:
| Strep. pneumoniae
Viridan
| Alpha
40
ID Lancefield group & type of hemolysis:
| Strep. sanguinis
Viridan
| alpha
41
ID the acronyms:
GAS
GBS
Group A Streptococcus
| Group B Streptococcus
42
Why are pregnant mothers screened for GBS during their pregnancy?
GBS (Streptococcus agalactiae) can cause neonatal meningitis & septicemia after birth if it's present during birth.
43
Why does the production of coagulase correlate with pathogenicity?
Coagulase reacts with prothrombin in plasma, resulting in staphylothrombin, which allows the enzyme protease to convert fibrinogen to fibrin. This clots the plasma. Bacteria can multiply inside a blood clot w/out being detected by host's immune system.
Basically, allows the bacteria to hide from immune system.
44
Chemical reaction in Catalase Test?
H2O2 -> H2O + O2
45
Is Hydrogen Peroxide (H2O2/Catalase test) more toxic to Staphs or Streps?
Streps
46
What does BAP stand for?
Blood Agar Plate
47
Is a BAP selective or differential medium?
differential - based on red blood cell hemolysis (alpha, beta, gamma)
48
What are the 3 designations of hemolysis & how to they appear on the plate?
BETA - complete clearing around colonies & stabs
ALPHA - incomplete hemolysis; results in green halos around colonies and/or stabs; green color is caused by hydrogen peroxide produced by the bacterium, oxidizing hemoglobin to green methemoglobin
GAMMA - no hemolysis at all; the agar is unchanged; no hemolysin production
49
What exoenzyme is produced by bacteria that results in hemolysis?
hemolysin
50
Hemolysis is significant for what group of G(+) bacteria?
Streptococcus
51
What causes the green halo around the colonies exhibiting alpha hemolysis?
The bacteria produce hydrogen peroxide that oxidizes hemoglobin to been methemoglobin.
52
What is the purpose of stabbing the agar w/the inoculating loop?
The hemolysins produced by streptococci perform better in an anaerobic environment. Stabbing the loop into the agar provides an area of lower oxygen concentration where the streptolysins can more effectively break down the blood cells.
53
Mannitol Salt Agar (MSA) is what kind of medium?
both selective & differential
selective for salt tolerance
differential for mannitol fermentation
54
Bacteria that grow well on a MSA plate are ______?
salt tolerant
55
What is produced from the fermentation of sugar ___________ (acid or bast)?
acid (low pH)
56
What is the indicator in a MSA plate?
phenol red
57
Phenol red (in a MSA plate) turns what color when pH is low?
yellow
58
Mannitol is what kind of organic compound?
carbohydrate
59
What color indicates a positive mannitol fermentation result?
yellow
60
What color indicates a negative mannitol fermentation result?
red (no change)
