Nanotechnology Enables 4-Hour Antibiotic Susceptibility Testing

Antibiotic resistance is a major public health challenge, as infections caused by bacteria resistant to prescribed drugs may not respond to treatment. Timely determination of bacterial susceptibility to antibiotics is therefore essential for evaluating effective treatment options and supporting clinical decision-making.

Conventional antibiotic susceptibility testing methods can take approximately 24 to 48 hours to produce results. To address this limitation, researchers from Tehran University of Medical Sciences and Iran University of Medical Sciences have developed a nanomaterial-based approach that evaluates bacterial responses to different antibiotic concentrations by measuring changes in color intensity. The findings were published in the scientific journal Scientific Reports.

The method uses a nanoscale composite consisting of gamma-phase iron oxide and Prussian blue, with the chemical formula γ-Fe₂O₃@Prussian blue. The composite exhibits peroxidase-like activity, enabling it to accelerate certain chemical reactions. Materials with such enzyme-mimicking properties are known as nanozymes.

In the study, researchers exposed bacterial samples to different concentrations of antibiotics and subsequently added reagents that produce a colorimetric reaction in the presence of the nanozyme. The intensity of the resulting blue color was then measured to assess changes in bacterial activity in response to the drugs.

The experiments involved four strains of E. coli, including two antibiotic-susceptible strains and two resistant strains. Four antibiotics—ampicillin, cefazolin, ceftriaxone, and kanamycin—were evaluated.

According to the reported results, the colorimetric signal increased substantially in susceptible strains as antibiotic concentrations rose and reached levels associated with bacterial growth inhibition.

In contrast, resistant strains showed relatively little change in color intensity across different antibiotic concentrations. These distinct response patterns enabled the researchers to differentiate between susceptible and resistant bacteria based on changes in color intensity.

The method was also used to estimate the minimum inhibitory concentration (MIC), defined as the lowest concentration of an antimicrobial agent that prevents visible bacterial growth under specified laboratory conditions. MIC is an important parameter in assessing bacterial susceptibility to antibiotics.

The researchers reported that the assay could be completed in approximately four hours. They also noted that the method does not require expensive reagents or equipment. However, the reported detection limit depended on the initial bacterial concentration in the sample and was determined to be 1.67 × 10⁷ colony-forming units per milliliter (CFU/mL).

Despite these preliminary findings, the study was conducted under laboratory conditions and was limited to four strains of E. coli. Consequently, the current results do not establish the method’s accuracy in detecting resistance in other bacterial species, its performance in actual patient samples, or its applicability to a broader range of antibiotics.

Further research involving a wider variety of bacterial strains, clinical specimens, and antibiotics will be necessary to establish the method’s reliability in diagnostic settings. Direct comparisons with standard antibiotic susceptibility testing methods will also be essential to determine its diagnostic performance and potential clinical utility.

If validated in subsequent studies, the approach could help reduce the time required to assess bacterial susceptibility to antibiotics. However, its ability to replace established diagnostic methods has not yet been demonstrated.