Contents

What reasons might lead to absence of growth on a streak plate?

Streak Plate – should appear near or in a vaccinity of streak lines and sections. E9 – What factor(s) could accunt for an absence of growth on a pour plate? The lack of oxygen, poor/ bad bacteria smear, or difference in temperature that prevents optimal growth, within media.

Why did my streak plate not work?

I have done 2 different method to isolate mercury resistant bacteria from Soil. 1. Streak plate method: From my mix culture in Nutrient Broth, I got 28 colonies.

What is a disadvantage of the streak plate technique?

What is a disadvantage of the streak plate technique? You can’t accurately count how many colonies there are. What is a disadvantage of the pour plate technique? Sometimes bacteria will clump together and look like a colony when they are not. Will the isolated colonies always be in the fourth sector on the streak plate …

What are the factors that might affect the number of colonies of bacteria in a plate media?

The major issues include the colony size and behavior (swarming?), and the surface area of the plate. The size particularly comes into play with plating a membrane for determination of CFU as the surface area of that membrane is so much smaller than that of a standard plate.

Why does the streaking method result in isolated colonies?

Why does the streaking methods you used to inoculate your plates result in isolated colonies? … This begins to dilute the bacteria by spreading it over distance and eventually the bacteria are spaced far enough apart to form single colonies.

How do you identify isolated colonies on a streak plate?

Isolated colonies were identified and transferred by streaking onto a new agar or gelatin plate using a sterile needle, a process called “picking colonies.” More rarely, a researcher would try to isolate organisms directly on the surface of a gelatin or agar plate.

What are the disadvantages of simple and radial streaking?

Streak plating is a microbiology laboratory method that has two major disadvantages.
  • Firstly, users will not be able to grow obligate anaerobes using this method.
  • Secondly, only organisms that were viable in the original sample are able to be grown.

What are the factors to be considered in inhibiting the growth of bacteria?

Warmth, moisture, pH levels and oxygen levels are the four big physical and chemical factors affecting microbial growth. In most buildings, warmth and moisture are the biggest overall issues present.

Which factors inhibit the size of bacterial colony?

Two of the main factors that affect bacterial growth in a laboratory are media nutrient density and media hardness, the latter being a result of agar concentration.

What is the most likely reason why the isolated colonies at the top edge of the plate are smaller than those in the middle?

What is the most likely reason why the isolated colonies at the top edge of the plate are smaller than those in the middle? There is more competition for nutrients in areas of denser bacterial growth.

What is an isolated colony?

An isolated colony is a bacterial colony that has been isolated from other contaminants, usually by placing a sample in a sterile petri dish or glass slide with nutrients. This process ensures any observations or experiments are free from outside biological contaminants. This colony is often called a “pure culture.”

What assumption do we make about an isolated bacterial colony that formed on an agar plate?

Pure cultures can be obtained by picking well-isolated colonies and re-streaking these on fresh agar plates. A common assumption is an isolated colony of bacteria is the progeny of a single bacterial cell (i.e. colony is the clone).

What are some consequences of not leaving a stain on a smear long enough under staining?

2. What are some consequences of not leaving a stain on a smear long enough (under- staining)? -Some consequences of under-staining are that the cells may lose their stain when washed with water or alcohol. Consider a coccus and a rod of equal volume.

Why should one make sure that the commercially available glass slide does not have a layer of grease before preparing the smear?

Why should one make sure that the commercially available glass slide does not have a layer of grease before preparing the smear? Because the stain and smear will not stay intact if any residual grease is not cleaned completely away. … As a result, they do not stain the bacteria, but color the background.

In which quadrant will you expect to see isolated colonies?

Which quadrant in streaking will have isolated colonies? Why? Quadrants II and III will have the isolated colonies because they have the least amount of bacteria in them. 1) Pure colonies can be used to start a large stock culture (subculture) of a single isolated bacteria.

What happens if you leave safranin on for too long?

Do NOT decolorize for a full minute!

If the decolorizer is left on too long, even gram positive cells will lose the crystal violet and will stain red.

What would happen if you left out the application of safranin?

A safranin counterstain is used to stain these Gram-negative cells pink. However, if the safranin counterstain were forgotten, the Gram-negative bacteria would remain unstained, as the original crystal violet stain would have been removed during the ethanol wash, and no additional stain would have been applied.

What happens when you fail to add iodine to a Gram stain?

If there is a failure to add iodine, then the cross-linking between the crystal violet and iodine won’t happen, which helps the stain fade away during decolorization. … In that case, the stain makes every bacteria purple, and we won’t be able to distinguish the difference between Gram-positive and gram-negative bacteria.

What are the common errors in staining methods?

The rank of errors is:
  • Over decolourisation.
  • Mixed cultures.
  • Misread stains.
  • Aged subcultures.
  • Disorganisation.
  • Inadequate fixation and Insufficient culture.

What is the purpose of the smear preparation?

The preparation of a smear is required for many laboratory procedures, including the Gram-stain. The purpose of making a smear is to fix the bacteria onto the slide and to prevent the sample from being lost during a staining procedure. A smear can be prepared from a solid or broth medium.

What happens if you over Decolorize?

Over-decolorizing will lead to an erroneous result where gram-positive cells may stain pink to red indicating a gram-negative result, and under-decolorizing will lead to an erroneous result where gram-negative cells may appear blue to purple indicating a gram-positive result.

Why might Gram staining fail sometimes?

Gram-positive bacteria may lose their ability to retain crystal violet and stain Gram negatively for the following reasons: Cell wall damage of bacteria due to antibiotic therapy or excessive heat fixation of the smear. Over- decolorization of the smear.

What are some problems that can occur when performing a Gram stain?

Several factors may affect the results of Gram staining: If the smear is too thick, proper decolorizing will not be possible. If the smear is overheated during heat fixing, the cell walls will rupture. Concentration and freshness of reagents may affect the quality of the stain.

What can cause false results in Gram staining?

False-negative Gram stains could occur due to inadequate specimen or smear preparation or failure to examine an adequate number of fields. In addition, training and maintenance of proficiency for Gram staining remain challenging (5, 20).