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SUMMARY: Of 46 strains of Haemophilus pertussis, 34 recently isolated strains were all agglutinated by Phase 1 antiserum. Of 12 laboratory strains, 5 had lost their agglutinability. The agglutinable strains were precipitated by aluminium phosphate, and lysed by sodium hydroxide or 10% sodium desoxycholate and were virulent to mice. The virulent strains, which were precipitable by aluminium phosphate, produced toxic substances in a fluid culture. Precipitation by aluminium phosphate provides a quick method for distinguishing virulent and avirulent strains of H. pertussis. Suspensions of strains of Haemophilus pertussis that are agglutinated by a Phase 1 antiserum have been found also to be completely precipitated with aluminium phosphate, whereas strains that become non-agglutinable by the Phase 1 antiserum also lose this precipitability (Ungar & Muggleton, 1948). The object of the present communication is to show the relationship between precipitability, agglutinability and certain other biological properties of different strains of H. pertussis, either freshly isolated from recent cases of pertussis or maintained in the laboratory for some time. It has long been known that strains of H. pertussis maintained in artificial culture can pass through a series of serologically differentiable phases. In our study no attempt was made to classify the strains used into phases, except that we assigned to Phase 1 all strains that were agglutinated to a high titre (over 1/8000) with a rabbit antiserum prepared by inoculation with a freshly isolated strain. Altogether we tested 46 strains, of which 34 were received, immediately after isolation, from the Central Public Health Laboratory of the Public Health Laboratory Service or from the North Western Group Laboratory of the L.C.C., and one from Prof. G. A. H. Buttle of the School of Pharmacy, University of London. The remainder were stock strains maintained in this laboratory for various periods; of these, six had been repeatedly subcultured on Bordet- Gengou medium and were no longer agglutinable with the Phase 1 antiserum and the rest had been freeze-dried and stored. All the strains were kept freeze- dried during the investigation and frequent culture from the freeze-dried state was made to ensure that the strains used in the tests remained constant. Aluminium phosphate precipitation of the strains A standard method of testing the precipitability of the strains was used throughout, The suspensions from 48 hr. Bordet-Gengou cultures were washed twice, resuspended in saline containing 0.2% formaldehyde, to give a con- centration of c. lolo organisms/ml., and held at room temperature overnight.

The Relationship of the Aluminium Phosphate Precipitation of Organisms of Haemophilus pertussis strains to their other Biological Properties