12/10/2023 0 Comments Xld agar e coliIn this study, we initially compared the appearances of known stock cultures of Salmonella, Shigella, other enteric organisms, and Candida spp. Experience with this formulation as a screen for Salmonella isolates is limited, and its utility in the routine examination of stool specimens has not been defined. A more recent formulation of CAS medium aiming to reduce these specificity issues is now available. aeruginosa was subsequently reduced by the addition of the antimicrobial agent cefsoludin into the medium ( 4). the proportion of false-positive results caused by P. False-positive results were, however, reported with Pseudomonas aeruginosa, Aeromonas hydrophila, and Candida spp. was similar to that of HEA on primary plating and after enrichment in broth culture (O. The sensitivity of an early formulation of CAS medium for the detection of Salmonella spp. CHROMagar Salmonella (CAS) is a newer selective chromogenic medium and purports to detect salmonellae as mauve colonies at 18 to 24 h of incubation, with other members of the family Enterobacteriaceae appearing as blue or uncolored colonies (CHROMagar Salmonella Product Information CHROmagar Microbiology, Paris, France). As a result, many of these earlier media cannot be recommended for use for the primary plating of stool specimens to screen for Salmonella spp. One particular formulation of chromogenic medium, Rambach agar, was highly specific for salmonellae but failed to detect S. Compared to conventional selective media such as Hektoen enteric agar (HEA), chromogenic media had higher specificities but lower sensitivities, with more false-negative results ( 2, 8, 11, 12). by the incorporation of chromogenic substrates have been introduced ( 2, 8, 10). Recently, media allowing the detection of Salmonella spp. The specificities of such media are poor, however, and time-consuming complementary testing is required to exclude as significant colonies of organisms with similar biochemical features. in stool specimens have been developed for this purpose. A variety of selective media which rely on visualization of simple biochemical features such as the nonfermentation of lactose and the production of hydrogen sulfide to identify Salmonella spp. Isolation of the organism by stool culture remains the most reliable method for detection, allowing precise identification of the bacteria and antimicrobial susceptibility testing, both of which are critical for disease control. While direct detection of Salmonella isolates in stool specimens by PCR is possible, this technique is not readily available for routine use in most clinical laboratories ( 13). Infections due to Salmonella spp., including Salmonella enterica serovar Typhi, continue to be a major global health problem. Other media (e.g., XLD) are required to detect Shigella spp. It can be recommended for use for the primary isolation of Salmonella spp. The use of plating on CAS medium demonstrated high levels of sensitivity and specificity and reduced the time to final identification of Salmonella spp., resulting in substantial cost savings. One biochemically inert Escherichia coli isolate required further identification to differentiate it from Salmonella spp. These were easily excluded as salmonellae by colony morphology, microscopic examination of a wet preparation, or oxidase testing. Twenty-nine non- Salmonella organisms produced mauve colonies on CAS medium, including 17 Candida spp. The specificity for the detection of salmonellae after primary plating on CAS medium (83%) was significantly ( P < 0.0001) higher than that after primary plating on the combination of SS and XLD media (55%) (a 28% difference in rates 95% confidence interval, 23.0 to 34%). The sensitivities for the detection of salmonellae after primary plating on CAS medium and the combination of XLD and SS after enrichment were 100%. Nine Salmonella strains were isolated from clinical specimens. All stock Salmonella isolates produced typical mauve colonies on CAS medium. CAS medium was then compared prospectively to XLD and SS for the detection and presumptive identification of Salmonella strains in 500 consecutive clinical stool samples. The growth and appearance of 115 stock Salmonella isolates on a new formulation of CHROMagar Salmonella (CAS) medium were compared to those on xylose-lysine-desoxycholate agar (XLD), Salmonella-Shigella agar (SS), and Hektoen enteric agar (HEA) media.
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