Bonus Recording Flashcards
What is fluorescence microscopy?
FISH - used one specific colour for a specific bacterium so if present that colour is seen under the microscope. Commonly used to see the distribution in dental plaque.
How do you sample dental plaque for viewing under a microscope?
Wet plaque sample from pocket with sterile curette or toothpick
Plaque samples mixed with BacLight reagent
What does BacLight reagent do?
Contains Syntox Green which causes live bacteria to appear bright green
Contains Propidium Iodide which causes dead bacteria to appear dull red when viewed under a microscope, because it can only enter the bacteria cell if the cell membrane is compromised, which can only happen if it is dead.
Composition of plaque from a healthy gingival crevice
Scanty and cells were dispersed
Mainly coccoid cells
Some straight rods
No motility
Desquamated epithelial cells
Neutrophils might be visible
Plaque from a site with gingivitis
Cells are more dense
Periphery of sample used to view a mono layer
Cocci and short rods
Filamentous cells
Spirchaetes may be seen but few in number
Clusters of motile rods
Plaque from an active periodontitis site
Mainly motile plaque
Morphotypes similar to gingivitis but higher percentage of spirochaetes and motile rods
Neutrophils observable and may be degranulating
Epithelial cell debris
Pros of fluorescent microscopy
Rapid and inexpensive
Valuable for educating patients and motivating to brush
Cons of fluorescent microscopy
Wide variation in results
Not a sole diagnostic indicator
What is AMR?
Antimicrobial resistance
What are antibiotics?
Variety of substances derived from microorganisms that control the growth of or kill bacteria
Why is AMR developed?
A lot of antibiotics are fed to livestocks, where it can get into the soil thus plants thus water systems and get to us. Also used in hospitals and prescribed by GPS and by humans transmitted to the environment. So since there are many antibiotics circulating, bacteria have an opportunity to become resistant.
What is the problem with AMR?
Resistance against Antimicrobial has been increasing
Discovery and development of new antibiotics is decreasing
Why is antibiotic sensitivity testing done?
It is important that the right antibiotic is given depending on which bacteria has infected the patient.
Describe the method of testing antibiotics by agar diffusion assays (assay 1)
Take the bacteria for testing and spread them very thinly onto the agar plate.
Place antibiotic discs onto it
Incubate plate overnight, 37° is what temp it grows on humans best
Examine plates for zones of inhibition
What is the halo found around antibiotic discs?
Zone of inhibitions. Clear area where bacteria have not been able to grow because the antibiotic that is in the disc has diffused into the agar and the bacteria are sensitive to this antibiotic and it halts their growth.
What happens in agar diffusion assays that are semi-autonomated?
Device with different filter discs with different antibiotics. Once bacteria is spread across the plate, press down one and the antibiotic disc will form in the same pattern every time. Then incubate them and see which antibiotics your bacteria are susceptible.
What is MIC?
Minimum inhibitory concentration - lowest dose of an Antimicrobial agent that is required to inhibit growth
What is the purpose of the agar diffusion assay E (ellipsometer) test for MIC?
To find out the exact concentration that will kill the bacteria
How does the E test for MIC work?
A strip is impregnated with antibiotic at different concentrations. Plastic strips contain a gradient of antibiotic and are printed with concentration. During incubation of the plate, the antibiotic diffuses out and sets up a gradient. Produces an elliptical zone of inhibition. Conc is highest at top of strip so no bacteria grows at top.
What is the MIC in an E test?
At some point, you see the bacteria come together, which is the lowest possible concentration that we can use to inhibit the bacteria.
How are broth dilution assays more accurate than agar diffusion tests?
It is quantitive, since different tubes containing broth of different concentrations.
What is the limitation of broth dilution?
An antibiotic can either kill bacteria or haunt their growth, depending on their mechanism of growth. Broth dilution does not tel, us which one it can do.
How are broth dilutions conducted?
Have a range of antibiotic concentrations in the dilutions
Inoculate the bacteria to each tube
See which tubes bacteria grew in
How can we tell whether antibiotic haunts growth or kills bacteria?
Plate from each broth dilution tube some onto the plate
Incubate
Might see some bacterial growth on a plate with the MIC but not on concentrations above it. MBC may be slightly higher than the MIC.
OR bacteria might grow on every single plate, because our antibiotic is not bactericidal but bacteriostatic. Antibiotic has just halted the growth of the bacteria, not killed it.
What is MBC?
Minimum bactericidal concentration
What does bactericidal mean?
A substance that kills bacteria
What does bacteriostatic mean?
Substance that halts bacteria growth
What is the breakpoint?
Breakpoint tells us the concentration of certain antibiotic that needs to be used against bacteria? Clinical breakpoint is the concentration for which, if bacteria can grow, they are called resistant, and if they cannot grow then they are susceptible.
What is a broad-spectrum antibiotic?
The antibiotic can work against main different bacteria
Describe penicillin G
Bactericidal
Inhibits bacterial cell-wall synthesis
Works well against gram positives
Describe ampicillin and amoxicillin
Bactericidal
Inhibits bacterial wall synthesis
Efferective against gram positive and some gram negative
Describe gentamicin
Can be bactericidal or bacteriostatic depending on the dose
Binds to 30S ribosomal subunit
Mainly against gram negative
Describe tetracycline
Bacteriostatic
Effective against gram positive and negative
Inhibits action of 30S ribosome
Describe chloramphenicol
Bacteriostatic
Inhibits protein synthesis
What are the targets for antibacterial action?
Cell walk synthesis inhibitors
Cell membrane
Protein synthesis
Nucleic acid synthesis
