Exam 2 Flashcards
Standardized suspension of bacteria must be prepared using what?
0.5 McFarland Standard
using a Barium sulfate solution, the turbidity must equal to 1.5 x 10⁸ CFU/ml bacteria
With Agar Disk Diffusion (Kirby-Bauer Method) in a Mueller Hinton agar, if the ions are too high % amino-glycosides tests …
falsely resistant
With Agar Disk Diffusion (Kirby-Bauer Method) in a Mueller Hinton agar, if the ions are too low % amino-glycosides tests …
falsely susceptible
What is cefinase used for?
disk test for beta lactamase detection
Why do you need to detect beta lactamase?
it’s resistant to penicillin and ampicillin
If the cefinase disk turns RED, what does that indicate?
positive for beta lactamase!!! interpret as resistant to penicillin and ampicillin
If the cefinase disk stays the same, what does that indicate?
negative for beta lactamase. but it can still possibly be sensitive to penicillin… aka useless result,, tells you nothing
What indicates you found the minimal inhibitory concentration (MIC)?
- do a serial dilution
- the first clear test tube will be the MIC
What indicates you found the minimal bactericial concentration (MBC)?
- do a serial dilution
- plate the test tubes with clear broth
- the first plate without growth is the MBC
What MBC/MIC ratio would be considered inhibitory?
> 4 (greater than 4)
What MBC/MIC ratio would be considered -cidal?
≤ 4 (less than or equal to 4)
T or F, Incubation of an isolate with an active antibiotic reduces the intensity and the number of the peaks
TRUE
T or F, Incubation of an isolate with an inactive antibiotic will modify the spectra (peak)
FALSE
What targets have manufactures addressed in Molecular Resistance Testing?
readily detectible, common in the population, and, when present, are always expressed
What is BacCapSeq?
What is the number one flaw to BacCapSeq?
you need KNOWN bacteria, so it cannot be used to find unknown bacterial genes
What is target modification in antibiotic resistance?
a pathogen will mutate a gene or enzyme to prevent the antibiotics from binding to target sites
What are examples of pathogens using target modification to become resistant to antibiotics?
- Mutations of gyrases and topoisomerases leading to fluoroquinolone resistance
- PBP2a – methicillin resistance
What is an example of pathogens inactivating enzymes to become resistant to antibiotics?
Production of β-lactamases and aminoglycoside modifying enzymes to become resistant to penicillin/ampicillin
What are the three categories of drug resistance?
Multi-drug resistant (MDR), Extensively-drug resistant (XDR), and Pan-drug resistant
What is MDR (multi-drug resistant)?
acquired non-susceptibility to at least one agent in three or more antimicrobial categories
What is XDR (extensively drug resistant)?
non-susceptibility to at least one agent in all but two or fewer antimicrobial categories
(susceptible to only one or two categories)
What is PDR (pandrug resistant)?
non-susceptibility to all agents in all antimicrobial categories (resistant to all)
How do you balance Mueller Hinton agar?
Ca+ and Mg+
(calcium and Magnesium)
What is the procedure for Agar Disk Diffusion?
- Streak bacteria on plate with cotton tipped swab
- Apply 6mm paper disks that contains single antibiotic
- Incubate for 16-24 hrs at 35*C
- Measure zone of diameter of inhibition of growth (mm)
If there are two rings around the antibiotic disk (agar disk diffusion), what ring do you measure? The outer or inner ring?
Inner ring (usually means a mixed specimen)
Does Agar Disk Diffusion have quantitative or qualitive results? able to determine MIC or MBC?
- qualitive (Resistant, Intermediate, Susceptible)
- MIC
Does E test (strip) have quantitative or qualitive results? able to determine MIC or MBC?
- quantitive
- MIC
What is the procedure for the E test?
Calibrated plastic strips impregnated with one antibiotic/concentration gradient (mcg/ml) embedded in plastic/carefully placed on the agar surface
How do you read an E test?
strip goes from high to low antibiotic conc.
Gradient created as antibiotic diffuses into agar in an elliptical shape
high conc. will look like an eclipse due to the lack of growth
MIC will be at the start of growth
low conc. will have… just growth due to low titer of antibiotics
What grows best for gradient diffusion tests?
Useful for some slow growing or fastidious organisms that cannot be tested by KB
What susceptibility test needs to be FURTHER DILUTED past the 0.5 McFarland standard?
broth dilution
What is the dilution for broth dilutions?
5x10⁵ organisms /ml in broth
What susceptibility tests need to be diluted to the 0.5 McFarland standard?
Agar Disk Dilution (Kirby-Bauer) and Gradient Dilution (like E test)
What are some characteristics of Staphylococcus?
Facultatively Anaerobic cocci that is catalase positive
What are some characteristics of Streptococci?
Facultatively Anaerobic cocci that is catalase negative
What clinically important Staphylococcus species are:
1. Coagulase positive
2. Coagulase negative (CoNS) [2]
- S. Aureus
- S. Epidermis and S. Saprophyticus
What clinically important Coagulase negative (CoNS) Staphylococcus species are:
1. novobiocin sensitive
2. novobiocin resistant
- S. Epidermis
- S. Saprophyticus
What tests are used to determine if the bacterium has coagulase?
- Slide Test (clumping factor [liquid to clumps])
- Tube Test (free coagulase [sediments at the bottom for positive results])
What color is S. Aureus on Mannitol Salt Agar? Why?
- Yellow!
- Growth and fermentation of mannitol is present
What does S. Aureus produce when it ferments glucose?
Fermentation of glucose produces mainly lactic acid
What are some skin/soft tissue disease caused by Staph. Aureus?
Abscess, Impetigo (blistered skin from bacterial infect.), Boil
What are some secondary infection disease caused by Staph. Aureus?
Pneumonia, Meningitis, Sepsis
What are some toxigenic disease caused by Staph. Aureus?
Staphylococcal Scalded Skin Syndrome, Toxic Shock Syndrome, Food Poisoning
What Staphylococcus is Coagulase Positive on slide, but Coagulase negative on test tubes? Positive for Pyrrolidinyl Aminopeptidase (PYR)?
S. Lugdunensis
Is Staph. Aureus normally found in the body? if so, where?
yes, in the upper respiratory tract and/or skin
What is Methicillin Resistant Staphylococcus aureus (MRSA)?
a strain of staph aureus that has mutated (mecA) to be resistant to methicillin (common name of penicillin)
How do you detect Methicillin Resistant Staphylococcus aureus MRSA?
in vitro with cefoxitin
What is the purpose of the Staphylococcal D Test?
test is employed to detect inducible clindamycin resistance
How do you determine the results of a Staphylococcal D Test?
- Positive: If there is a “blunt”, not a circle but similar to a “D” rather than a perfect resistance ring, normal
- Negative: perfect circular ring, iMLS absent and susceptible to clindamycin
What staph species is a opportunistic social butterfly? (attacks the immunosuppressed and associated with “foreign bodies”)
Staphylococcus Epidermidis
What is used to treat S. Epidermidis based UTIs?
quinolones
What is the 2nd most common cause of UTIs?
Staphylococcus Epidermidis
What type of hemolysis causes iron to oxidize changing the blood agar from red to the “green” color?
alpha-hemolytic (partial hemolysis)
What type of hemolysis causes complete rupture of RBCs causing a clear paths in the blood agar?
beta-hemolytic
Lancefield grouping for Streptococci is based on what present in the bacterial cell wall?
C-carbohydrates
What are the characteristics of Streptococcus Pyogenes (Group A Beta-Hemolytic Strep [GABHS])?
- beta-hemolysis (Group A)
- PYR positive
- TMP-SMX* resistant
- Bacitracin (A disc) sensitive
What color will the disk turn to in L-Pyrrolidonyl b-Naphthylamide Test (PYR test)?
bright pink or cherry-red
What test easily differentiates S. Pneumoniae from other strep. species?
Optochin Test!
Strep. Pneumoniae is the only Streptococci that is sensitive to optochin
How can you tell a part Strep group:
1. D
2. A
3. B
- Strep., optochin resistant, bile resistant, no Hemolysis
- Strep., optochin resistant, Beta Hemolysis, Bacitracin Sensitive
- Strep., optochin resistant, Beta Hemolysis, Bacitracin resistant, CAMP positive
CAMP test, what is a:
1. Positive Reaction
2. Negative Reaction
- No perpendicular line
- Perpendicular line
What strep organism is CAMP test used to differentiate for?
S. Agalactiae (Group B Strep)