acm Annals of Clinical Microbiology Ann Clin Microbiol 2288-0585 2288-6850 The Korean Society of Clinical Microbiology 10.5145/ACM.2015.18.1.7 acm-18-7 Original Article Evaluation of a Quantitative Sonication Method of Catheter Tip Culture for Diagnosis of Catheter-Related Bloodstream Infection KimSoo-Kyung KimHyun-Ki KoYoung Jin SungHeungsup KimMi-Na Department of Laboratory Medicine, University of Ulsan College of Medicine and Asan Medical Center, Seoul, Korea Correspondence: Mi-Na Kim, Department of Laboratory Medicine, University of Ulsan College of Medicine and Asan Medical Center, 88, Olympic-ro 43-gil, Songpa-gu, Seoul 138-736, Korea. (Tel) 82-2-3010-4511, (Fax) 82-2-478-0884, (E-mail) mnkim@amc.seoul.kr 032015 5032015 181 713 16102014 12122014 13122014 Copyright © 2015 The Korean Society of Clinical Microbiology 2015 This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Background

The diagnosis of catheter-related bloodstream infection (CRBSI) should demonstrate catheter colonization of the same organism as the isolate from peripheral blood cultures, by catheter tip culture or by differential time to positivity (DTP) of catheter- drawn blood cultures versus peripheral blood cultures. The purpose of this study was to compare the sonication and the roll-plate methods of catheter tip culture.

 Methods

One hundred and sixty-one catheter tips from 122 patients were submitted for catheter tip culture. Distal segments of the catheter were first inoculated using a roll-plate, and then inoculated by sonication. Sonication was performed using a BactoSonic device (Bandelin GmbH, Germany). A total of 1,018 sets of blood cultures from 7 days before to 1 day after catheter removal were analyzed for isolated or-ganisms and DTP. Cutoffs of catheter colonization were ≥15 CFU for the roll-plate method, ≥100 CFU for sonication, and ≥2 h for DTP.

 Results

Twenty-four catheter tips (14.9%) showed colonization with at least one of the two methods: 21 (13.0%) with the roll-plate method and 22 (13.7%) with sonication. The positivity rates for the two methods showed no significant difference, and the con-cordance rate for the two methods was 96.9% (k=0.866, P＜0.001). Blood culture was positive in 56 episodes in 44 patients, and 14 episodes of CRBSI were diagnosed in 12 patients: 10 by tip culture (two by sonication only) and 8 by DTP. Of the 122 specimens that were negative according to both methods, 4 were from the episodes of CRBSI diagnosed by DTP.

 Conclusion

Roll-plate and sonication methods are comparable in diagnostic sensitivity for catheter colonization. The roll-plate and sonication catheter tip culture methods and DTP are complementary for diagnosis of CRBSI.

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Detection of catheter colonization and catheter-related bloodstream infections according to the diagnostic method employed

Sonication method Roll-plate method (No. of CRBSIs/No. of CRBSIs diagnosed by DTP)
Colonization∗ No colonization
Mixed growth Insignificant growth No growth Total
Colonization†   19 (9/4) 1 (0/0) 0 2 (1/0) 22 (10/4)
No colonization Mixed growth 0 1 (0/0) 0 2 (0/0) 3 (0/0)
  Insignificant growth 1 (0/0) 0 2 (0/0) 3 (0/0) 6 (0/0)
  No growth 1 (0/0) 0 7 (0/0) 122 (4/4) 130 (4/4)
  Total 21 (9/4) 2 (0/0) 9 (0/0) 129 (5/4) 161 (14/8)

The cut-off used for the detection of colonization was ≥15 CFU for the roll-plate method;

The cut-off used for detection of colonization was ≥100 CFU for the sonication method; Correlation of colonization detection between roll-plate and sonication method was significant (P＜0.001, Chi square test).

Abbreviations: CRBSI, catheter-related bloodstream infection; DTP, differential time to positivity.

Quantitative comparison of CFU for the sonication and roll-plate methods

Quantification by the roll-plate method (CFU) Quantification by sonication method (CFU)
0 1-99 100-999 ≥1,000 Total
0 122 3 4 0 129
1-14 7 2 0 1 10
15-99 1 2 2 0 5
≥100 0 1 3 13 17
Total 130 8 9 14 161

Correlation of quantification between roll-plate method and sonication method was significant (P＜0.001, linear-by-linear asssociation).

Species distribution of the isolates from catheter tip cultures in combinations of roll-plate and sonication method

Microorganism RP+/SO+ (n=22) RP+/SO− (n=2) RP−/SO+ (n=4) Total (n=28)
CNS 3 1 3 7 (25.0%)
 Staphylococcus epidermidis 2 1 1 4
 Staphylococcus haemolyticus 1 0 1 2
 Staphylococcus capitis 0 0 1 1
Staphylococcus aureus 6 0 0 6 (21.4%)
Corynebacterium spp. 1 0 0 1 (3.6%)
Gram-negative bacteria 5 0 1 6 (21.4%)
 Acinetobacter baumannii 3 0 0 3
 Klebsiella oxytoca 1 0 0 1
 Klebsiella pneumoniae 1 0 0 1
 Acinetobacter lwoffii 0 0 1 1
Candida spp. 7 1 0 8 (28.6%)

Abbreviations: CNS, coagulase-negative staphylococci; RP, semiquantitative roll-plate method; SO, quantitative sonication method.