Background From the beginning of the 21st century Enterococcus cecorum has emerged as a significant health problem for poultry raised under intensive production systems. To obtain new insights into this bacterial species, we investigated 82 clinical isolates originating from different poultry flocks in Poland between 2011 and 2014. Results Phenotypically, isolates from clinical cases showed ability to growth at low temperatures (4?°C, 10?°C), and differences in growth at 45?°C (74.4?%). Survival at high temperatures (60?°C, 70?°C) was observed for 15, 30?min. More than half of strains survived at 60?°C even after prolonged incubation (1?h), but none survived after 1?h at 70?°C. Total growth inhibition was observed on agar supplemented with tergitol or potassium tellurite. Relatively high number of isolates gave positive reactions for β-galactosidase (βGAL 80?%), Voges Proskauer test (60?%), less for β-mannosidase (17?%), glycogen and mannitol (12?%). The metabolic fingerprinting for E. cecorum obtained in Biolog system revealed ability to metabolise 22 carbon sources. Only 27/82 strains contained?≥?1 virulence genes of tested 7, however 2.4?% isolates carried 6. Increased antimicrobial resistance was observed to enrofloxacin (87?%), teicoplanin (85?%), doxycycline (83?%), erythromycin (46?%). Most strains (75/82) showed multidrug resistance. The single isolate was resistant to vancomycin (VRE) and high level gentamicin (HLGR). Linezolid resistance among clinical isolates was not found. PFGE revealed diversity of E. cecorum from cases. It could be assumed that transmission of pathogenic strains between flocks regardless of type of production or geographical region may be possible. Conclusions Clinical infections in poultry caused by E. cecorum may indicated on new properties of this bacterial species, previously known as a commensal. Despite many common phenotypic features, differences were found among clinical isolates. Several, widely distributed pathogenic E. cecorum strains seemed to be responsible for infection cases found in different poultry types.
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