Laboratory Cultures

General Description

A culture is a microbiological technique used to detect the presence of microorganisms, such as bacteria, fungi, or parasites, in a sample of tissue or bodily fluids. Therefore, a culture helps confirm or rule out an infection in the body and identify the pathogenic agent responsible.

Some of the most commonly performed cultures include:

• Blood culture: a culture of a blood sample.
• Urine culture: a culture of a urine sample.
• Throat swab culture: a culture of a sample taken from the throat.
• Stool culture: a culture of a fecal sample.
• Wound culture: a culture of samples taken from the cells or secretions (pus) of a wound or burn.
• Sputum culture: a culture of mucus (phlegm) produced in the respiratory tract.
• Semen culture: a culture of a semen sample.

When Are Cultures Indicated?

A culture is indicated when a patient presents symptoms consistent with an infection. Although these symptoms vary depending on the causative microorganism and the affected organs or tissues, there are several symptoms common to various infectious diseasesInfectious diseasesInfectious Diseases :

• Fever
• Chills
• Fatigue
• Muscle aches
• General discomfort

Specific symptoms include:

• Cough
• Difficulty breathing
• Diarrhea
• Skin rashes
• Presence of pus
• Sore throat
• Painful urination or ejaculation
• Blood in the cough, stool, or urine

How Are They Performed?

The first step in performing a culture is sample collection. The specific procedure depends on the type of sample needed: a swab may be used, as in the case of the throat or a wound; venipuncture may be performed, as in a blood culture; or the patient may collect and deposit the sample in a container, as with urine, stool, sputum, or semen cultures. In all cases, the sample is collected in a sterile container and taken to the laboratory as soon as possible to prevent deterioration.

A tissue or fluid sample does not contain enough cells to identify the microorganism causing the infection under a microscope, so it must be cultured. To achieve this, the sample is placed in a Petri dish, a special container that holds a liquid or solid solution composed of substances and nutrients necessary for microorganism growth. There are different culture media, each with specific conditions to allow the growth of different microorganisms.

The Petri dish is incubated at a temperature similar to that of the human body (37°C or 98.6°F) for approximately 24 to 72 hours, although the growth of certain microorganisms may take longer. After this period, the culture is examined under a microscope to confirm the presence of pathogens, and if positive, to identify the species. Additional methods are also used for identification, such as Gram staining, a procedure in which a dye is applied to the culture, and microorganisms are classified based on the color they acquire in reaction to the stain.

If the culture is positive, an antibiogram is also performed. This technique measures the microorganisms' sensitivity to antimicrobial medications, helping determine the most effective treatment for the infection.

Risks

One of the main risks when performing a culture is the possibility of sample contamination. This occurs when, during collection or handling, the sample comes into contact with other microorganisms from the body's natural flora, the surrounding environment, or external substances. When this happens, the culture result is invalid and unreliable.

What to Expect from a Laboratory Culture

Depending on the type of sample needed, it may be collected at the medical facility or by the patient at home. In any case, proper hygiene measures should be taken beforehand, including washing or disinfecting hands and the area from which the sample will be taken, to minimize the risk of contamination.

Sample collection procedures are generally simple, quick, and usually painless, although they may be uncomfortable in some cases. Once the sample is submitted, the patient can leave and wait to be notified of the culture results.

Medical Specialties That Request Laboratory Cultures

Laboratory cultures are requested in various medical specialties, depending on the study's objective. The specialties responsible for performing and analyzing cultures include infectious diseasesInfectious diseasesInfectious Diseases , microbiology, and parasitology.