Etiology of vertebral osteomyetilis in broilers

Abstract

Locomotor disorders represent a major challenge in modern poultry production worldwide and they may be related to non-infectious and infectious etiologies. Vertebral osteomyelitis is a bacterial disease described in outbreaks in many countries, characterized by infection of the mobile thoracic vertebra (T4), which results in the compression of the spine, reduced mobility and death of affected broilers. The objective of this study was to determine the frequency of vertebral osteomyelitis in broilers in the state of Minas Gerais, and to determine the bacterial etiologies involved in disease and their molecular characteristics. For this, we analyzed 608 broilers with locomotor disorders, which had their clinical signs recorded and then necropsied. Vertebral column samples and joints with gross changes were collected for bacterial isolation, molecular and histopathological analysis. Vertebral osteomyelitis was found in 5.1% (31/608) of the birds, which had different degrees of limited mobility, related to the level of spinal cord compression. The bacteria most frequently isolated from lesions were: Enterococcus spp.(53.6%), E. faecalis (32.1%) and E. hirae (7.1%); Escherichia coli (42.8%) in co-infection with E. faecalis in two cases; Staphylococcus aureus (14.3%) in co-infection with Enterococcus spp. or E. hirae in two cases. E. coli strains harbored different genetic pattern as assessed by PFGE, regardless of flock origin and lesion site (vertebral osteomyelitis or arthritis). The E. coli strains belonged to seven sequence types (STs) described previously (ST117, ST101, ST131, ST371 and ST3107) or newly described in this study (ST5766 and ST5856). Most strains belonged to ECOR phylogenetic group D (66.7%) and diverse serogroups (O88, O25, O12 and O45), some of worldwide importance. The antimicrobial susceptibility profile also showed the diversity of the strains and revealed a high proportion of multidrug-resistant strains (73%), mainly to quinolones and beta-lactams. Multilocus sequence typing (MLST) analysis of E. faecalis revealed that the strains belonged to eight different STs, being six (ST49, ST100, ST116, ST202, ST249, and ST300) previously described and ST708 and ST709 first identified in this study. ST49 was the most frequently isolated from vertebral osteomyelitis lesions. E. faecalis strains showed the highest resistance to aminoglycoside antibiotics, mainly to gentamicin (40.0%), and low resistance to vancomycin (10%). The results indicated that, in Brazil, vertebral osteomyelitis in broilers may not be caused by a single infectious agent and suggested geographical differences concerning the frequency and etiology of the disease, as comparing our region in Brazil with reports in other countries. Furthermore, our results showed the diversity of E. faecalis STs involved with this disease and high frequency of aminoglycoside resistance and low frequency of vancomycin-resistance. Also, vertebral osteomyelitis and arthritis could be associated with highly diverse E. coli, which were often multidrug-resistant. Some E. coli strains belonged to STs described also in humans, which may represent a concern to public and animal health.