Three commercially available rapid slide agglutination tests for the identification of Staphylococcus aureus were evaluated with 354 recent clinical isolates (165 strains of S. aureus). The test results of two latex agglutination products, SeroSTAT Staph (Scott Laboratories, Inc.) and Staphylatex (American Micro Scan), and one hemagglutination product, Staphyloslide (BBL Microbiology Systems), were compared with the results of the tube coagulase test, which was read at 4 h (4-h tube coagulase test) and, if negative, again after overnight incubation at room temperature (24-h tube coagulase test). Discrepancies between agglutination and tube coagulase identifications were resolved by use of the thermonuclease, mannitol fermentation, and slide coagulase tests. All sensitivities, specificities, predictive values of a positive result, and predictive values of a negative result for the three agglutination tests were at least 98.8% and comparable with the 4-h tube coagulase test. Best results were obtained with the 24-h tube coagulase test, which yielded one false-negative and no false-positive tests. Agglutination identifications may be performed on organisms taken directly from a primary plate when sufficient growth is present. Kit agglutination procedures yield rapid and reliable identifications and are easy to perform. This study also demonstrates the usefulness of the 24-h tube coagulase test.
Culture of blood is the most frequent means of diagnosing bacteremia. However, conventional blood culturing methods are slow in isolating bacteria. We developed a method for isolation of bacteria by centrifugation and filtration. Fresh human whole blood was inoculated with facultatively anaerobic and aerobic microorganisms (3 to 172 microorganisms per 5 ml). Seeded blood was then mixed with Ficoll-Hypaque (density, 1.149 +/- 0.002 g/ml) and centrifuged (386 x g) for 30 min at ambient temperature. The entire gradient (plasma, leukocytes, and Ficoll-Hypaque) was removed and filtered through a 0.22-micron membrane filter (Millipore). The filters were then placed on chocolate agar plates and incubated at 35 degrees C in a humidified atmosphere containing 5% CO2. For each bacterium tested, approximately 35 to 100% of the viable microorganisms were recovered when compared with control cultures (pour plates of seeded blood). All bacteria produced isolated colonies on filters after overnight incubation (18 h). This procedure may prove to be a more rapid method for isolating bacteria from clinical blood samples than the blood culture bottle technique.
Microfiltration has become a popular procedure for the concentration and enumeration of bacteria. We developed a rapid and sensitive method for the differentiation of gram-positive and gram-negative bacteria, utilizing a polycarbonate membrane filter, crystal violet, iodine, 95% ethanol, and 6% carbol fuchsin, that can be completed in 60 to 90 s. Gram reactions of 49 species belonging to 30 genera of bacteria were correctly determined by the filter-Gram stain. The sensitivities of the filter-Gram stain and conventional slide-Gram stain were compared by testing dilutions of Escherichia coli, Neisseria meningitidis, Streptococcus pneumoniae, and Haemophilus influenza suspensions in the presence and absence of whole human blood. The filter-Gram stain was approximately 100-fold more sensitive than the slide-Gram stain. The filter-Gram stain detected 2 to 100 bacteria, whereas the slide-Gram stain failed to detect less than 1,000 bacteria. The sensitivities of the methods were not significantly altered by the addition of whole human blood to the dilutions of bacteria tested. The filter-Gram stain could be a useful tool for the examination of body fluids with very low numbers of bacteria. * Corresponding author. MATERIALS AND METHODS Microorganisms. A total of 49 clinical and reference isolates belonging to 30 genera of aerobic, anaerobic, and facultatively anaerobic bacteria (Achromobacter sp., Acinetobacter calcoaceticus subsp. anitratus, Aeromonas hydo
A quantitative, indirect, fluorescence immunoassay (FIAX; Whittaker Bioproducts, Inc.) was compared with the conventional indirect fluorescent-antibody test for detection of serum antibody to Borrelia burgdorferi. FIAX correlated well with the indirect fluorescent-antibody test (r = 0.72). FIAX is a convenient and dependable means of measuring serum antibody to B. burgdorferi.
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