Intra-specific diversity and host specificity within Pasteurella haemolytica based on variation of capsular polysaccharide, lipopolysaccharide and outer-membrane proteins.

Intra-specific diversity within Pasteurella haemolytica was assessed by analysing variation in the capsular polysaccharide (serotypes), lipopolysaccharide (LPS) and outer-membrane proteins (OMPs) of 184 isolates recovered from cattle and sheep. Four 12 serotypes comprised 83% of the total number of isolates, including A1 and A2 as the most frequently recovered serotypes from cattle and sheep, respectively. Nine distinct LPS profiles were identified. Four different core-oligosaccharide patterns were present, each of which occurred alone as rough LPS and also in association with single O-antigen profile as smooth LPS; the ninth LPS type was also smooth but had a different O-antigen profile. The capsular serotypes could be divided into four groups based on the dominant LPS profile within each serotype: (1) A1, A6, A9, A12 and A5; (2) A2, A8, A14 and A16; (3) A7 and A13; and (4) A11. Smooth LPS of type 1A, which was found only in the first group, was associated primarily with bovine disease isolates, whereas rough LPS of types 1B and 3B were associated primarily with group 2 serotypes and ovine disease isolates. Similarly, the variation of OMP profiles generated three groups: (1) A1, A6 A9, A12, A5 and A8; (2) A2, A14 and A16; and (3) A7, A11 and A13. Isolates belonging to groups 2 and 3 exhibited greater diversity in their OMP profiles than those belonging to group 1. Although the majority of group 3 isolates possessed profiles unique to that group, a smaller number of A7 isolates possessed profiles with similarities to those of serotypes A1 or A2. OMP profiles clearly differentiated bovine from ovine isolates of the same serotypes. The association both of specific LPS and OMP profiles with bovine or ovine disease isolates suggested a correlation between specific cell-surface structures and host specificity. The combined analysis of capsular serotypes, LPS types and OMP profiles identified seven major groups within P. haemolytica which were responsible for 59% of the disease cases, suggesting a clonal structure for this species. Overall, comparison of the capsular serotypes, LPS types and OMP profiles proved extremely useful for assessing diversity within P. haemolytica.