Quiz 2 Flashcards
antibiotic
a chemical synthesized by a microbe that will kill or inhibit other microbes
important producers of antibiotics
streptomyces, bacillus, penicillum, and cephalosporium
tube dilution antibiotic sensitivity assay
a known concentration of antibiotic is diluted in a twofold tube dilution series and a drop of test organism is added to each tube to observe if good growth will occur. The antibiotic in the highest dilution tube that shows no culture growth is called the minimum inhibitory concentration (MIC)
kirby-bauer or disc method of determining antibiotic sensitivity
paper discs containing antibiotic are used to test for inhibition of bacterial growth in the vicinity of the disc on an agar plate. For standardization of the technique, a type agar called Mueller-Hinton is used for the plates. To determine if an isolate is resistant or sensitive to an antibiotic, the growth inhibition zone diameter (including disc diameter) is compared with values produced by reference organisms of the same species on a standard table. Two antibiotics that produce the same inhibition zone diameter do not have the same efficacy because of many factors, such as diffusion rates effects results.
organism used for antibiotic disc assay
escherichia coli & staphylococcus epidermidis
disc assay: CAR 100
concentration: 100
inhibition zones:
e. coli:
s. epidermidis:
disc assay: C30
concentration: 30
inhibition zones:
e. coli:
s. epidermidis:
disc assay: Te30
concentration: 30
inhibition zones:
e. coli:
s. epidermidis:
disc assay: K30
disc assay: Did the two organisms tested show the same sensitivity pattern? Why?
No, because bacteria react differently to different antibiotics
Minimum Inhibitory Concentration (MIC)
least amount of antibiotic to stop bacteria
bactericidal antibiotic
antibiotic that kills microorganism
bacteriostatic antibiotic
antibiotic that prevents growth
penecillinase
hydrolyzes penicillin
How are plasmids associated w/ the efficacy of antibiotic therapy?
they decrease the efficacy of antibiotic therapy because they introduce genes that are resistant to the antibiotics
serum titer
the greatest dilution of serum which causes agglutination
acute serum
a sample taken from a patient at the onset of an illness
convalescent serum
a sample taken from a patient during recovery of an illness or several days after the onset
identification of etiological agent
if the microorganism being tested as an antigen results in the observation of an increase in convalescent titer at least 4 fold greater than the acute titer, it is likely to be the infectious agent
explain the methods for the experiment
- placed PBS in each of the 9 tubes
- place 1 ml of the serum(aby) in position 1
- place .5 of serum in tube 2 which is one to two dilution
- take .5 from tube 2 and put in tube 3 this is one to four dilution
- continue two-fold dilution for all tubes and discard 0.5 ml from last tube
- add 0.5 of washed cells (sheep red blood cells -> antigen) to all 10 tubes
- incubate
- determine the titer
what was the serum titer
-the 1/32 dilution which was tube 6
-serum titer because it’s the greatest dilution that causes agglutination
-serum titer is usually 1/16 or 1/32
what is agglutination
-when antigen combines with its antibody
-causes clumping of cells
what happens in agglutination reaction when there is an excess of antibodies and what is it called
-called prozone
-agglutination will not occur
-antibodies will bind to antigens univalently instead of multivalently
-antibodies that bind univalently cant crosslink one antigen to another
what occurs in agglutination when there is excess of antigens and what is it called
-agglutination will not occur
-called post-zone
-not enough aby and too many ag
-no crossbridging
what is required for agglutination rxn to work optimally
specific ratio of aby:ag
how does an antibody affect a germ/bacteria
- aby doesnt kill
- aby just signals
- wbc comes to kill
- complement binds and starts series of rxns
- complement proteins put holes in cell membrane
- water rushes into cell -> hemolysis
what creature makes the best complement
guinea pig
major illnesses caused by staphylococci
boils, scalded skin syndrome, toxic shock syndrome, food poisoning (staphylococcus aureus)
major diseases caused by streptococci
contagious skin disease, sore throat, rheumatic fever, glomerulonephritis (streptococcus pyogenes: the flesh eating bacteria); Pneumonia (streptococcus pneumoniae)
beta-hemolysis in staphylococci
this activity produces the lysis of red blood cells in agar plate medium. Blood agar is prepared by mixing 5% sterile defibrinated sheep blood with a nutritional blood agar that has been cooled to aboute 45 degree C after autoclaving. The medium is then dispensed into tubes or plates
hemolysis in streptococci
lysis of red blood cells in agar (beta-hemolysis), conversion of red blood cells to green (alpha-hemolysis), no effect on blood cells (gamma-hemolysis)
selective medium
medium to prevent growth of some species but permitting others to thrive
differential medium
medium that enables the investigator to distinguish one species from another. This is usually done through use of a chemical reaction which causes the color of the medium or colonies to change
gram stain results
S. aureus: gram positive, coccus, cluster
S. epidermidis: gram positive, coccus, cluster
S. faecalis: gram positive, coccus, chain
G. tetragena: gram positive, coccus, tetrad
catalase reaction
S. aureus: +
S. epidermidis: +
S. faecalis: -
G. tetragena: -
staphylococci
S. aureus: positive for all tests (hemolysis on blood agar, mannitol fermentation, gelatinase, coagulase)
S. epidermidis: negative for all tests(hemolysis on blood agar, mannitol fermentation, gelatinase, coagulase)
bile esculin azide agar
s. faecalis: good growth and blackening of medium
g. tetragena: no growth
Under the microscope, how can staphylococcus be differentiated from gaffkya tetragena?
Staph has grape-like clusters and g. tetragena is in tetrad
What is the chemical reaction mediated by the enzyme catalase?
2H2O2 > O2 + 2H2O
hydrogen peroxide to water and oxygen
What simple test can differentiate staph from strep
Catalase
Describe the mechanism by which staphylococcal coagulase causes plasma to clot?
conversion of fibrinogen to fibrin
-s. aureus produces bound & free coagulase (bound directly to fibrinogen)
major intestinal diseases
typhoid (salmonella typhi), dysentery (shigella dysenteriae), cholera (vibrio cholerae), travelers diarrhea (escherichia coli)
enterobacteria
gram-negative rods that are frequently found in the intestinal tract
facultative anaerobe
a bacterium that can grow in the anaerobic intestinal tract but also in the presence of oxygen
selective medium
medium to prevent growth of some species but permitting others to thrive
differential medium
medium that enables the investigator to distinguish one species from another. This is usually done through use of a chemical reaction which causes the color of the medium or colonies to change
macconkey agar
lactose fermenting organisms produce red colonies on this plate medium. Gram-positive bacteria are inhibited. The ingredients include lactose, bile salts and neutral red (pH indicator)
XLD
organisms that ferment the constituent carbohydrates produce yellow or red colonies on this plate medium. If lysine decarboxylase is produced colonies are red. Colonies may be black if H2S is produced. The medium contains xylose, lactose, sucrose, phenol red (pH indicator), bile salts, lysine, and ferric ammonium citrate (H2S detection)
TSI
triple sugar iron agar is used in the form of a slant tube. If an organism can use lactose or sucrose, the entire tube will turn yellow (acid). Gas may push the agar up the tube or form large bubbles. If only glucose is used, the base (butt) of the agar slant will turn yellow but the slant itself will remain red. An organism that produces H2S will cause the formation of a black pigment in the tube. Besides the sugars, the medium containts phenol red (pH indicator) and iron salts (H2S)
Simmons Citrate
this medium will turn blue if inoculated organism can use citrate. The medium includes citrate and thymol blue (pH indicator) and is prepared as an agar slant.
urea agar
organisms that can break down urea can be recognized by changing the color of this medium. Phenol red is used as an indicator.
iron Agar
this medium is for the detection of H2S produced by some species
Fermentation Broth
this is a test to determine if an organism can use a specific carbohydrate. The broth includes phenol red to test for acid produced from the carbohydrate.
A tiny inverted tube (durham tube) is present to assay production of gas
Decarboxylase Broth
this medium can detect the ability to produce decarbyoxylases by a color change of the tube
Motility Medium
if growth spreads from a straight vertical stab line of inoculation, the bacterium may be motile
enterotube II
this is a multiple test medium made by Roche diagnostics that can assay for several qualities at once
organisms used for biochemical characterization of enteric bacteria
e. coli
klebsiella pneumoniae
proteus vulgaris
pseudomonas aeruginosa
