What Should I Know About Bacterial Identification?

Mary McMahon

Bacterial identification is a process which is used to pinpoint the identity of specific bacteria. It is an important part of medical treatment, since many treatments are heavily dependent on the identity of the particular organism causing a medical problem, and it is also an important part of scientific research. A number of techniques are used in bacterial identification, and new techniques are constantly being devised as people learn more about bacteria and new medical equipment is developed.

Bacterial identification is an important part of medical treatment.
Bacterial identification is an important part of medical treatment.

The first stage in bacterial identification involves the creation of an isolate, a working sample of the bacteria in question. Isolates start with a small swab of the suspected bacteria taken from a patient or an object. The isolate is created by finding a growth medium which will support the bacteria, and successfully culturing enough of the bacteria for study. This can be a real challenge, since bacteria are very picky, and they will not grow in just any medium. It's also important to avoid contaminating the growth medium or sample, as this can result in confusing results.

Samples collected from the back of the throat may be grown for several days before lab results are available.
Samples collected from the back of the throat may be grown for several days before lab results are available.

Once a bacteria has been cultured, a wide variety of tools can be used to provide clues into its identity. Once of the most basic is a Gram stain, which divides bacteria into Gram-positive and Gram-negative bacteria with the use of a chemical stain. Other stains can be used to increase contrast, making the bacteria easier to see under a microscope. Visual identification under a microscope can commonly be accomplished with familiar bacterial species, especially those with a distinctive shape.

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There are more tools in the bacterial identification arsenal. A researcher can use serological methods, which involve exposing a sample of unknown bacteria to various antibodies to see if there is a reaction, or gene sequencing, in which the genetic code of a bacterium is unraveled. Gene sequencing can also be used to differentiate between two closely related strains of bacteria, providing information about why one strain responds to a particular course of medication while another does not. Responses to various chemicals and stimuli like ultraviolet radiation may also be studied.

Bacterial identification is classically performed in a lab, since labs have medical equipment, chemicals, and tools which can be used in the course of tracking down the identity of a bacterium. Some labs specialize in culturing and identifying samples from hospitals and medical clinics, while others focus on research, identifying samples of new and unknown bacteria so that they can be classified. The lab environment is tightly controlled to prevent contamination and accidental infection of lab workers, with especially virulent organisms being studied in high-security labs which include several layers of protection for the scientists.

Familiar bacteria can often be identified by shape.
Familiar bacteria can often be identified by shape.

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Discussion Comments


We learned about the gram stain procedure in school today. It's very interesting. It has more steps than I expected, thirteen steps in total!


@stoneMason-- I agree with you. Unfortunately, in some developing countries, bacterial identification is still not used very much. It is usually used in situations where a sexually transmitted disease might be suspected. Otherwise, patients are treated mostly based on their symptoms.

I think bacterial identification needs to be used more often worldwide. Sometimes bacterial identification is as simple as looking at the shape of the bacteria under a microscope to identify it like the article described. And yet, doctors in some countries don't bother and haphazardly prescribe antibiotics without even knowing if the cause is bacterial or viral.


The only time a doctor has taken a swab sample for me for bacterial identification was when I had a severe sore throat. The doctor suspected strep throat (streptococcus bacteria) and sent a sample to the lab. The results showed that it was not strep and I was not given any treatment.

I think we are very lucky that we have the advanced medical technology to identify bacteria. It makes life so much easier and also prevents the unnecessary use of medications.

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