What technique is used to measure the concentration of bacteria in a liquid culture?

Using OD600 with a spectrophotometer is a widely accepted technique for measuring the concentration of bacteria in a liquid culture. This method involves measuring the optical density (OD) of the culture at a wavelength of 600 nanometers. At this wavelength, the turbidity caused by the bacteria in the liquid culture is quantified, allowing researchers to estimate the number of cells present.

As the concentration of bacteria increases, the culture becomes more turbid and absorbs more of the light passing through it. By comparing the OD600 readings to a standard curve, which relates optical density to cell concentration, one can quickly assess and monitor bacterial growth over time. This technique is rapid, non-destructive, and allows for real-time tracking of bacterial growth, making it a preferred method in many microbiological applications.

In contrast, other techniques listed, such as agar plate counting, the streaking method, and inoculation of solid growth media, are primarily used for isolating bacteria, assessing their viability, or culturing them to study specific characteristics, rather than directly measuring concentration in a liquid medium.