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Evaluation of disc susceptibility tests performed directly from positive blood cultures
  1. T Y Tan,
  2. L S Y Ng,
  3. L L Kwang
  1. Division of Laboratory Medicine, Changi General Hospital, Singapore
  1. Dr Thean Yen Tan, Division of Laboratory Medicine, Changi General Hospital, 2 Simei Street 3, Singapore 529889; thean_yen_tan{at}


Aims: To evaluate the accuracy of direct disc susceptibility testing performed from positive BACTEC blood culture vials, using a predetermined dilution protocol.

Methods: Direct susceptibility testing was performed from 432 positive blood culture vials, generating 3829 antibiotic-organism results. Results were compared with those obtained by standard disc susceptibility testing according to Clinical Laboratory Standards Institute (CLSI) methods.

Results: When results were compared with the reference method, no very major errors were detected. One (0.03%) major error and 89 (2.3%) minor errors were found. Error rates by organism group ranged from 1.3% for Pseudomonas aeruginosa to 8.2% for β-haemolytic streptococci.

Conclusions: Direct susceptibility testing provided accurate susceptibility results for most organism–antibiotic combinations, with the exception of the β-haemolytic streptococci.

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  • Funding: Internal hospital grant.

  • Competing interests: None.

  • Data from the pilot study were presented in part at the 12th International Congress on Infectious Diseases, Lisbon, 15–18 June 2006.