Microbiology Test

Test : Throat culture


Indications : The test is mostly employed when symptoms of Strep throat are observed in a person.

A throat culture is ordered for the following reasons -

• Sore throat / throat infections

• Identify the causative bacteria in case of throat infections and determine the antibiotic that is best suited for the patient

• Determine carriers of throat infections who are likely to spread it to others

The test does not require any prior preparation. However, you have to inform the doctor regarding any medicine that you may be taking. Also, do not use a mouthwash prior to the test.

While taking the swab, you will have to tilt your head backward and, widely open your mouth. The doctor will use a flat stick, known as the tongue depressor, to press your tongue downward. A clean cotton-tipped swab will be run over the tonsils and the back region of the throat. This may have to be repeated a few times. Swabbing your throat may be painful if your throat is sore.

In some cases a throat washout method is employed where you will be made to gargle with a small amount of salt water and spit into a clean cup. This gives a larger sample than a swab.

The swab is then streaked on to culture dishes containing growth media and allowed to grow. Bacterial cultures take about two days to grow while fungus takes a week. However, strep throat test results can be acquired rapidly, within 10-15 minutes.

Physiology : A throat swab culture is carried out to detect a bacterial or fungal infection affecting the throat. Most sore throats and throat infections are caused by virus. However, throat cultures for viruses are not usually carried out as they don’t grow well in culture. Besides, these tests are expensive.

The throat swab test is a good diagnostic tool to differentiate between bacterial and viral infections and to determine the appropriate treatment.

Interpretation : Normal –Negative

No growth of micro organisms seen in culture. It could mean that your throat infection is caused by a virus and not by a bacteria or a fungi.

Some of the virus that cause throat infections include Enterovirus, Epstein-Barr virus, Herpes simplex virus, Respiratory syncytial virus (RSV).

Abnormal – Positive

Growth of micro organisms observed in the culture, indicating a throat infection. Some common micro organisms and infections are listed below -

• Candida albicans (fungus) - causes ‘thrush’ an infection of mouth tongue and throat

• Group A streptococcus (bacteria) - causes strep throat, rheumatic fever and scarlet fever

• Neisseria meningitides (bacteria) - causes meningitis

Sample : Throat swab

Test Method : Aerobic culture

Related Tests : Antihyaluronidase Titer, Antistreptolysin O titer, Bacterial serology, Gram stain, Sputum fungus culture.

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