A comparison of the efficiency in serotyping of Pseudomonas aeruginosa from cystic fibrosis patients using monoclonal and polyclonal antibodies

A well-known problem in serotyping Pseudomonas aeruginosa strains from cystic fibrosis patients using polyclonal sera is that more than half of the strains cannot be assigned to a single O-serogroup because of the high occurrence of polyagglutinable strains and nontypable strains. In the present study, the efficiency of a set of O-specific monoclonal antibodies in the simple slide agglutination test was compared with polyclonal sera for the serotyping of 243 isolates of P. aeruginosa from cystic fibrosis patients. Using the monoclonal antibodies, 213 (88%) strains were found to be typable and only 30 (12%) strains were nontypable. In contrast, when the polyclonal sera from Statens Seruminstitut were used, only 53 (22%) strains were typable. Similar results were obtained when polyclonal sera manufactured by Difco were used where only 61 (25%) strains were typable. We also investigated the consistency of each set of antibodies in typing of the same isolates on different days and found that the polyclonal sera showed higher reproducibility. The Statens Seruminstitut sera were found to have an 86% reproducibility while the Difco sera scored 81%; however, the percentage of strains that are nontypable remains below 25% despite the highly reproducible results obtained. The monoclonal antibodies were found to score a 75% reproducibility when the serotyping of the same strains was done both in the laboratories of Copenhagen and of Guelph. However, it should be noted that although the reproducibility was somewhat lower with the monoclonal antibodies, these highly specific antibodies are still clearly superior when compared with polyclonal sera used because more than 80% of the strains from cystic fibrosis can now be assigned to a single O-serogroup.