Eight swine strains were classified into 2 genotypes using theompAsequence analysis [35]. genetic aspects ofC.pecorumare also reviewed. Keywords:Chlamydophila pecorum, pathogenesis, typing, epidemiology == 1. INTRODUCTION == Chlamydiaeare obligate intracellular bacteria that develop inside eukaryotic cells within membrane-bound vacuoles termed inclusions, with a unique biphasic developmental cycle Vorapaxar (SCH 530348) alternating between an extracellular metabolically inert form (elementary body, EB) and an intracellular metabolically active replicating form (reticulate body, RB) [52].Chlamydia trachomatisandChlamydia psittaciwere the first two species to be assigned to the genusChlamydiaon the basis of differences in inclusion morphology, glycogen content, susceptibility to sulfadiazine and natural host [25,54].C.trachomatisencompasses allChlamydiaefound in man.C.psittacicomprises all otherChlamydiaefound in birds and animals except the mouse pneumonitis agent, classified asC.trachomatison the basis of its biological properties.C.pneumoniaeis separated from your other two species on the basis of ultrastructural differences in the elementary body, DNA homology values and serological reactions [26]. Until 1993,C.pecorumstrains were considered as users of theC.psittacispecies, sharing many similar phenotypic characteristics, including inclusion morphology, the absence of glycogen in inclusions and sulfadiazine resistance. The word pecorum comes from the Latin word for flocks of sheep or herds of cattle [20]. The first isolation ofC.pecorumwas from a sporadic encephalomyelitis of cattle reported by McNutt and Waller [51], and at that time it was considered as aC.psittacistrain. C.psittacistrains isolated from ruminants were subdivided into two serotypes using a plaque-reduction test [69,70]: serotype 1 comprises the strains causing abortion and enteritis (C.abortus), Vorapaxar (SCH 530348) and serotype 2 consists in the strains inducing polyarthritis and conjunctivitis (C.pecorum). Further work dividedC.psittacistrains isolated from ruminants into three main biotypes based on their culture characteristics, although only a small number of strains was used in this study [73]. Biotype 1 comprises strains causing Vorapaxar (SCH 530348) abortion (C.abortusstrains in the classification [16]) with compact inclusion morphology and inclusions appearing within 48 h. Biotype 2 comprises strains causing polyarthritis, conjunctivitis, and encephalomyelitis. Strains isolated from faecal samples were included in biotype 3. The two latter biotypes, which correspond toC.pecorumstrains, have diffuse inclusion morphology and inclusions appearing within 24 h. The abortion type develops well in a sheep fibroblast culture, unlike the enteric type [57]. A micro-immunofluorescence (MIF) test confirmed the two serotypes ofC.psittaciidentified by a plaque reduction test (serotype 2 corresponding toC.pecorum) [14]. Following subcutaneous inoculation into the footpad of mice, theC.psittacistrains were subdivided into three groups: (1) highly invasive strains causing splenomegaly and massive contamination of the spleen; (2) invasive strains inducing a moderate enlargement of the spleen with a low level of splenic contamination; and (3) non-invasive strains (C.pecorum) inducing neither increased spleen excess weight nor splenic contamination1. The invasive and highly invasive strains corresponded to serotype 1, i.e.C.abortus, in the new classification [16]. Genetic differences between theC.pecorumandC.psittacistrains were identified through restriction Vorapaxar (SCH 530348) endonuclease analysis [18,67], DNA-DNA hybridization, and Southern blot analysis with genomic DNA probes [18]. In 1992, Fukushi and Hirai [19] suggested separating theC.pecorumspecies fromC.psittacibased around the results of DNA-DNA hybridization and immunological analysis.C.pecorumstrains exhibit 10% or less DNA relatedness to strains of the other three Chlamydial species (C.trachomatis,C.psittaciandC.pneumoniae), while the homology levels are 88% or greater within theC.pecorumspecies. Restriction enzyme and gene probe analysis indicated that this Chlamydial strains infecting koalas belong to two unique genotypes ofC.psittaci, one Vorapaxar (SCH 530348) corresponding to the strains causing urogenital diseases and similar to the SBEC.pecorumstrain and the other grouping the ocular isolates [22]. This observation was confirmed byompA(major outer membrane protein-MOMP gene) sequence analysis, indicating that the two Chlamydial species infecting koala areC.pecorumandC.pneumoniae[23]. New taxonomic methods were developed with the discovery of the polymerase chain reaction (PCR) and sequence analysis. This made it possible to DC42 analyse a greater number of strains using a small DNA sample, unlike former methods (biological, morphological, and DNA-DNA hybridization techniques, etc.) which required isolation and culture of the bacteria, a difficult procedure for an obligate intracellular bacterium such asChlamydia. The isolates ofChlamydiawere grouped into two lineages using the 16S/23S intergenic spacer and domain name I of the 23S gene [15]:C.trachomatiscomprising human, swine, and mouse-hamster groups, and non-C.trachomatiscomprisingChlamydia pecorum,Chlamydia pneumoniae, andChlamydia psittaciabortion, avian, feline, and guinea pig groups. Then in 1999, Everett et al. [16] proposed a new classification dividing the Chlamydiaceae family into two genera,ChlamydiaandChlamydophila, the former comprising 3 species,Chlamydia trachomatis,Chlamydia muridarumandChlamydia suis, and the latter 6 species,Chlamydophila psittaci,Chlamydophila abortus,Chlamydophila caviae,Chlamydophila felis,Chlamydophila pneumoniaeandChlamydophila pecorum. SomeChlamydiaespecialists have rejected this classification, particularly the division of the Chlamydiaceae family into two genera. According to these specialists [71], the new classification plan is based on minor sequence differences in the 16S and 23S rRNA genes, and some of.