Evaluation of CHROMagar STEC and STEC O104 Chromogenic Agar Media for Detection of Shiga Toxin-Producing Escherichia coli in Stool Specimens

Abstract

The performance of CHROMagar STEC and CHROMagar STEC O104 (CHROMagar Microbiology, Paris, France) media for the detection of Shiga toxin-producing Escherichia coli (STEC) was assessed with 329 stool specimens collected over 14 months from patients with suspected STEC infections (June 2011 to August 2012). The CHROMagar STEC medium, after an enrichment broth step, allowed the recovery of the STEC strain from 32 of the 39 (82.1%) Shiga toxin-positive stool specimens, whereas the standard procedure involving Drigalski agar allowed the recovery of only three additional STEC strains. The isolates that grew on CHROMagar STEC medium belonged to 15 serotypes, including the prevalent non-sorbitol-fermenting (NSF) O157:H7, O26: H11, and O104:H4 serotypes. The sensitivity, specificity, and positive and negative predictive values for the CHROMagar STEC medium were between 89.1% and 91.4%, 83.7% and 86.7%, 40% and 51.3%, and 98% and 98.8%, respectively, depending on whether or not stx-negative eae-positive E. coli was considered atypical enteropathogenic E. coli (EPEC) or STEC that had lost Shiga toxin genes during infection. In conclusion, the good performance of CHROMagar STEC agar medium, in particular, the high negative predictive value, and its capacity to identify NSF O157:H7 as well as common non-O157 STEC may be useful for clinical bacteriology, public health, and reference laboratories; it could be used in addition to a method targeting Shiga toxins (detection of stx genes by PCR, immunodetection of Shiga toxins in stool specimens, or Vero cell cytotoxicity assay) as an alternative to O157 culture medium. This combined approach should allow rapid visualization of both putative O157 and non-O157 STEC colonies for subsequent characterization, essential for real-time surveillance of STEC infections and investigations of outbreaks. C ertain strains of Shiga toxin-producing Escherichia coli (STEC) are important causes of food-borne disease in industrialized countries. The clinical manifestations of STEC infections range from mild diarrhea to severe and specific complications, such as hemolytic-uremic syndrome (HUS), which occurs primarily in young children (1, 2). These STEC strains associated with human infections are also called enterohemorrhagic E. coli (EHEC). Animals, and especially cattle, serve as reservoirs for STEC. Transmission occurs via ingestion of contaminated food or water, person-to-person contact, direct animal contact, and exposure to the environment. STEC strains are characterized by their ability to produce toxins related to those of Shigella dysenteriae type 1 (3): two types have been described among STEC isolates, Shiga toxin 1 and Shiga toxin 2, respectively, encoded by the stx 1 and stx 2 genes carried on temperate bacteriophages (4, 5). Most STEC isolates also carry the chromosomally located locus of enterocyte effacement (LEE), a pathogenicity island, first described in enteropathogenic E. coli (EPEC). LEE promotes the development of attaching-and-effacing lesions in the host intestinal mucosa c...

Prevalence and antimicrobial sensitivity of Shiga-toxin-producing Escherichia coli among underfives presenting with diarrhoea at hospitals in Mwanza City, Tanzania

“…The STEC isolation rate of 10.5% in this study is higher compared to a study done in Morogoro region within the same country but close to a prevalence of 8.4% report in a study done in Nigeria (Raji et al, 2008;Onanuga et al, 2014). The observed differences in prevalence can be due to the isolation methods used in these studies whereby the present study used the current recommended culture method for STEC screening (Gouali et al, 2013) in contrast to other studies that used molecular methods. The overall prevalence of pathogenic bacteria causing diarrhoea in the studied population was 14.5% which is lower compared to 22.9% and 35.7%, previously reported in a studies conducted at Tanzanian National (Moyo et al, 2007) and Regional hospitals (Vargas et al, 2004).…”

Estimation of Listeria monocytogenes and Escherichia coli O157:H7 Prevalence and Levels in Naturally Contaminated Rocket and Cucumber Samples by Deterministic and Stochastic Approaches

“…Consequently, parallel testing would improve E. coli 0157:H7 detection if one of the two media tested, Fluorocult or CT-SMAC, were used in combination with another medium that produced far fewer false-positive results. Rainbow agar, Biosynth culture media, and CHROMagar have been reported to produce fewer false-positive results (14,26). The need for a second medium is supported by the need to detect sorbitolfermenting E. coli 0157:H7 strains (15,21,43).…”

Practical Guidance for Clinical Microbiology Laboratories: Diagnosis of Bacterial Gastroenteritis

“…CHROMagar O157 detects O157 serogroups, and CHROMagar STEC detects both O157 and the six most common STEC serogroups other than O157 isolated in the United States (O26, O45, O103, O111, O121, and O145). This product is labeled for research use only in the United States, but a recent study demonstrated that CHROMagar STEC had a sensitivity of 89.1% and specificity of 86.7% (272). In HardyChrom SS Isolation of Salmonella (black on this medium) and Shigella (teal on this medium) Inositol-brilliant green-bile salt Isolation of P. shigelloides (white to pink on this medium) (not part of routine setup unless requested) MacConkey agar with sorbitol (SMAC) or cefixime-tellurite SMAC (CT-SMAC)…”