As commonly prescribed treatments for bacterial infection, antibiotics are substances or compounds that kill (bactericidal) or inhibit the growth (bacteriostatic) of various bacterial pathogens. Many factors impact the efficacy of an antibiotic, such as the location of infection, the bioavailability of the antibiotic at this site, and the ability of the bacteria to resist or inactivate the antibiotic. As a result, antibiotic susceptibility testing has become an extremely important process to accurately assess the activity of specific antibiotics against a target infection.
Usually carried out to determine which antibiotic will be most successful in vivo, antibiotic susceptibility testing can be conducted using a nephelometer or a photometer to assess the turbidity of a liquid sample.
The measure of turbidity, or optical density (OD), refers to the scattering of light through the measured sample. Therefore, when measuring the OD of a bacterial culture, the amount of scattered light is directly proportional to the number of bacterial cells in the sample.
If the antibiotic has been successful, the bacterial growth is inhibited and a low OD value will therefore be obtained. If the antibiotic has been ineffective, the bacteria will continue to proliferate and the OD will consequently be higher.
In this study, we investigate the effectiveness of a filter-based microplate photometer, the Thermo Scientific Multiskan® FC from Thermo Fisher Scientific, in producing reliable and accurate bacterial turbidity measurements in antibiotic susceptibility studies. Growth curve measurements, turbidometric measurements, and liquid evaporation were all studied.