Lab Exam Flashcards
How do you prepare a methanol-fixed bacterial smear?
From solid culture: one drop sterile saline mixed with one loopful bacteria From liquid culture: transfer two loopfuls to slide smear around slide to thin out Allow smear to air dry Cover surface of slide in methanol After 1 minute, pour off excess methanol and allow to air dry once again
TRUE OR FALSE: Streptococcus species are catalase positive
FALSE, STAPHYLOCOCCUS species are the ones that are catalase positive
When differentiating gram positive cocci, what is the first test you would use and why?
First test would be a catalase test to determine if it is a Staphylococcus or Streptococcus species. (Staph is positive)
_____ is the only coagulase-positive Staphylococcus species
S. aureus
How does one perform a coagulase test? What is a positive result?
Mix one loopful bacteria into one drop sterile saline. Add a drop of rabbit coagulase to the slide and mix. Watch for grainy/gritty coagulation (positive)
What is the purpose of DNase agar? What is DNase and how is it identified by the medium?
Purpose is to differentiate Serratia from Enterobacter and S.aureus from other Staph. DNase is an exoenzyme that catalyzes hydrolysis of DNA. After incubation, HCl is added and if a cloudy precipitate (HCl reacting with DNA but not nucleotides) forms around bacteria, result is positive. - or can have methyl green as indicator and changes to clear if pos
What does blood agar test for? What does it contain?
Tests for type of haemolysis. Beta is indicated by clearing around bacteria, alpha indicated by darkening, and gamma indicated by nothing. Gamma means no haeomolysis occurred. Usually blood agar is 5% sheep’s blood
What does the blood agar test mean when identifying gram positive cocci?
Usually used for differentiating Lancefield groupings of Strep. Alpha haemolysis is utilized by group D strep (Sanguinis, mitis, pneumoniae, salivarius), Beta by group A, B, and C strep, and gamma sometimes present in group D as well
Idenitfy the types of haemolysis
A - Beta haemolysis
B - Alpha haemolysis
C - Gamma haemolysis
What tests shouldone use to differentiate Staphyloccocus species?
Mannitol Salt, Novobiocin sensitivity, DNase, coagulase
Why is Mueller-hinton agar used for antibiotic susceptibility testing
Because it is a non differential medium and it contains starch, which can absorb toxins produced by bacteria (which may interfere with antibiotics)
Briefly describe the purpose of the Novobiocin susceptibility test
For differentiating coagulase-negative (Non S. aureus) Staph. Typically used to differentiate Staph. saprophyticis, which is resistant.
What does Mannitol Salt agar contain and what does it select for? How does it specifically select for S. aureus?
Contains 7.5-10% NaCl, which is inhibitory to most non-staph bacteria. Contains pH indicator phenol red - yellow indicates fermentation of mannitol.
S. aureus will have yellow halos around the growth on the plate.
What preliminary tests are used to differentiate Streptococcus species?
Bloodagar, bacitracin sensitivity, CAMP agar, bile esculin agar, 6.5% NaCl broth
Explain the CAMP test and what it differentiates
Identifies group B strep -looking for CAMP-factor. Group B strep like Strep. agalactiae will augment haemolysis by S. aureus, creating an arrow-shaped zone of clearing (when plated perpendicularly to S. aureus, within 1cm but not quite touching).
Explain the results seen on this Mannitol Salt agar. What would it mean if there were third and fourth organisms plated in the remaining quadrants that didn’t grow?
- S. aureus* is positive for fermentation of mannitol.
- S. epidermidis* is negative for fermentation of mannitol.
If no growth is found, it is likely not a pathogenic staphylococcus
Descibe these results of the CAMP test. What is organism C? What can you assume about organism A?
C must be S. aureus
A must be a group B Streptococcus like Strep. agalactiae
Describe the bile esculin test and what it differentiates
Used to differentiate Enterococcus (group D strep) and Strep. bovis. Bile salts select for group D strep. Esculin can be hydrolyzed by Enterococcus and becomes black from iron salts produced. Therefore, pos is black
What do the results on this Bile Esculin agar plate mean? What does this indicate about the organism on the left?
Organism on left is positive for hydrolyzing esculin. This result means it must be Group D strep (Enterococcus or S. bovis)
Describe 6.5% NaCl medium and what it differentiates
Differentiates Enterococcus from other group D strep. IF growth occurs (turbid), it is enterococcus.
What tests are generally used to differentiate between Streptococcus mitis and Streptococcus pneumoniae?
Bile solubility, negative stain, optochin sensitivity test
Describe the bile solubility test, how it is performed and what it differentiates
Performed by inoculating tubes of equal amounts of sterile saline with a bacterial culture. Then, 1mL bile salt is added to one and 1mL of sterile saline is added to the other as a control. It is heated at 37 celcius on a heat block for one hour. Turbidity indicates growth, which means it is bile soluble (bile salt lyses cell wall)
What does the bile solubility test mean when differentiating S. mitis and S. pneumoniae
S. pneumoniae is a positive (bile soluble)
Why is a negative stain performedto differentiate S. pneumoniae and S. mitis?
S. pneumoniae has a capsule, which will show up under negative stain
Why is optochin sensitivity testing used to differentiate S. pneumoniae and S.mitis
S. pneumoniae is the only sensitive Streptococcus species
What is the purpose of an Acid-fast stain? What cellular mechanisms allow the acid fast stain to work?
To detect cells that are capable of retaining a stain when treated with an acid alcohol. It is often used to differentiate* Mycobacterium*. Very few organisms are acid-fast so it is primarily used when infection with *Mycobacterium (either tuberculosis *or leprae) is suspected. They are also used on patients with TB to determine how well drugs are working.
Mycolic acid is a waxy substance on the cell walls of acid fast organisms, which gives them such a high affinity for primary stain that even acid does not decolorize it
Describe each step of the Ziel-Neelsen acid-fast stain
- Prepare methanol fixed slide of suspected Mycobacterium and a known non-acid fast bacteria like S. aureus
- Place slide over boiling beaker of water and put a small square of paper towel over it
- Apply primary stain - carbol fuchsin for 5 minutes. Re-apply regularly to prevent drying
- Allow slide to cooland rinse with water
- Add acid alcohol dropwise until runoff is almost clear, rinse with water
- Apply methylene blue counterstain for 2 minutes, rinse
- Blot in bibulous paper and view.
Describe these acid-fast stain results
A is non-acid fast
B is acid fast, could be Mycobacterium
How does the Kinyoun method of acid-fast staining differ from the one we used?
There is no heat applied, but instead a stronger carbol-fuchsin mixture is used.
What dilution is achieved if someone transfers 1 mL of a 10-1 food sample into 99mL of sterile water?
A 10-3 dilution
How can one use 100mL of a 10-3 dilution to create 10-3 and 10-4 agar pour plates?
Use 1mL of sample on one agar plate (results in 10-3), and 0.1mL of sample on the other (results in 10-4)
What is the standard plate count equation
of colonies on plate/dilution factor of sample x volume plated (mL) = CFU/mL of original sample
What was used in the lab asan alternative to Salmonella-Shigella agar?
Brilliant Green
What does Brilliant Green agar contain and what does it select for?
Selects for *Salmonella *(non typhoid). Both *Salmonella *and *E. coli *will grow on the medium, they just produce completely different results. It contains a pH indicator, bile salts, and brilliant green dye. Brilliant green inhibits gram positives and most gram negatives. It contains lactose and sucrose, and if those are fermented by the organism (ex. E. coli) it will turn the medium green-yellow. Salmonella species will remain white, pink, or red.
Describe these results on Brilliant Green agar
A - Lactose fermentor, maybe E. coli
B - Non-lactose fermentor, possible a Salmonella species
Describe the components of CAMPY (Campylobacter blood) agar and what the purpose is. What is unique about its incubation? Why do you think we do this?
A medium that functions specifically to identify *Campylobacter *(especially C. jejuni) infections. It contains antibiotics such as trimethoprim to inhibit other enteric bacteria.
It must be incubated in 5% O2, 10% CO2.
This is likely because that is closer to the environment of the large intestine
What is the purpose of Endo agar and what does it contain?
Used to detect fecal contamination in water/dairy. Usually used to identify enteric lactose fermentors. It inhibits gram positives. Lactose fermentors will appear slightly red/pink. Lactose non-fermentors appear colourless or pink. If large amounts of acid are produced during lactose fermentation (ex. E.coli), the growth will have a metallic seen.
Describe these Endo agar results
A - Lactose fermentor
B - Strong lactose fermentor (like maybe E. coli)
C - Non-fermentor
What colour will *Salmonella *be on Endo agar?
Colourless
Describe Kenner Fecal agar and what it differentiates?
Selects for fecal streptococci. Gram negatives are suppressed, and it contains a pH indicator. Positive results are red/pink
Where are fecal streptococci found?
In animals
What does MacConkey agar contain? What does it differentiate?
Used to isolate and differentiate members of the *Enterobacteriaceae *based on lactose-fermentation. Has crystal violet to inhibit gram positives. pH indicator is pink when acidic (aka when lactose has been fermented)
Describe these MacConkey agar results
1 and 2 are lactose fermentors. 4 is a lactose non-fermentor (still gram neg) and 3 is likely a gram positive organism
What is MacConkey agar + Sorbitol used for?
To differentiate pathogenic E. coli strains from nonpathogenic strains. Pathogenic strains do not ferment sorbitol and are therefore colourless
What is the purpose of Pseudomonas F agar and what does it contain? What procedure is used to analyze the results?
Is a selective and differential medium for identifying nonfermenting gram negs such as *Pseudomonas *species. In low-iron environments, *Pseudomonas *species can create a fluorescent pigment called fluorescin, which will show up under UV light (as a green/blue glow). The antibiotic triclosan is used to inhibit many gram pos and neg species.
What is the purpose of Eosin Methylene Blue agar? What does it contain?
Used for isolation of fecal coliforms. Dyes inhibit growth of gram positives, agar contains lactose. Lactose fermenters will be pink, non-lactose fermenters willbe their normal colour, and vigorous lactose fermenters will have a metallic green sheen.
Describe these results on EMB agar
A - Lactose negative result
B - Lactose positive result
C - Strong lactose positive result
A positive result on the oxidase test is indicated by?
Paper turning purple after 30 seconds
What does litmus milk contain? What are the potential results and what do they mean?
Litmus milk contains lactose, casein and litmus (a pH indicator that is purple at neutral, blue in bases and pink in acids).
Pink colour = Lactose fermented
Blue colour = lactose not fermented but proteins metabolized
Coagulated curd formed = casein digested
Brownish liquid = casein completely broken down (protealysis)
White colour = litmus reduced
What are the results of tests A, B, and C for glucose fermentation?
A - Negative
B - Positive, acidic
C - Positive, acidic, gas bubble (CO2) produced
Label each of these Litmus milk results as positive or negative for lactose fermentation. Are they alkaline or acidic?
A - Acidic, positive
B - Alkaline, negative
Explain the results of each of these litmus milk tests.
A - Alkaline, negative for lactose fermentation
B - Acidic, positive for lactose fermentation
C - Alkaline, negative for lactose fermentation
D - Positive for casein digestion (protealysis)
E - Positive for casein digestion and lactose fermentation (acidic)
D - Positive for casein digestion, lactose fermentation and breakdown of litmus
What does the methyl red test test for? How does one perform this test? What indicates a positive or negative result?
Mixed-acid fermentation of glucose. Grow bacteria in MR-VP broth and then mix in 5 drops methyl red.
Red colour = positive
Remaining yellow = negative
What is a Negative stain and what stain should be used?
A simple stain that stains the background of the slide without actually staining the cell.
Nigrosin.
What is the procedure for a negative stain?
Place a small drop of Nigrosin on the slid containing the sample.
Take a cover slide, tilt it 45º and spread across the slide.
Let air dry
What does the Triple Sugar-Iron agar slant contain? What does an uninoculated slant look like? What do the varying results mean?
Contains 1% lactose, 1% sucrose, and 0.1% glucose, peptones, pH indicator phenol red.
Uninoculated look orange all the way up.
Yellow = acidic, red = alkaline
Slant + Butt acidic = only ferments lactose and sucrose
Slant alkaline (red), butt acidic (yellow) = only ferments glucose
Slant alkaline, butt has no change = only ferments peptones aerobically
Slant and butt alkaline = organism can ferment peptones aerobically and anaerobically
Whole slant raised in tube = gas production
If there is any black in the tube it is likely Salmonella
How is a nitrate reduction test done? Describe the possible results and what they mean.
5 drops sulfanilic acid plus 5 drops alpha-naphthylamine. If the broth turns red, that means the bacteria can convert nitrates to nitrites. If it does not, you must add a small amount of zinc. If it stays clear, that means the bacteria can convert nitrates to nitrogen or ammonia
What is a positive result in the urea broth? What does that mean and what causes it?
Positive is pink. pH indicator is phenol red, indicating an alkaline reaction
What does the citrate agar slant contain? What indicates a positive result?
Sodium citrate, ammonium dihydrogen phosphate, and pH indicator.
Agar turns blue if the organism can use sodium citrate - turns blue because the nitrogen creates an alkaline environment
What do these results of the citrate utilization test mean?
A - Positive
B - Negative
Describe these test results for TSI test
A - Slant + butt acidic
B - CO2 produced, slant alkaline butt acidic
C- Slant acidic
D - Slant alkaline butt acidic
E - Slant alkaline
D - Slant alkaline, butt?, H2S produced
What is the sulfur indole motility test?What reagent must be added?
Add 5 drops Kovac’s reagent. Tests for H2S production, motility of the organism, and test for production of indole.
Red is indole positive
Black is H2S positive
What indicates a positive and negative result for the indole spot test?
Pos = blue/green
Neg = pink
To what class does Haemophilus influenzae belong to?
Gammaproteobacteria
What was Haemophilus influenzae give it’s name? The Haemo part.
In order for the bacteria to grow, it requires X and V blood factors.
Which strain of Haemophilus influenzae the most pathogenic and what does it commonly cause?
Of all the strains the mosty pathogenic one is the F strain.
It commonly causes bacterial meninigitis if the kid isn’t vaccinated. It always seems to be the kids that aren’t vaccinated.
What other illnesses can be caused by Haemophilus influenzae if the bacteria is encapsulated?
Epiglottitis, cellulitis, otitis, pneumonia, septicemia, and endocarditis
Give me some characteristics on Haemophilus influenza
Gram negative, rod, pleomorphic, facultative anaerobe, non motile, and it’s apparently small.
Divided into 6 serogroups (a-f) and 8 biotypes (I-VIII)
How do you differentiate between serotypes and biotypes in H. influenzae?
Serotypes:
You examine the capsule formation of the bacteria
Biotype:
Differentiated based on three tables; urease, indole and ornithine decarboxylase.
What is the treatment for Haemophilus influenzae?
3rd bgeneration cephalosporin, chloramphenicol or fluoroquinolones.
You can use ampicillin however 25% of H. influenzae produce a beta-lactamase
What bacteria is the causative agent for Tuberculosis?
Mycobacterium tuberculosis
What is the difference between primary and secodary tuberculosis?
Primary: intial exposure to the bacillus. The bacteria enters the alveoli and are ingested by macrophages. Then then move throughout the body reproducing intracellularly in the macrophages. Eventually they get their asses kicked and form granules called tubercles.
Secondary: Immunocompromised people experience necrotic lung inflammation. The one most associated with the disease
Give me some characteristics for M. tuberculosis?
Nonmotile, acid-fast, nonsporing, weakly G +, the fucker is a bacillus
How can people test for tuberculosis?
An acid fast stain, tuberculin skin test, lumbar puncture, sputum, biopsy or use some of the bodily fluid for a culture, and PCR.
How do you treat tuberculosis?
Administer isoniazid and rifampin individually or together and then use pyrazinamide ethambutol or streptomycin
What was once the leading cause of death in children and is spread from person to person aerosol droplets? Also what is the name of bacteria that causes said disease?
Diphtheria
Cornyebacterium diphtheriae
What the two syndromes of diphtheria?
Systemic poisoning
local respiratory infection
How does C. diphethriae cause respiratory infection? Or generally fuck it up.
Produces a thick membrane that obstructs the upper airway
composed of bacteria, fibrin, immune cells, and dead cells
Give me some characteristics for C. diphtheriae.
Non-motile
G+ rod
nonsporing
Produces acid from glucose and maltose
Negative for urease, pyrazinamidase, and alkaline phosphatase
How does N. gonorrhoeae attach to your cells?
Attaches to your urethral and vaginal epithelial cells using its type IV pili
What other issues can this N. gonorrhoaea cause?
endocarditis, meningitis, epididymitis, procitis, pharyngitis, conjunctivis, peritonitis, and perihepatiis
Give me some characteristics for N. gonorrhoeae?
G- diplococcus
twitching motility
ferments glucose
Where does N. meningitidis typically reside before it quickly passes?
nasopharynx, oropharynx, and anogenital region
What factors increase N. meningitidis virulence?
surface pili which allow for attachment
heavy capsule
hemolysins
some strains produce a surface component similar to red blood cells so no antibodies are produced
Give me some characteristics for N meningitidis.
G- diplococcus
aerobic
twitching motility
ferments glucose and maltose
Give me some characteristics for S. mutans.
alpha to non-hemolytic
nonmotile
G+ coccus
facultative anaerobe
Where will you find Propionibacterium acnes and give me some characterisitics?
G + coccus
found in the pores of your skin where they consume the oil on your skin for nutrients
Why is Saccharomyces cervisiae different than normal bacteria?
S. cervisiae is actually a fungus but unlike other fungi, it produces colonies similar to bacteria rather than mycelium.
Not an important human pathogen
What happens when you stain S cerevisiae with acid-fast stain and what do they look like when stained with normal Gram stain?
You will see two results.
Gram Stain:
The asci will stain G - while the vegetative cells stain G +
Acid (Kinyoun)
Asci and ascospores stain pink while vegetative cells stain blue
What does 4S agar stand for?
Single Step Staphlylococcus Selective agar
What does 4S agar test for?
It test for a bacterias ability to grow and produce lecithinase in the prescence of high salt concentration and potassium tellurite.
The agar contains an egg yolk emulsion which turns opaque when lecithinase is produced.
How can you differentiate S. aureus and Staph. saprophyticus on 4S agar?
S. aureus produces greyish-black colonies with white halos
S. saprophyticus can also produce this morphology however takes a really long time for it to occur.
What is in the TSY+G agar?
TS = Tryptic Soy
Y= Yeast extract
G = Glucose
In terms of the lab, what was cultivated on the TSY+G agar?
Propionibacterium acnes
What is the sabourand agar used for?
Grows fungi and yeasts because it meets their nutrional requirements. Has to be incubated at room temperature.
What does the MSB in MSB agar mean?
Mitis-Salivarius Bacitracin
What does the MSB agar select against?
Selectes against
G+ because of the crytsal violet
G- because of the tellurite
If Strep. mutans is grown on a MSB agar, what will it look like?
Will appear as white-frosted glass because of the extracellular polysaccharides derived from the glucose in the media
What dye causes Strep and Enterococcus bacteria to turn blue on the MSB agar?
Tryphan blue
What is tellurite agar used for?
isolation of coagulase positive staph from other sources
What are the primary ingredients in tellurite agar and what are they there for?
Mannitol
Potassium tellurite
lithium chloride
Mannitol serves as a fermentable carb
Tellurite is reduced turning the bacteria black
If a S. aureus, S. epidermidis, and E.coli were plated on tellurite, what would the colonies look like?
S. aureus = black colonies, grows easily
S. epidermidis (G+, coag -) = clear colonies but easily witnessed colonies
E. coli = inhibited growth
What is chocolate agar used for?
Isolation and cultivation of Neisseria and Haemophilus
What are the prime ingredients in Chocolate agar?
It’s a blend of casein, peptones, phosphate buffer, corn starch and bovine hemoglobin.
Also contains amino acids and nucleic acids (serves for the X and V factors)
Total coliform counts are done on _____ agar. Explain the properties of this medium
mEndo agar.
Bile salt inhibits gram positives, contains a pH indicator that turns lactose fermenters pink
Faecal coliform counts are done on ____ agar. Describe this agar.
mFC agar.
Contains bile salt to inhibit gram positives, rosolic acid to inhibit non-faecal coliforms. Blue indicates lactose fermenting colonies
interpret this mFC agar plate
All blue colonies count toward total FCC (fecal coliform count)
Interpret these mEndo agar results
Green metallic sheen = E. coli. Anything pink or green counts toward the Total Coliform Count, but presence of E. coli is enough to indicate fecal contamination
Faecal streptococcal counts are done on ____ agar. Describe this agar.
KF (kenner-fecal) agar.
supresses gram negs, maltose and lactose are fermentable carbohydrates utilized by most fecal streptococci. Acid formation detected by colour change from purple to yellow
Describe these Kenner-Fecal agar results
Yellow zone around bactera indicates positive - fecal streptococci. This indicates fecal contamination from animals
How does one determine the origin of pollution using mEndo, KF, and mFC agar?
Divide Fecal coliform count by fecal streptococcal count. If answer is less than 0.7, it is animal pollution, if it is 2-4, it is human and animal pollution, and if it is over 4, it is human pollution.
What is the purpose of the API20E microsystem?
Rapid identification of *Enterobacteriaceae *and other gram negative rods
What does the API20E contain and how does it work?
Contain 20 microtubules/cupules filled with dehydrated substances. Adding liquid bacterial broth rehydrates media and inoculates it. Colour changes occur either during incubation or after adding reagents. The oxidase test is performed seperatelybut still counts as one of the tests.
The presumptive test is a ______ (qualitative or quantitative) analytical test?
Qualitative
The standard plate count is a ______ (qualitative or quantitative) analytical test?
quantitative
Vacuum membrane filtration testing is a ______ (qualitative or quantitative) analytical test?
Quantitative
How is the presumptive test for water quality performed?
15 brilliant green bile broth tubes (with inverted Durham tubes) are inoculated with a water sample of a given concentration. One set of tubes inoculated with 10mL, one set with 1mL, and one set with 0.1mL. All tubes incubated
Which of these results of the presumptive water quality test using brilliant green bile broth is a positive?
The one on the left - it is turbid and has gas
If someone started with a 100 dilution of river water and transferred 10nL of it to 90mL of water, then 10mL of that solution to another 90mL sample, what would be the dilution factor of the final sample?
10-2
How much molten plate count agar must be added to empty petri shell plates?
20mL, or about 2/3rds of the way up
How does one perform vacuum membrane filtration?
carefully - with 20mL of diluted water poured into reservoir and how the hell do I describe this?
If 20mL of a 10-3 dilution is filtered, what is the concentration of the resultant filter paper?
2 x 10-2
how does one calculate CFU/100mL of water using agar pour plates?
colony count x 100/dilution factor of water x volume of water tested (either 1mL or 0.1mL)
how does one calculate CFU/100mL of water using Total coliform count, fecal coliform count, and fecal streptococcal count?
Colony count x 100/dilution factor of water x volume of water tested (for us was 20mL)
How does one perform the “confirmed” water quality test?
Choose a brilliant green bile broth tube that is turbid and gas positive and transfer onto EMB agar for a four-quadrant streak.
How does one perform the “completed” water quality test?
If EMB (plated using positive Presumptive test broth) exhibits strong lactose fermentation (metallic green sheen), an isolated colony should be selected and used for lactose broth and gram stain test. A positive result for lactose broth is lactose-positive and gas positive, and a positive gram stain is a Gram-neg bacillus
What is the purpose of a phase contrast microscope when observing a wet mount?
Adjusts for contrasting light between background and bacteria, basically shutting down the light reflected by the background and resulting in a dark background and highly visible light bacteria
What is the difference between an antibiotic vs a disinfectant?
Anti: chemical substances cultivated from living organisms that are used to treat and kill bacteria that inhabit a living tissue
Dis: similar function but may be chemically synthesized. Usually done on inanimate surfaces.
Which of the antibiotics used in the lab were bacteriostatic?
Chloramphenicol
Tetrecycline
Vancomycin
Which of the antibiotics were bactericidal?
Gentamicin
Penicillin
Streptomycin
Which of the antibiotics are aminoglycosides and how does it fuck up bacteria?
Gentamicin and Streptomycin
It irreversibly binds to the 30S ribosomal subunit, fucking up protein synthesis
Only gentamicin is still active after autoclave
How does Chloroamphenicol mess with bacteria?
It’s bacteriostatic, it binds to the 50S ribosomal subunit messing with protein synthesis
How does Penicillin mess up bacteria?
Since it contains a beta-lactam ring, it fucks with bacteria by preventing peptidoglycan synthesis so those fuckers pop
Tetracycline is like gentamicin in what regards?
They both combine on the 30S ribosomal subunit messing with the bacteria’s protein synthesis
Why is vancomycin so special? Like whats it all about?
It’s bactericidal
its a glycopeptide
It inhibits cell wall synthesis for G+ bacteria
Why might you add two drugs together instead of increasing the dose?
You might enhance the drug activity with synergism
You reduce the possibility of host toxicity
You lower the incidence of drug resistance
What is the difference between synergisitic effects and additive effects?
Syn: The effects are greater than the sum of the effects used individually
Add: Each drug works as well independently as you’d expect
What is the beta-lactamase test used for?
To quickly identify the isolates that are resistant to both penicillin and cephalosporins
How do beta-lactam mess with bacteria?
It competes for sites against the transpeptidase. By taking over these sites, cross linking does not occur and the peptidoglycan become useless
What drug is used for testing the beta-lactamase test?
Nitrocefin (cephalosporin)
It’s essentially a punk bitch because it’s susceptible to most beta-lactamases.
What determines a positive test in the beta-lactamase test?
If the disc turns pink. This is positive as nitrofecin turns pink when it is hydrolyzed
What is another names for the Kirby-Bauer test?
Disc Diffusion test
What are the standardized procedures for the Krby-Bauer Test?
Mueller Hinton (between 7.2-7.4 ph, 4mm deep in either 100 or 150 mm perti plates)
The culture must be 0.5 McFarland units (I don’t know but it says so in the photographic atlas)
Incubated at 35 +/- 2 degrees celcius for 16 to 18 hours
What is the MIC?
The Minimum Inhibitory Concentration is the minimal concentration that is needed to inhibit the growth of the bacterium
What is the difference between direct and indirect agglutination?
Direct = antibodies to naturally particulate antigens
indirect = artifically constructed systems in which agglutination occurs
