Chicken embryo as an animal model for gonorrhea.

Parameters of infection of the chicken embryo with Neisseria gonorrhoeae were defined in order to standardize infectious and lethal doses. Virulent (T1) and avirulent (T3) gonococci from two strains were used to infect 7- to 12-day-old White Leghorn chicken embryos via the yolk sac (YS) or chorioallantoic membrane (CAM) route. Infection of embryos was established following YS inoculation of 1 to 10 viable gonococci. Although 8- to 10-day-old embryos were the most susceptible, an inoculum of less than 100 gonococci was sufficient to kill any age embryo via this route. Embryos were less susceptible to infection via the CAM, where an inoculum of from 10(5) to 10(6) colony-forming units was lethal by 42 h. Strain and morphological type had a variable influence on the ability of the gonococcus to infect and kill the chicken embryo by either route; however, agar-grown and broth-grown organisms produced consistently similar mean lethal dose (LD(50)) and mean infective dose (ID(50)) values. LD(50) and ID(50) differences between T1 and T3 gonococci from strain 72H641 were not apparent after either YS or CAM inoculation of 8- or 10-day chicken embryos, respectively. YS and CAM LD(50) values for strain 72H641 T1 and T3 and CDC 9 T3 were also similar; however, these values were slightly lower for CDC 9 T1. In terms of infectivity or colonization, CDC 9 T1 and T3 had higher ID(50) values via the YS and lower ID(50) values via the CAM than 72H641. CDC 9 T1 was slightly more infective via the YS and less infective via the CAM than its T3 counterpart. Although the gonococcal strain used will influence interpretation of results, infection of both YS and CAM was highly reproducible in terms of gross pathology and of LD(50) and ID(50) data for a particular strain and colony type.