Influence of Selective Media on Successful Detection of Shiga Toxin–ProducingEscherichia coliin Food, Fecal, and Environmental Samples

Abstract

Shiga toxin-producing Escherichia coli (STEC) strains have caused a large number of human illness outbreaks worldwide. In most cases, the infection was traced to consumption of meats or vegetables contaminated with cattle feces. To combat this public health problem, pre- and post-harvest control strategies are continuously implemented to assure food safety. Thus, rapid, reliable, and sensitive methods for STEC detection must be available to provide confidence not only in the meats or vegetables entering the food chain but also in testing humans with illnesses. As a result, enrichment for STEC has been a critical step in any successful protocol for their detection. The base media commonly used for STEC enrichment include sorbitol MacConkey agar, tryptic soy broth (TSB), E. coli broth, enterohemorrhagic E. coli broth, buffered peptone water (BPW), and brain heart infusion broth. In addition to bile salts, antibiotics (e.g., tellurite, cefixime, novobiocin, vancomycin, cefsulodin, and acriflavin) are used at different concentrations to enrich for STEC. In most published reports, however, the reasons for choosing the selective medium were not provided. Thus, this review was intended to evaluate the base media and antibiotics commonly used for STEC detection. The efficacy of a detection method will certainly depend on the choice of the base medium, selective agents, and their concentrations. The interactions among these factors are also expected to affect sensitivity of the detection method, especially when the test sample contains a small number of STEC cells. Because sensitivity of detection is expected to decline when testing for stressed or injured STEC cells, as is the case in environmental samples, a pre-enrichment step in TSB or BPW without antibiotics may be necessary. Future research should focus on identifying possible antibiotic combinations that effectively inhibit most background bacteria without affecting pathogenic STEC strains in the test sample.

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

“…Since the first reported STEC outbreak in 1982 (12), various methods for the detection of STEC, especially E. coli O157: H7, which is the most prevalent group of STEC, have been developed (13). STEC O157:H7 had been found to be non-sorbitol fermenting (NSF), and consequently, culture media containing sorbitol have been marketed and widely used.…”

Microbiological quality and potential public health risks of export meat from springbok (Antidorcas marsupialis) in Namibia

“…However, the absence of STEC in pooled rectal contents suggests a relatively low risk of contamination of meat derived from those animals. While sorbitol MacConkey agar is recommended for STEC O157:H7 (March & Ratman, 1986), there is no universal media catering for all STEC serotypes (Hussein & Bollinger, 2008). In this respect, subjecting the samples to a pre-enrichment step in BPW or TSB without antibiotics is considered a vital step toward successfully isolating STEC from food, feces or environment (Hussein & Bollinger, 2008).…”

Evaluation of an Immuno-Chromatographic Detection System for Shiga Toxins and the E. coli O157 Antigen

“…The bacteria may be stressed during the processing and storage of food. The enrichment procedure provides an optimal growth medium and a period of time that can be effectively used, allowing the resuscitation of the bacterial cells (Hussein and Bollinger 2008). The detection of stressed STEC from samples depends largely on the choice of the cultivation media and conditions.…”

“…The detection of stressed STEC from samples depends largely on the choice of the cultivation media and conditions. Non-selective media such as buffered peptone water were found to be advantageous for the resuscitation of damaged STEC from various samples (Hussein and Bollinger 2008;Jahn and Beutin 2009). …”