Journal
BIOMATERIALS
Volume 23, Issue 21, Pages 4233-4239Publisher
ELSEVIER SCI LTD
DOI: 10.1016/S0142-9612(02)00171-0
Keywords
biomaterial-associated infections; Staphylococcus epidermidis; slime; ica genes; polymerase chain reaction (PCR); microtiter plate method; Congo red agar
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This investigation was conduced on a collection of 113 S. epidermidis strains isolated front biomaterial-associated infections. All strains were examined both for the presence of icaA and icaD genes responsible for slime synthesis by a PCR method and for the in vitro slime production ability by the Congo red agar (CRA) plate test. In the present study, the original CRA test was optimised adopting a six-colour reference scale for a fine classification of colonies colours. The six-colour tones of the scale were Lis follows: very black (vb), black (b), almost black (ab), which were considered as positive results, and bordeaux (brd), red (r), and very red (vr), interpreted as negative. 57.5% of all the strains were found to be icaA icaD-positive Lis well as slime-forming onto CRA, exhibiting the following colonies colours: vb (35.4%) b (15.9%): ab (6.2%). The percentage of icaA icaD-negative strains was 42.5% and all of them were negative onto CRA: brd (19.5%), r (14.2%), vr (8.8%). The comparison of colour classification with the information on ica genes confirmed the validity of the scale adopted, providing Support to the criteria used for a correct interpretation of the colonies colour during the execution of the CRA test. Overall these results indicate a fine consistency between these two experimental methods and a good reliability of CRA plate test, especially when this is supported by a colourmetric scale. (C) 2002 Elsevier Science Ltd. All rights reserved.
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