DR HASSAN MIDTERM LAB BIOL 261 Q1. What is the purpose of inverting inoculated p
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DR HASSAN MIDTERM LAB BIOL 261 Q1. What is the purpose of inverting inoculated plates duringincubation? Q2. Define or explain: i) Aseptic Technique ii) Axenic Culture iii) Complex or Nutrient media iv) Anaerobic v) Defined synthetic media Q3 What is the purpose of oil with the microscope that you use in your class? What can't viruses with your microscope? Q4. What is the total magnification of your microscope if the ocular has 10X, the objective lens is 43x and the condenser lens is 20X. it required to fix the bacterial smear on the slide, What is the advantage or disadvantage to "Heat fix" or "Air bacterial smears. What may happen during staining if the smear is not fixed? Q6. A mixed smear of Staph, epidermidis and Ecoli is Gram stained. Describe how the smear will stain under the following conditions i) smears stained for 24-hour old culture i) smears stained from 7-day old cultures Q7. Why should controls be used with each experimental procedures?Explanation / Answer
1.Plates are kept inverted while incubation to so as to prevent any condensed water to drip onto the culture and thus avoid contamination.Also,it reduces the rate of evaporation and prevents the media from drying resulting in good microbial growth.The lids of petridishes may contain contaminants which might interfere with the microbial growth;so keeping the plate inverted helps to prevent the contamination.
2.
i ) Aseptic technique : It is defined as the culture of microorganisms in a sterile media under sterile laboratory conditions.
ii) Axenic culture :It is defined as the culture that allows the growth of only a single species or strain of microorganism thus excluding the growth of other contaminating microorganisms.
iii) Complex or nutrient media : A complex media is one that contains all essential elements as well as components of biological origin such as beef extract, milk, blood whose exact chemical composition is not known and are required for growth of all bacteria thus are not selective against growth of any particular bacteria.
iv) Anearobic : It means in microorganisms that respire in absence of oxygen or grow under oxygen deficient conditions.
v) Defined or synthetic media:It is a type of media in which the exact composition of all the components are known.
3.Oil immersion increases the resolving power of the microscope and the microbial structures can be viewed accurately.Viruses are very small in size i,e 1/10th the size of bacteria.Under light microscopy, 200nm sized particles can be viewed and viruses are much smaller than this size.
4.Total magnification = ocular mafnification * objective magnification = 10X * 43 X = 430 X.
5.In order to prevent the washing away of bacteria during the staining step and to study the structures of bacteria by staining it properly,it is required to fix the smear on slide.The advantage of heat fix and air dry is that it kills the bacteria and fixes it to the slide thus allowing the stain to be taken up properly.Air dry dries off all the bubbles of water that may interfere with staining.
6.
i)For 24 hour old culture , staph.epidermis will stain gram positive while E.coli will stain gram negative.
ii) for 7 day old culture , staph.epidermis will stain gram negative while E.coli will stain gram negative.This is because as cultures become old,the cell integrity is lost and gram positive bacteria fail to adhere the crystal violet stain and so appear gram negative.
7.A control setup helps to distinguish and compare between the effect of independent variable on the experimental set up. So it is used in the experimental procedure.
8.Advantages:
i) Liquid broth : It allows for growth of much more bacteria as entire solution is available for bacteria to grow.Also it allows the growth of different aerotolerant bacteria.
ii)Pour plate :Advantage is that we can study microbial contamination of food and water and can calculate the microbes present per ml of sample.
iii)Streak plate : It allows for individual colony forming to be formed and the streaking done reduces the number of bacterial cells each time making the colonies more visible.
iv)Slants :Help to maintain pure culture of bacteria that can be maintained for longer period of time.
9.
EMB agar :It is a selective media that contains EMB dye to stain gram negative bacteria and mostly coliforms but are toxic to gram positive bacteria.
MacConkey agar :MacConkey agar contains crystal violet and bile salts that prevent growth of gram positive and fastidious gram negative bacteria but promotes growth of enteric gram negative bacteria such as E.coli.
Mannitol salt agar : It contains 7.5%-10% of NaCl that favours the growth of Gram-positive bacteria such as Staphylococcus and Micrococcaceae but inhibits the growth of other bacteria. It also contains mannitol that favours the growth of staphylococci that ferment mannitol.
10.UTI are caused by gram negative enteric E.coli.MacConkey agar contains crystal violet and bile salts that prevent growth of gram positive and fastidious gram negative bacteria but promotes growth of enteric gram negative bacteria such as E.coli.So plating of aurine with UTI agar will confirm that infection is caused by E.coli.
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