Counting bacteria and determining their susceptibility to antibiotics

A method for detecting bacteria suspended in a biological fluid in which a portion of said biological fluid is filtered to exclude particles larger than said bacteria and a sample of said filtered portion is contained in a cuvette having at least one window illuminated with a coherent and collimated light, said method comprising the steps of:

• a. repeatedly measuring at a predefined repetition rate the intensity of light scattered by said sample at least at one scattering angle;
• b. calculating a difference plot of the light intensity measurements at said at least one scattering angle by calculating the absolute value of the difference between an intensity level of light measured at a first time at said at least one scattering angle and an intensity level of light measured at a second time at said at least one scattering angle, said difference plot calculated such that stationary particles are excluded from the difference plot and non-stationary particles are preserved in the difference plot;
• and
• c. matching said difference plot with a calibration curve to provide an estimate of the concentration of the bacteria in the sample.