Genomic Distribution of a Serotype 1‐Specific Antigen‐Coding DNA Fragment of Pasteurella Haemolytica

A genomic fragment of Pasteurella haemolytica biotype A coding for a serotype 1‐specific agglutinating antigen was used as a probe in a series of hybridization experiments to determine distribution of the fragment in various P. haemolytica serotypes as well as other bacteria. Results showed presence of the fragment in seven out of the 12 serotypes tested, all of which belonged to biotype A. Two other serotypes belonging to biotype A, all three serotypes belonging to biotype T, two Pasteurella multocida isolates and Escherichia coli did not have the fragment in their genome. Thus the expression of the P. haemolytica biotype A serotype 1‐specific agglutinating antigen (PHA1SAA) seems to be due to serotype‐specific regulation of protein expression rather than to genetic deletion. Differences in methylation of the PHA1SAA‐coding fragment was also noted in Dpnl and Sau3Al genomic DNA digests from the various serotypes analyzed by Southern blot. However, no apparent correlation was observed between methylation and PHA1SAA expression. E. coli with a recombinant plasmid containing a homologous genomic fragment derived from P. haemolytica serotype 2 also expressed PHA1SAA.