Validation of growth as measurand for bacterial adhesion to food and feed ingredients

AIMS

A miniaturized adhesion test was designed to study the binding capacity of food and feed ingredients for bacterial cells.

METHODS AND RESULTS

Bacteria were allowed to adhere to different fibrous materials supplied as well coatings in microtitration plates. The amount of bacteria retained on the materials was determined in an automated way as growth after addition of liquid medium. The test principle was based on an inverse relationship between initial cell densities and the appearance of growth: The higher adhering cell numbers are, the shorter are the detection times of growth. The growth curves obtained were fitted by nonlinear regression analysis employing a sigmoidal curve model. Growth parameters as (i) the time after incubation at which half of the maximum growth yield was reached; (ii) the time-coordinate of the point of inflection; (iii) the detection time calculated as x-axis intercept of the maximum specific growth rate in the point of inflection; and (iv) the time-coordinate of a growth detection threshold at OD = 0.05 were highly separating for the binding capacity of different food and feed ingredients for bacteria.

SIGNIFICANCE AND IMPACT OF THE STUDY

With growth as measurand for adhesion, a simple, high-throughput method was developed for the screening of huge numbers of different binding matrices and bacteria.

In vitro inhibition of ETEC K88 adhesion by pea hulls and of LT enterotoxin binding by faba bean hulls

Enterotoxigenic Escherichia coli (ETEC) expressing K88 (F4) adhesins are associated with post-weaning diarrhoea in piglets. Different grain fractions from pea (Pisum sativum) and faba bean (Vicia faba) were tested in vitro for their capacity to counteract aetiological factors, which contribute to the development of diarrhoea. In detail, adhesion of E. coli O149:K91:K88ac (ETEC K88ac) to grain legume products, intended to impair the colonization of the host, was studied as well as interference with receptor binding of the pathogen's heat-labile enterotoxin LT, intended to reduce toxin-inflicted gut cell damage. When comparing different pea and faba bean products tested for their binding capacity of ETEC K88ac, especially pea hulls, but also whole pea meal, starch-enriched and protein-enriched pea meal, and digestion-resistant pea hull and meal fractions showed a higher binding of ETEC K88ac than faba bean products. In contrast to the ETEC K88ac adhesion results, bean hulls proved more effective than pea hulls in preventing GM1 receptor binding of LT. Previous small intestinal segment perfusion experiments we performed with ETEC K88ac-challenged piglets indicated that both pea and bean hulls have the potential for successful application in diarrhoea prophylaxis and treatment, which is in agreement with and refined by our detection of their different modes of functioning.