Diagnostic particle agglutination using ultrasound: a new technology to rejuvenate old microbiological methods

Microbial antigen in clinical specimens can be detected rapidly by commercial test-card latex agglutination, but poor sensitivity is a potential difficulty. Antigen detection by immuno-agglutination of coated latex micro-particles can be enhanced in comparison with the conventional test-card method in both rate and sensitivity by the application of a non-cavitating ultrasonic standing wave. Antibody-coated micro-particles suspended in the acoustic field are subjected to physical forces that promote the formation of agglutinates by increasing particle-particle contact. This report reviews the application of ultrasound to immuno-agglutination testing with several commercial antibody-coated diagnostic micro-particles. This technique is more sensitive than commercial card-based agglutination tests by a factor of up to 500 for fungal cell-wall antigen, 64 for bacterial polysaccharide and 16 for viral antigen (in buffer). The detection sensitivity of meningococcal capsular polysaccharide in patient serum or CSF has been increased to a stage where serotyping by ultrasound-enhanced agglutination is comparable to that achievable with the PCR, but is available more rapidly. Serum antigen concentration as measured by ultrasonic agglutination has prognostic value. Increasing the sensitivity of antigen detection by increasing the acoustic forces that act on suspended particles is considered. Employing turbidimetry to measure agglutination as part of an integrated ultrasonic system would enable the turnover of large numbers of specimens. Ultrasound-enhanced latex agglutination offers a rapid, economical alternative to molecular diagnostic methods and may be useful in situations where microbiological and molecular methods are impracticable.