Researchers from IIT-Bombay and Manipal Institute of Technology, Manipal, have developed an inexpensive and simple way to check if food items contain antibiotics.

Why is this important? Antibiotics are useful in fighting bacteria. But the more you ingest them over time, the less effective they tend to become in treating bacteria-induced illnesses — a condition known as ‘antibiotic resistance’. The antibiotic-resistant germs find ways to survive. They are “badmaash”, as Prof Soumyo Mukherji, who led the research, puts it. They influence other microbes to turn antibiotic-resistant, too.

Unfortunately, antibiotics get into our food and water in three ways: Sewage (via urine and faeces of humans under treatment with antibiotics); floor cleaners and soaps that have antibiotics as antimicrobial agents; and effluents (of manufacturers of antibiotics).

The researcher group has developed a sensor to detect whether a sample contains certain kinds of antibiotics, identified as beta-lactam antibiotics.

The likes of penicillin and cephalosporin belong to this category. They are distinguished by the presence of a nitrogen ring in their molecular structure. The nitrogen ring targets the wall of the microbe to destroy it. Drug-resistant microbes, however, secrete an enzyme called beta-lactamase, which breaks the nitrogen ring to make it powerless.

Cost advantage

There are different methods to check if a sample contains an antibiotic, but few quantify it with such simplicity and at low cost. “Methods such as mass spectroscopy or standardised chromatography can measure the levels of antibiotics but are expensive and require experts to handle them,” says the IIT-Bombay website, which explains the science behind the principle. In contrast, “the sensor developed by Mukherji and team is easy to use, affordable, robust and reliable. It can be used to check the presence of beta-lactam antibiotics in the likes of water, milk and meat. Importantly, no expert is required to use the sensor,” the site says.

The sensor is made of optical fibre, with cladding removed from the sensing region, which is bent into a U-shape and smaller than a U-pin. “The bending of the fibre is for higher sensitivity. The sensing region is coated with polyaniline, which is further coated with specific sensing molecules,” says Mukherji.

The sensor is in a cartridge, which can be inserted in an instrument that has a light source, a light detector, electronics and display. “A few drops of water (or the sample) are applied to the sensor. Measurements are taken and the user can see the result on the instrument’s display unit within 10-15 minutes,” he says.

“Measuring 7 by 4 by 1.5 inches, the instrument can run for two days in one battery charge. When made at scale, the instrument could cost ₹10,000-15,000. In contrast, mass spectrometers cost ₹40-50 lakh,” says Mukherji.

The team estimates that, when made at scale, the sensor could cost less than ₹35 apiece. It can be reused multiple times, which further reduces the testing cost, says Mukherji.

The chemistry behind the reading

“When beta-lactam in the test sample gets broken down by the beta-lactamase enzyme coating on the sensor, hydrogen ions are released, and acid byproducts form. This alters the polymeric backbone of polyaniline — changing its form from emeraldine base to emeraldine salt,” says Mukherji.

This alters the level of light it absorbs, which is proportionate with the concentration of antibiotic in the sample.

“We found the sensor was most sensitive when the sample was slightly acidic (pH 5.5),” Mukherji says.

So it was not as sensitive to antibiotics in meat compared to milk. However, as the use of beta-lactam antibiotics is typically banned in poultry, merely the ability to detect the presence of antibiotic could make the sensor useful across countries.

There were other challenges, too, such as equipping it to detect the lowest possible antibiotic concentration, says team member Dr Pooja Nag.

Significantly, the sensor was seen immune to the presence of molecules other than beta-lactam antibiotics. So, it was at its best only for these kinds of antibiotics.

Storage is another challenge. “When not coated with the enzyme, the sensors can be stored for a long time. However, once coated, the sensor must be kept at 4 degrees C,” says Mukherji.

K Bharat Kumar