Summary.A total of 16 909 cultures of Streptococcus pyogenes (Lancefield group A) isolated in Britain during 1980-90 were examined for T-and M-protein antigens. One or other M antigen was detected in 92.6 % of the strains. The numbers of isolates of some serotypes, such as M3 and M12, did not show great variation from year-to-year, whereas there were nationwide epidemics, extending over several years, caused by strains of serotypes M1 and M49. Isolates of serotypes M1 and M3 were associated particularly with invasive disease and fatal infections. Representatives of serotypes M80, M81 and the provisional types PT180, PT1658 and PT5757 were isolated most often from cases of pyoderma. Erythromycin resistance was detected in 30 serotypes but one half of all of the resistant isolates belonged to serotype M4.

The distribution of T- and M-protein antigens was determined in 12,469 cultures of Streptococcus pyogenes sent to a reference laboratory. Of these 7232 (58%) were isolates from hospital patients, 249 (2%) from hospital staff and 4988 (40%) from the community. The survey extended from January 1980 to June 1987. During this time the numbers of isolates of M-types 6, 49 and 81 rose then fell, being replaced by types 1, 3 and 28. The proportion of isolates of M-types 4 and 12 remained constant. Few strains were received from cases of nephritis or rheumatic fever but there has been an increase in the number of strains from serious infections and deaths. Forty-four of the 55 (80%) strains received since 1985 from fatal infections have belonged to M-type 1. All other strains, bar two, received from fatal infections in those years belonged to M-type 3. Representatives of M-type 1 were also associated with erysipelas. Types 3 and 4 predominated among the isolates from scarlet fever, types 1, 4, 12 and 49 from nephritis, types 49 and 81 from skin infections in meat workers and type 28 in cases of puerperal sepsis. The M-typability rate was 97% but new M antigens await definition among strains causing pyoderma.

Rhizobium leguminosarum showed positive chemotaxis towards root exudates of its host the edible pea (Pisum sativum L.). Only the fraction of the exudate containing substances with molecular weights less than 1000 showed significant chemotactic activity. Cationic, neutral and anionic fractions were all attractive, the cationic being the most potent and the anionic the least. A range of amino acids, sugars and carboxylic acids were present in the exudate, and many were shown to be attractants. Other Rhizobium species and Escherichia coli were also attracted by pea exudate, and R. leguminosarum and the other bacteria were attracted by exudates from roots of a range of plants including non-legumes. It was concluded that although positive chemotaxis probably facilitates infection of legumes by R hizobium, it has little or no role in host-symbiont specificity.

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