Poster Presentation Australian Society for Microbiology Annual Scientific Meeting 2016

Detection of Propionibacterium acnes – a comparison study of different incubation times.   (#206)

Ki Yung Brian Chung Tai Him 1 , Michael C Wehrhahn 1 , Riaz Rasul 1
  1. Microbiology Department, Douglass Hanly Moir Pathology, Macquarie Park, NSW, Australia

Introduction

Propionibacterium acnes (P.acnes) is a recognised pathogen in implant-associated infection. However, optimal incubation protocols remain uncertain due to its slow growing nature and association as a specimen contaminant. Studies have recommended incubation for at least 14 days to maximise recovery of P.acnes. We sought to compare the effect of different incubation periods on P.acnes isolation rates.

Method

Operative orthopaedic and neurosurgical specimens were prospectively reviewed from January to March 2016. Swabs and fluids were plated onto chocolate (CHOC) and blood agar (BA), and incubated in CO2 and anaerobically respectively at 35oC. Fluids and tissues were inoculated in cooked meat medium (CMM), then subbed onto CHOC and BA after 48 hours and again on BA after 7 days. CHOC plates were checked daily for bacterial growth until Day 5, while BA plates were reviewed on Day 2, 5 and 10. Negative 48 hour and 7 day CMM subcultures were reviewed again on Day 14. Bacterial isolates were identified using MALDI-TOF (Biomerieux Vitek-MS). Phone interview of the requesting surgeon was performed to ascertain clinical significance of P.acnes isolates.

Results

1102 samples (440 tissues, 171 fluids, 491 swabs) were received.  A positive culture was obtained in 184 (17%) samples (82 tissues, 31 fluids and 71 swabs), of which 29 (3%) grew P.acnes (15 tissues, 4 fluids and 10 swabs) from 24 individual patients.  10 (34%) of the P.acnes were isolated on Day 5 , 17 (59%)  on Day 10, and 2 (7%) on Day 14. Clinical information was available for 14 of 29 patients. P.acnes was considered significant in 1 of 2 patients with isolation at 5 days and in 3 of 12 patients with isolation at 10 days.

Conclusion

With prolonged (7 day) broth enrichment, 93% of P.acnes isolates were detected after 10 days with only 2 isolates detected after a further 4 days incubation. However, the majority of isolations at 10 days were not considered clinically significant. Further studies are required to determine the merit of prolonged incubation and the significance of late P.acnes cultures.

 

  1. Butler-Wu S., Burns E, Pottinger P.,Magaret A.,Rakeman J., Matsen F. and Cookson B. (2011). Optimization of Periprosthetic Culture for Diagnosis of Propionibacterium acnes Prosthetic Joint Infection. Journal of Clinical Microbiology 49:2490–2495.
  2. Frangiamor S., Saleh A., Grosso M., Alolabi B., Bauer T, Iannotti J., and Ricchetti E.(2015). Early Versus Late Culture Growth of Propionibacterium acnes in Revision Shoulder Arthroplasty. The Journal of Bone and Joint Surgery 97:1149-58
  3. Schafer P., Fink B., Sandow D., Margull A., Berger I., and Frommelt L. (2008). Prolonged Bacterial Culture to Identify Late Periprosthetic Joint Infection- A Promising Strategy. Diagnosis of Periprosthetic Infection 47:1403-1409.