Abstract
Abortions in cattle have a significant economic impact on animal husbandry and require prompt diagnosis for surveillance of epizootic infectious agents. Since most abortions are not epizootic but sporadic with often undetected etiologies, this study examined the bacterial community present in the placenta (PL, n = 32) and fetal abomasal content (AC, n = 49) in 64 cases of bovine abortion by next generation sequencing (NGS) of the 16S rRNA gene. The PL and AC from three fetuses of dams that died from non-infectious reasons were included as controls. All samples were analyzed by bacterial culture, and 17 were examined by histopathology. We observed 922 OTUs overall and 267 taxa at the genus level. No detectable bacterial DNA was present in the control samples. The microbial profiles of the PL and AC differed significantly, both in their composition (PERMANOVA), species richness and Chao-1 (Mann–Whitney test). In both organs, Pseudomonas was the most abundant genus. The combination of NGS and culture identified opportunistic pathogens of interest in placentas with lesions, such as Vibrio metschnikovii, Streptococcus uberis, Lactococcus lactis and Escherichia coli. In placentas with lesions where culturing was unsuccessful, Pseudomonas and unidentified Aeromonadaceae were identified by NGS displaying high number of reads. Three cases with multiple possible etiologies and placentas presenting lesions were detected by NGS. Amplicon sequencing has the potential to uncover unknown etiological agents. These new insights on cattle abortion extend our focus to previously understudied opportunistic abortive bacteria.
Highlights
Infectious abortion in ruminants is a problem in animal husbandry worldwide
16S rRNA gene—polymerase chain reaction (PCR) screening We confirmed the presence of bacterial DNA in the 81 samples of abortion material
After subsampling 9 000 reads/sample, 913 operational taxonomic units (OTUs) remained in the dataset that was used for further analysis
Summary
The most common bacterial abortive agents involved in ruminant abortion are Brucella spp., Coxiella burnetii and Chlamydia abortus [2,3,4]. While Brucella spp. and C. burnetii are typically involved in bovine fertility problems as abortion, stillbirth and weak offspring [5], chlamydial infections may cause a variety of syndromes including conjunctivitis, polyarthritis, encephalomyelitis, mastitis and other urogenital tract infections [2]. Brucellosis, Q fever (C. burnetii) and chlamydiosis should be considered among the most common zoonotic diseases. Laboratories conducting abortion diagnostic examinations should perform standard tests covering the major abortive infectious diseases; costs dictate that these tests are limited to the most common etiologies [8]. First-line routine bacteriological abortion diagnostics in cattle in Switzerland only include serology and staining for B. abortus and C. burnetii
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