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The taxonomic position ofHaemophilus equigenitalis Taylor et al. 1978, the causative agent of contagious equine metritis, was studied in comparison with phenotypically similar organisms such asMoraxella, Legionella, and others.Haemophilus equigenitalis is a microaerophilic, Gram-negative, nonmotile, short rod; the mean base composition of deoxyribonucleic acid of this organism is 36.5±0.5 mol% G+C. It shows best growth on chocolate agar, but very poor or no growth on plain nutrient agar and blood agar, although it requires no X- or V-factors for the growth. It is positive in catalase, oxidase, phosphatase, and phosphoamidase tests, but very unreactive in other biochemical tests for routine use. It produces no acid from any carbohydrates nor glycosidase. Arylamidase activities of the organism to β-naphtylamide derivatives of various amino acids, and di- and tripeptides were also compared with those of other taxa. The group of this organism was different from other known taxa in the numerical analysis of its phenotypic characteristics, DNA base composition, and DNA-DNA hybridization. These data indicate thatH. equigenitalis does not belong in the genusHaemophilus nor other known genera, but rather in a new genus. Therefore, we propose thatHaemophilus equigenitalis be reclassified in a new genusTaylorella asTaylorella equigenitalis.

Contagious equine metritis (CEM) is a highly contagious venereal infection of equids caused by Taylorella equigenitalis, a bacterium with fastidious growth requirements. A disease of major international concern, CEM can be the cause of short-term infertility and, very rarely, abortion in mares. Unlike the mare, stallions exposed to T. equigenitalis do not develop clinical signs of disease. CEM is transmitted by direct or indirect venereal contact. The carrier state occurs in the mare and the stallion and carrier animals are frequently the source of infection for new outbreaks of the disease. There are streptomycin-sensitive and -resistant biotypes of T. equigenitalis, and diagnosis is based primarily on culture of the bacterium from its predilection sites in the reproductive tract of the mare and the stallion. Treatment modalities are available for elimination of the carrier state. Prevention and control of CEM is achievable through a comprehensive programme of breeding farm management that includes early detection and treatment of carrier mares and stallions.

In this study, a novel betaproteobacterium, strain DPN7T, was isolated under mesophilic conditions from compost because of its capacity to utilize the organic disulfide 3,3′-dithiodipropionic acid. Analysis of the 16S rRNA gene sequence of strain DPN7T revealed 98.5 % similarity to that of Tetrathiobacter kashmirensis LMG 22695T. Values for sequence similarity to members of the genera Alcaligenes, Castellaniella and Taylorella, the nearest neighbours of the genus Tetrathiobacter, were about 95 % or less. The DNA G+C content of strain DPN7T was 55.1 mol%. The level of DNA–DNA hybridization between strain DPN7T and T. kashmirensis LMG 22695T was 41 %, whereas it was much lower between strain DPN7T and Alcaligenes faecalis LMG 1229T (7 %) or Castellaniella defragrans LMG 18538T (5 %). This genotypic divergence was supported by differences in biochemical and chemotaxonomic characteristics. For this reason, and because of the differences in the protein and fatty acid profiles, strain DPN7T should be classified within a novel species of Tetrathiobacter, for which the name Tetrathiobacter mimigardefordensis sp. nov. is proposed. The type strain is strain DPN7T (=DSM 17166T=LMG 22922T).