Impact of Encapsulated Iron Availability on the Growth Kinetics of Campylobacter jejuni

Campylobacter jejuni, a leading foodborne pathogen in poultry, relies heavily on iron for survival and colonizes the gastrointestinal tract (GIT). Iron supplementation in poultry diets can inadvertently promote pathogen growth, particularly when excess or poorly absorbed iron accumulates in the lower GIT. Encapsulated iron products, such as SQM^® Iron, offer a controlled-release mechanism that may mitigate this risk by reducing iron availability to microbes.

This study evaluated the effects of free (FeSO₄) versus polysaccharide-iron complex (PIC) on C. jejuni growth under iron-limited conditions, hypothesizing that encapsulated iron would support slower and more limited bacterial proliferation due to delayed iron release.

Growth kinetics of C. jejuni ATCC 700819 were assessed in chelated Mueller-Hinton broth supplemented with three iron concentrations (10, 20, and 50 ppm) of FeSO₄, PIC, or PIC matrix without iron. Optical density was measured every 20 min over 48 h under microaerophilic conditions. Maximum growth rate (µmax) and carrying capacity (K) were derived using non-linear curve modeling. ANOVA evaluated statistical significance with Tukey's HSD post hoc comparisons.

Free iron (FeSO₄) consistently supported the highest µmax and K values across both trials, indicating rapid and robust C. jejuni proliferation. The effect of encapsulated iron was variable: at higher concentrations (50 ppm) it approached FeSO₄ performance, but at lower concentrations (10 ppm) its effect differed markedly between trials, sometimes supporting growth comparable to free iron and sometimes supporting substantially slower growth. The PIC matrix alone did not promote growth. These variable results indicate that the relationship between encapsulated iron and C. jejuni proliferation is complex and concentration-dependent.

Free iron consistently promotes robust C. jejuni growth due to immediate bioavailability. The impact of encapsulated iron on C. jejuni proliferation is nuanced and variable, particularly at lower concentrations, suggesting its role in pathogen control is not straightforward and requires further investigation under controlled conditions. Furthermore, in vivo research is warranted to validate its utility in poultry pathogen management strategies.