Inoculating loop and inoculating needle
What are inoculating loops?
Inoculating loops, also known as smear loops, inoculation rods, or microstreakers, are a simple tool used primarily by microbiologists to take and transfer a small sample, or called inoculum, of a microorganism culture, such as for stripping on a culture plate. They are widely used in many disciplines such as microbial detection, cellular microbiology, and molecular biology.
What is inoculating needle?
Inoculating needle is a necessary tool for picking mycelium blocks during inoculation. It is made by attaching a section of nichrome alloy inoculation hook to the front end of the lead rod. You can also sharpen one end of an inoculating wire and bend it into a small hook (hook length 3~5cm) to make an inoculation needle. Remember to cover the hand-held end with ebonite.
Inoculating loop and needle
Inoculating loops and needles are both handheld devices for inoculating plated or tubed growth media with microorganisms such as bacteria or yeasts before incubation, multiplication, and growth. Inoculums are typically streaked onto or stabbed into, solid agar-based media, or simply introduced and dispersed into liquid media. Both inoculation needle and loop are also useful for sampling and transferring small quantities of microorganisms before further analysis, microscopic examination, or serial dilution.
The difference between loops and needles is that the front end of the needle is pointed, while the front end of the loop is a circle. If you straighten the circle of the inoculating loop, it can be used as an inoculating needle. In this sense, the inoculation needle is the inoculation loop.
Features of inoculating loops (inoculating needle)
a. Hydrophilic after special surface treatment.
b. Ultra-smooth surface.
c. Easy to pick single colonies; easy to collect and inoculate specimens.
d. Multiple colors to distinguish between different sizes of inoculating loops and needles.
e. Thin, soft, bendable needle handle for narrow or specially shaped containers.
f. Gamma sterilized and unsterilized products available.
g. Easy-tear, anti-pollution bags with paper-plastic packaging.
h. Use sterilized, self-sealing pocket packaging and crush-proof, good-quality carton outer packaging to ensure the safety of transportation.
i. The boxes have batch numbers for easy quality tracking.
j. Ideal for microbiological experiments, bacterial experiments, and cell and tissue culture experiments.
Types of inoculating loops & inoculating needle
According to the usability, inoculating loops can generally be divided into disposable inoculating loops and reusable metal inoculating loop.
The disposable inoculating loop is usually a plastic inoculation loop.
The metal inoculating loop is typically included the nichrome wire loop, platinum inoculum loop, and steel inoculating loop and wire. Platinum wire material is the best among them, because of its features of easy heat transfer, heat dissipation, rust-proof, and durability. However, because of the high cost of platinum, nickel wire is usually used instead.
According to usage, there are streaking loop for microbiology, sterilizing inoculating loop, nichrome wire loop in microbiology, bacteriological loop, and inoculating needle microbiology.
The diameter of inoculating loops that are commonly used is 2mm to 4mm.
The needle length of inoculating needles that are commonly used is 50mm to 80mm.
Sterile disposable inoculating loops / sterile plastic inoculating loops
Nichrome loop / nichrome loop wire / nichrome inoculating loop
Use of inoculating loops (inoculating needle)
Methods of using inoculating loop needle
Use an inoculating loop to stick the bacteria-containing material and scribe it on the surface of the solid medium.
b. Spot planting
Touch a few points on the surface of the solid medium with an inoculating needle.
A small amount of bacteria-containing material is placed in a sterile Petri dish and poured with melted agar medium at about 48°C. Then shake well and leave to cool.
The microorganism is punctured with an inoculum loop and entered into a deep culture of the semi-solid medium.
e. Infection washing
Bacteria-containing material is picked off with an inoculation loop and washed in a liquid medium.
Flaming inoculating loop
Early microbiologists had to rely on open flames to ensure sterility while working on certain techniques on the bench. With modern advances in technology, including the introduction of biosafety cabinets, the use of open flames is almost no longer necessary. Flaming inoculating loops used with biohazardous materials produce aerosols, potentially exposing personnel and the environment to infectious airborne droplets. Sterile disposable loops should be used instead of flaming whenever possible. Generally, flames are not required inside the biosafety cabinet (BSC) because the BSC provides a sterile environment. A more important reason for not using an open flame inside a BSC is that open flames inside BSC can damage the HEPA filter and cause a buildup of flammable materials. If a flame is required for the procedure, an alternative flame device can be used inside the biosafety cabinet, and approval from the appropriate authorities is required before use.
Sterilizing inoculating loop
Flame heating or scorching sterilization devices commonly used in laboratories are alcohol lamps, Bunsen burners, and infrared sterilizers. Among them, the inoculating loop infrared sterilizer is the sterilization equipment that can be used inside the biosafety cabinet. The inoculating loops
should be cauterized before inoculation. The purpose of this is to ensure that the culture is not contaminated during inoculation. Cauterizing after inoculation is to prevent the strain from floating out and contaminating the inoculation room or ultra-clean table, which may affect the overall inoculation environment. Sterilization of the inoculating needle
is a measure to reduce the contamination rate.
The flame lamp is a piece of necessary equipment for the sterilization of inoculators
and sterilization treatment of test tubes and other items during bacteriological testing operations. The Bunsen burner is ideal for inoculation sterilization equipment in the laboratory because the size of the flame can be adjusted as needed. The flame can be divided into two layers: outer flame and inner flame. The outer flame should be used when cauterizing the inoculating loop
because it is hot due to the contact with more oxygen. When the laboratory is not equipped with a Bunsen burner
, an alcohol lamp can be used for cauterizing the inoculating needle
, but the temperature is not as high as the Bunsen burner.
Use of alcohol lamp
a. Ignite the alcohol lamp.
b. Take out the inoculating loop from the ethanol.
c. Sterilize the inoculum loop by cauterizing it over a flame no less than three times. Note that the rest of the inoculation ring that may be deep inside the tube should also be cauterized, especially at the bend.
d. The inoculation operation should be done after the inoculating needle has cooled slightly in case the microorganism will be scalded to death.
Matters need attention
a. Soak inoculating loops in 70% ethanol before use.
b. In the interval between inoculation operations, the inoculating needles need to be re-soaked in ethanol and cauterized for sterilization.
Use of infrared sterilizer
Infrared sterilizers are commonly used in laboratories in developed countries such as Europe and the United States for high-temperature sterilization. It is usually used for high-temperature sterilization of small objects like inoculating loops and inoculating needles. As an alternative flame device, it can replace the alcohol lamp and Bunsen burner to be used in the biosafety cabinet.
Advantages of infrared sterilizer
a. Convenient and fast, sterilization only takes 5-7 seconds.
b. no open flame, no gas, windproof, environmentally friendly, safe to use, no harm to the human body.
c. Truly efficient, energy-saving, and environmental protection.
d. Prevent infectious spills or cross-contamination.
e. Widely used in biological safety cabinets, purification workbenches, next to extractor fans, mobile vehicles, and even in harsh environments like the field.
f. Disinfected at high temperature at any time.
g. The sterilization process of electrothermal inoculation rings (needles) is fully compatible with microbiological requirements.
The inoculating loop infrared sterilizer does not consume oxygen during operation. It can be used in anaerobic chambers, and the sterilization is complete. The temperature inside the chamber can reach nearly 800 degrees Celsius, and it only takes 5 to 7 seconds to sterilize all the microorganisms completely. Based on the electronic infrared principle, the main body of the instrument is made of stainless steel.
Matters need attention
a. Inoculating loops must be used when observing the morphology of bacteria from the specimen or culture being examined.
b. The metal or glass rod portion of the inoculating needle needs to be rotated in the infrared sterilizer chamber for sterilization.
c. The infrared sterilizer can also sterilize microbial culture tubes made of glass, but special attention should be paid to not having any liquid or other objects in the tubes to avoid dangerous accidents such as the spilling of liquid or explosion.
d. Non-stained specimens and stained specimens should be put into sterilization solution immediately after observation.
e. After using the slide, you should thoroughly eliminate the stained bacteria from the slide before using it again. Otherwise, re-use of a slide that has not been thoroughly sterilized may lead to seriously biased results.
f. Prepared plates that used inoculating loop can be stored for 2-5 days. They should be protected from direct light.
g. Dried medium should be placed in a dark and dry place, stored at 2-8°C, and protected from light.
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