A complement fixation test with rabbit antisera was used to differentiate 82 cultures ofMycoplasmafrom man, mammalian cell cultures, laboratory rats and mice, cattle, goats, poultry, embryonated eggs and sewage.Seventeen serotypes were distinguished, 5 from man, 1 from mammalian cell cultures, 4 from rats and mice, 4 from cattle and goats, 2 from poultry and one saprophytic. Most of these corresponded to recognized species ofMycoplasma, but 1 of human origin (represented by 1 strain, Navel), and 1 from tissue cultures (5 strains), may represent new species. R38, one of the serotypes from rats, could be distinguished from the speciesM. arthritidis, but is probably an antigenic variant rather than a distinct species. Two species hitherto recognized as distinct,M. arthritidisandM. hominis type2, could not be distinguished and appear to constitute a single species. These findings illustrate the necessity, from the viewpoint of taxonomy, of comparing mycoplasma strains by serological methods.The serotypes of human and animal origin were largely host-specific. Exceptions were the inclusion ofM. arthritidisfrom rats andM. hominis type2 from man in a single serotype, the finding of a bovine organism among the strains isolated from goats and of a saprophytic strain in a rat.In relation to the aetiology of disease in man and animals, the isolation of an endogenousMycoplasmafrom embryonated eggs used to passage infective material illustrates the importance of identifying these organisms serologically. The demonstration of mixed mycoplasma infections in lesions in two rats shows the necessity of adequately purifying all cultures ofMycoplasmabefore examination.I would like to thank those workers mentioned in Table 1 who kindly provided the cultures which they isolated. In addition I wish to thank the following who sent cultures: Prof. A. C. Ruys and Dr D. Herderscheê (Amsterdam) for G2, Prof. H. E. Morton (Philadelphia) for Campo and 07, Dr D. G. ff. Edward (Beckenham) for Campo (PG27),M. bovigenitalium(PG11),M. iners, andM. gallinarum, Dr R. G. Wittler for H606 and Miss A. G. Newnham for A36, TU, PSU4 and TC727.My thanks are also due to Dr L. H. Collier of this Institute, Dr G. W. Csonka (London), Prof. A. E. Macdonald (Aberdeen), Dr J. Payne (Edmonton, Alberta), Mr A. A. Tuffrey (Carshalton) and Dr D. Weisinger (Basle) who provided material from which PPLO were isolated. I gratefully acknowledge all the information so generously supplied by these workers about the strains or material provided.I am indebted to Miss A. G. Newnham for carrying out an agglutination test on the avian strains.Part of this work was carried out by the author under the author aegis of the Medical Research Council Working Party on Non-Specific Urethritis with the aid of a grant from the U.S. Public Health Service.

Purified axial filaments from eight serotypes of Treponema hyodysenteriae and two nonpathogenic intestinal spirochaetes were characterized by SDS-PAGE and Western blotting. Axial filaments of all ten strains had similar SDS-PAGE profiles; five major axial filament polypeptides were identified, with molecular masses of 43.8, 38, 34.8, 32.8 and 29.4 kDa. Hyperimmune gnotobiotic pig serum raised against purified axial filaments of strain P 18A (serotype 4) cross-reacted with all other serotypes and with the non-pathogens, and convalescent serum taken from a pig with persistent swine dysentery also showed a strong response to the axial filament polypeptides. Hyperimmune gnotobiotic pig serum raised against axial filaments failed to agglutinate viable organisms and did not inhibit growth in vitro. Hence, the axial filaments of T. hyodysenteriae have been identified as major immunodominant antigens, although the role that antibodies to these antigens play in protection has yet to be established.

SUMMARYA genital strain ofMycoplasma hominiswas fractionated by differential centrifugation after disruption of the cells by alternate cycles of freezing and thawing, by gas cavitation under nitrogen, or by ultrasonic treatment.Antigens of the cell membrane were distinct from those in the soluble cell contents, judging from metabolic inhibition (MI), indirect haemagglutination (IHA), gel-diffusion and immunoelectrophoresis tests, and by the antibody response in rabbits inoculated with these fractions. The antigens which gave rise to MI and IHA antibody were located in the cell membrane.Extraction of whole cells ofM. hominisby various chemical methods suggested that the active components were protein in nature and that there was no lipid hapten, as inM. pneumoniae, or polysaccharide, as inM. mycoidesvar.mycoides.This work was partly supported by a Medical Research Council grant, which provided the remuneration of MRH.We thank Professor R. A. Kekwick and Dr J. M. Creeth of the Biophysics Department of this Institute for their advice on the processing of plasma and density gradient centrifugation, and Mr F. C. Belton of the Microbiological Research Establishment, Porton, Wilts, for growing a 50 litre batch ofM. hominis.

SUMMARYSixteen serological types of Mycoplasma previously distinguished by complement-fixation tests were compared by means of a gel precipitin (Ouchterlony) technique. Each of the sixteen gave a consistent pattern of three to seven precipitation lines with its homologous antiserum. Cross-reactions occurred between heterologous strains, especially with antisera produced with the aid of an adjuvant. Homologous reactions were complex and sufficiently distinctive for the technique to be used to identify unknown strains. Two of the sixteen types, Mycoplasma mycoides var. mycoides and M . mycoides var. cupri, had certain antigenic components in common. The appearance of other cross-reactions suggested that the majority were due to the presence in different species of partly related rather than identical antigens.

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