A total of 110 enterococcal strains (34 Enterococcus faecalis, 15 Enterococcus faecium, and 61 nonhemolytic and nonspeciated strains), 30 S. bovis strains (2 alpha-hemolytic and 28 non-hemolytic strains), and 110 non-group D viridans group streptococcal strains (83 alpha-hemolytic and 27 nonhemolytic strains) were tested. Washington, DC 20036 The slants were incubated at 35°C in ambient air (2) with loose caps for 48 h. Readings were taken at 24 and 48 h. A reaction was considered positive when one-half or more of the medium was blackened (4). The hydrolysis of esculin has traditionally been determined by the … Table 1 gives the percentages of false-positive bile-esculin tests for 110 non-group D viridans group streptococcal strains. To determine the effect of Optochin (ethyl hydrocupreine hydrochloride) on test organism. On the other hand, false-positive reports ofS. In liquid media, S pneumoniae replicates in chains. Differentiating S bovis from Streptococcus salivarius is sometimes very difficult because S salivarius yields a positive reaction on the bile-esculin test. diacetylactisstrains. It is especially useful in differentiating species of the genus Streptococcus. The hydrolysis of esculin in the presence of bile has been utilized for many years for the identification of bacteria. Other alpha-hemolytic streptococci do … bovis is important, since the organism is associated with colonic carcinoma, which should be ruled out in such patients (7). This … These results were obtained with agar slants containing 4% oxgall (bile salts), inoculated with 1 or 2 drops of a 24-h Todd-Hewitt both culture of the organism (“next-day” inoculation), and incubated for 48 h. In routine diagnostic bacteriology, such a protocol is impractical, since it requires 3 days from the time colonies are detected on primary plates. Staphylococcus epidermidis are catalase view the full answer All 30 strains of S. bovis were positive at 24 and 48 h regardless of the bile concentration or the method of inoculation (100% sensitivity). The first selective ingredient in this agar is bile, which inhibits the growth of Gram-positives … Bile-esculin-positive organisms from blood and normally sterile sites should be speciated. It is a low cost, rapid test with good sensitivity and specificity (>90%). ... Gamma Hemolysis on Blood Agar. Journal of Microbiology & Biology Education, Microbiology and Molecular Biology Reviews, Non-group D streptococcal meningitis misidentified as enterococcal meningitis. Therefore, we evaluated the sensitivity and specificity of the bile-esculin test with two different methods of same-day inoculation (standardized and nonstandardized) and two different incubation times (24 and 48 h). We found that the specificity (100% minus the percent false positive) was maximal (97%) with a standardized inoculum streaked on agar slants containing 4% oxgall and read after 24 h. False positives were obtained with two Streptococcus milleriand one Streptococcus lactis subsp. Isolates in this group are negative for acetoin production, arginine, esculin, and mannitol and are sorbitol fermentation negative (14). We also compared esculin slants containing 2 and 4% oxgall in formulations currently available from two major commercial sources in the United States. No Growth in BHI Broth with 6.5% NaCl. Catalase-negative, gram-positive cocci in pairs and chains forming alpha-hemolytic or nonhemolytic colonies that were negative for PYR, did not grow in 6.5% NaCl, were positive for group D antigen by latex agglutination (Murex), and had a suggestive (≥90% probability) biochemical pattern by the API Rapid Strep system were identified as S. bovis. Most textbooks and procedure manuals recommend inoculating agar slants directly from a few colonies (“same-day” inoculation) rather than from a 24-h subculture in broth, but data supporting this nonstandardized alternative technique are lacking. First, the bacterium must grow in a particular concentration of bile, and second, it must hydrolyze esculin. hemolysis on blood agar. S pneumoniae are non-beta-hemolytic streptococci that are optochin-positive, bile-soluble, and bile esculin-negative. Abstract. Streptococcus, viridans group. Group B Streptococcus (S. agalactiae) Alpha Hemolysis on Blood Agar Optochin Sensitive. Phone: (202) 737-3600, Copyright © 2020 American Society for Microbiology | Privacy Policy | Website feedback, Print ISSN: 0095-1137; Online ISSN: 1098-660X, Clinical Microbiology Laboratory, Duke University Medical Center, and Departments of, Medicine, Duke University School of Medicine, Durham, North Carolina, Bile-Esculin Test for Presumptive Identification of Enterococci and Streptococci: Effects of Bile Concentration, Inoculation Technique, and Incubation Time, Sign In to Email Alerts with your Email Address. The gram stain is an example of a test that can be used to determine the ___ characteristics of a bacterium. In conclusion, the bile-esculin test works well to rapidly separate enterococci and group D streptococci from non-group D viridans group streptococci at low cost and with good sensitivity (>99%) and specificity (97%), provided it is performed on agar slants containing 40% bile, done with a standardized inoculum (10 μl of a 0.5 McFarland standard bacterial suspension), and read at 24 h. C. Chuard was supported by a grant from the Swiss Academy of Medical Sciences. Instead, use a sterile loop to inoculate the Bile-Esculin Agar plate and the 6.5% NaCl broth with your Strep unknown. A positive presumptive identification of S. pneumoniae is made when a well defined zone of inhibition results around the impregnated disk. The strains were isolated consecutively from blood cultures performed at Duke University Medical Center during a 4-year period, except for 19 S. bovisstrains that were obtained from the Mayo Clinic. Optimal sensitivity (>99%) and specificity (97%) of the bile-esculin test can be obtained with a bile concentration of 40%, a standardized inoculum of 106 CFU, and incubation for 24 h. Recognition and differentiation of catalase-negative, alpha-hemolytic and nonhemolytic gram-positive cocci in pairs and chains as enterococci; group D streptococci (mainlyStreptococcus bovis); and non-group D viridans group streptococci are clinically important (10).