study guide Flashcards
What is the Kirby-Bauer test used for?
to determine which antibiotics a specific bacterium is most susceptible or resistant to
What is meant by the term resistant?
Antibiotics will have no effect on bacteria growth; they don’t work
What is meant by the term susceptible?
Antibiotics work; bacteria is sensitive to antibiotics
What is a zone of inhibition?
Area of no growth
Why must a chart be used to read the results?
every antibiotic has different diameters in which they show they are effective
Given the information on a chart, be able to determine an antibiotics effectiveness
Disk potency: _____________________________
Resistant: _____________________________
Intermediate: _______________________
Susceptibility: __________________
PG. 34
1) measurement of antibiotic strength
2) the ability of the microbe to grow in the presence of antibiotics
3) bacteria falls short of resistance
4) antibiotics work
What is an antibiotic?
Substances that kill or prevent the growth of bacteria
What is the difference between broad spectrum and narrow spectrum? Why would one be used over the other?
Broad spectrum kills a large range of things while narrow spectrum targets a specific thing. We would use broad spectrum if we don’t know what is causing the disease. Narrow is when we have a good indicator as to what is causing disease
What is the difference between bacteriostatic and bactericidal?
Bacteriostatic: slows/stops bacteria growth
Bactericidal: kills bacteria
What is a disinfectant?
Chemical substances that kill or inhibit the growth of microorganisms.
How did we determine which disinfectant worked best?
seeing which disinfectant produced the largest zone of inhibition
What effect does pH have on bacterial growth?
- different bacterial species grow best in different pH ranges. Each bacteria has it’s own set of cardinal pH’s (minimum growth pH, Maximum growth pH, and optimum pH). Bacteria grows best in their optimum pH. If the pH falls below the minimum tolerable pH or rises above the maximum tolerable pH, the bacterium is unable to produce energy and enzymes may become ineffective.
- If the pH falls below the minimum tolerable pH or rises above the maximum tolerable pH, the bacterium is unable to produce energy and enzymes may become ineffective.
What are the terms applied to bacteria at different pH ranges?
pH below 5.5 = _____________
pH 5.5 – 8.5 = _____________
pH above 8.5 = ____________
1) acidiophiles
2) neutrophiles
3) alkaliphiles
What effect does temperature have on bacterial growth?
- At optimum temperature, bacteria will show its highest growth rate. Below the minimum temperature and above the maximum temperature, the bacterium will not survive.
- Temperature increases or decreases the rate at which the bacteria replicate
What is meant by the term optimum temperature?
Optimum temperature: bacteria shows highest growth rate
What are the terms applied to each type of aerotolerance?
- Obligate aerobes : require O2
- Facultative anaerobes : will grow with or without O2, but grow better with O2
- Aerotolerant anaerobes : do not require O2 but are not harmed by it, spread throughout tube
- Obligate anaerobes : cannot grow in the presence of O2
1= obligate aerobe, 2= obligate anaerobe 3= facultative anaerobes 5= aerotolerant
What test did we use to differentiate staphs from streps?
Catalase test
- Simple and immediate
- Identifies organisms that possess the enzyme catalase, which breaks down hydrogen peroxide into water and gaseous oxygen
- Staph = catalase-positive; bubbles form
- Strep = no catalase; no bubbles
What are other ways that could have differentiated these two?
What specific tests/stains would help you differentiate?
1) By their morphology. Staphylococcus forms clusters of grape like shapes. While Streptococcus forms chains of “pearl necklaces.”
2) catalase, gram stain, simple stain,
What tests were used on the staphs?
- _____________: uses rabbit plasma tubes
to identify if a bacteria is _______________ by identifying the presence of the enzyme coagulase. Coagulase is an enzyme used by S. aureus to cause_________________________. WHICH acts as a mechanism of envading the hosts’ immune system.
1) Coagulase
2) staphlococcus aureus
3) the formation of blood plasma clots around themselves
What tests were used on the staphs?
- __________: Uses DNAse plate
- Another method of differentiating between forms of Staphylococci
- Only ________________ produces the enzyme DNase
- _________________ in host cell
- DNase agar is __________ but presence of enzyme (DNAse) will leave a clearing around bacterial growth
1) DNAse
2) Staphylococcus aureus
3) Breaks down DNA
4) green
What tests were used on the staphs?
- ________________: Uses MSA plate
- Selective for all Staphylococci
- _________ inhibits growth of most other organisms, but staphylococcus does very well in this high salt environment
- Differentiates between ____________________
- pH indicator phenol red in the agar will turn ________ as fermentation decreases the pH of the media. (phenol red is yellow below pH 6.8, red at pH 7.4 to 8.4, and pink above pH 8.4)
- Selective → high salt only selects _____________
- Differential → yellow means ______________, hence differentiates staph aureus from the different staphs (which don’t ferment mannitol)
1) Mannitol Salt Agar (MSA)
2) 7.5% salt
3) mannitol-fermenting pathogenic Staphylococci and non-mannitol fermenting Staphylococci
4) yellow
5) staphylococcus to grow
6) it ferments mannitol
What tests were used on the staphs?
- _________________: uses blood agar plate
- Novobiocin is an ____________
- This test will differentiate __________ from other Staphylococci
- S. saprophyticus is resistant to novobiocin, while ___________ and _________ are susceptible
- If there is a zone of inhibition, not S. Saprophyticus bacteria
1) Novobiocin Sensitivity Test
2) antibiotic
3) Staphylococcus saprophyticus
4) S. aureus
5) S. epidermis
If there What is hemolysis? What are the different types? What is each one doing? And what does each look like?
- An enzyme that destroys or partially destroys red blood cells
- Beta-hemolytic streptococci completely hydrolyze (breakdown with water) red blood cells
- Alpha-hemolytic streptococci partially hydrolyze red blood cells
- Gamma-hemolytic (or Non-hemolytic) are not hemolytic at all and do not affect the red blood cells
- Beta – Bad (complete breakdown of RBC); Alpha – almost as bad (partial breakdown); Gamma - good (no breakdown)
- β (Beta): clearing around colonies, yellow;
- ἇ (alpha): appears as a green coloration;
- Ɣ (gamma): will not produce a color change in the media just growth in colonies.
For all of the staph and strep tests:
________________: uses blood agar plate
- Objective is to identify _________________ based on its susceptibility to the antibiotic bacitracin.
- The test is useful in differentiating the beta-hemolytic group A strep (Streptococcus pyogenes is bacitracin susceptible) from other beta-hemolytic streptococci. Streptococcus pyogenes is Bacitracin __________ while most others are resistant
1) Bacitracin Sensitivity
2) streptococcus pyogenes
3) sensitive
For all of the staph and strep tests:
- _____________: uses bile esculin plate
- Selects for Group D Streptococci and Enterococci
- Media contains bile, which allows the growth of Group D Strepto/Enterococci, but inhibits others
- Differentiates between Group D Strepto/Enterococci and non-Group D’s
- Group D Strepto/Enterococci can hydrolyze esculin into glucose and esculetin.
- The glucose is used for _______________ and the esculetin reacts with iron salts in the media to form a black precipitate which verifies presence of a Group D Strepto/Enterococci.
1) Bile Esculin Test
2)
