Detection of slime production by means of an optimised Congo red agar plate test based on a colourimetric scale in Staphylococcus epidermidis clinical isolates genotyped for ica locus

Carla Renata Arciola, Davide Campoccia, Simonetta Gamberini, Marina Cervellati, Elena Donati, Lucio Montanaro

Research output: Contribution to journalArticle

Abstract

This investigation was conduced on a collection of 113 S. epidermidis strains isolated from 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 as 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 as 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 colourimetric scale.

Original languageEnglish
Pages (from-to)4233-4239
Number of pages7
JournalBiomaterials
Volume23
Issue number21
DOIs
Publication statusPublished - 2002

Keywords

  • Biomaterial-associated infections
  • Congo red agar
  • ica Genes
  • Microtiter plate method
  • Polymerase chain reaction (PCR)
  • Slime
  • Staphylococcus epidermidis

ASJC Scopus subject areas

  • Biotechnology
  • Bioengineering
  • Biomedical Engineering

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