Culture, Bacterial, Stool

Culture, Bacterial, Stool

Synonym/acronym: N/A.

Common use

To identify pathogenic bacterial organisms in the stool as an indicator for appropriate therapeutic interventions to treat organisms such as Clostridium difficile and Escherichia coli.

Specimen

Fresh, random stool collected in a clean plastic container.

Normal findings

(Method: Culture on selective media for identification of pathogens usually to include Salmonella.Shigella,Escherichia coli O157:H7, Yersinia enterocolitica, and Campylobacter; latex agglutination or enzyme immunoassay for Clostridium A and B toxins). PCR may be used to identify bacterial, protozoan, or viral pathogens. Negative: No growth of pathogens. Normal fecal flora is 96% to 99% anaerobes and 1% to 4% aerobes. Normal flora present may include Bacteroides,Candida albicans,Clostridium,Enterococcus,E. coli,Proteus,Pseudomonas, and Staphylococcus aureus.

Description

Stool culture involves collecting a sample of feces so that organisms present can be isolated and identified. Certain bacteria are normally found in feces. However, when overgrowth of these organisms occurs or pathological organisms are present, diarrhea or other signs and symptoms of systemic infection occur. These symptoms are the result of damage to the intestinal tissue by the pathogenic organisms. Routine stool culture normally screens for a small number of common pathogens associated with food poisoning, such as S. aureus,Salmonella, and Shigella. Identification of other bacteria is initiated by special request or upon consultation with a microbiologist when there is knowledge of special circumstances. An example of this situation is an outbreak of C. difficile in a nursing home or hospital unit where the infection can spread rapidly from one person to the next. A life-threatening C. difficile infection of the bowel may occur in patients who are immunocompromised or are receiving broad-spectrum antibiotic therapy (e.g., clindamycin, ampicillin, cephalosporins). The bacteria release a toxin that causes necrosis of the colon tissue. The toxin can be more rapidly identified from a stool sample using an immunochemical method than from a routine culture. Appropriate interventions can be quickly initiated and might include IV replacement of fluid and electrolytes, cessation of broad-spectrum antibiotic administration, and institution of vancomycin or metronidazole antibiotic therapy. The laboratory will initiate antibiotic sensitivity testing if indicated by test results. Sensitivity testing identifies the antibiotics to which organisms are susceptible to ensure an effective treatment plan. The subspecialty of microbiology has been revolutionized by molecular diagnostics. Molecular diagnostics involves the identification of specific sequences of DNA. The application of molecular diagnostics techniques, such as PCR, has led to the development of automated instruments that can identify a single infectious agent or multiple pathogens from a small amount of stool in less than 2 hr. The instruments can detect the presence of bacteria, viruses, or protozoans commonly associated with gastrointestinal infections.

This procedure is contraindicated for

    N/A

Indications

  • Assist in establishing a diagnosis for diarrhea of unknown etiology
  • Identify pathogenic organisms causing gastrointestinal disease and carrier states

Potential diagnosis

Positive findings in:

  • Bacterial infection: Gram-negative organisms such as Aeromonas spp., Campylobacter,E. coli including serotype O157: H7, Plesiomonas shigelloides,Salmonella,Shigella,Vibrio, and Yersinia.
  • Bacterial infection: Gram-positive organisms such as Bacillus cereus,C. difficile, and Listeria. Isolation of Staphylococcus aureus may indicate infection or a carrier state
  • Botulism: Clostridium botulinum (the bacteria must also be isolated from the food or the presence of toxin confirmed in the stool specimen)
  • Parasitic enterocolitis

Critical findings

  • Bacterial pathogens: Campylobacter,C. difficile,E. coli including 0157:H7, Listeria,Rotavirus (especially in children),Salmonella,Shigella,Vibrio,Yersinia, or parasites Acanthamoeba,Ascaris (hookworm), Cyclospora,Cryptosporidium,Entamoeba histolytica,Giardia, and Strongyloides (tapeworm), parasitic ova, proglottid, and larvae.

  • Note and immediately report to the health-care provider (HCP) positive results for bacterial pathogens or parasites and related symptoms.

  • It is essential that a critical finding be communicated immediately to the requesting health-care provider (HCP). Lists of specific organisms may vary among facilities; specific organisms are required to be reported to local, state, and national departments of health.

  • Timely notification of a critical finding for lab or diagnostic studies is a role expectation of the professional nurse. Notification processes will vary among facilities. Upon receipt of the critical value the information should be read back to the caller to verify accuracy. Most policies require immediate notification of the primary HCP, Hospitalist, or on-call HCP. Reported information includes the patient’s name, unique identifiers, critical value, name of the person giving the report, and name of the person receiving the report. Documentation of notification should be made in the medical record with the name of the HCP notified, time and date of notification, and any orders received. Any delay in a timely report of a critical finding may require completion of a notification form with review by Risk Management.

Interfering factors

  • A rectal swab does not provide an adequate amount of specimen for evaluating the carrier state and should be avoided in favor of a standard stool specimen.
  • A rectal swab should never be submitted for Clostridium toxin studies. Specimens for Clostridium toxins should be refrigerated if they are not immediately transported to the laboratory because toxins degrade rapidly.
  • A rectal swab should never be submitted for Campylobacter culture. Excessive exposure of the sample to air or room temperature may damage this bacterium so that it will not grow in the culture.
  • Therapy with antibiotics before specimen collection may decrease the type and the amount of bacteria.
  • Failure to transport the culture within 1 hr of collection or urine contamination of the sample may affect results.
  • Barium and laxatives used less than 1 wk before the test may reduce bacterial growth.

Nursing Implications and Procedure

Pretest

  • Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
  • Patient Teaching: Inform the patient this test can assist in identification of the organism causing infection.
  • Obtain a history of the patient’s complaints, including a list of known allergens.
  • Obtain a history of the patient’s gastrointestinal and immune systems, symptoms, and results of previously performed laboratory tests and diagnostic and surgical procedures.
  • Obtain a history of the patient’s travel to foreign countries.
  • Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values online at DavisPlus).
  • Note any recent medications that can interfere with test results.
  • Review the procedure with the patient. Address concerns about pain and explain that there may be some discomfort during the specimen collection. Inform the patient that specimen collection takes approximately 5 min.
  • Sensitivity to social and cultural issues, as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
  • Note that there are no food or fluid restrictions unless by medical direction.

Intratest

  • Potential complications: N/A
  • Ensure that the patient has complied with medication restrictions prior to the procedure.
  • Instruct the patient to cooperate fully and to follow directions. Direct the patient to breathe normally and to avoid unnecessary movement.
  • Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient, and label the appropriate collection containers with the corresponding patient demographics, date and time of collection, and any medication the patient is taking that may interfere with test results (e.g., antibiotics).
  • Collect a stool specimen directly into a clean container. If the patient requires a bedpan, make sure it is clean and dry, and use a tongue blade to transfer the specimen to the container. Make sure representative portions of the stool are sent for analysis. Note specimen appearance on collection container label.
  • Promptly transport the specimen to the laboratory for processing and analysis.

Post-Test

  • Inform the patient that a report of the results will be made available to the requesting HCP, who will discuss the results with the patient.
  • Instruct the patient to resume usual medication as directed by the HCP.
  • Instruct the patient to report symptoms such as pain related to tissue inflammation or irritation.
  • Advise the patient that final test results for culture may take up to 72 hr but that antibiotic therapy may be started immediately. Test results for PCR methods are generally available a few hours after testing is completed. Instruct the patient about the importance of completing the entire course of antibiotic therapy even if no symptoms are present. Note: Antibiotic therapy is frequently contraindicated for Salmonella infection unless the infection has progressed to a systemic state.
  • Recognize anxiety related to test results. Discuss the implications of abnormal test results on the patient’s lifestyle. Provide teaching and information regarding the clinical implications of the test results, as appropriate.
  • Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP. Emphasize the importance of reporting continued signs and symptoms of the infection. Answer any questions or address any concerns voiced by the patient or family.
  • Depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.

Related Monographs

  • Related tests include capsule endoscopy, colonoscopy, fecal analysis, Gram stain, ova and parasites, and proctosigmoidoscopy.
  • Refer to the Gastrointestinal and Immune systems tables at the end of the book for related tests by body system.