Four capsule serogroups (A, B, D, and E) have been described by using passive hemagglutination tests. Serogroups A and D predominate in pasteurelloses of avian species. A new capsule serogroup of Pasteurella multocida has been isolated from turkeys in Arkansas, California, Indiana, Iowa, Missouri, New Jersey, and Virginia. Strains belonging to the new serogroup were somatic serotype 1, 3, 7, or 12, and they varied in virulence for mice and poults. Antisera made in rabbits passively protected mice against challenge with the same serogroup regardless of somatic serotype.

Avian strains of Pasteurella multocida representing a variety of host types, geographic locations, and somatic serotypes were examined to provide information on the distribution of capsular serogroups. Of the 246 strains studied, 166 were capsular group A, 4 were group B, 4 were group D, and 14 were group F; 58 strains were non-encapsulated and consequently not serogroupable. This is the first report of serogroup B P. multocida from avian hosts in the United States. The 188 serogroupable strains represented 12 variations in somatic serotypes and were isolated from 11 types of avian hosts representing 25 states of the United States, Bangladesh, Singapore, and Canada.

Forty-six strains of Pasteurella anatipestifer isolated from different avian species were examined to determine their serologic types and physiologic characteristics. Serologic types were determined by a gel-diffusion precipitin test. Antigens from 39 field isolates reacted with antisera prepared from seven P. anatipestifer reference strains representing serotypes 1, 2, 4, 6, and 7. Antigens from five isolates did not react and could not be typed with available reagents. Gel precipitin reactions involving serotype 1 (43.6%) and serotype 2 (25.6%) were the most prevalent. Generally, the physiologic characteristics from 40 tests were typical for P. anatipestifer, and variations were observed among the strains in urease production, hemolysin production, litmus milk reaction, and gelatin liquefaction.

Gel-diffusion precipitin tests demonstrated an additional Pasteurella multocida serotype, designated serotype 16. Isolate P-2723, antigenically distinct from the other (previously reported) 15 serotypes, was from a turkey affected with fowl cholera. This serotype is not widely distributed. Isolate P-2723 was of mild virulence in turkeys, resulting in local infections in the hock joint and sternal bursa of only 1 of 9 turkeys exposed.

Glutaraldehyde-fixed sheep erythrocytes (GA-SRBC) were used in the indirect hemagglutination test for the detection of Pasteurella antibody. GA-SRBC were stable for at least 6 months. Heat extract or potassium thiocyanate extract antigens of Pasteurella strains could be adsorbed onto GA-SRBC or tanned GA-SRBC, respectively. The indirect hemagglutination test reaction was capsular group specific with heat extract antigen-sensitized GA-SRBC but not potassium thiocyanate extract antigen-sensitized tanned GA-SRBC.