PHYLOGENETIC-RELATIONSHIPS AND DIVERSITY WITHIN THE PASTEURELLA-HAEMOLYTICA COMPLEX BASED ON 16S RIBOSOMAL-RNA SEQUENCE COMPARISON AND OUTER-MEMBRANE PROTEIN AND LIPOPOLYSACCHARIDE ANALYSIS

The outer membrane protein (OMP) and lipopolysaccharide (LPS) profiles of 30 untypeable isolates of Pasteurella haemolytica were examined by sodium dodecyl sulfate polyacrylamide gel electrophoresis and compare d with the profiles of typeable isolates. The phylogenetic relationshi ps of 28 isolates representing each of the serotypes of P. haemolytica and Pasteurella trehalosi, as well as untypeable isolates of P. haemo lytica, were determined by comparing 16S rRNA sequences. The analysis of the OMP and LPS profiles of the untypeable isolates revealed five g roups, which were designated untypeable groups 1 (UG1) through UG5, Th e UG1 and UG2 isolates had OMP and LPS profiles identical to the profi les of certain serotype A1 and A2 isolates, respectively, Furthermore, UG1 isolates originating from cattle and sheep could he clearly diffe rentiated on the basis of their OMP profiles, The OMP and LPS profiles of UG3 isolates were similar in appearance to the profiles of serotyp e All isolates, suggesting that these two groups are closely related, The OMP profiles of UG4 and UG5 isolates were unique and different fro m the OMP profiles of the UG1 through UG3 isolates, A comparison of 16 S rRNA sequences revealed that typeable isolates of P. haemolytica cou ld be divided into the following three groups: (i) serotype A1, A5 thr ough A9, A12 through A14, and A16 isolates, (ii) serotype A2 isolates, and (iii) serotype All isolates, The isolates belonging to the first group all had identical sequences, whereas the sequences of isolates b elonging to the second and third groups differed from the sequences of the isolates belonging to the first group at two and four base positi ons, respectively, The sequence data for the untypeable isolates confi rmed the conclusions derived from the OMP and LPS analysis. Isolates b elonging to UG1 and UG2 were identical to serotype Al and A2 isolates, respectively; isolates belonging to UG3 were related to serotype All isolates, although there was some sequence heterogeneity within this g roup; and isolates belonging to UG4 and UG5 were more distantly relate d to P, haemolytica than were isolates belonging to UG1 through UG3 an d were clearly members of two different species, As expected, isolates of P, trehalosi were even more distantly related to P. haemolytica th an were the untypeable isolates, but there was significantly more sequ ence variation among the four serotypes of this species than there was among the serotypes of P. haemolytica, The correlation of the OMP and LPS data with the 16S rRNA sequence data suggested that OMP and LPS a nalyses might be useful for preliminary screening and comparing large numbers of isolates in taxonomic and epidemiological studies of the Pa steurellaceae.