Human norovirus (NoV) remains the most common cause of viral gastroenteritis and the leading cause of viral foodborne outbreaks globally. NoV is highly pathogenic with an estimated median viral infective dose (ID 50 ) ranging from 18 to 1015 genome copies. For NoV detection, the only reliable and sensitive method available for detection and quantification is reverse transcription quantitative polymerase chain reaction (RTqPCR). NoV detection in food is particularly challenging, requiring matrix specific concentration of the virus and removal of inhibitory compounds to detection assays. Hence, the RTqPCR method poses some challenges for rapid in-field or point-of-care diagnostic applications. We propose a new colorimetric NanoZyme aptasensor strategy for rapid (10 min) and ultrasensitive (calculated Limit of Detection (LoD) of 3 viruses per assay equivalent to 30 viruses/mL of sample and experimentally demonstrated LoD of 20 viruses per assay equivalent to 200 viruses/mL) detection of the infective murine norovirus (MNV), a readily cultivable surrogate for NoV. Our approach combines the enzyme-mimic catalytic activity of gold nanoparticles with high target specificity of an MNV aptamer to create sensor probes that produce a blue color in the presence of this norovirus, such that the color intensity provides the virus concentrations. Overall, our strategy offers the most sensitive detection of norovirus or a norovirus surrogate achieved to date using a biosensor approach, enabling for the first time, the detection of MNV virion corresponding to the lower end of the ID 50 for NoV. We further demonstrate the robustness of the norovirus NanoZyme aptasensor by testing its performance in the presence of other nontarget microorganisms, human serum and shellfish homogenate, supporting the potential of detecting norovirus in complex matrices. This new assay format can, therefore, be of significant importance as it allows ultrasensitive norovirus detection rapidly within minutes, while also offering the simplicity of use and need for nonspecialized laboratory infrastructure.
Enterotoxigenic Escherichia coli (ETEC) are the most common bacterial cause of gastrointestinal disease and diarrhoea in the world, including travellers' diarrhoea and severe infection in some animal species, particularly calves and piglets. Many similarities exist between infections in animals and humans and extensive research has been done into the pathogenesis, prevention and treatment of ETEC infections. ETEC is an important infective agent in post-weaning diarrhoea (PWD) of piglets, leading to serious animal welfare issues and economic loss through decreased growth rate, mortality (estimated at 2-5%) and medication requirements. Virulence of ETEC strains is characterized by production of adhesins specific to intestinal receptors and potent enterotoxins that generate the disease symptoms. It is a complex multi-factorial condition with decreased passive immunity, stress induction, physiological changes in the gastrointestinal tract, genetic susceptibility, diet and viral infections all implicated in the infection. There has been a worldwide increase in incidence of PWD, most notably as a result of antibiotic-resistant strains of E. coli, and although the reasons for this are not fully understood it is likely that contributing factors include changes to husbandry practices, weaning at a younger age and prophylactic or growth promotional use of low-dose antibiotics. Strategies for prevention and treatment include antibiotics, vaccination, diet and supplements, prebiotics, probiotics, bacteriophage and breeding for resistance.
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