A survey of antibiotic resistance and virulence factors in Enterococcus species isolated from poultry farms in Benin City, Nigeria

Abstract

Background: Enterococci are commensal bacteria resident in the gastrointestinal tract of humans and animals. However, their increasing  resistance to clinically important antimicrobial agents remain a global threat. The objective of this study is to determine the prevalence, antimicrobial resistance profile and virulence factors of Enterococcus isolated from selected poultry farms in Benin City,  Nigeria.

Methodology: Sixty samples (20 feed, 20 water and 20 faecal samples) were randomly collected from five selected poultry farms in  different commercial farming areas between August and September 2020. The samples were first enriched in Tryptone Soy Broth (TSB)  and then cultured on Bile Aesculin Azide (BAA) agar aerobically at 37^oC for 18-24 hours. Black colonies on BAA agar were presumptively  identified as Enterococcus and confirmed by conventional biochemical tests and Analytical Profile Index (API) rapid ID 32 STREP. The
antibiotic susceptibility of the isolates was determined by the Kirby-Bauer disc diffusion method. The virulence factors and biofilm  formation were evaluated using standard bacteriological and microtitre plate methods.

Results: In total, Enterococcus-positive samples were 32/60 (53.3%) with a total of 45 Enterococcus isolates. The speciation of the  Enterococcus isolates based on API rapid ID 32 STREP were Enterococcus faecium 15/45 (33.3%), Enterococcus faecalis 12/45 (26.7%),  Enterococcus durans 8/45 (17.8%), Enterococcus casseliflavus 5/45 (11.1%) and Enterococcus hirae 5/45 (11.1%). The isolates showed the  highest antibiotic resistance to ampicillin (100.0%), fosfomycin (95.6%) and penicillin G (88.9%) and the least resistance to ciprofloxacin (22.2%) and chloramphenicol (28.9%). The virulence factors of Enterococcus species observed were gelatinase, β-hemolytic and  hyaluronidase activity, biofilm, and S-layer formation. The degree of biofilm formation by the Enterococcus species was strong biofilm  formation (19/45, 42.2%), moderate biofilm formation (10/45, 22.2%), weak biofilm formation (11/45, 24.4%) and no biofilm formation  (5/45, 11.1%).

Conclusion: Findings from this study emphasized on the potential health implications associated with antimicrobial  resistance and phenotypic virulence factors of Enterococcus in poultry products