Genome Degradation in Brucella ovis Corresponds with Narrowing of Its Host Range and Tissue Tropism

Abstract

Brucella ovis is a veterinary pathogen associated with epididymitis in sheep. Despite its genetic similarity to the zoonotic pathogens B. abortus, B. melitensis and B. suis, B. ovis does not cause zoonotic disease. Genomic analysis of the type strain ATCC25840 revealed a high percentage of pseudogenes and increased numbers of transposable elements compared to the zoonotic Brucella species, suggesting that genome degradation has occurred concomitant with narrowing of the host range of B. ovis. The absence of genomic island 2, encoding functions required for lipopolysaccharide biosynthesis, as well as inactivation of genes encoding urease, nutrient uptake and utilization, and outer membrane proteins may be factors contributing to the avirulence of B. ovis for humans. A 26.5 kb region of B. ovis ATCC25840 Chromosome II was absent from all the sequenced human pathogenic Brucella genomes, but was present in all of 17 B. ovis isolates tested and in three B. ceti isolates, suggesting that this DNA region may be of use for differentiating B. ovis from other Brucella spp. This is the first genomic analysis of a non-zoonotic Brucella species. The results suggest that inactivation of genes involved in nutrient acquisition and utilization, cell envelope structure and urease may have played a role in narrowing of the tissue tropism and host range of B. ovis.

Species-specific nested PCR as a diagnostic tool for Brucella ovis infection in rams

“…Antibody titers were detected by AGID in all animals in the third week after inoculation, decreasing soon after the fifth week, remaining variable as time passed, which confirms that the experimental challenge resulted in infection in all rams. The serological results are in accordance with previous reports, in which antibody titers were detected between 2 to 9 weeks after intraprepucial inoculation of B. ovis, and then became intermitent (Webb et al, 1980;Xavier et al, 2010) In semen samples, the positivity of the speciesspecific nested PCR was 50.6% (42/83), which was significantly different from the genusspecific PCR (P<0.001) which had a positivity rate of 27.7% (23/83) (Figure 1). Similarly, when the urine samples were subjected to speciesspecific nested PCR, the percentage of positive samples was 65.3% (49/75), which was significantly higher (P<0.001) than that obtained by genus-specific PCR, which detected 14.6% (11/75) of positive samples (Figure 1).…”

“…Speciesspecific PCR used a primer pair targeting the ORF AO503 (F: 5'-ATCCCCCCATCACCATAACCGAAG-3'and R: 5'-GCCTACGCTGAAACTTGCTTTTG-3') located in the B. ovis-pathogenicity island 1 (BOPI-1) (Tsolis et al, 2009;Silva et al, 2011) as previously described (Xavier et al, 2010). PCR reaction and cycle parameters were performed as previously described (Xavier et al, 2010) and a volume of 2.5µL of template DNA was added per reaction.…”

“…Some infected rams do not develop palpable lesions (Webb et al, 1980) or, conversely, have genital disease compatible with infection but have been exposed to different bacteria (Hughes e Claxton, 1968). The bacteriology of B. ovis is time consuming and not always efficient, because bacteria can be excreted intermittently in the semen of infected animals (Worthington et al, 1985;Baigun et al, 2000).…”

“…Furthermore, PCR allows a rapid identification of the pathogen in semen (Saunders et al, 2007;Xavier et al, 2010) or urine samples (Xavier et al, 2010) collected from infected rams. Xavier et al (2010) recently developed a PCR based on the amplification of an open reading frame (ORF) specific for chromosome II of B. ovis (Tsolis et al, 2009) which has a remarkably good sensitivity when compared to bacteriological culture and has proven to be highly specific for detecting B. ovis infection. The authors demonstrated that the target sequence was conserved in 18 different B. ovis field strains and absent in other classical species of Brucella, in bacteria species that can cause epididimitis in rams, and in those microorganisms phylogenetically related to B. ovis (Xavier et al, 2010), confirming the specificity of the technique developed.…”

Indirect ELISA for diagnosis of Brucella ovis infection in rams

“…However, VirB12 has not been tested as a serological marker of B. ovis infection. This study also included a putative hemagglutinin that has been identified by Tsolis et al (2009) as part of a recently characterized B. ovis pathogenicity island 1 -BOPI-1 (Silva et al, 2011). A potential pathogenic role of this gene has been evaluated and it proved to play no role during in vivo infection in the mouse (Silva et al, 2011), although it's antigenic protential has not been evaluated.…”