SALMONELLA, a harmful bacteria, is one of the biggest causes of food contamination and food-borne diseases in the world. Conventional methods to detect Salmonella in food are complicated and time consuming. Scientists have now developed a biosensor which can detect the contamination in minutes.
The biosensor involves use of peptides, chemicals made up of two or more amino acids, instead of the currently used commercial antibodies like alamethicin. “The biosensor can be customised to detect any type of bacteria and different strains of the same bacterium,’’ says Sibani Lisa Biswal from Rice University, US, one of the researchers in the study. The biosensor is made up of a set of mircocantilevers coated with different peptides that have unique binding affinities to various strains of Salmonella. When the peptide catches a bacterium, the cantilever bends due to a mismatch in surface stress. A laser then catches the motion in the surface and triggers the alarm.
To test the biosensor, four peptides (MSal020401, MSal 020404, MSal 020415, and MSal 020417) were used. The bacteria used included a cocktail of eight commonly found Salmonella serotypes (Enteritidis, Typhimurium, Dublin, Infantis, Senftenberg, Hadar, Mbandaka, Virchow), Listeriamonocytogenes and Escherichia coli K12.
“We found that not only were the peptides more sensitive (than antibodies) in detecting pathogens, but the microcantilevers could also detect many different strains of Salmonella at once,” says Biswal. “One particular peptide, MSal 020417, demonstrated a higher binding affinity to Salmonella and was able to distinguish among eight Salmonella serotypes,’’ she adds.
According to the researchers, another good point about peptides is that they are more robust than antibodies. “They can handle much harsher conditions and still remain stable. Antibodies are large proteins and break down easily,” Biswal points out. The biosensor has other advantages as well. Microcantilevers can be cleaned and reused. Also, the system is sensitive enough to warn about the presence of even a single pathogen. However, Arun K Bhunia, professor of food microbiologyÃ”Ã‡Ãªat Purdue University, US, says, “This technology is in a very early stage. One of the concerns I have is that researchers have not determined the detection threshold for this sensor. It appears they tried only with one concentration (100 million cells). Most biosensor technologies can detect pathogens present in the concentration of 100-1,000 cells. The other challenge is that there are millions and billions of bacteria in food which may generate false positive results. The team has only tested with Listeriamonocytogenes and E coli to show specificity.”
The study was published in the February issue ofÃ”Ã‡ÃªAnalytical Chemistry.
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