Peritoneal Effluent Culture Laboratory Processing

The correct microbiological culturing of peritoneal effluent is of utmost importance to establish the microorganism responsible for the infection. Identification of the organism and subsequent antibiotic sensitivities will not only help guide antibiotic selection, but, in addition, the type of organism can indicate the possible source of the infection. Culture-negative peritonitis rates should not be more than 20% of episodes. Standard culture technique is the use of blood culture bottles, but culturing the sediment after centrifuging 50 mL of effluent may lower the risk of a culture-negative occurrence.

Procedure:

  • Centrifuge 50 mL of peritoneal effluent at 3000 g for 15 minutes
  • Follow centrifugation with resuspension of the sediment in 3 to 5 mL of sterile saline
  • Inoculate this material both on solid culture media and into a standard blood-culture medium (method most likely to identify the causative organisms; with this method, less than 5% will be culture-negative)
  • The solid media should be incubated in aerobic, microaerophilic, and anaerobic environments
  • Blood-culture bottles can be directly injected with 5–10 mL of effluent if equipment for centrifuging large amounts of fluid is not available (this method generally results in a culture-negative rate of 20%)
  • The removal of antibiotics present in the specimen may increase the isolation rate if the patient is already on antibiotics

Important Points:

  • The speed with which bacteriological diagnosis can be established is very important
  • Concentration methods not only facilitate correct microbial identification but also reduce the time necessary for bacteriological cultures to turn positive
  • Rapid blood-culture techniques (e.g., BACTEC, SEPTI-CHEK, BacT/ALERT) may further speed up isolation and identification. A resin culture bottle should be used if patient is on antibiotics or antibiotics were discontinued less than 24 hours prior to culture
  • The majority of cultures will become positive after the first 24 hours and, in over 75% of cases, diagnosis can be established in less than 3 days

Mycobacterium Examination:

  • Examine smear of the peritoneal effluent with the Ziehl-Neelsen stain (“smear-negative” disease is common)
  • The sensitivity of the smear examination by the Ziehl-Neelsen technique can be enhanced by centrifuging 100–150 mL of the dialysate sample
  • Prepare smear from the pellet
  • A specific diagnosis can be made by culturing the sediment, after centrifugation of a large volume of effluent (50–100 mL), using a solid medium (such as Lowenstein-Jensen agar) and a fluid medium (SEPTI-CHEK, BACTEC; Becton Dickinson; etc.)
  • The time of detection for growth of mycobacteria is decreased considerably in fluid medium
  • Repeat microscopic smear examination and culture of dialysis effluent is mandatory for better yield in suspected cases of mycobacterial peritonitis

References used in this Appendix section

  1. Li PK, Szeto CC, Piraino B, et al. Peritoneal dialysis-related infectious recommendations: 2010 update. Perit Dial Int 2010;30(4):393–423.
  2. Li PK, Szeto CC, Piraino B, et al. ISPD peritonitis recommendations: 2016 update on prevention and treatment. Perit Dial Int 2016;36:468-508.