Photometric Approach to Microbiological Analysis
Several instrumented systems designed for microbiological analysis, especially antibiotic susceptibility testing, use photometric techniques as the method of measurement of changes in bacterial populations. When photometric techniques measuring light at a single angle are employed, the angle chosen is of importance. Light dispersion can be used in microbiological analyses because it can be shown that the optical density of a sampling vessel containing growth media and growing bacteria will increase as the bacterial population increases. The amount of light emerging from a standardized bacterial suspension in the presence and absence of antimicrobial agents is read by a photometer at a single angle of measurement and is converted into a number referred to as a light scattering index. Since forward-angle light dispersion techniques can measure an increase in biomass, this approach can be used for detection of bacteria. Bacteria are often identified by characteristic patterns shown by reactions to selective or inhibitory media.