Variability in derivative strains of Bordetella pertussis

Abstract

Bordetella pertussis strain UT25 was isolated on Bordet-Gengou(B-G) agar from a child with whooping cough in 1977. Derivative strains were isolated from UT25 by serial passages on Trypticase Soy Agar (TSA) containing blood,followed by serial passages on plain TSA. At passage 69, UT25 was subcultured in parallel on TSA and B-G. For experiments, strains were grown in defined liquid medium, adjusted to a standard turbidity, and tested in parallel. Tests were performed to detect changes in immunogenicity, production of dermonecrotic toxin, histamine sensitizing ability, serologic properties, infectivity for mice by the intranasl route, production of adenylate cyclase, patterns of outer membrane proteins. Notable changes occurred in the properties of UT25 at passage 16, just when stable growth on blood-fresh medium was established. After 5 additional passages on TSA, however, the strain resembled the original isolate. At about passage 45, biological activity began to decline, and by passage 60 most biological activities were sharply diminished or undetectable. No recovery of biological activity was observed during a further 15 passages on TSA. Strains derived from the sixty-ninth passage of UT25, after passage on B-G for 5 subcultures, showed partial recovery of biological activity. Ten additional subcultures on B-G yielded strains which showed even higher biological activity. Fluorescent antibody staining confirmed that all strains studied were B. pertussis, and maintained reactive surface antigen(s), in spite of loss of agglutinability in specific antiserum.