BACTERIOLOGICAL LOOP: CHARACTERISTICS, TYPES, USES - BIOLOGY - 2024

The bacteriological loop is a working instrument used by microbiologists for the sowing of microbial cultures (bacteria or fungi). It is perhaps the instrument most used by these professionals.

Its use seems simple, but in reality it requires a lot of training. Before starting sowing, the loop must be sterilized in the Bunsen burner, then the microbial inoculum that can come from a liquid culture or a solid culture is taken.

Types of bacteriological loops. Source: No machine-readable author provided. ば や お assumed (based on copyright claims).

Once the inoculum is taken, it can be deposited in a liquid medium or seeded in a solid medium. After each procedure the loop is sterilized again. The handle is also suitable for making microbial smears on a slide.

The bacteriological loop has many names, including: platinum loop or loop, inoculation loop or seed loop, however its real name is Kohle loop.

The material with which the handle is made is generally a nickel-chromium (nichrome) alloy or platinum. Another variety available in the market are the plastic disposable bacteriological loops.

On the other hand, there are several types of bacteriological loops, each one fulfills a function within the tasks carried out by a microbiologist. The choice of handle will depend on what needs to be done.

For example, to perform a striatum by depletion in order to isolate a microorganism, the platinum loop is used, which ends in a closed ring, regardless of whether it is calibrated or not.

Whereas, if it is to sow a urine sample, where it is important to quantify CFUs, it is necessary to use the calibrated loop. Likewise, to inoculate biochemical tests, which require to be sown by puncture, the needle loop is essential. It is important that the handle is handled by trained personnel.

characteristics

Bacteriological loops are made up of two extremes. One end corresponds to the handle or base, while the other is the handle itself.

Handle base or handle

The base serves to grip the handle during handling. It is usually metallic, but has a heat insulator to prevent the operator from being burned when the tip of the handle is sterilized on the lighter. It measures approximately 20 cm, although it can be longer. It has a thread to adjust the handle.

Handle

It is the functional end, that is, it is the part that comes into contact with microorganisms and with the culture media. It consists of a fine wire that is inserted into the base.

The handle can be made of nichrome or platinum, which is why it is sometimes called a platinum handle. It is approximately 6.5 cm long and has a gauge of approximately 0.20 mm. The handle with the handle can measure 26.5 cm. Measurements may vary from manufacturer to manufacturer.

Types

There are several types of bacteriological loops and each one has a specific use. The types of handles are as follows: calibrated ring-shaped handle, uncalibrated ring-shaped handle, straight or needle handle, spatulate handle, “L” -shaped handle and sharp-tipped handle.

On the other hand, the handles can be permanent or disposable. Those for permanent use are sterilized in the lighter, being reusable and very durable. While disposables are sterile from the factory, they are used only once and are discarded.

Applications

Ring handle, not calibrated

It is the most used handle in the microbiology laboratory. It is used to take an inoculum of a microbial suspension (liquid medium) or a portion of colony (solid medium), to be seeded in another culture medium, either a biochemical test or a more enriched or selective medium, as the case may be. It is also useful for making microbial smears on a slide.

With this type of loop, the initial inoculum can be streaked. It is also designed so that it glides smoothly on the agar, without damaging it. Of course, this requires a trained staff to handle the seeding technique, applying the correct force and movements to make a good striation.

Various seeding techniques can be performed with this handle. Example, solid media in Petri dishes are usually seeded by exhaustion (there are several techniques, see video 1).

This technique is intended to obtain isolated colonies in order to study and identify them, especially when the sample is polymicrobial, that is, the culture is not pure (it contains more than one type of microorganism).

Instead, the wedges are planted in a simple zigzag to obtain bacterial mass, not being necessary in this case to isolate colonies.

Sometimes they are also used to take certain samples. For example, Rojas et al. Used the bacteriological loop to collect scraped vaginal tissue samples from rats.

Bacteriological loop with ring tip, not calibrated. Source: Pixinio.com

Ring-shaped handle, calibrated

This handle as its name implies is calibrated to take a specific amount of microbial suspension. It is used when it is necessary for the inoculum to comply with what is standardized in the art.

For example, it is very common for planting urine cultures. In this case, a 0.01 ml and a 0.001 ml calibrated loop can be used.

It should be noted that calibrated handles have a margin of error, which varies according to the angle with which the sample is taken and the size of the mouth of the container.

If the 0.001 ml loop is inserted vertically into a container with a small mouth (≤ 7 mm), the amount taken will be 50% less than desired.

This occurs because the smaller the diameter of the mouth of the container, the higher the surface tension and therefore the adhesion forces between (glass - liquid) increase. This causes the liquid charge taken by the handle to be less.

Whereas, if it is taken at an angle of 45 ° in a container with a wide mouth (≥ 22 mm), 150% more than the required amount can be collected. In this case, the surface tension is lower and the glass / plastic cohesion forces decrease, while the liquid-liquid cohesion force increases.

Because of the above, other methods for the quantification of colony-forming units are sometimes preferred for urine cultures.

Straight or needle handle

It is also called a thread handle. It is used to inoculate certain biochemical tests, especially those that require to be seeded by the puncture technique. Example, semi-solid media that are prepared in the form of a block, such as: SIM, MIO and O / F medium.

In addition, in the case of MIO and SIM that assess motility, it is essential that the puncture be performed with a needle loop, since the interpretation of a positive motility occurs when the bacteria grow towards the sides of the initial inoculum.

A test inoculated with a loop loop can falsify results (false positive). For this reason, in this type of seeding, care must be taken that the puncture is unique, and that when it is removed it comes out in the same direction it entered.

Another test that must be needle seeded even though it is prepared in a wedge shape is the Kligler. In this test, it is not recommended for oxygen to penetrate deep into the agar, as an oxygen-poor medium is required for certain chemical reactions to occur. This handle is also used to touch a specific colony for the purpose of subculturing.

Spatulate handle

Most microorganisms give soft, easy-to-shed colonies. However, there are some microbial agents whose colonies are hard and dry, for example mycobacteria in general and some fungi. In these cases it is useful to use the spatulate handle.

"L" shaped handle

Its most frequent use is to chime fungal cultures, especially molds.

Sharp tip handle

It is useful for taking very small colonies present in polymicrobial cultures, in order to be able to subculture them.

Sowing techniques

Video 1

Sterilization of the platinum handle

The handle must be sterilized before and after use. To sterilize the bacteriological loop in the lighter, proceed as follows: the handle should be placed at the top of the flame, adopting a position as vertical as possible, in such a way as to sterilize from the tip up.

When the fine filament turns bright red, it can be said to be sterile. To use it, it is cooled and the chosen sample is taken. (See video 2).

Sterilization of the bacteriological loop

Video 2

References

1. "Bacteriological loop" Wikipedia, The Free Encyclopedia. 23 Jul 2019, 13:31 UTC. 18 Aug 2019, 22:45. Wikipedia.
2. Herrera D, López P, Duque J, Pérez L, Golding R, Hernández C. Calibrated metal handles for microbiologists: An alternative of national manufacture. Soc. Come. Microbiol. 2010; 30 (1): 37-42. Available at: ve.scielo.org
3. Forbes B, Sahm D, Weissfeld A. (2009). Bailey & Scott Microbiological Diagnosis. 12 ed. Editorial Panamericana SA Argentina.
4. Koneman E, Allen S, Janda W, Schreckenberger P, Winn W. (2004). Microbiological Diagnosis. 5th ed. Editorial Panamericana SA Argentina.
5. Rojas A, Pardo-Novoa J, Río R, Gómez-Hurtado M, Limón D, Luna F, et al. Determination of the analgesic effect of hexane extract from Eupatorium arsenei flowers in an acute pain model in rats. mex. science. farm. 2015; 46 (1): 64-69. Available at: scielo.org