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What is the correlation between corrected O.D. and cell number for your culture?
The higher the O.D. the greater the growth
When performing a standard plate count, why are the counts reported as colony forming units (CFUs) rather than cells?
Uncertain how may cells there are
How would you inoculate a plate to get a 1:10 dilution? A 1:100 dilution?
1 ml inoculate into 9ml water blank. 1ml inoculate into 99 ml water blank
Why is it necessary to perform a plate count in conjunction with the turbidimetry procedure/
Because the turbidimetry procedure measures protein, DNA and dry weight whereas a plate count is more accurate.
Which antimicrobics would be suitable for the control of the following organisms?
none, R to all
Gentamycin, tetracycline, polymyxin B
Ampicilin, Gentamicin, Streptomycin
Antibiotics and antimicrobial drugs
Antimicrobics are compounds that kill or inhibit MOs. Sulfisoxazole is an example.
Antibiotics are usually antimicrobics, usually of low molecular weight, produced by MOs that inhibit or kill other MOs
Broad- and narrow- spectrum antibiotics
Broad- when all bacteria have 70S ribosome which are necessary for protein synthesis.
Narrow- not all bacterial cells can synthesize folic acid, whose synthesis is inhibited by this drug
What factors influence the size of the zone of inhibition for an antibiotic?
Temperature, age of disk, thickness of medium
Why are certain gram-negative bacteria more resistant than gram-positive bacteria to antibiotics that attack cytoplasmic targets?
The outer membrane of gram - bacteria acts as a permeability barrier and can restrict the entry of antimicrobials into the cell
Why are gram + bacteria typically more resistant than gram - bacteria to antibiotics that disrupt plasma membranes such as polymyxin B?
Even though it disrupts, it still has a thick layer of peptidoglycan that can make it more resistant
If a bacterial isolate shows intermediate to moderate resistance to an antibiotic, how might this antibiotic still be successfully used in the treatment of this microbe?
If you use a higher dose of the antibiotic so long as toxicity is not an issue
What specific medium must be used in testing the effectiveness of antibiotics?
The Mueller-Hinton II agar
What is the role of oxygen for cellular respiration?
It is the terminal electron acceptor in the electron transport chain
What type of metabolism occurs in the absence of oxygen
Anaerobic respiration, fermentation
Name two enzymes that are present in obligate aerobes but lacking in obligate anaerobes. What is the function of each enzyme?
Catalase- degrades hydrogen peroxide into O2 and H20
Peroxidase- degrades hydrogen peroxide
Differentiate between a microaerophile and an aerotolerant organism
Microaerophile- low 02 concentration necessary for respiratory metabolism
Aerotolerant- tolerate 02 and can grow but do not need it for energy production
What is resazurin a useful media additive for the study of anaerobes?
It is an oxidation/reduction indicator
Why is a GasPak anaerobic jar necessary for the culture of anaerobes on plates of Brewer's anaerobic agar but not in tubes of fluid thioglycollate medium (FTM) ?
Becasue the Gas Pak anaerobic jar is an oxygen-free incubation environment. The FTM supports growth of aerobes as well so oxygen is present
Define the optimal growth temperature for each of the following classes of bacteria
above 80 C
between 50 C and 80 C
20 C and 50 C
between -5 C and 20 C
Differentiate between psychrophile and psychrotroph
Psychrophiles grow between -5 C and 20 C. Psychotrophs grow above or below optimum temperatures for example, and grow at refrigerate temperatures and cause food spoilage
Why are psychrotrophic bacteria of concern to those in the food-service industry?
They can grow at refrigerated temperatures and can cause food spoilage
What is the optimum growth temperature for most human pathogens? Explain.
35 C and 40 C because this is the human body temperature
Name three cellular components involved in metabolism that are influenced by temperature changes
Enzymes, cell membranes and transport ribosomes
How does pH negatively affect the metabolism of MOs?
If pH levels exceed the optimum for an organism, the solubility of charged molecules can be adversely affected and molecules can participate out of the sol'n.
Define 3 groups of MOs in regard to their optimum pH for growth
Neutrophiles= 7 pH
Acidophiles >5 pH
Alkaliphiles < 8 pH
How would the pH of the culture medium be influenced by sugar fermentation? By urea hydolysis?
The pH would be higher because fermentation releases acids. The p H would also go up because urea hydrolysis releases ammonia to raise the pH level
Which chemical was the most effective for inhibiting growth of
- tincture methyolate
- tincture methyolate/ H202
Which chemical was the least effective for inhibiting growth of S
S. aureus: 70% ETOH, mouthwash
P. aeruginosa: Lysol, 70% ETOH, Bleach, mouthwash, Betadine
What do your results indicate about the relative chemical resistances of these two species?
P. aeruginosa is much more resistant than S. aureus
Differentiate between antiseptic and disinfectant. Include examples of each in your answer. Indicate whether any chemicals can be used as both.
Antiseptic: use on living tissues for example, hand soap
Disinfectant: use on inanimate objects for example 10% Lysol
What factors influence the size of the zone of inhibition produced by a chemical?
Diffusibility of the agent, size of inoculum, and the type of medium and temp
How might the physical differences between gram + and gram - bacteria contribute to differences in chemical resistances?
The outer membranes of gram - bacteria acts as a permeability barrier and can restrict the entry of antimicrobials into the cell
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