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Lab Quiz 3
Terms in this set (20)
Endoscope-forming bacteria include:
Clostridium; C. tetani = tetanus
Bacillus; B. anthracis = anthrax
What is an endospore?
Cell structure that makes bacteria hard to kill and able to survive in dormant state.
What is vegetative cell?
Active bacterial cell
Why heat malachite green in endospore staining?
To force the dye into the cell
Is the endospore stain a differential stain?
Yes; it differentiates bacteria based on presence of endospore or not
The type of microbes and level of microbial contamination
How does bioburden influence contact time of disinfectant?
High bioburden = high contact time; more organisms require more time to kill them
Characteristics of a good lab disinfectant:
Kills a broad spectrum of organisms;
Unaffected by presence of blood, pus, feces, etc.;
Non-toxic to humans and non-corrosive to the materials it's used on;
Inexpensive and easy to prepare;
Shelf-Stable and able to be shipped
What are the four mechanisms by which bacteria become resistant to antibiotics?
1) Change in the structure of the drug binding site;
2) Change in membrane permeability;
3) Gaining a gene to allow for production of enzyme to destroy drug
4) Acquisition of a gene that enables the bacterium to produce an MDR (multiple drug resistance) pump
What are the five modes of action of antibiotics?
1) Inhibition of Cell Wall Synthesis; Beta-Lactam
2) Inhibition of Protein Synthesis; Tetracycline
3) Inhibition of Enzyme Activity; Trimethoprim
4) Injury to Cell membrane; Polymyxins
5) Inhibition of DNA synthesis; Ciprofloxacin
How are the clinical steps to identifying an unknown different than classical microbiology steps?
In clinical, we make a list of possible suspects using the symptoms and location of the infection to narrow down our scope and THEN we streak for isolation on differential or selective media.
suppress growth of unwanted bacteria and encourage growth of desired microbes
allows growth of several types of microbes and displays visible differences among those microbes
Used to isolate Salmonella and Shigella from a stool sample;
Also used to determine the ability of an organism to ferment Lactose.
Positive result= Pink
Negative result= White
selects for gram negative
Used to isolate fecal coliforms;
Contains sucrose and lactose;
Strong lactose fermenters = green sheen or black centers
Weak lactose fermenters = pink/purple
What are the ingredients in a Mannitol Salt Agar?
High Salt content, mannitol sugar, and phenol red pH indicator;
High salt content makes it selective, mannitol and pH indicator make it differential;
Positive for mannitol fermentation = yellow;
Negative = pink
A clear zone seen around a bacterial colony growing on blood agar.
partial clearing of blood that results in a green discoloration of the medium
Steps in identifying Staph aureus
Streak for isolation on Mannitol Salt Agar and on Blood Agar;
Do catalase test;
Perform coagulate test
Staphylococcus aureus is:
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