Laser nephelometric semi-automated system for rapid bacterial susceptibility testing

Experiments with a semi-automated susceptibility test system are described. The system was based on a laser nephelometer which was used to estimate extinction in broth cultures, and ready-to-use cuvettes containing antibiotics. Each antibiotic was tested at two concentrations, the cuvettes were manually inoculated and the results were obtained after 3-5 h incubation in an agitator-incubator. The system was used to test 70 strains (mainly Gram-negative) for susceptibility to 14 antibiotics. The results were compared with the minimal inhibitory concentration (MIC) determined in a solid medium and partially with the ABAC semi-automatic antibiotic sensitivity test. No major discrepancy was observed between the semi-automated laser nephelometric system and MIC and the results were in complete agreement in 91.2%. The laser nephelometric system was found slightly superior to the ABAC system which showed a full accord rate of 88% with MIC. Since the method used a common apparatus in protein immunochemistry, it was found applicable in routine diagnostic microbiology laboratories.