Evaluation of a New Chromogenic Medium for the Isolation and Presumptive Identification of Salmonella Species from Stool Specimens

Abstract

The performance of BBL CHROMagar Salmonella (Becton Dickinson, France), a new selective chromogenic medium for the isolation and presumptive identification of Salmonella spp., was evaluated. On this medium, which is a modification of CHROMagar Salmonella (CHROMagar Microbiology, France) with enhanced selectivity, the colonies of Salmonella are stained in mauve (rose-violet), while those of other organisms appear in blue-green or are not stained by any of the chromogens of the medium. The medium was evaluated with a total of 176 strains of Salmonella and other organisms, consisting of 18 reference strains and 158 clinical isolates. All Salmonella strains except subspecies IIIa and IIIb strains and Salmonella Gallinarum yielded typical mauve colonies. During the evaluation with 107 known positive and 332 unknown stool specimens in a clinical laboratory, a total of 115 and 105 Salmonella isolates were obtained on BBL CHROMagar Salmonella and Hektoen enteric agar, respectively. From the known positive stool specimens, 92 true positive cultures were obtained on BBL CHROMagar Salmonella and 89 on Hektoen enteric agar, yielding sensitivities of 86 and 83%, respectively. From the unknown stool specimens, a total of 27 Salmonella isolates were obtained, with 23 isolated from BBL CHROMagar Salmonella and 16 from Hektoen enteric agar by direct plating (sensitivity 85 and 59%, specificity 99 and 97%, respectively). Seroagglutination tests could be performed directly from BBL CHROMagar Salmonella. Compared to conventional isolation media, the time needed for confirmatory biochemical and serological tests was shortened by about 1 day when BBL CHROMagar Salmonella was used. On the basis of these results, the medium can be recommended for the primary isolation and presumptive identification of Salmonella spp. from clinical stool specimens.

Salmonella Türlerinin Hızlı Tanısında Kromojenik Besiyeri İle Birlikte “Matrix-Assisted Laser Desorption Ionization - Time of Flight Mass Spectrometry” Yönteminin Phoenix Otomatize Sistemi ile Kıyaslanması

“…Salmonella taramasında kullanılmak üzere Salmonella'ya özgü enzimleri saptayabilecek kromojenik substratlar içeren besiyerleri geliştirilmiştir 6 . Bu besiyerleri ile yapılan çalışmalarda diğer konvansiyonel besiyerleri ile kıyaslandığında doğrulama için gereken biyokimyasal ve serolojik testlerle birlikte gereken sürenin yaklaşık olarak 24 saat kısaldığı gösterilmiştir 7 . Bu besiyerleri kullanılarak Salmonella türlerinin tanısında yük-sek oranda duyarlılık ve özgüllük sağlandığı, ayrıca tanının konması için gereken sürenin azalmasının yanısıra yapılan maliyet analizinde de kullanılan besiyerleri ve teknisyen zamanı hesaplandığında maliyetin de %26 azaldığı gösterilmiştir 8 .…”

Evaluation and Implementation of a Chromogenic Agar Medium for Salmonella Detection in Stool in Routine Laboratory Diagnostics

“…Eigner et al tested BBL with stool samples and found a sensitivity of 85% and a specificity of 99% after 48 h of incubation of direct plates (5). In two other studies, BBL and SM were compared using stock isolates and stool samples, respectively (2,4).…”

Comparison of Salmonella Chromogenic Medium with DCLS Agar for Isolation of Salmonella Species from Stool Specimens

“…The selective agents used in these agars include dyes, antibiotics, and bile salts (7). Differentiation of most salmonellae from other organisms usually relies on the visualization of simple biochemical features such as the production of hydrogen sulfide or the nonfermentation of lactose (2,3,6,16; D. E. Post, Folio LT0435A [1997], Oxoid, Ltd., Basingstoke, United Kingdom). These media are useful for the confirmation of suspect colonies but most are highly nonspecific, mainly due to Proteus and Citrobacter strains from the normal flora, which closely resemble Salmonella strains.…”

“…These media are useful for the confirmation of suspect colonies but most are highly nonspecific, mainly due to Proteus and Citrobacter strains from the normal flora, which closely resemble Salmonella strains. Such suspect colonies must be differentiated further by biochemical or serological tests before a final result is obtained (5,6,10,20). Due to high rates of false-positive results, screening of stool samples for Salmonella becomes labor-intensive, with additional costs for subsequent identification (5).…”

“…In the last decade chromogenic media have been developed for the detection of Salmonella species (2,4,6,18). These media use a combination of chromogenic substrates and conventional biochemical tests and are, therefore, highly specific.…”