Quick Answer: How Can A Streak Plate Become Contaminated?

How do you sterilize a petri dish with autoclave?

Sterilize equipment in an autoclave at 121 °C (250 °F) for 15 minutes.

Borosilicate glass items may be sterilized with dry heat at 170 °C (338 °F) for a minimum of 1 hour..

Does the pour plate or streak plate technique take more skill?

Does the pour plate or streak plate method take more skill? The streak plate requires more skill, as you need to have some “sleight-of-hand” to properly “drag” and “squiggle” your inoculum across your plate quadrants, allowing proper spacing between colonies.

How can you tell if a streak plate is contaminated?

Checking for Contamination Look for signs of fungal contamination. Fungal contamination will appear as fuzzy, filamentous, or hair-like growths, and should be visible to the unaided eye. Fungal contamination often occurs right along the edge of an agar plate.

How do you streak a plate with bacteria?

Start by streaking a vertical line of bacteria along one edge of the plate. Then streak horizontal lines in another section of the plate, and then diagonal lines in another section of the plate.

Why do we need to sterilize the growing media?

When microbiological media has been made, it still has to be sterilized because of microbial contamination from air, glassware, hands, etc. Within a few hours there will be thousands of bacteria reproducing in the media so it has to be sterilized quickly before the microbes start using the nutrients up.

How can we prevent agar plate contamination?

Clear the work space of all non-essential items. Clean the desk with disinfectant. Reason – this kills all unwanted bacteria and so decreases the chance of the agar plate becoming contaminated.

How long does it take for bacteria to start growing?

Bacteria grow most rapidly in the range of temperatures between 40 °F and 140 °F, ( 4.4°C- 60°C) doubling in number in as little as 20 minutes. This range of temperatures is often called the “Danger Zone.” To learn more about the “Danger Zone” visit the Food Safety and Inspection Service fact sheet titled Danger Zone.

What is the difference between streak plate and spread plate technique?

The key difference between streak plate and spread plate is that the streak plate is used to isolate and purify a particular bacterial species from a mixture of bacteria while the spread plate is used to enumerate and quantify bacteria in a sample.

Can some bacteria grow on the streak plate?

Can some bacteria grow on the streak plate and not be seen if the pour plate technique is used? Yes, the pour plate is O2 limited. Thus, some bacteria will only grow on the streak plate as it provides ample O2.

What happens if you incubate bacteria too long?

If a bacterial culture is left in the same media for too long, the cells use up the available nutrients, excrete toxic metabolites, and eventually the entire population will die. Thus bacterial cultures must be periodically transferred, or subcultured, to new media to keep the bacterial population growing.

What is the purpose of a streak plate?

Agar streak plates are an essential tool in microbiology. They allow bacteria and fungi to grow on a semi-solid surface to produce discrete colonies. These colonies can be used to help identify the organism, purify the strain free of contaminants, and produce a pure genetic clone.

How can a petri dish become contaminated?

The most exasperating problem confronting attempts to cultivate moulds is contamination by other moulds. Most mould spores are very light and easily transported by air. Even opening the lid of a Petri dish for a few seconds may allow the entry of contaminating organisms.

How would you know if a stock culture was contaminated?

So, although the threat of contamination from these microorganisms is ever-present, you can easily spot their presence by the turbidity of the growth medium or the floating, branching mycelia. Bacterial contamination can often be confirmed under a 10x microscope within a few days of contamination.

How long can bacteria survive on agar plate?

Table 1. Approximate time bacterial cultures remain viable in different storage conditions.ConditionTemp (°C)Time (approx.)Agar plates44 – 6 weeksStab cultures43 weeks – 1 yearStandard freezer-201 – 3 years2 more rows

Why do we Flame the loop between streaks?

Flaming the loop between streaks ensures that the loop starts clean and that only this small amount of bacteria is used to inoculate the next quadrant.