Investigation of the ability to form biofilms in-vitro in sanitary-indicatory bacteria isolated from chickens

Biofilms provide resistance to antimicrobial agents and the body’s immune response in microorganisms that colonise the digestive tract of animals, in particular poultry. The study of biofilm formation of indicatory bacteria isolated from chickens under different keeping conditions allows assessing the impact of environmental factors on their phenotypic adaptation and potential risk to animal and human health. The purpose of the study was to determine the ability ofEscherichiacoliandEnterococcus faecalisbacteria isolated from chickens kept in a vivarium and on free range to form biofilms. Bacteriological, morphological, biochemical, and microscopic research methods were applied. The intensity of biofilm formation in indicatory microorganisms was assessed by the adsorption/resorption index of a 0.1% solution of crystal violet using polystyrene Petri dishes. The optical density was measured spectrophotometrically at a wavelength of 570 nm. It was found thatE. coli,E. faecalis,Klebsiella spp. andPseudomonas aeruginosawere isolated in samples from chickens kept in a vivarium, while in free-range chickens, representatives of the genus Klebsiella and Pseudomonas aeruginosa were not detected, indicating a lower presence of potential pathogens in natural conditions. All the cultures under study formed low- or medium-density biofilms. ForE. coliisolates obtained from free-range chickens, the average value λ = 0.264 ± 0.09, while for vivarium isolates – λ = 0.187 ± 0.07. Cultures ofE. faecalisbiofilms were formed with an intensity of λ = 0.217 ± 0.04 in free-range chickens and λ = 0.137 ± 0.03 in vivarium chickens. Consequently, isolates obtained from natural conditions were characterised by a higher intensity of biofilm formation – by 41.2% (E. coli) and 58.4% (E. faecalis) in comparison with the conditions of a controlled microclimate. This may indicate a stimulating effect of environmental factors on the expression of adhesion and biofilm formation genes. However, all cultures under study were isolated from clinically healthy chickens, which indicates a commensal nature of the microbiome. The results obtained are important for assessing the risks of horizontal transfer of resistance genes and the formation of stable microbial biofilms in poultry farming