An inoculating loop is a simple laboratory tool consisting of a thin metal or plastic handle terminating in a small loop used to transfer a small amount of microorganisms from one medium to another.
Explanation
In microbiology, inoculating loops (also called wire loops) are used to pick up and deposit tiny volumes of bacteria, fungi or yeasts onto agar plates, into liquid broths or onto microscope slides. Traditional loops are made from nichrome or platinum wire shaped into a loop of defined diameter. Before use, the loop is sterilized by flaming until red‑hot and then allowed to cool to avoid killing the organisms being transferred. Disposable plastic loops are presterilized and eliminate the need for flaming. Loops may be calibrated to deliver a specific volume, such as 1 µL or 10 µL, which is important for quantitative urine cultures. Proper handling includes holding the loop like a pencil, using gentle streaking motions to spread cells for isolation and avoiding contact with surfaces outside the medium to maintain aseptic conditions. Inoculating needles, which have no loop, are used instead for stab cultures or for transferring small colonies without disrupting delicate agar surfaces.
Uses and examples
A laboratory technician uses a 10 µL calibrated loop to streak a urine specimen onto CLED agar to estimate bacterial count. When isolating Escherichia coli, a sterile loop is flamed, cooled and then used to streak the organism across sectors of a MacConkey agar plate to obtain single colonies. A microbiologist employs a loop to pick an isolated colony from a previous plate and transfer it into nutrient broth for further testing. Loops are also used to smear a small drop of culture onto a glass slide for Gram staining. Disposable plastic loops provide convenience in high‑throughput clinical laboratories.
Inoculating loops are essential tools for manipulating microorganisms in a controlled way. By transferring small, defined amounts of cells while maintaining sterility, loops allow microbiologists to isolate, quantify and prepare cultures with precision.
Related Terms: Inoculate, Aseptic Technique, Streak Plate, Culture, Inoculum