Is green metallic sheen in emb agar accurate to assist the Escherichia coli identification?

Escherichia coli is an essential bacteria as a human and animal pathogen, although this species can also be disseminated in the environment. The clinical laboratories use EMB agar (Eosin Methylene Blue) to identify E. coli from the observation of metallic green sheen. However, other bacterial species may show sheen when sown on EMB agar, or in some cases, the pH sample influences the presence of this sheen by E. coli. In this study, MALDI-TOF was used as the gold standard to detect E. coli from human, animal, and environmental samples by analyzing the presence of green glow on EMB agar. The positive predictive values (PPV) were higher (above 85%) in human, animal, and environmental samples studied, and the negative predictive value (NPV) was variable between the samples. Specificity and sensitivity were also variables suggesting the influence of the pH of the samples in the presence of metallic green brightness. This work demonstrated that it is necessary to implement biochemical tests or, when possible, molecular assays to confirm E. coli since only the observation of the production of metallic green glow in EMB can generate false negative results in the identification of E. coli. Keywords: Biochemical tests; Escherichia coli; Laboratory Analysis; MALDI-TOF.