Sensor captures bacteria's movements to measure antibiotic efficacy

Ward Johnson, a NIST physicist, looks at signals generated by the changing motion of bacteria to see if an antibiotic is working against a particular bacteria. (National Institute of Standards and Technology)

Scientists at the National Institute of Standards and Technology have created a rapid test that indicates if an antibiotic fights a given infection, which could speed up treatments and reduce improperly prescribed antibiotics.

The overuse of antibiotics, both in humans and livestock, has led to the rise of antibiotic-resistant bacteria. Because these bacteria do not respond to often-used drugs, physicians must use alternative treatments that may not be as effective as the first-choice medicines, the Centers for Disease Control (CDC) said. The CDC estimated that up to 50% of antibiotics are not “optimally” prescribed—either they are prescribed when they are not needed, or they are given in the wrong dose or for the wrong amount of time.

To address this, the NIST team developed a sensor that determines within an hour if an antibiotic will be effective against an infection. Current tests require colonies of bacteria to be cultured for days, which can allow an improperly treated infection to advance and give the bacteria a chance to develop drug resistance.

The NIST sensor is a quartz-crystal resonator that vibrates differently when bacterial cells on its surface change their behavior. It detects the mechanical motion of microbes to gauge a response to antibiotics, the team said in a statement. Proof-of-concept tests showed that the amount of frequency noise emitted by the bacterial cells increased with the density of bacteria.

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The team then exposed E. coli bacteria to the antibiotics polymyxin B and ampicillin. The sensor showed that frequency noise from the bacteria fell to zero within seven minutes of being treated with polymyxin B. The same happened within 15 minutes of receiving ampicillin. This mirrors the normal speed at which the drugs work. The study is published in Scientific Reports.

Researchers are seeking new ways to address antibiotic resistance, including creating new medicines that exploit alternative targets on the bacterial cell. A team from Rutgers, for example, blocked an enzyme crucial for replication to target rifampin-resistant bacteria. Rockefeller University scientists are using unfamiliar human-germ hybrids to kill bacteria.

Using bacterial motion to measure drug response is another idea that's gaining steam in research circles. But previously, changes in motion could only be detected in bacteria that can “swim,” using a propeller of sorts called the flagellum.

The NIST approach is much more sensitive. Testing it on bacteria with paralyzed flagella, the team found that the vibrations measured by the sensor actually come from the cell walls of the microbes.