Sputum culture
Encyclopedia
A sputum culture is a test
to detect and identify bacteria
or fungi
that infect the lung
s or breathing passages
. Sputum
is a thick fluid produced in the lungs and in the adjacent airways. A sample of sputum is placed in a sterile container and sent to the laboratory for testing. Sampling
may performed by sputum being expectorated (produced by coughing), induced (saline is sprayed in the lungs to induce sputum production), or taken via an endotracheal tube with a protected specimen brush (commonly used on patients on respirators) in an intensive care setting. For selected organisms such as Cytomegalovirus or "Pneumocystis jiroveci" in specific clinical settings (immunocompromised patients) a bronchoalveolar lavage might be taken by an experienced pneumologist. If no bacteria or fungi grow, the culture
is negative. If organisms that can cause the infection
(Pathogenicity
organism
s) grow, the culture is positive. The type of bacterium or fungus is identified by microscopy
, colony morphology and biochemical tests of bacterial growth.
If bacteria or fungi that can cause infection grow in the culture, other tests can determine which antimicrobial agent will most effectively treat
the infection. This is called susceptibility
or sensitivity testing.
In a hospital setting, a sputum culture is most commonly ordered if a patient has a pneumonia
. The Infectious Diseases Society of America
recommends that sputum cultures be done in pneumonia requiring hospitalization, while the American College of Chest Physicians
does not. One reason for such a discrepancy is that normal, healthy lungs have bacteria, and sputum cultures collect both normal and pathogenic bacteria. However, pure cultures of common respiratory pathogens in the absence of upper respiratory flora combined with symptoms of respiratory distress provides strong evdience of the infectious agent, and its significance. Such pathogens include Streptococcus pneumoniae
, Haemophilus influenzae
and the highly infectious M tuberculosis, which are transmitted by inhailing aerosols. For this reason, laboratory processing of sputum for respiratory pathogens are performed with the aid of a biological safety cabinet.
Experiment
An experiment is a methodical procedure carried out with the goal of verifying, falsifying, or establishing the validity of a hypothesis. Experiments vary greatly in their goal and scale, but always rely on repeatable procedure and logical analysis of the results...
to detect and identify bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
or fungi
Fungus
A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...
that infect the lung
Lung
The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...
s or breathing passages
Bronchus
A bronchus is a passage of airway in the respiratory tract that conducts air into the lungs. The bronchus branches into smaller tubes, which in turn become bronchioles....
. Sputum
Sputum
Sputum is mucus that is coughed up from the lower airways. It is usually used for microbiological investigations of respiratory infections....
is a thick fluid produced in the lungs and in the adjacent airways. A sample of sputum is placed in a sterile container and sent to the laboratory for testing. Sampling
Sampling (medicine)
In medicine, sampling is gathering of matter from the body to aid in the process of a medical diagnosis and/or evaluation of an indication for treatment, further medical tests or other procedures...
may performed by sputum being expectorated (produced by coughing), induced (saline is sprayed in the lungs to induce sputum production), or taken via an endotracheal tube with a protected specimen brush (commonly used on patients on respirators) in an intensive care setting. For selected organisms such as Cytomegalovirus or "Pneumocystis jiroveci" in specific clinical settings (immunocompromised patients) a bronchoalveolar lavage might be taken by an experienced pneumologist. If no bacteria or fungi grow, the culture
Microbiological culture
A microbiological culture, or microbial culture, is a method of multiplying microbial organisms by letting them reproduce in predetermined culture media under controlled laboratory conditions. Microbial cultures are used to determine the type of organism, its abundance in the sample being tested,...
is negative. If organisms that can cause the infection
Infection
An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...
(Pathogenicity
Pathogenicity
Pathogenicity is the ability of a pathogen to produce an infectious disease in an organism.It is often used interchangeably with the term "virulence", although virulence is used more specifically to describe the relative degree of damage done by a pathogen, or the degree of pathogenicity caused by...
organism
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
s) grow, the culture is positive. The type of bacterium or fungus is identified by microscopy
Microscopy
Microscopy is the technical field of using microscopes to view samples and objects that cannot be seen with the unaided eye...
, colony morphology and biochemical tests of bacterial growth.
If bacteria or fungi that can cause infection grow in the culture, other tests can determine which antimicrobial agent will most effectively treat
Pharmacotherapy
Pharmacotherapy is the treatment of disease through the administration of drugs. As such, it is considered part of the larger category of therapy....
the infection. This is called susceptibility
Kirby-Bauer antibiotic testing
Kirby-Bauer antibiotic testing is a test which uses antibiotic-impregnated wafers to test whether particular bacteria are susceptible to specific antibiotics. A known quantity of bacteria are grown on agar plates in the presence of thin wafers containing relevant antibiotics...
or sensitivity testing.
In a hospital setting, a sputum culture is most commonly ordered if a patient has a pneumonia
Pneumonia
Pneumonia is an inflammatory condition of the lung—especially affecting the microscopic air sacs —associated with fever, chest symptoms, and a lack of air space on a chest X-ray. Pneumonia is typically caused by an infection but there are a number of other causes...
. The Infectious Diseases Society of America
Infectious Diseases Society of America
The Infectious Diseases Society of America is a medical association representing physicians, scientists and other health care professionals who specialize in infectious diseases. As of 2010, IDSA had approximately 9,000 members...
recommends that sputum cultures be done in pneumonia requiring hospitalization, while the American College of Chest Physicians
American College of Chest Physicians
The American College of Chest Physicians is a medical organization in the United States consisting of physicians and non-physician specialists in the field of chest medicine, which includes pulmonology, thoracic surgery, and critical care medicine....
does not. One reason for such a discrepancy is that normal, healthy lungs have bacteria, and sputum cultures collect both normal and pathogenic bacteria. However, pure cultures of common respiratory pathogens in the absence of upper respiratory flora combined with symptoms of respiratory distress provides strong evdience of the infectious agent, and its significance. Such pathogens include Streptococcus pneumoniae
Streptococcus pneumoniae
Streptococcus pneumoniae, or pneumococcus, is Gram-positive, alpha-hemolytic, aerotolerant anaerobic member of the genus Streptococcus. A significant human pathogenic bacterium, S...
, Haemophilus influenzae
Haemophilus influenzae
Haemophilus influenzae, formerly called Pfeiffer's bacillus or Bacillus influenzae, Gram-negative, rod-shaped bacterium first described in 1892 by Richard Pfeiffer during an influenza pandemic. A member of the Pasteurellaceae family, it is generally aerobic, but can grow as a facultative anaerobe. H...
and the highly infectious M tuberculosis, which are transmitted by inhailing aerosols. For this reason, laboratory processing of sputum for respiratory pathogens are performed with the aid of a biological safety cabinet.