Affiliation:
1. Division of Medical Microbiology, The Johns Hopkins Hospitalthe
2. Department of Pathology, The Johns Hopkins University School of Medicine, Baltimore, Maryland
Abstract
ABSTRACT
Screening for
Staphylococcus aureus
has become routine in certain patient populations. This study is the first clinical evaluation of the BBL CHROMagar Staph aureus agar (CSA) medium (BD Diagnostics, Sparks, Md.) for detection of
S. aureus
in nasal surveillance cultures and in respiratory samples from cystic fibrosis (CF) patients.
S. aureus
colonies appear mauve on CSA. Other organisms are inhibited or produce a distinctly different colony color.
S. aureus
was identified from all media by slide coagulase, exogenous DNase, and mannitol fermentation assays. Susceptibility testing was performed using the agar dilution method. A total of 679 samples were evaluated. All samples were inoculated onto CSA. Nasal surveillance cultures were inoculated onto sheep blood agar (SBA) (BD Diagnostics), and samples from CF patients were inoculated onto mannitol salt agar (MSA) (BD Diagnostics). Of the 679 samples cultured, 200 organisms produced a mauve color on CSA (suspicious for
S. aureus
) and 180 were positive for
S. aureus
on SBA or MSA. Of 200 CSA-positive samples 191 were identified as
S. aureus
. Nine mauve colonies were slide coagulase negative and were subsequently identified as
Staphylococcus lugdunensis
(one),
Staphylococcus epidermidis
(three),
Staphylococcus haemolyticus
(one), and
Corynebacterium
species (four). CSA improved the ability to detect
S. aureus
by recovering 12
S. aureus
isolates missed by conventional media. Of the 192
S. aureus
isolates recovered, 122 were methicillin susceptible and 70 were methicillin resistant. Overall, the sensitivity and specificity of CSA in this study were 99.5 and 98%, respectively. There was no difference in the performance of the slide coagulase test or in susceptibility testing performed on
S. aureus
recovered from CSA compared to SBA or MSA. Our data support the use of CSA in place of standard culture media for detection of
S. aureus
in heavily contaminated respiratory samples.
Publisher
American Society for Microbiology
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