An account is given of the examination by biochemical and serological methods of 800 strains of brucella sent for identification to the Brucella Reference Laboratory of the Public Health Laboratory Service.
Most of the strains were isolated from milk in Great Britain, but strains from other countries, and from cases of undulant fever, were also examined.
Of 738 strains from milk in Britain, 680 were Br. abortus, of which sixty-two (9·1 %) were of a type inhibited by all the usual test-dyes in their customary concentrations. Thirty strains of Br. melitensis, behaving typically in all laboratory tests, were obtained from milk from individual cows, herds or bulk sources. Br. melitensis has now been identified from twenty-four separate farms and one Tuberculin Tested bulk supply in this country. Eighteen strains behaved like Br. abortus in biochemical tests, but serologically like Br. melitensis.
Of the relatively small number of strains isolated from patients with undulant fever in Britain, all those from persons infected in this country were Br. abortus, with the exception of two laboratory infections with Br. melitensis. The organisms isolated in Britain from patients infected abroad comprised three strains of Br. melitensis, one strain behaving biochemically like Br. abortus and serologically like Br. melitensis, and two behaving biochemically like Br. melitensis and serologically like Br. abortus. One of the latter was from a patient infected in southern Italy, and the examination of nineteen strains from that country showed that thirteen were of this type. The thionin-resistant type of Br. abortus was identified several times, from undulant fever cases in Rhodesia, Kenya and Italy. No strains of Br. suis were observed.
I wish to thank the numerous bacteriologists who sent cultures and provided details of their isolation. A few submitted large numbers of strains and enabled a general picture of the prevailing types to be obtained. I am grateful to these and to the other bacteriologists who provided information about the herds from which Br. melitensis was isolated, in particular Dr P. H. Martin and Dr J. A. Sykes (Ipswich), Dr L. M. Dowsett (Norwich), Dr J. Kennedy (Newcastle, then at Stafford), Dr J. H. C. Walker (Luton), Dr E. H. Gillespie and Dr N. S. Mair (Leicester) and Dr J. E. Jameson (Brighton). I have also to acknowledge the help of Dr A. W. Stableforth, Director of the Ministry of Agriculture and Fisheries Veterinary Laboratory, who provided much bacteriological and veterinary information about the infected herds.