Bacteriology Specimens Flashcards
List general guidelines for proper specimen collection from a suspected site of infection.
The specimen should be obtained during the acute phase, before antibiotics are given. The appropriate site should be sampled and a sufficient quantity obtained. Contamination with normal flora should be avoided. The specimen should be collected in a sterile, leak-proof container and delivered to the lab within 30 minutes of collection.
Which type of swabs may contain fatty acids that inhibit some strains of fastidious bacteria?
Cotton
What type of swabs are suitable for collection of a specimen for culture of Neisseria gonorrhoeae?
Dacron or rayon. Calcium alginate and cotton may contain inhibitory substances.
What can be used as a preservative for stool specimens for culture?
Cary-Blair, Stuart’s, Amies, and phosphate buffered saline.
What can be used as a preservative for urine specimens?
Boric acid
How should specimens for microbiology be transported?
In a sealed secondary container such as a plastic zip-lock bag. The bag should be marked with a biohazard symbol.
What information is required on microbiology requisitions?
The Patients name, identification number, age or date of birth, gender, and diagnosis; the name of the ordering physician; the source of the specimen; information about antibiotic therapy; the tests requested; the date and time of collection, and the date and time the specimen was received in lab.
List several causes for specimen rejection in the microbiology laboratory.
An unlabeled or improperly labeled specimen, prolonged transit time (over 2 hours without preservation), improper temperature during transport or storage, a leaking specimen, an improper transport medium, a dried out swab, a specimen received on a dried our or expired agar plate, wood or calcium alginate swab for viruses or Chlamydia, a specimen submitted in a unsterile container, insufficient quantity, or an inappropriate specimen for the culture requested.
As a rule, in what situation should every effort be made not to reject a specimen?
For invasive specimens like tissue and CSF or other specimens that are difficult to recollect. the Physician should be consulted.
Which specimens may be refrigerated?
Sputum, urine, swabs, and specimens for viral culture (if the delay will not exceed 24 hours).
Which specimens should never be refrigerated?
Cerebrospinal fluid (CSF) and other body fluid, blood, cultures for N. gonorrhoeae, and specimens for anaerobic culture. Some labs don’t refrigerate stool specimens either because Shigella may be killed at low temperatures. it is best to process stool and respiratory specimens without delay. Ideally, CSF should be held at 37C.
Which microorganisms are particularly susceptible to adverse environment conditions such as atmosphere, temperature, and pH?
Anaerobes, Chlamydia, Haemophilus influenza, Neisseria gonorrhaeae, Neisseria meningitides, Salmonella, Shigella, Streptococcus pneumonia, viruses, and parasites. Specimens likely to harbor these pathogens require special consideration with regard to transit time, preservation, and storage temperature.
When is the ideal time to obtain a blood culture?
Half an hour before the temperature spike because that is when the highest number of organisms is circulating.
What is the maximum number of blood cultures that should be drawn in a 24 hour period, according to most investigators?
Three. Blood cultures are usually collected in 2 bottles - aerobic and anaerobic. Each set of blood cultures is drawn from a different site to help differentiate skin contaminants from pathogens. The optimum amount of blood to be drawn per set is 10-20 mL from an adult and 1-5 mL from a child.
Which anticoagulant is used for blood cultures and why?
Sodium polyanethol sulfonate (SPS). It prevents clotting of the blood, has anti-complementary and anti-phagocytic properties, and inactivates some antibiotics.
